# Who thinks Faster Than Light travel is possible?



## Serendipity (Aug 16, 2022)

Ever since Miguel Alcubierre published his paper saying that there is a theoretical solution to Einstein's General Relativity equations that allow FTL travel, the prospect of it eventually becoming reality has been dangled in front of our noses. 

Who here thinks if can become a reality and why?


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## Swank (Aug 16, 2022)

I think it is possible, but only because there are other solutions to paradox other than a prohibition on FTL.

Alcubierre seems to be offering to make one thing possible by violating a different fundamental law.


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## Venusian Broon (Aug 16, 2022)

Serendipity said:


> Ever since Miguel Alcubierre published his paper saying that there is a theoretical solution to Einstein's General Relativity equations that allow FTL travel, the prospect of it eventually becoming reality has been dangled in front of our noses.
> 
> Who here thinks if can become a reality and why?


At the moment *absolutely not*. Because all such solutions are _so astronomically _unphysical both in scale and in the conditions required. Furthermore, just because you can solve a mathematical equation, that models the universe, does not mean its solution is real. Finally, we know that relativity can't be totally right.

So come back when (or if) we crack quantum gravity or some deeper theory of reality - a new theory of everything may allow FTL by revealing something new about the universe that lets us 'go warp speed' (or may just rule out all these ideas anyway and we remain sub-FTL.)  Or perhaps when (and again, if!) we can start to easily manipulate matter and energy on the scale probably billions of times more than our civilisation does today.


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## Wayne Mack (Aug 16, 2022)

I'm not sure if this is a direct answer, but this is an interesting tidbit I found in researching a story. The universe expands faster than the speed of light. My physics-fu isn't strong enough to understand the explanations, but here is one link: How Can the Universe Expand Faster Than the Speed of Light?


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## Swank (Aug 17, 2022)

Wayne Mack said:


> I'm not sure if this is a direct answer, but this is an interesting tidbit I found in researching a story. The universe expands faster than the speed of light. My physics-fu isn't strong enough to understand the explanations, but here is one link: How Can the Universe Expand Faster Than the Speed of Light?


Two beams of light traveling in opposite directions are moving away from each other at twice the speed of light.

I can move my gaze between stars many light years apart at thousands of times the speed of light.


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## Robert Zwilling (Aug 17, 2022)

I believe it is likely that a lump of matter physically accelerated faster than the speed of light would change into something else, probably no way to get it back.

Then there the ultimate problem solver of the proverbial wormhole, which connects sections of space together by utilizing folds in space. It sounds practical but you still have to travel long distances inside and outside of the worm. To be practical there would have to be wormholes all over the place. There is still the problem of how folded space could be. Although if it did get you anywhere it would be something, unless it ended up in the middle of nowhere.

This brings up multiple planes of existence which I do believe in and figure there are different rules governing how things work in them. Would it support physical FTL, I don't know, but probably not. Which brings up the idea of transporting matter or an energy pattern by replicating the exact pattern of an object and its place in space such that the space around it represents another location in space. An advanced form of spooky action at a distance. It would be recreating a pattern in another location which would be everything it was in the original location.

Would consciousness also be able to travel the same way. Probably not, as it is just a recreation of a physical pattern that gets transported. This is where it gets whimsical. The body could either arrive with a blank state for memories or the memories could also be physically copied such that the person would know what was going on. If the person didn't know what was happening, they would need a set of instructions to tell them what was happening.

Another scenario in which FTL is not needed is one in which stars are not so far away from each other or where multiple planets of the same solar system have life on them which makes traveling between them not impossible. Traveling hundreds of years to get to another planet sounds like a long time but if the situation did exist I'm sure someone would try it. If it was multiple stars close to each other I guess they would have to be fairly small to minimize interactions between the stars that could make life unlikely. Or maybe it would promote the existence of life if there were interactions between the stars.


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## alai (Aug 17, 2022)

Swank said:


> Two beams of light traveling in opposite directions are moving away from each other at twice the speed of light.


I'm afraid not.  Their relative speed isn't even strictly definable, as there's no "photon's eye view" available in formal theory, much less to any experimenter.  But consider a notionally feasible limiting sort of case.  Two spaceships are moving apart, each at 0.9c (or 0.99c, or 0.999c, or any such value you like).  They're separating at 1.8c, right?  (Or 1.98, 1.998...)  Nope!  Still less than c, from either of their frames of reference.



Swank said:


> I can move my gaze between stars many light years apart at thousands of times the speed of light.


Sure, but your "gaze" in this sense is a non-physical abstraction.  No matter, energy, or information is "moving" at that speed.



Wayne Mack said:


> I'm not sure if this is a direct answer, but this is an interesting tidbit I found in researching a story. The universe expands faster than the speed of light. My physics-fu isn't strong enough to understand the explanations, but here is one link: How Can the Universe Expand Faster Than the Speed of Light?


One way of thinking of it is like this:  imagine your "universe" is a gigantic (3D) balloon that someone's constantly inflating.  Now imagine you're travelling in a teeny-tiny (2D) car _over the balloon's surface_.  Everywhere there are cute little "MAXIMUM SPEED 55mm/h!  ENFORCIBLE BY NATURAL LAW!" signs.  (Drawn on the roads, of course, because 2D, and as we don't want to start sticking pins in the balloon.)  Naturally as you're a law-abiding citizen and don't want to vanish in a puff of causality, you adhere strictly to this limit.  But!  As measured from a large distance away, due to expansion of the balluniverse, you could actually be going faster.


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## Swank (Aug 17, 2022)

alai said:


> I'm afraid not. Their relative speed isn't even strictly definable, as there's no "photon's eye view" available in formal theory, much less to any experimenter. But consider a notionally feasible limiting sort of case. Two spaceships are moving apart, each at 0.9c (or 0.99c, or 0.999c, or any such value you like). They're separating at 1.8c, right? (Or 1.98, 1.998...) Nope! Still less than c, from either of their frames of reference.


I'm afraid so. Like my gaze example, you can add up the movement of multiple things moving away from you and make a statement about the velocity of their separation. But the point is that separation (like the expansion of the universe) isn't a thing. It is an abstraction. The expansion of the universe is below c. The expansion in two different directions added together can be more can c. 

No different than claiming two planes going in opposite directions at 400 miles and hour are breaking the sound barrier because the are going away from each other at 800 mph.


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## Christine Wheelwright (Aug 17, 2022)

Swank said:


> Two beams of light traveling in opposite directions are moving away from each other at twice the speed of light.
> 
> I can move my gaze between stars many light years apart at thousands of times the speed of light.


In my frame of reference I might have light moving in one direction (at the speed of light) and light moving in the opposite direction (at the speed of light) as you describe.  However, in the frame of reference of the first beam, the second beam is not moving away from it at twice the speed of light.  It is simply moving away at the speed of light.  This is modelled by the Lorentz transformations.  Nothing can exceed the speed of light in any frame of reference.

[EDIT: In other words, what alai said!......You beat me to it!]


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## paranoid marvin (Aug 17, 2022)

I suspect that if the human race is around long enough to travel outside of our galaxy (assuming we can even leave our solar system),  a lot of the things that we take as 'facts' will be as accurate as the scientific knowledge will held to be irrefutable 1000 years ago. In fact it could only take one alien spacecraft landing landing in Central Park tomorrow to turn our scientific knowledge on it's head.

Granted we have come along way in the last 1000 years, and the probes and satellites that we have sent out into space (along with the development of computers which can calculate in seconds what would have taken a lifetime) have left us in an infinitely stronger position to determine facts, but we are still trying to judge the mysteries and mechanics of the universe from a tiny planet in a remote part of the galaxy. 

I do think that it's likely that there are ways of travelling from point A to point B faster than the light is able to. Whether that means 'bending' space, slowing down time, or something else I do not know. Does that mean moving at faster than the speed of light? In a way yes, in a straight-line race, then probably no. But I do hope and suspect that there is far, far more to the universe than we could ever comprehend or imagine even in our wildest dreams. It's just too darn vast a place for that not to be the case.


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## Swank (Aug 17, 2022)

Christine Wheelwright said:


> In my frame of reference I might have light moving in one direction (at the speed of light) and light moving in the opposite direction (at the speed of light) as you describe.  However, in the frame of reference of the first beam, the second beam is not moving away from it at twice the speed of light.  It is simply moving away at the speed of light.  This is modelled by the Lorentz transformations.  Nothing can exceed the speed of light in any frame of reference.
> 
> [EDIT: In other words, what alai said!......You beat me to it!]


I was demonstrating what was in the example about the expansion of the universe from the reference frame of earth. It is a legitimate reference frame, and nothing more than that. We can quite definitely observe things moving away from us in two directions that sum to more than c.


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## alai (Aug 17, 2022)

Robert Zwilling said:


> Which brings up the idea of transporting matter or an energy pattern by replicating the exact pattern of an object and its place in space such that the space around it represents another location in space. An advanced form of spooky action at a distance. It would be recreating a pattern in another location which would be everything it was in the original location.
> 
> Would consciousness also be able to travel the same way. Probably not, as it is just a recreation of a physical pattern that gets transported. This is where it gets whimsical. The body could either arrive with a blank state for memories or the memories could also be physically copied such that the person would know what was going on. If the person didn't know what was happening, they would need a set of instructions to tell them what was happening.


To take those in reverse order, imagine the 'copying' part with no 'transmission problem' aspect.  Just a ma-HOO-sive USB-omega cable, let's say.  If your copy lacks memories, it presumably also lacks the cognition to reconstruct them from written or verbal instructions!  Unless there's some poorly understood mechanism wherein some of the processes of consciousness have a very different biological basis from others.  Either way, if you're a brutal materialist reductionist like me, you'd ascribe that to a defect or deficiency in the copying process;  maybe you replicated the 'hardware' but not its 'state', and we need a Jupiter-sized accelerator to scan the original you with sufficiently high resolution.  If you're a Vitalist, Dualist, or other flavour of woo-salesperson, you might say this is evidence of the uniqueness of souls, Platonic barcodes, or the like.

But if the USB-omega method works, then surely it's in principle to generalise that to non-spooky action at a distance -- i.e., transmitting your copy at the speed of light.

Then there's the matter of whether you can transmit information via 'quangles'.  If that's possible, and the previous step is too, then essentially spooky-teleportation is just a question of scaling that up to the required number of bits of information.  Gets us into all sorts of causality problems, so you either have to invoke some sort of Cosmic Censorship, or dispense with that entirely.

I suppose there might be some sort of way of bundling the two things, so you can have human-scale spook-action without the intermediate steps, but I can't think offhand for what a rationale for that might be.


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## Robert Zwilling (Aug 17, 2022)

The memories are physically recorded so theoretically they could be replicated along with the rest of the body. If the copying mechanism was really good, then copying everything including the soul might be possible. If the copying isn't that perfect, then perhaps the entity that makes the "I" part of the mind doesn't get copied. So now the body arrives, or is activated, in a remote location, complete with memories, as those can be copied, but only a loose way of attaching them together. Kind of like amnesia, you can walk, talk, eat, do complex things, remember some things, but you don't know who you are. You have all the facts, you're functional, but there are too many facts to have a clear idea of what to do next. That's where the instructions come in, the game plan so to speak. Based on how the memories are remembered, some people might just walk away from the job, ready to live their life the way they think they want to.


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## Astro Pen (Aug 17, 2022)

If the universe is expanding then every beam of light is travelling away FTL as it surfs the wave of expansion. By a minute amount of course but it is.
_If_ you subscribe to Guth's 'inflation' theory then outer galaxies are travelling away from us FTL right now.

Personally I regard cosmic inflation as 'the science of the gaps', a convenient elastoplast applied to awkward numbers in denial of general relativity. 
Should it ever be proven physically possible with a replicable methodology then I will be on board for that FTL cruise on the good ship _Paradox_


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## Overread (Aug 17, 2022)

Well so far we've almost got everything else from Star Trek including sliding doors! 


Personally I always think its important to remember that science can only tell us what is impossible at the point in time at which science currently is. The future is unpredictable and many things thought impossible have been proven to be possible through the steady advance of science and understanding. 
At one time flying for humans was impossible, let alone flying hundreds of people at once; carrying the whole of a library on something no bigger than your finger; flying to the moon; actually looking at the surface of mars, the bottom of the ocean; predicting the weather. There are many many things that we do today, either personally or as a species which at one time were considered totally impossible to so outlandish they wouldn't even have conceived them as things to do. 



Of course there's always a chance that things diverge down a different pathway - eg we forget about travelling faster than light because we discover a way to use wormholes to move around and thus negate the need for FTL travel options.


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## Astro Pen (Aug 17, 2022)

ps
There is something else at play here, an anthropic* error. @Swank alluded to it earlier. We try to model the universe from a single point position. We can barely think outside that "you are here" box.
If you try to form an omniscient model of the universe rather than a point one, you will begin to reshape your perspective.
The other anthropic error is to use human reference points like extremely hot, incredibly fast, huge distance and such. A temperature simply is what it is and we should not ladle 'relative to me' adjectives on to science, because they are only relative to us, our speed of neuron firing and biological comfort zone.

*this may not be the right word use, but I think you know what I mean. Feel free to correct me.


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## Ursa major (Aug 17, 2022)

Wayne Mack said:


> The universe expands faster than the speed of light.


Apart from anything else, the universe isn't expanding _inside_ the universe -- indeed, as far as we can tell, it's expanding into _absolutely_ nothing at all, an absolutely nothing at all that has no dimensions of space or time) -- so is not constrained by the _internal_ rules of the universe (one of which is that nothing can travel faster than _c_).


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## Christine Wheelwright (Aug 17, 2022)

Swank said:


> I was demonstrating what was in the example about the expansion of the universe from the reference frame of earth. It is a legitimate reference frame, and nothing more than that. We can quite definitely observe things moving away from us in two directions that sum to more than c.


Can we though? If I step outside my space station and throw one ball left at the speed of light and one ball right at the speed of light, how far apart are they when I observe them a year later? The answer is one light year not two Remember I am looking back in time six months but I cannot reason that the objects are two light years apart in 'their present'.   In fact the objects see each other one light year apart (the first ball sees the second still at the space station....that image having traveled along side it).  Thr second ball effectively does indeed exist at the space station in terms of it's effects on the first ball.  And vice versa of course.


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## Astro Pen (Aug 17, 2022)

Ah but what does my omniscient observer see?


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## Christine Wheelwright (Aug 17, 2022)

Astro Pen said:


> Ah but what does my omniscient observer see?


Ah but the concept of an omniscient observer is meaningless. There is no such thing as a snapshot of the universe that shows the balls in my example two light years apart at a moment in time one year later. Because that particular moment only exists at the location where I threw the balls.  Space and time are not separate parameters.


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## Swank (Aug 17, 2022)

Christine Wheelwright said:


> Can we though? If I step outside my space station and throw one ball left at the speed of light and one ball right at the speed of light, how far apart are they when I observe them a year later? The answer is one light year not two Remember I am looking back in time six months but I cannot reason that the objects are two light years apart in 'their present'.   In fact the objects see each other one light year apart (the first ball sees the second still at the space station....that image having traveled along side it).  Thr second ball effectively does indeed exist at the space station in terms of it's effects on the first ball.  And vice versa of course.


They are two light years apart from the observation of the station. One ball has no influence on the other.

If you aimed each ball at targets 1ly away in each direction and 2ly total, 2 years after launch you would see the simulataneus impact. (Ball out, light of impact back.)


This really isn't a relativity problem. It is just the fact that if you add two unrelated events up and divide by time, the number is larger than the velocity that objects can travel. It is silly to conflate observation with velocity.


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## sciwriterPark (Aug 17, 2022)

i think the first thing we have to overcome is how to generate tremendous energy in a small form factor.


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## Christine Wheelwright (Aug 17, 2022)

Swank said:


> If you aimed each ball at targets 1ly away in each direction and 2ly total, 2 years after launch you would see the simulataneus impact. (Ball out, light of impact back.)


I agree with that.  But my point is that, to me as the observer, they *exist* where I see them.  If I check them one year after releasing them they are half a light year away as per my observation.  Any effect they have on me (their light or heat reaching me, their gravitational effect on me) demonstrates them to be half a light year away in _*my*_ present moment.


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## Daysman (Aug 17, 2022)

AFAIK, we've not observed any massive objects _actually_ moving FTL?

They'd need to interact with photons we can see, of course, but once discovered we'd have to handle not agreeing the order of events with anyone ever again...

I'm not sure why any future theory would address this topic directly, or expose any loophole that might allow it. 

I'm guessing someone will prompt a suitable AI at some point and we'll suddenly have two dozen solutions, most of which are very bad ideas, except we won't know which ones or why... not at first.

As for playing with spacetime, that's really a _topology_ thing isn't it?

I need food.


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## Swank (Aug 17, 2022)

Christine Wheelwright said:


> I agree with that.  But my point is that, to me as the observer, they *exist* where I see them.  If I check them one year after releasing them they are half a light year away as per my observation.  Any effect they have on me (their light or heat reaching me, their gravitational effect on me) demonstrates them to be half a light year away in _*my*_ present moment.


I'm not sure I see the relevance. You might not be able to see a train in a tunnel, but it's there.


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## Christine Wheelwright (Aug 17, 2022)

Swank said:


> I'm not sure I see the relevance. You might not be able to see a train in a tunnel, but it's there.


I think we are probably on the same page.  My point is that after a year I check on the ball and it is half a light year away.  That is what I see.  That is what I measure by any means possible.  I feel a gravitational field from it confirming that it is half a light year away.  Every physical property or measurement or observation tells me it is half a light year away.  That is my reality!  You say it is actually one light year away and I am looking six months back in time, which is perhaps valid.  And I notice the new telescope guys say we are looking at galaxies billions of years ago (rather than using the phrase 'billions of light years away').  That's all good.

The other thing worth mentioning is that the velocity of the object can be ascertained by looking at the dopler shift in the frequency of the light it emits (in case the object we are looking at is not the ball we threw one year ago....the velocity of which we know).


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## Christine Wheelwright (Aug 17, 2022)

And in answer to the original question - not a chance we will ever travel faster than light.  I doubt we will get manned travel outside the solar system (and, indeed, what would be the point if we can't reach the stars?).  I see the physics as a hard limit, I'm afraid.


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## psikeyhackr (Aug 17, 2022)

I do not think it is possible, I just hope that it is not impossible. 

It took about 200 years to notice that the precession of Mercury showed that something was wrong with Newtonian physics. It was not until the 1990s that someone figured out that the increasing rate of expansion of the universe demonstrated that Poul Anderson's Tau Zero was fundamentally flawed. 

As long as there is unexplained physics out there then there can be hope. But if we can get to 20% of light speed, extend human life spans to 300 years and come up with some form of suspended animation then infinite possibilities cannot be excluded. 

Ad Astra!

Aliens be damned!  Argh!

To be trapped in this solar system for the next 100,000 years is a dismal prospect.


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## Overread (Aug 18, 2022)

Christine Wheelwright said:


> And in answer to the original question - not a chance we will ever travel faster than light.  I doubt we will get manned travel outside the solar system (and, indeed, what would be the point if we can't reach the stars?).  I see the physics as a hard limit, I'm afraid.


The thing is physics is only a hard barrier as we understand physics today. 

Don't forget go back in time and at various points many technologies we have today had hard barriers in logical thinking at the time. 

Things like jumbo jets or rockets were impossible. The idea that you could fly not just 1 person but hundreds at once; or go around the world in only 3 days (Concord) etc... Even a lot of basic things like mobile phones, the internet, computers and such were all impossible at various points in time. All with very sound logical thinking for the time. 

That's the key with science. It can't really tell you what is or isn't possible. It can only tell you what is and isn't possible within the context of understanding today and what might be within the understanding of tomorrow. But next week; next month; next year - the further off you try and forecast the more wildly inaccurate it becomes.


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## Swank (Aug 18, 2022)

Overread said:


> The thing is physics is only a hard barrier as we understand physics today.
> 
> Don't forget go back in time and at various points many technologies we have today had hard barriers in logical thinking at the time.
> 
> ...


80 years ago some engineers thought the sound barrier would destroy aircraft.


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## J Riff (Aug 18, 2022)

Not 'faster' but it amounts to the same thing, so yeah.


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## THX1138 (Aug 18, 2022)

One problem I see is that as a ship travels closer to light speed, the entire electromagnetic spectrum in the surrounding space will become more coherent: a full spectrum laser the diameter of the ship's width cross section. That's a lot of energy to absorb.

We know that science today has made materials that self-generate low level magnetic fields, and these fields can be amplified with by a low amp external power source. So, cover the entire ship with a front plane highly/absolute reflective surface that also self-generates a total'ish refractive field above it, that can be amplified by the ships power source to refract the entire known electromagnetic spectrum (+- for unknown frequencies).

This would allow the ship the 'slip' into the coherent wall of light, thus closer to LS. 
Now the view from inside the ship looking out would be...as close to absolute black as you could get. No star streaks or cloud tunnels. The entire/close to entire electromagnetic spectrum is being bent around the ship. Thus, darkness.

Less friction = closer to the speed of light. With this in mind about this type of system, you would need to travel the path of less electromagnetic spectral friction. The darker the better, full spectrum wise.

I agree with the near light limit theory because just as the mass of water limits the speed of fish, subs, torpedoes, UWLBM. The same is for the speed of sound and light too. That is where material science came in for both. The same is for LS. 

Science fiction plus a positive result from a science theory could become science fact.  
Until then, this is both theory and fiction!


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## Astro Pen (Aug 18, 2022)

FTL, I think, will always be impossible. As will 'gravity shields' which are also based on flawed thinking.

 So- what _is_ possible for future technology to deliver?
Again I suggest that we think outside the mental trap of of our single point biology .
Once we are fully digitised and consist of a pure information structure, no longer facing 'three score years and ten', the light barrier will cease to be of such great concern.
We can be both eternal and duplicable (which leads to a whole philosophical discussion on where the "self" is. But that is for another day. 

(Stross's _Accelerando is a _ quite transformative SF read in this regard.)


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## Harpo (Aug 18, 2022)

Swank said:


> Two beams of light traveling in opposite directions are moving away from each other at twice the speed of light.
> 
> I can move my gaze between stars many light years apart at thousands of times the speed of light.


How about if we built a gigantic particle accelerator all the way around the sun (like in Ringworld or whatever) so the particles could be sped up to almost lightspeed, and then make two collide, producing (my hypothesis, unless others have also said this) tachyon particles.

Probably nonsense, of course


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## Swank (Aug 18, 2022)

Harpo said:


> How about if we built a gigantic particle accelerator all the way around the sun (like in Ringworld or whatever) so the particles could be sped up to almost lightspeed, and then make two collide, producing (my hypothesis, unless others have also said this) tachyon particles.
> 
> Probably nonsense, of course


If tachyon's existed, this would be a great plan. Why not just build the warp field using dilithium crystals? Or get the computer to calculate the jump to lightspeed so we don't fly through any stars? Or travel in a police call box?


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## TheEndIsNigh (Aug 18, 2022)

So....

Faster than light;-

The moon is orbiting the earth happily shining down on us poor peasants.

If the earth were to suddenly disappear the gravitation force holding the moon would also no longer exist.

Does anyone think that the moon would hang around for a few seconds to travel in a straight line until the speed of light caught up with it.

No it would immediately whip off at a tangent instantaneously.

Yeah but that can never happen I hear you say. You can't just disappear the earth so it's a pointless examlpe you say.

But we're in the world of thought experiments here. If old the E=mc2 guy can think up experiments that can't be implimented that prove his theory surely I can have a bash too.

In any case the Earth is disappearing from it's current position every pica-second as it waltzes round the sun, galaxy, universe.

I can't recall anyone saying the moon is dragging it's feet to catch up - otherwise it would be drifting away at an alarming rate.

as in

"Oooh look that blue thing I can't get away from is moving again.  I'll wait for the speed of light to tell me about it and then catch up."

Two hundred and fifty miliseconds later...

"HEY! Earth, wait for me!"


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## Wayne Mack (Aug 18, 2022)

Another thing to consider is that the discussion is really about much faster than the speed of light. Correct me if I'm wrong, but Alpha Centauri is the nearest star at 4.3 light years away; a nearly 9 year round trip at the speed of light. Although there will be some sort of time dilation effect for those on the ship, a nearly decade long launch to return period seems like a large hurdle to overcome ("Let's go make some crop circles, it'll only take us nine years to do it."). To go much further requires speed at orders of magnitude greater than the speed of light.


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## mosaix (Aug 18, 2022)

TheEndIsNigh said:


> So....
> 
> Faster than light;-
> 
> ...


In thought gravity operated at the speed of light. If so the ‘moon would hang around’. Not sure how long for.


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## Mon0Zer0 (Aug 18, 2022)

Swank said:


> Two beams of light traveling in opposite directions are moving away from each other at twice the speed of light.
> 
> I can move my gaze between stars many light years apart at thousands of times the speed of light.



In case you're not joking:

C doesn't apply to relative speed as each is independently travelling at light speed. Both particles are moving in opposite directions at the speed of light. Each particle has its own inertial reference frame.

"You can ask how fast the distance between them is increasing in a particular inertial reference frame, and the answer will indeed be that it's increasing at 2c, but the light-speed limit only applies to things like particles and information, it doesn't apply to concepts like "the distance between two objects"."

Reference: Light in opposite directions

Edit: Christine and Alai beat me to it

Your gaze is moving between photons arriving at your eyes, not between the galaxies.

I love the idea of your eye actually moving from one object to another as you look at them - as if you were touching them with your eyeball.


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## paranoid marvin (Aug 18, 2022)

Christine Wheelwright said:


> And in answer to the original question - not a chance we will ever travel faster than light.  I doubt we will get manned travel outside the solar system (and, indeed, what would be the point if we can't reach the stars?).  I see the physics as a hard limit, I'm afraid.




I agree that human beings in their current form are extremely unlikely to travel outside of our solar system; if this is the case, we therefore will not travel faster than the speed of light.

On the other hand, I do believe we have not come to the end of our scientific discoveries of the universe. It's could be that the next discovery will be yet another one that makes us have to re-position our understanding of what and what isn't possible. As I mentioned earlier, there is so much in the universe that has yet to be discovered, that dismissing the _theoretical _possibility of travelling faster than light would be an over-estimation of our current understanding.

There is so much space out there, that who knows what could be whizzing around undetected, perhaps travelling at many times the speed of light. It's entirely possible that when you reach a certain velocity, the laws and physics of the universe are turned on their heads. 

Apparently the universe is expanding, but also there (apprently) is no 'edge' to it. How can that be? If there was no edge, we would either be going around in circles or the universe would be (somehow) expanding into itself. We are faced with so many anomalies and contradictions that almost anything is both possible and _impossible at the same time. _The more we are told, the more I think that Douglas Adams had a better understanding of the meaning and workings of the universe than all of the astronomers and scientists combined.


----------



## Mon0Zer0 (Aug 18, 2022)

Astro Pen said:


> Ah but what does my omniscient observer see?



If they're all knowing, does their vision matter? They know it all anyway. Maybe they just see clouds and harps and stuff, whilst the knowledge just pops in there at the moment it happens.

Or are we talking about seeing like... observing, in the physics sense? Like... their brains are entangled with every particle in the universe, with an observer that causes all probabilities to collapse, man? 

*inhales*  
*passes one reefer*
*blows smoke*


----------



## Mon0Zer0 (Aug 18, 2022)

paranoid marvin said:


> Apparently the universe is expanding, but also there (apprently) is no 'edge' to it. How can that be? If there was no edge, we would either be going around in circles or the universe would be (somehow) expanding into itself. We are faced with so many anomalies and contradictions that almost anything is both possible and _impossible at the same time. _The more we are told, the more I think that Douglas Adams had a better understanding of the meaning and workings of the universe than all of the astronomers and scientists combined.



Aren't those only contradictions because we lack the imaginative faculties to be able to picture them as they are? The meaning of the words is so beyond our realm of experience it's like trying to imagine a new colour.


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## Mon0Zer0 (Aug 18, 2022)

As for FTL? I think probably not. Putting aside the physics, the engineering and power challenges of the Alcubierre drive are unsurmountable.  If we move beyond our world, it'll be at a snail's pace and over many centuries. 

Pessimistically, I'm not sure we'll last long enough to make the leap to an interplanetary civilisation. I hope I'm wrong.


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## Astro Pen (Aug 18, 2022)

At the end of the day it is very simple, and yet it makes our heads hurt.
*The speed of light IS the speed of time*
So there goes the "now" winging away at lightspeed. But every point in the universe has a 'now' romping out from it at the same time. Other nows arrive at a single observer at origin dependent times.
The omniscient veiwpoint is a way to model that. Forget your single viewpoint and your clock, look instead at the cats cradle of motion. The continuous dynamic of nows on the temporal axis, and the things moving on the velocity curve with various balances between time and space.
If inflation theory is true then Lots of stuff was lobbed 'outside' of our space time. WE can never ever access it from our single viewpoint but that doesn't mean it doesn't exist in the 'big picture'.


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## paranoid marvin (Aug 18, 2022)

Mon0Zer0 said:


> Aren't those only contradictions because we lack the imaginative faculties to be able to picture them as they are? The meaning of the words is so beyond our realm of experience it's like trying to imagine a new colour.




I think that most scientific advances are based around mathematics and numbers. Because the 'numbers' involved in calculating anything in our universe are so mind-bogglingly huge, you get to the point where they become redundant. What are the odds of me and you and everyone on this forum discussing this topic? From the 'big bang' to the creation of planets, to the evolution of life and then technology to a state where we can be sat in front of keyboards/on mobile phones. The odds/numbers are so staggeringly large as to be a mathematical impossibility. Numbers just are sufficient.


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## Astro Pen (Aug 18, 2022)

Yes @paranoid marvin  The Ford Mustang is a product of nature. 
It is a shame so many take the view that nature is a walk in the spring woodland rather that everything that biology and geology, working together, makes.


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## psikeyhackr (Aug 18, 2022)

mosaix said:


> In thought gravity operated at the speed of light. If so the ‘moon would hang around’. Not sure how long for.


Less than 2 seconds.

Which way it would go would depend on time of month. At new moon it would drop into an orbit closer to the Sun. At full moon farther out.

In between gets more complicated. Maybe more elliptical orbits around the Sun.


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## msstice (Aug 19, 2022)

Christine Wheelwright said:


> Ah but the concept of an omniscient observer is meaningless. There is no such thing as a snapshot of the universe that shows the balls in my example two light years apart at a moment in time one year later. Because that particular moment only exists at the location where I threw the balls.  Space and time are not separate parameters.


Scenario: Two objects A, B, each giving off little flashes of light, are accelerated to slightly less than _c_ and released in opposite directions from a station C.

In one year station C will observe A (and B) to be each 0.5 LY from the station (a separation of 1 LY). Computed speed will be 0.5c (though redshift will tell a different story). Rate of increase of separation will be _c_.

In two years station C will observe A (and B) to be 1 LY from the station. Computed speed will be 0.5c for each object and rate of increase of the distance between them will be c.

Now consider an observer D who is far from C, and perpendicular to the line A C B. Say the observer D is 10000 LY from C.

D sees A and B shoot out from C at some time. 1Y later D sees A at a distance of ~1 LY from C and ~2LY from B. Inferred speed will be ~c for each object and ~2c for the lengthening of the gap.

From geometry it seems that D will see A and B slowing down the further they go because of the larger angles.

But I vaguely recall Euclidean geometry doesn't apply so I'm likely wrong, but don't know how I'm wrong.


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## Swank (Aug 19, 2022)

Mon0Zer0 said:


> In case you're not joking:
> 
> C doesn't apply to relative speed as each is independently travelling at light speed. Both particles are moving in opposite directions at the speed of light. Each particle has its own inertial reference frame.
> 
> ...


Your post sounds like you disagree with me and agree with Alia and Chistine, but you are making the same point I was: Relative speed is a concept. 

My example of moving my eyes was to demonstrate other types of conceptual speed rather than actual velocity.


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## Christine Wheelwright (Aug 19, 2022)

msstice said:


> From geometry it seems that D will see A and B slowing down the further they go because of the larger angles.


Yes, that does all seem correct.


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## Swank (Aug 19, 2022)

Christine Wheelwright said:


> Yes, that does all seem correct.


Like the opposite of ground rush?


----------



## TheEndIsNigh (Aug 19, 2022)

Mon0Zer0 said:


> In case you're not joking:
> 
> C doesn't apply to relative speed as each is independently travelling at light speed. Both particles are moving in opposite directions at the speed of light. Each particle has its own inertial reference frame.
> 
> ...


Of course technically if I was sat on a photon observing another bloke on a photon travelling in the opposite direction I wouldn't be able to observe him at all. Likewise if we were travelling toward each other the first observation would be when his head impinged on my personal space. (all visible light having been squashed into the ultra violet)

I've mentioned it before but here we go again.

Humans are so self centred. It used to be the sun revolves around the Earth.

The it was we are the only planet.

Then it was we are the only planet with intelligent life (well any life at all).

Now it's the universe is big- so big it contains all matter.

Yet since no one has or ever will understand how all this stuff around came into being and how it all works my I suggest the following.

There was/is/willbe/can be/ many such events. Maybe our big bang is just that. A localised event in a vastness of other places that bangs have and will occur. If it can happen once why not many times.

If there are other localised dollops of matter all around us it would also explain why our bit is expanding because the gravitational pull of, oh I don't know lets say 10,000,000,000,000 such dollops, would be pulling us this way and that. Obviously space is not at a premium so why limit it.

AND I'm not talking parallel universes here - God forbid


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## Mon0Zer0 (Aug 19, 2022)

Relevant:


> A Slower Speed of Light is a first-person game in which players navigate a 3D space while picking up orbs that reduce the speed of light in increments. A custom-built, open-source relativistic graphics engine allows the speed of light in the game to approach the player's own maximum walking speed. Visual effects of special relativity gradually become apparent to the player, increasing the challenge of gameplay. These effects, rendered in realtime to vertex accuracy, include the Doppler effect; the searchlight effect; time dilation; Lorentz transformation; and the runtime effect.


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## Mon0Zer0 (Aug 19, 2022)

Swank said:


> Your post sounds like you disagree with me and agree with Alia and Chistine, but you are making the same point I was: Relative speed is a concept.



I was making the point that "conceptual speed" is not speed. In the example you gave the "relative speed" is not speed but a ratio of two objects moving at speed. Speed is a physical process, comparisons or relations of objects at speed are not.


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## Astro Pen (Aug 19, 2022)

As the condemned man, and his whole world, rushed toward the stationary bullet.


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## Swank (Aug 19, 2022)

Mon0Zer0 said:


> I was making the point that "conceptual speed" is not speed. In the example you gave the "relative speed" is not speed but a ratio of two objects moving at speed. Speed is a physical process, comparisons or relations of objects at speed are not.


Correct. That was exactly what I was demonstrating when it was suggested that after 1 year two opposite beams of light are only 1 light year apart. They are 2 light years apart, and that isn't a conflict with the max speed of light because the two aren't connected except in our minds.


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## Wayne Mack (Aug 19, 2022)

msstice said:


> Scenario: Two objects A, B, each giving off little flashes of light, are accelerated to slightly less than _c_ and released in opposite directions from a station C.
> 
> In one year station C will observe A (and B) to be each 0.5 LY from the station (a separation of 1 LY). Computed speed will be 0.5c (though redshift will tell a different story). Rate of increase of separation will be _c_.
> 
> ...


My understanding is slight different. To repeat the scenario (at least my understanding), there is a central point C. At time 0, light beams A and B are released in opposite directions. Assuming some magic form of observation, an observer at point C will see A and B being 1 lightyear distant from C. There have been no relativistic alterations at C. At C, an observer would see a 2 lightyear separation between A and B without requiring either to travel faster than the speed of light.

An alternate way to view this scenario would be to have point C1 with points A1 and B1 each 1 lightyear distant along a straight line and not moving relative to each other. A1 and B1 simultaneously release a beam of light towards C1. Each beam, travelling at the speed of light will take 1 year to reach C1. This is the basic definition of velocity. Furthermore, each beam will take 2 years to reach an opposite point at A1 and B1. 

Where things get really bizarre (and where I am moving beyond my knowledge of physics) is when one uses an observation point at A in the original scenario. In my understanding, A would observe C moving away at the speed of light. However, A would also observe B moving away at the speed of light, yet there would also be an expanding gap between B and C. I do wish to reiterate that the latter is only my (mis)understanding of relativistic physics and I would appreciate someone more knowledgeable stepping in and setting me straight.


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## Christine Wheelwright (Aug 19, 2022)

Swank said:


> Correct. That was exactly what I was demonstrating when it was suggested that after 1 year two opposite beams of light are only 1 light year apart. They are 2 light years apart, and that isn't a conflict with the max speed of light because the two aren't connected except in our minds.


But doesn't this depend on the concept of the omniscient observer who can look at both objects at a single moment in time and say; "yes, they are now two light years apart having travelled at 1C for one year in opposite directions."  The problem I have with this is that there is no single point in time that exists across multiple frames of reference.  Time is inseparable from space. You have to pick a frame of reference and observe from that.  And there is no frame of reference in which the two objects are two light years apart after one year.


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## SilentRoamer (Aug 19, 2022)

TheEndIsNigh said:


> There was/is/willbe/can be/ many such events. Maybe our big bang is just that. A localised event in a vastness of other places that bangs have and will occur. If it can happen once why not many times.
> 
> If there are other localised dollops of matter all around us it would also explain why our bit is expanding because the gravitational pull of, oh I don't know lets say 10,000,000,000,000 such dollops, would be pulling us this way and that. Obviously space is not at a premium so why limit it.
> 
> AND I'm not talking parallel universes here - God forbid



There seems to be a logical disconnect here. The Big Bang wasn't an explosion of matter in an existing space - in fact the terminology of "Big Bang" is not a great descriptor.

The "Big Bang" is the metric scale expansion of spacetime, it is not expanding "into" anything because spacetime itself is part of the expansion.

Any other such "dollops" are actually parallel universes, because they are not part of our spacetime. The Big Bang was not an explosion in a pre-existing space, it was the expansion of all spacetime.

Now it is possible there are infinite "dollops" but they cannot operate in the same "space" because "space" is not nothingness, there are properties to spacetime - it is not the nothingness that existed before the Universe came into being (where even the term "before" has little value because there was no before, spacetime began at the Big Bang.) It would be like standing at the North Pole and asking which way is further North.

I hope that makes some sense.


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## Mon0Zer0 (Aug 19, 2022)

Wayne Mack said:


> Where things get really bizarre (and where I am moving beyond my knowledge of physics) is when one uses an observation point at A in the original scenario. In my understanding, A would observe C moving away at the speed of light. However, A would also observe B moving away at the speed of light, yet there would also be an expanding gap between B and C. I do wish to reiterate that the latter is only my (mis)understanding of relativistic physics and I would appreciate someone more knowledgeable stepping in and setting me straight.



From A's perspective, C would remain in place as the photons from C moving in the opposite direction would not be able to catch up with A, travelling at the speed of light.

See the video above too, you also get some freaky visual effects travelling at the speed of light. Looking forwards the entirety of your field of vision changes to encompass the entire field of view. Looking backwards everything goes black. Navigating at the speed of light is a nightmare.


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## hitmouse (Aug 19, 2022)

paranoid marvin said:


> I think that most scientific advances are based around mathematics and numbers.


Except for those advances which are not primarily mathematical, which is most of science. For example: molecular biology, materials science, physical geography, etc. This should be obvious if you look at the research papers in a few issues of Nature or Science.

There is a bit of maths involved, for sure, but it is a tool, and the science itself is not by and large extrapolated from pure maths. Some clever boffin did not do some sums on the back of a napkin and come up with plate tectonics, the behaviour of social insects, penicillin, or with the Covid vaccine.


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## Swank (Aug 19, 2022)

Christine Wheelwright said:


> But doesn't this depend on the concept of the omniscient observer who can look at both objects at a single moment in time and say; "yes, they are now two light years apart having travelled at 1C for one year in opposite directions."  The problem I have with this is that there is no single point in time that exists across multiple frames of reference.  Time is inseparable from space. You have to pick a frame of reference and observe from that.  And there is no frame of reference in which the two objects are two light years apart after one year.


I think you can say that two places that exist at similar velocity vectors are essentially in the same refernce plane, like us and Alpha Centauri. And you csn observe distant quasars to affirm that. So when our light beam hits Centauri, it does so in a reference frame that functions just like ours does to where we can say "This is happening there right now."


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## mosaix (Aug 19, 2022)

psikeyhackr said:


> Less than 2 seconds.
> 
> Which way it would go would depend on time of month. At new moon it would drop into an orbit closer to the Sun. At full moon farther out.
> 
> In between gets more complicated. Maybe more elliptical orbits around the Sun.



Thanks. I’ve found it’s 1.3 seconds to be precise.  

I thought that one of the things that made FTL travel a no no was that as an object speeds up it gains mass and as it approaches the speed of light it gains infinite mass. True or not?


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## Ursa major (Aug 19, 2022)

mosaix said:


> it gains infinite mass


That sounds like the ultimate in sea see food diets....


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## TheEndIsNigh (Aug 19, 2022)

SilentRoamer said:


> There seems to be a logical disconnect here. The Big Bang wasn't an explosion of matter in an existing space - in fact the terminology of "Big Bang" is not a great descriptor.
> 
> The "Big Bang" is the metric scale expansion of spacetime, it is not expanding "into" anything because spacetime itself is part of the expansion.
> 
> ...


You're  being too "local". Why limit the extent of nothing?

If spacetime can expand from nothing and expand into the nothingness then why not twice or as many times as it likes.

Think bubbles in water, where the water here is nothingness. The bubbles can be far apart and might never know of each others existence. 

Just because they can't be observed doesn't mean they don't exist.

Plus if there was a time zero, then there was a time - 1. 

I.E. the time before time 0. Something must have happened before 0 - else why did anything happen at all?

As in

Effect < cause


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## Swank (Aug 19, 2022)

TheEndIsNigh said:


> You're  being too "local". Why limit the extent of nothing?
> 
> If spacetime can expand from nothing and expand into the nothingness then why not twice or as many times as it likes.
> 
> ...


Maybe time was one of the things to come out of the Big Bang, like light and matter.


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## Robert Zwilling (Aug 20, 2022)

Slipping in and out of a parallel universe where time didn't exist would make travel a whole lot easier.


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## psikeyhackr (Aug 20, 2022)

mosaix said:


> Thanks. I’ve found it’s 1.3 seconds to be precise.
> 
> I thought that one of the things that made FTL travel a no no was that as an object speeds up it gains mass and as it approaches the speed of light it gains infinite mass. True or not?



Yes!

That is why we get stories with HYPERSPACE where physics works differently or some kind of wormhole technology. 

With almost 300 years from Newton to Einstein I won't assume that something amazing might not be discovered/figured out by some bizarre genius in the next 1000 years. After that I will worry.


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## Swank (Aug 20, 2022)

Robert Zwilling said:


> Slipping in and out of a parallel universe where time didn't exist would make travel a whole lot easier.


Or putting teflon on your rocket fins.


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## TheEndIsNigh (Aug 20, 2022)

mosaix said:


> Thanks. I’ve found it’s 1.3 seconds to be precise.
> 
> I thought that one of the things that made FTL travel a no no was that as an object speeds up it gains mass and as it approaches the speed of light it gains infinite mass. True or not?


And yet we are told there are an *almost* infinite (can't be infinite - or can it) number of particles (you all know the names) whizzing around the universe willy nilly at near c and actual c at any moment in none time.

Oops just had a trillion neutrinos pass straight through my head and they didn't even ask permission but maybe they triggered this thought.

No that can't be right because to have triggered this thought they would have been travelling in negative time to get here now.


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## paranoid marvin (Aug 20, 2022)

hitmouse said:


> Except for those advances which are not primarily mathematical, which is most of science. For example: molecular biology, materials science, physical geography, etc. This should be obvious if you look at the research papers in a few issues of Nature or Science.
> 
> There is a bit of maths involved, for sure, but it is a tool, and the science itself is not by and large extrapolated from pure maths. Some clever boffin did not do some sums on the back of a napkin and come up with plate tectonics, the behaviour of social insects, penicillin, or with the Covid vaccine.




It's just that whenever the universe is discussed on tv, it's usually inm the form of numbers. Amount of galaxies, stars, age of the universe etc. And we all know what the chances of anything coming from Mars are. But the numbers are all so ridiculously huge that they largely become meaningless.


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## TheEndIsNigh (Aug 20, 2022)

*OY*

I've warned you lot before.

If you don't stop tipping your rubbish up here on Mars there'll consequences.

The chances of that are low and make no mistake.

And don't think that whirly thing you left up here is going to survive much longer.

We'll be returning that with interest soon too.


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## Wayne Mack (Aug 20, 2022)

TheEndIsNigh said:


> Plus if there was a time zero, then there was a time - 1.


I suggest that there is a difference between Time 0 and having No Time. In my imagination, the minimal characteristics needed to produce time would be having three particles with some sort of interaction between them. 

I suggest that the necessary characteristic of time is of relative change. With a single particle, there can be no motion, because there is no reference point. The only point in existence is the particle, so there is no way to identify movement.

If there are two particles, but they do not interact through some means, then essentially there are two isolated particles--two independent universes--and the situation is the same as in the single particle scenario. With two particles, the concept of distance becomes meaningful. One can compare the size of each particle to the void between particles. This distance may change, but I do not feel there a way to compare rate of change. There would be no concept of velocity or acceleration, thus no concept of time.

When there are three particles with some type of interaction between them, then change in distance between A and B can be compared to changes between A and C and B and C. The relative differences between these allow the definition of time. 

Both Zero and Negative Numbers are abstract concepts and do not truly exist in the physical world. Distance and Time are relational concepts and need a baseline and something outside the baseline to compare against.

That said, this is only my personal thought experiment. Something about only having three particles still bothers me, as that only defines a plane and not a three dimensional space.


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## Swank (Aug 20, 2022)

*A short summary of the thread so far:*

1. The Hard-science Hardliners assure the public that our current understanding of physics is good and complete enough to preclude any changes to our understanding that C is an absolute limit. (Despite current physics also telling us that the vast majority of the universe is made of matter and energy we can neither find nor define.)

2. The Dreamers head right off the deep end with soliloquys on physics ideas that didn't come from scientific theories, but would play well in the newest pages of Marvel comics.

3. The Maybes, who are probably dirty agnostics in their private lives as well.


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## Swank (Aug 20, 2022)

mosaix said:


> Thanks. I’ve found it’s 1.3 seconds to be precise.
> 
> I thought that one of the things that made FTL travel a no no was that as an object speeds up it gains mass and as it approaches the speed of light it gains infinite mass. True or not?


Yes and no. If you define mass by its ability to be accelerated from an external viewer, than yes. But since time is dilating for that mass, acceleration doesn't predict mass accurately.

On the ship the acceleration is linear.


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## Christine Wheelwright (Aug 20, 2022)

TheEndIsNigh said:


> Plus if there was a time zero, then there was a time - 1.
> 
> I.E. the time before time 0. Something must have happened before 0 - else why did anything happen at all?
> 
> ...



Not too sure about that.  Time is a property of our universe.  Therefore it has no context unless the universe exists.  Cause and effect is also a concept that relies upon time for meaning.


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## Wayne Mack (Aug 20, 2022)

Swank said:


> *A short summary of the thread so far:*
> 
> 1. The Hard-science Hardliners assure the public that our current understanding of physics is good and complete enough to preclude any changes to our understanding that C is an absolute limit. (Despite current physics also telling us that the vast majority of the universe is made of matter and energy we can neither find nor define.)
> 
> ...


I generally accept that nothing can move faster than the speed of light, but I still get tripped up over the idea that the rate of expansion of the universe has galaxies moving apart from each other faster than the speed of light. The only explanation that I have seen appears to be a complete cop out, namely that the galaxies aren't moving, it's just that the distance between them is getting larger.








						Is space expanding faster than the speed of light? - Ask an Astronomer
					

In the November/December 2015 edition of StarDate Magazine, I quote Merlin as follows, “Astronomers see the earliest galaxies as they looked about 13 billion



					askanastronomer.org
				




To me, this implies that there is some capability for items move faster than the speed of light.


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## Swank (Aug 20, 2022)

Wayne Mack said:


> I generally accept that nothing can move faster than the speed of light, but I still get tripped up over the idea that the rate of expansion of the universe has galaxies moving apart from each other faster than the speed of light. The only explanation that I have seen appears to be a complete cop out, namely that the galaxies aren't moving, it's just that the distance between them is getting larger.
> 
> 
> 
> ...


I wrote 3 posts about this. 60% C in one direction and 60% C in.the opposite direction is 120% C. But no one object is going faster than light.


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## Ursa major (Aug 20, 2022)

The number of times something is written makes no difference to how correct (or otherwise) it is.


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## Swank (Aug 20, 2022)

Ursa major said:


> The number of times something is written makes no difference to how correct (or otherwise) it is.


No, but it gives someone more opportunities to encounter and read it.


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## TheEndIsNigh (Aug 20, 2022)

Wayne Mack said:


> Both Zero and Negative Numbers are abstract concepts and do not truly exist in the physical world. Distance and Time are relational concepts and need a baseline and something outside the baseline to compare against.


The square root of -1 doesn't exist either, but many a physics and mathmatical solution rely it's existence.

As in

e ^ (i x Pi) - 1 = 0

for a starter.


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## psikeyhackr (Aug 21, 2022)

Ursa major said:


> The number of times something is written makes no difference to how correct (or otherwise) it is.


What?
You mean that we can't just believe that a 1360 ft skyscraper can collapse straight down without knowing the distribution of steel just because the NIST says so?


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## Serendipity (Aug 21, 2022)

TheEndIsNigh said:


> The square root of -1 doesn't exist either, but many a physics and mathmatical solution rely it's existence.
> 
> As in
> 
> ...


Hm... All numbers can be derived from Natural Numbers (0,1,2,3,4,5....). Example is if you can add numbers together then you can do the opposite operation of subtraction and get negative numbers. This gives you Integers (... -2, -1, 0, 1, 2 ....). By similar arguments we get other types of numbers. The start of the list is:

Natural Numbers
Integers
Real Numbers
Complex Numbers
Quarternions
Octonions
etc
I very doubt that without Quartonions we would have ever been able to come up with matrix theory, which of course was more or less essential in identifying the rules of Quantum Physics.


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## Wayne Mack (Aug 21, 2022)

Swank said:


> I wrote 3 posts about this. 60% C in one direction and 60% C in.the opposite direction is 120% C. But no one object is going faster than light.


I am not sure that those numbers are additive, certainly not without changes in frame of reference. One cannot say an object is moving at both 60% C and 120% C. If one changes from the frame of reference of the center point to that of one of the outer points, it is my understanding that time dilation or some other effect ensures that, from that frame of reference, the speed of light is not violated.


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## Christine Wheelwright (Aug 21, 2022)

Wayne Mack said:


> I am not sure that those numbers are additive, certainly not without changes in frame of reference. One cannot say an object is moving at both 60% C and 120% C. If one changes from the frame of reference of the center point to that of one of the outer points, it is my understanding that time dilation or some other effect ensures that, from that frame of reference, the speed of light is not violated.



I am reaching the limits of my understanding here.  My initial thought was that you are correct.  No two objects can move apart at greater than the speed of light in any single frame of reference.  However, @msstice (I think it was) gave us the example of the observer being offset from the line of trajectory of the objects.  Say hundreds of light years away, observing from a point perpendicular to the direction of motion from the origin of the objects.  In this case, surely we would indeed see 1.2 light years increased distance between the two objects when we make two observations one year apart?  I think this was what @Swank was referring to when he talked about us moving our eyes in a moment, from one distant object to another(?).  It remains true that no object can move at greater than the speed of light *relative to the observer.  *


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## Wayne Mack (Aug 21, 2022)

Christine Wheelwright said:


> I am reaching the limits of my understanding here.  My initial thought was that you are correct.  No two objects can move apart at greater than the speed of light in any single frame of reference.  However, @msstice (I think it was) gave us the example of the observer being offset from the line of trajectory of the objects.  Say hundreds of light years away, observing from a point perpendicular to the direction of motion from the origin of the objects.  In this case, surely we would indeed see 1.2 light years increased distance between the two objects when we make two observations one year apart?  I think this was what @Swank was referring to when he talked about us moving our eyes in a moment, from one distant object to another(?).  It remains true that no object can move at greater than the speed of light *relative to the observer.  *


I think the confusion may arise from trying to convert distance into velocity. This requires a shift in frame of reference, which is inconsequential at non-relativistic speeds. Trying to add 0.6 C to 0.6 C to get 1.2 C is shifting from a neutral observation point to the frame of reference of one of the moving objects. Due to time dilation, that point will not observe a speed of 0.6 C from the neutral point nor a speed of 1.2 C from the other moving point. 

Putting some numbers on my initial confusion. The universe is currently assumed to be slightly less than 14 billion years old. The diameter of the universe is supposed to be 93 billion light-years. To me, the size should be limited to less than 28 billion light-years if it was expanding at the speed of light. This would suggest that the outer edge of the universe (whatever that might mean) needed to travel at an average rate of 3 1/3 C.

I admit that I do not understand this and I have read several explanations, which I also failed to understand. It does seem to imply that relative motion beyond the speed of light is possible. I may be guilty of using math, especially with regards to time dilation, incorrectly, but I am not seeing my error in analysis.

References:





						WMAP- Age of the Universe
					

Public access site for The Wilkinson Microwave Anisotropy Probe and associated information about cosmology.




					map.gsfc.nasa.gov
				











						Observable universe - Wikipedia
					






					en.wikipedia.org


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## Danny McG (Aug 21, 2022)




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## Swank (Aug 21, 2022)

Wayne Mack said:


> I am not sure that those numbers are additive, certainly not without changes in frame of reference. One cannot say an object is moving at both 60% C and 120% C. If one changes from the frame of reference of the center point to that of one of the outer points, it is my understanding that time dilation or some other effect ensures that, from that frame of reference, the speed of light is not violated.


I think one can say that this event and this other event can be related to each other in our minds without breaking a physical limit. We are just creating this relationship, not observing an actual rate that something is moving. I think observer effects and Lorentz diagrams cause some confusion as to how relative everything has to be. But if you are the origin of both sets of movement, you can speak about their sum movement in relation to your (relatively) static starting point without there being a paradox.

If Neptune and Saturn happened to be about equal distance from earth due to their orbits, and we fired a laser at both at the same instant, we would see the reflected light from both at the right number of minutes later that is the light minute distance from earth to Jupiter and back to earth, and we would see the same from earth to Neptune and back. The fact that we lased Neptune at the same time that we lased Jupiter doesn't change the distance that either laser traveled, and if we sum the distance the light traveled to Jupiter and Neptune that sum does not represent a total distance that light traveled, but two light beams traveling at the same time.


All of which is useful here in our local galaxy group, where universal expansion is not a factor. The current cosmological model says that the very large spaces between galaxies are growing not in simple distance, but that actual spacetime is growing. This is not the fault of the weird relativistic way we have to deal with lightspeed and time dilation, but that some natural process creates space between places at a rate that exceeds the ability of light to cross it.

This theory requires dark mass and dark energy which we know nothing about, and is ultimately linked to how we have observed the speed of distant objects via redshift. However, while redshift makes very far objects appear to be riding this expansion wave at a very high rate, the dimming of their luminosity is not. In other words, a galaxy so distant that it has doppler shifted to that degree should also be less bright, and that doesn't seem to be happening. Which is not to say that our current expanding universe model is wrong, but it would not be shocking if it turned out the red shift is not due to expansion after all and the distances we are computing due to red shift are wrong.


So you aren't going to better understand the light speed limit problem by trying to understand the expansion of the universe. Light speed limits aren't dictating what we observe in terms of expansion - light is just as confounded as we are by this extra force of nature. And locally we can treat light in a mostly Newtonian way, as long as we keep an un-accelerated reference frame to make our statements about what is happening.


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## psikeyhackr (Aug 21, 2022)

It is somewhat annoying when you cannot prove true stories but:

I was a college freshman majoring in electrical engineering. I had just read Tau Zero by Poul Anderson. I went to a senior physics major in the fraternity to discuss saying I really didn't understand what was going on with Einsteinian physics. 

He said, "You don't try to understand it. You memorize the equations and how to apply them."

Since I have never seen a practical application for my truly understanding near light speed physics I gave up on it. But I do wonder how many people with physics degrees really do.


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## Astro Pen (Aug 21, 2022)

Christine Wheelwright said:


> Not too sure about that.  Time is a property of our universe.  Therefore it has no context unless the universe exists.  Cause and effect is also a concept that relies upon time for meaning.


The seems to be a school of thinking that time is kind of an emergent property from events. I think the question of whether there is still time when there are _no_ events or observers is, I feel, a significant one.
I might even have a -pre big bang story- idea brewing here: "The Loneliness of the Unwatched Clock."


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## AllanR (Aug 21, 2022)

Lets say I have a shinny new FTL ship and I go for lunch at Alpha Centarie.  Say I get there in just a few hours (by my watch).... when I am at Alpha Centarie, the light I see from the Sun left 4 years before I did. The light being emitted by the Sun is still another 4 years further behind that.
After lunch I decide to go home right away. Again lets say this takes just a few hours.
When I get back to Earth it will be 8 years before I left.


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## Christine Wheelwright (Aug 21, 2022)

Wayne Mack said:


> The universe is currently assumed to be slightly less than 14 billion years old. The diameter of the universe is supposed to be 93 billion light-years. To me, the size should be limited to less than 28 billion light-years if it was expanding at the speed of light.



I'm curious about this.  Is the 93 billion light years an extrapolated number?  I mean, if I look at an object 100,000 light years away I am seeing it as it was 100,000 years ago.  I can work out its velocity relative to my position by checking the Doppler shift in the light coming from it.  I can then extrapolate a position for it right now (the position it was observed in plus velocity x time).  Has such extrapolation been used in calculating the universe is 93 billion light years across?

What I'm struggling with here is perhaps philosophical.  As the object can have no effect on me (other than in the position I observe it) can it really be understood to be anywhere else?


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## Christine Wheelwright (Aug 21, 2022)

Astro Pen said:


> The seems to be a school of thinking that time is kind of an emergent property from events. I think the question of whether there is still time when there are _no_ events or observers is, I feel, a significant one.
> I might even have a -pre big bang story- idea brewing here: "The Loneliness of the Unwatched Clock."


This might be related to the concept of entropy.  The energy in the Universe is gradually being equalized.  Warm things impart heat to cool things.  Moving things hit each other - their energy being redistributed.  Chemical energy is released through reactions.  Eventually, every point in space will be at the same energy and literally nothing will be happening.  The question is; does time still exist (and how can we even tell).


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## msstice (Aug 21, 2022)

psikeyhackr said:


> Since I have never seen a practical application for my truly understanding near light speed physics I gave up on it. But I do wonder how many people with physics degrees really do.



"Understanding" is a deceptively difficult word.

All through graduate school I, along with some other classmates, wrestled with the age old question of what it means to "understand" something. After graduate school, I still did not understand what it mean to understand, but I marched on.

I think when we say we "understand" something, it means we've memorized (internalized) the steps needed, or pointers to the steps needed, to answer a question about something. We have a mental model (probably with pointers to external knowledge) of the thing in question.

I understand the oven in my house. If I need to bake something, I put it in the oven and turn on the switch. 

When the oven element burned out, I stretched my understanding of the oven, by realizing it is the oven element that heats the oven. I understand that electricity flowing in the metal heats it up and this heat radiates or convects to the rest of the oven.

The higher the current, the more the number of electrons "flowing" in the wire. The electrons agitate the atoms in the metal, which vibrate and that is heat.

Now my understanding is breaking down. Are electrons little billiard balls that bounce around the metal? That model kind of works, but people have found cases where it doesn't.

Is heat the vibration of atoms/molecules. Yes, but I've heard people think of heat as information.

At some level, when the thing is complex enough, or far enough from everyday experience, we can't mask the illusion of understanding, and have to admit: I just work out the equations.

Many of you will know this as the great physicist throw down of the last century between Einstein and Bohr complete with Einstein's catch phrase "God does not play dice." which he said every time he tossed Bohr on the mat and did a pile drive. I may have made that last bit up.


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## TheEndIsNigh (Aug 21, 2022)

@Christine Wheelwright

The problem I havewith the old red shift thing is what was the source.

With all the hoo har about the JW eyeball in the sky thing is they've set their detectors to detect things in the IR frequencies because - They say - The objects they are observing were originally super bright ultra violet suns and because of the speed/red shift effect the frequencies will have been toned down.

The trouble I have is what's to say that what they are actually observing are IR sources that have been traveling across a much larger space for a much longer time.

I.E. Whats the difference between a UV source red shifted and a plane old IR source?

As for the 93B light years across surely that is just bunkum unless a light year now is less distance than a light year way back when.

Oh wait that would mean....


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## Swank (Aug 22, 2022)

TheEndIsNigh said:


> I.E. Whats the difference between a UV source red shifted and a plane old IR source?


An unnatural lack of anything in the shorter wavelengths.


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## psikeyhackr (Aug 22, 2022)

msstice said:


> "Understanding" is a deceptively difficult word.
> 
> All through graduate school I, along with some other classmates, wrestled with the age old question of what it means to "understand" something. After graduate school, I still did not understand what it mean to understand, but I marched on.
> 
> I think when we say we "understand" something, it means we've memorized (internalized) the steps needed, or pointers to the steps needed, to answer a question about something. We have a mental model (probably with pointers to external knowledge) of the thing in question.



Graduate school in what subject?

I was one of those kids that thought mathematics was fun. The nitwit nuns I had in 8th grade gave us an algebra book but did not teach the subject.  My older sister was in high school and her trigonometry book looked more interesting than my algebra book so I started teaching myself trigonometry. 

I will admit that trying to explain the difference between memorizing and understanding to someone else is a problem but it is like I can feel it in my brain when the transition happens. The solutions to problems become obvious instead of following a recipe. 

I had a mathematics teacher my junior year in high school who would assign homework but only intermittently collect it. Part of our grade was dependent on homework so it became a game. If I didn't do it and he didn't collect it I won. If he did collect I lost. It didn't really matter since I always got an A on the tests so the worst that happened was I got a B that grading period. I think I pissed him off because I didn't care.

But the people who just memorize must pretend that they understand.  Sometimes you can catch them on the basis of their mistakes. 

That is what pisses me off about the Twin Towers Affair. Look at the shape of the 10,000 tons of wrought iron down the Eiffel Tower.  The lower portions must be strong enough support all of the weight above. So it increases exponentially. 

Where is the data on the distributions of the 100,000 tons of steel and the never specified tons of concrete down the North Tower? The straight down collapse cannot be understood. Only believed by some people. 

The memorizers are unlikely to go beyond Einstein. Whoever does will almost certainly understand.


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## Astro Pen (Aug 22, 2022)

Under the rules here I can only skirt.
But I have to eat humble pie when I look at the state the world is now in.
Retrospectively, the 'foil hatters' were right on just about everything, and probably will be going forward.


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## Lumens (Aug 22, 2022)

https://www.sffchronicles.com/threads/552431/


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## Brian G Turner (Aug 22, 2022)

Getting back on topic seeing as the original discussion about relatively has burned itself out...

Is it my imagination, or didn't I read a while back that synchrotron radiation effectively requires electrons to travel FTL, just not in a linear way?


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## msstice (Aug 22, 2022)

Brian G Turner said:


> Getting back on topic seeing as the original discussion about relatively has burned itself out...
> 
> Is it my imagination, or didn't I read a while back that synchrotron radiation effectively requires electrons to travel FTL, just not in a linear way?



I never heard that one, but I did hear the one about there only being one electron in the universe and what we see is the same electron repeatedly intersecting our paltry four dimensional space as it wends its way through its higher dimensional existence.


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## Foxbat (Aug 22, 2022)

Brian G Turner said:


> Getting back on topic seeing as the original discussion about relatively has burned itself out...
> 
> Is it my imagination, or didn't I read a while back that synchrotron radiation effectively requires electrons to travel FTL, just not in a linear way?


As I understand it, it will be the resultant gamma photon that will be travelling at the speed of light but the electron producing the effect will be slightly slower.


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## Venusian Broon (Aug 22, 2022)

Brian G Turner said:


> Getting back on topic seeing as the original discussion about relatively has burned itself out...
> 
> Is it my imagination, or didn't I read a while back that synchrotron radiation effectively requires electrons to travel FTL, just not in a linear way?


It is your imagination.


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## Brian G Turner (Aug 22, 2022)

Venusian Broon said:


> It is your imagination.


Winky face - you mean there's something behind this? 

I remember coming across the concept around 1996/1997, so it must have been something mentioned in _New Scientist_. All I can find on the topic with a quick search, though, is this: Device Makes Radio Waves Travel Faster Than Light


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## Venusian Broon (Aug 22, 2022)

Brian G Turner said:


> Winky face - you mean there's something behind this?
> 
> I remember coming across the concept around 1996/1997, so it must have been something mentioned in _New Scientist_. All I can find on the topic with a quick search, though, is this: Device Makes Radio Waves Travel Faster Than Light


There were some physicists who thought they had detected neutrinos travelling faster than light a few years ago, but in the end it turned out to be a flaw in their experiment. 

After reading the article, I have to say, along with others who have read it, I am a bit sceptical. It is possibly because the description given by the journalist seems a bit confused - I think the physicist is talking about phase velocity. Phase velocities apparently can exceed _c_, but "a phase velocity above _c_ does not imply the propagation of signals with a velocity above _c_." It is a fuzzy bit of physics that can (clearly!) confuse. 

Actually if you want to find real FTL the closest you find is in Quantum mechanics. So taking the entangled pair of particles, take them far apart then observe one of them, the wavefunction collapse that fixes the property of the other particle is said to be instantaneous and therefore not bound by the speed of light. So far, to my understanding, all experiments to test this have shown this to be the case. Einstein doesn't like this, of course.


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## BAYLOR (Aug 22, 2022)

Brian G Turner said:


> Winky face - you mean there's something behind this?
> 
> I remember coming across the concept around 1996/1997, so it must have been something mentioned in _New Scientist_. All I can find on the topic with a quick search, though, is this: Device Makes Radio Waves Travel Faster Than Light


What about Tachyon particles ? Supposedly , they move faster than light ?


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## Venusian Broon (Aug 22, 2022)

BAYLOR said:


> What about Tachyon particles ? Supposedly , they move faster than light ?


When you observe one, then you can go and pick up a Nobel prize   

i.e. no experimental evidence has been found for them. Would be a pretty big thing for physics if they were real, but going back to my original post at the top, just because you come up with a theoretical idea, does not mean that reality has to produce it!


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## BAYLOR (Aug 22, 2022)

Venusian Broon said:


> When you observe one, then you can go and pick up a Nobel prize
> 
> i.e. no experimental evidence has been found for them. Would be a pretty big thing for physics if they were real, but going back to my original post at the top, just because you come up with a theoretical idea, does not mean that reality has to produce it!



VB be very careful what  you say. Tachyon particles  have ears and they don't like people who doubt their existence.


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## Venusian Broon (Aug 22, 2022)

BAYLOR said:


> VB be very careful what  you say. Tachyon particles  have ears and they don't like people who doubt their existence.


 That's okay, I'll add it to list of other imaginary things that people have told me exist that for some reason generally threaten me.


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## Guttersnipe (Aug 22, 2022)

I don't have much to add in the way of science, but I do think it's a "maybe" that could be realized in the very distant future by posthumans with godlike technology. Not any time soon, though. I say this because, well, do you think early humans ever dreamed of the stuff we have now?


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## Ursa major (Aug 22, 2022)

BAYLOR said:


> Tachyon particles have ears and they don't like people who doubt their existence.


What I want to know is what they are tacky on. (And doesn't whatever it is slow them down?)


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## BAYLOR (Aug 22, 2022)

Venusian Broon said:


> That's okay, I'll add it to list of other imaginary things that people have told me exist that for some reason generally threaten me.



Hey , laughter  is a good thing. 


The more we learn about the universe  we live in, the less we actually know and understand its actual workings    Einstein not withstanding, one day  we may discover  that exceeding the speed of light is actually possible .


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## BAYLOR (Aug 22, 2022)

Ursa major said:


> What I want to know is what they are tacky on. (And doesn't whatever it is slow them down?)



They don't go for things fancy dress . Tachyon sare come as you are working class particles .


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## psikeyhackr (Aug 22, 2022)

Venusian Broon said:


> When you observe one, then you can go and pick up a Nobel prize
> 
> i.e. no experimental evidence has been found for them. Would be a pretty big thing for physics if they were real, but going back to my original post at the top, just because you come up with a theoretical idea, does not mean that reality has to produce it!


Aren't they hypothetical rather than theoretical.


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## hitmouse (Aug 22, 2022)

BAYLOR said:


> The more we learn about the universe  we live in, the less we actually know and understand its actual workings


I fundamentally disagree with that statement.


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## Astro Pen (Aug 22, 2022)

If you get into Einstein's tram and exceed the speed of light you will watch the town clock appear to go backwards. That seems nice and logical until you have gone back ten minutes and realize that you can see Albert, who is sat next to you, - is also still in the queue, waiting for the tram.


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## Serendipity (Aug 23, 2022)

Astro Pen said:


> If you get into Einstein's tram and exceed the speed of light you will watch the town clock appear to go backwards. That seems nice and logical until you have gone back ten minutes and realize that you can see Albert, who is sat next to you, - is also still in the queue, waiting for the tram.


Let's do a thought experiment... you are you in your own frame of reference in time and space. You then go faster and faster as you say until you exceed the speed of light and realise you are seeing your friend ten minutes ago. You then continuing at a speed greater than light turn around and go an tap Albert and yourself on the shoulders. But your earlier you never felt those taps. The question is why not? 

Or putting it another way, if things are travelling faster than the speed of light, why aren;t we experiencing them?


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## Foxbat (Aug 23, 2022)

Serendipity said:


> Or putting it another way, if things are travelling faster than the speed of light, why aren;t we experiencing them


Maybe we are experiencing them but just aren’t aware that we are.

After all, our bodies are subjected all the time to things we aren’t aware of (at least without measuring equipment). Example… Radon gas daughter product particles that often fill our homes without us realising that they are there. They can produce alpha particles that  enter our lungs and potentially irradiate soft tissues but we just don’t experience any of that on a conscious level.

Edit, I don’t actually believe that we are experiencing FTL without awareness but, as it’s a thought experiment then I thought I’d add a thought alternative.


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## Rufus Coppertop (Aug 23, 2022)

Christine Wheelwright said:


> Can we though? If I step outside my space station and throw one ball left at the speed of light and one ball right at the speed of light, how far apart are they when I observe them a year later? The answer is one light year not two



So........if you throw two balls in opposite directions at the speed of light and look at the one that you threw to the right, a year later, it will have travelled half a light year by travelling at the speed of light for a full year?




Christine Wheelwright said:


> Remember I am looking back in time six months



You're looking back in time only six months when you observe them twelve months later and they've both travelled half a light year away from the space station even though they've travelled at the speed of light for a full year?




Christine Wheelwright said:


> but I cannot reason that the objects are two light years apart in 'their present'.   In fact the objects see each other one light year apart (the first ball sees the second still at the space station....that image having traveled along side it).  Thr second ball effectively does indeed exist at the space station in terms of it's effects on the first ball.  And vice versa of course.



The first ball's "seeing" of the second ball still at the space station does not compel you to see the second ball hovering at the space station though, does it?


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## Christine Wheelwright (Aug 23, 2022)

Rufus Coppertop said:


> So........if you throw two balls in opposite directions at the speed of light and look at the one that you threw to the right, a year later, it will have travelled half a light year by travelling at the speed of light for a full year?
> 
> 
> 
> ...


Each ball takes half a year to travel to a point that is half a light year away. The light from each ball then takes half a year to travel back to the origin. If I observe the objects after one year, I see them half a light year away from me.


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## Rufus Coppertop (Aug 23, 2022)

Christine Wheelwright said:


> Each ball takes half a year to travel to a point that is half a light year away. The light from each ball then takes half a year to travel back to the origin. If I observe the objects after one year, I see them half a light year away from me.


Aaaaaah!

Okay. I get what you're saying. After a year, we're looking at light that is six months old. It makes perfect sense. What I don't get though, is the concept that the ball really is only half a light year away considered from its own point of view.

If we imagine that Auntie Dorris has just hung out her washing on a space station one light year away and one of the balls knocks her knickers off the line a year later and she rings up on a magic telephone that can transmit messages instantly, she'll surely be shouting "Oi! Knock that off!" a year later, won't she?

And when she does, we'll know that the ball actually travelled a full light year in that year even though it looks to us as if it's only halfway to her knickers.


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## Wayne Mack (Aug 23, 2022)

Serendipity said:


> Let's do a thought experiment... you are you in your own frame of reference in time and space. You then go faster and faster as you say until you exceed the speed of light and realise you are seeing your friend ten minutes ago. You then continuing at a speed greater than light turn around and go an tap Albert and yourself on the shoulders. But your earlier you never felt those taps. The question is why not?
> 
> Or putting it another way, if things are travelling faster than the speed of light, why aren;t we experiencing them?


Okay, I'll play. The part about Albert confused me, so I'll omit him. Assuming the frame of reference accelerates to the speed of light and then goes past it, the observer would see time slow and then stop. Assuming negative time, the observer would move back to earlier times. One cannot assume the observer both moves forward in time and backwards in time, so the observer cannot create new events. The observer would be walking back through past events.

From an external frame of reference, when the moving object starts going backwards in time, then it no longer goes forward in time. From an external point of view, the object would hit the speed of light and then cease to exist. From an external point of view, the speed of light was not violated, though there is the pesky matter of conservation of matter and energy.


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## Christine Wheelwright (Aug 23, 2022)

Rufus Coppertop said:


> If we imagine that Auntie Dorris has just hung out her washing on a space station one light year away and one of the balls knocks her knickers off the line a year later and she rings up on a magic telephone that can transmit messages instantly, she'll surely be shouting "Oi! Knock that off!" a year later, won't she?



No.  Because her voice down the phone line must also travel at less than the speed of light.  If I was the one that threw the ball, I will hear her after two years telling me that the ball is at her position one light year away.

The point is, there is no omniscient observer who sees the true position of everything at a fixed point in time.  There is no fixed point in time.  Time is not independent of space.  So, I think in a very real sense, the object is indeed where I observe it after one year; half a light year away.  Its effects on me are the effects of an object half a light year away.  I can mathematically extrapolate a different position for it if that makes me happy (knowing that I am looking back in time).  But I'm not sure how useful this is.  I'm sure this kind of extrapolation is used in calculations of the 'present' size of the universe. 

From the object's point of view, the origin point appears to be frozen in time because light from the origin has travelled alongside it.  Looking back, it still sees me standing there, my arm extended as I throw it.  As if time has stood still.  Time therefore slows down (relative to the origin) for objects as they get faster relative to the origin point.  Time stops when the speed of light is reached.


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## Christine Wheelwright (Aug 23, 2022)

Wayne Mack said:


> Okay, I'll play. The part about Albert confused me, so I'll omit him. Assuming the frame of reference accelerates to the speed of light and then goes past it, the observer would see time slow and then stop. Assuming negative time, the observer would move back to earlier times. One cannot assume the observer both moves forward in time and backwards in time, so the observer cannot create new events. The observer would be walking back through past events.
> 
> From an external frame of reference, when the moving object starts going backwards in time, then it no longer goes forward in time. From an external point of view, the object would hit the speed of light and then cease to exist. From an external point of view, the speed of light was not violated, though there is the pesky matter of conservation of matter and energy.



[Redacted.  I had an incorrect explanation of time dilation in here]


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## Mon0Zer0 (Aug 23, 2022)

Swank said:


> *A short summary of the thread so far:*
> 
> 1. The Hard-science Hardliners assure the public that our current understanding of physics is good and complete enough to preclude any changes to our understanding that C is an absolute limit. (Despite current physics also telling us that the vast majority of the universe is made of matter and energy we can neither find nor define.)



You don't need our current understanding of physics to be complete or good. In order to assume something exists there must be evidence. See Russel's teapot. 

Physicists don't assume dark matter exists, they posit as a potential solution to the evidence of inflation. There's a high probability they're wrong.

There's nothing within the models that suggests ftl travel exists, nor have we seen evidence of it. We've only seen evidence that c is the limit of causality. Should we see or find models that suggest otherwise we  can update our understandings accordingly. 



Swank said:


> 3. The Maybes, who are probably dirty agnostics in their private lives as well.



Dirty agnosticism is where it's at, baby!


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## Christine Wheelwright (Aug 23, 2022)

Christine Wheelwright said:


> From the object's point of view, the origin point appears to be frozen in time because light from the origin has travelled alongside it.  Looking back, it still sees me standing there, my arm extended as I throw it.  As if time has stood still.  Time therefore slows down (relative to the origin) for objects as they get faster relative to the origin point.  Time appears to stop at the origin when the speed of light is reached relative to it.



I should add that time can appear accelerated at an object as I move towards it (or as the object moves towards me....basically the same thing in a relativistic universe).  An object moving towards me can even appear to be moving at faster than the speed of light because of this effect.

There is also an effect known as _time dilation_ which is not the same as that described above.


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## Swank (Aug 23, 2022)

Mon0Zer0 said:


> You don't need our current understanding of physics to be complete or good. In order to assume something exists there must be evidence. See Russel's teapot.
> 
> Physicists don't assume dark matter exists, they posit as a potential solution to the evidence of inflation. There's a high probability they're wrong.
> 
> ...


I don't think FTL exists, I just don't think it should be ruled out at this stage. Especially by SF writers. Along with all the other unlikely but not actually disprovable stuff that they might dote upon.


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## Christine Wheelwright (Aug 23, 2022)

Swank said:


> I don't think FTL exists, I just don't think it should be ruled out at this stage. Especially by SF writers. Along with all the other unlikely but not actually disprovable stuff that they might dote upon.


Absolutely.  It is often said the purpose of SF is to ask 'what if?' rather than attempt to accurately predict the future.  I personally do not think we will reach the stars, but by all means we should write about starships.  For entertainment, and through entertainment to explore the universe and the human spirit (its strengths and frailties).


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## Extollager (Aug 23, 2022)

Christine Wheelwright said:


> Absolutely.  It is often said the purpose of SF is to ask 'what if?' rather than attempt to accurately predict the future.  I personally do not think we will reach the stars, but by all means we should write about starships.  For entertainment, and through entertainment to explore the universe and the human spirit (its strengths and frailties).


Sure, but also it might be appropriate for the sf community to be a bit more visible with the point of view you have expressed, i.e. that the science we actually have discourages the popular expectations of FTL travel, the development of psionic powers, time travel, the existence of life off the earth and even of contact with extraterrestrial civilizations, and so on.  It might not hurt if we were a bit more visibly capable of distinguishing between our favorite entertainment genre and our sense of what is probable.

Here are some polls that were easy to find that suggest popular notions are at odds with the science we actually have.  I suspect a lot of this is due to the immersion of popular culture in sf tropes.  I also included an article from *National Geographic* about living on Mars.









						Do Americans Believe in UFOs?
					

UFOs could be anything from figments of the imagination to cases of mistaken identity to alien spacecraft. Learn what Americans think on the issue.




					news.gallup.com
				







__





						Poll: 25 Percent Believe Time Travel Will Happen Before Female Parity in Fortune 500
					






					www.nysscpa.org
				











						Is there life on other planets? Here’s what Americans think | YouGov
					

Recent data from a YouGov poll of more than 7,000 US adults finds that nearly half (47%) believe that there are basic life forms on other planets within our solar system.




					today.yougov.com
				











						Will Humans Ever Colonize Other Planets? They Should.
					

Futurist Michio Kaku sees humans doing ballet on Mars and projecting their brains into the cosmos. And aliens? Oh, they're coming.




					www.nationalgeographic.com


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## Swank (Aug 23, 2022)

Extollager said:


> Sure, but also it might be appropriate for the sf community to be a bit more visible with the point of view you have expressed, i.e. that the science we actually have discourages the popular expectations of FTL travel, the development of psionic powers, time travel, the existence of life off the earth and even of contact with extraterrestrial civilizations, and so on.  It might not hurt if we were a bit more visibly capable of distinguishing between our favorite entertainment genre and our sense of what is probable.
> 
> Here are some polls that were easy to find that suggest popular notions are at odds with the science we actually have.  I suspect a lot of this is due to the immersion of popular culture in sf tropes.  I also included an article from *National Geographic* about living on Mars.
> 
> ...


These polls strike me as having less to do with the impact of SF on culture and much more to do with critical thinking skills and the prevalence of magical and conspiratal thinking.

Even without SF, the human mind revisits past events and tries to re-do them, tries to insert itself into the minds of others through empathy, offers dreams of flying and treats impossibly distant places as imaginable. No wonder we think about time travel, ESP, super powers and FTL. They fit our mental biases.


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## Wayne Mack (Aug 23, 2022)

Christine Wheelwright said:


> [Redacted.  I had an incorrect explanation of time dilation in here]


Aside. I have found that I can delete quoted (or replied text) by simply deleting all of the text within the reply block. Of course, this has to be done within the edit time period, but I have used that to make a reply just go away.


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## Extollager (Aug 23, 2022)

Swank wrote, "These polls strike me as having less to do with the impact of SF on culture and much more to do with critical thinking skills and the prevalence of magical and conspiratal thinking."

In a culture saturated with sf movies, games, TV shows, etc., science fiction will be likely to influence the forms conspiracy theorizing and magic thinking take.  Sf can be an enabler of these.


----------



## Christine Wheelwright (Aug 23, 2022)

Extollager said:


> Sure, but also it might be appropriate for the sf community to be a bit more visible with the point of view you have expressed, i.e. that the science we actually have discourages the popular expectations of FTL travel, the development of psionic powers, time travel, the existence of life off the earth and even of contact with extraterrestrial civilizations, and so on.  It might not hurt if we were a bit more visibly capable of distinguishing between our favorite entertainment genre and our sense of what is probable.
> 
> Here are some polls that were easy to find that suggest popular notions are at odds with the science we actually have.  I suspect a lot of this is due to the immersion of popular culture in sf tropes.  I also included an article from *National Geographic* about living on Mars.
> 
> ...



Yes, exactly.  You have hit on one of my pet topics.  The scientifically illiterate public (if that isn't too arrogant a phrase) has way too much optimism and way too much faith in science and technology.  And I speak as a scientist.

I cringe whenever some know-nothing (like, say, Elon Musk) pops up with his latest nonsense about AI-enabled self-driving robo-taxis or manned Mars missions in a handful of short years.  People lap that stuff up, and they don't seem to notice when it doesn't happen.  They just keep sticking their hands in the flames.  The danger, of course, is that complacency results when it comes to humanity's very real problems; like climate change.  There is an irrational belief that some 'invention' by some 'genius' will save us and that everything will be ok.  Of course, the situation is made even worse by all these ridiculous announcements and investment-seeking cgi videos from start-ups claiming to have made new discoveries that will 'revolutionize' everything.  All just scams.  But it is comforting for folks to assume science and technology will save us.


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## Extollager (Aug 23, 2022)

I think too that the public sometimes gets the impression that the scientific knowledge we actually have isn't all that interesting; it's what scientists _might _discover and what _might_ then be its applications that are of interest.  Surely that's not really true.  Can't there be some other "narrative"?  For example, let's look at what has been accomplished lately in regard to space-based telescopes, or actually landing on a comet, etc., with the budgets that supported these successes -- i.e. tiny amounts (relative to what's spent on many costly non-science programs and agencies).  Some sciences don't seem to get much responsible attention at all, e.g. archeology.


----------



## Mon0Zer0 (Aug 23, 2022)

Extollager said:


> I think too that the public sometimes gets the impression that the scientific knowledge we actually have isn't all that interesting; it's what scientists _might _discover and what _might_ then be its applications that are of interest.  Surely that's not really true.  Can't there be some other "narrative"?  For example, let's look at what has been accomplished lately in regard to space-based telescopes, or actually landing on a comet, etc., with the budgets that supported these successes -- i.e. tiny amounts (relative to what's spent on many costly non-science programs and agencies).  Some sciences don't seem to get much responsible attention at all, e.g. archeology.



The future is always exotic. The present, prosaic. We routinely use technology our great grandparents would have been astounded by. It's so much easier to get worked up over travel to Kepler-22b than it is half way around the globe, yet the latter is a miracle in human history. Quite sad, really.


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## AllanR (Aug 23, 2022)

Extollager said:


> with the budgets that supported these successes -- i.e. tiny amounts (relative to what's spent on many costly non-science programs and agencies)


Like India launching a probe to Mars the same year Interstellar came out, and they did it cheaper than the cost of the movie. $57 million vrs $165 million


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## Swank (Aug 23, 2022)

I wouldn't say our society is saturated with SF. Super hero movies do well, otherwise it's pretty niche.


----------



## Ursa major (Aug 23, 2022)

Swank said:


> Super hero movies


...are fantasy, not SF.


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## asp3 (Aug 23, 2022)

At this point in time I think it is possible but also think my opinion comes from a state of ignorance.  I don't think I know enough to have an opinion of any value.


----------



## Extollager (Aug 23, 2022)

Ursa major said:


> ...are fantasy, not SF.


Of course superhero movies are fantasy, but they are usually presented with an "sf" framework.  As someone who's watched quite a few of the Marvel ones (but none in the past three years or so), I'm confident about saying that.  Thor, the Avengers, the Guardians of the Galaxy, Black Panther... they zip around in spaceships or the like, turn on force fields, use hi-tech blasters, that sort of thing.  Their enemies may include "aliens."  All of these are much more "SF" than, say, the LotR movies, which are indeed fantasy.  Even Dr. Strange is a guy who navigates "other dimensions," etc.; the Marvel franchise would allow that you could get to some, at least, of those "mystic realms" by super-technology, I suppose.

Sure, we might well define these entertainments as fantasy and not sf, but they use sf tropes and certainly contribute to the constant streaming of sfnal imagery and expectations in popular consciousness.


----------



## Ursa major (Aug 23, 2022)

Whatever they travel about in, their superpowers (well, the superpowers of those that have them) are pure fantasy.

But to find, perhaps, a compromise, a more suitable descriptive name for them might be science fantasy.


----------



## Extollager (Aug 24, 2022)

Ursa, you and I probably agree about the non-sfnal quality of the superhero movies.  But whatever we choose to call them, they do contribute to the culture's immersion in _broadly_ sfnal notions -- aliens, space travel, multiple dimensions, hi-tech weapons and body armor and so on.


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## Swank (Aug 24, 2022)

Ursa major said:


> ...are fantasy, not SF.


That depends. Iron Man or Guardians of the Galaxy are pretty much SF, and the Matrix straddles the line.


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## Robert Zwilling (Aug 24, 2022)

But to find, perhaps, a compromise, a more suitable descriptive name for them might be science fantasy.

That's the old science fiction vs fantasy discussion which never has a definite solution. If you want to get technical about it, 99 percent of what passes for science fiction is science fantasy. Might as well drag Speculative Fiction back out into the spot light.

Anything with space travel past the asteroid belt is pure fantasy, within the belt that's science fiction so long as it is done in tiny ships and not giant massive dreadnaught size ocean liners. I say that because I believe that is entirely possible. Just because the people trying to get out there are not playing with a full deck doesn't mean they won't get out there in their tiny ships. Then again, the Vikings had tiny ships for the most part and they could have gone around the world if they had wanted to. Sometimes they dragged the ships over land to get to the other side.

Perhaps life can never be accelerated past the speed of light without becoming a monument to its previous existence. All the ftl has a magic bubble around the ship so it stays intact, inside people are walking around breathing the vapors as if nothing extraordinary was happening. If we can't do ftl perhaps no one else can either, so you can throw all the alien intervention stuff under the bus as well. The first and maybe only contacts will probably be robots.

What does seem to be completely blowing the fantasy out of science fiction is anything based on genetics. Perhaps real life super heroes will be bred in the proverbial test tube. The mind is a portal and maybe we can step into other dimensions through enhanced brains with just the thoughts in our minds, as nothing materialistic can be dragged along inside with us. Inside our heads we are in touch with everything quantum, and if we were bred to travel into those regions we might find a whole new way of getting around. Perhaps it is just the materialistic garbage that is restricted from traveling around the universe.


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## Swank (Aug 24, 2022)

Robert Zwilling said:


> But to find, perhaps, a compromise, a more suitable descriptive name for them might be science fantasy.
> 
> That's the old science fiction vs fantasy discussion which never has a definite solution. If you want to get technical about it, 99 percent of what passes for science fiction is science fantasy. Might as well drag Speculative Fiction back out into the spot light.
> 
> ...


So, now any SF with ships larger than the space shuttle is fantasy, even though the surface of the moon is aluminum?


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## Extollager (Aug 24, 2022)

I wonder if there is any American or British physicist, currently employed by a university or a private corporation, who would accept a bet on the following basis.

1.If he or she wins the bet, the physicist will win $10 million or the equivalent in sterling; if he or she loses the bet, the loss is 10% of one year's top earnings.  That is, if during the 20 years the losing physicist's top earnings for a year were $250,000, he or she would pay the bettor $25,000.  (I figured that was enough of a loss to hurt, but not enough to deter someone who really believes he or she had a good chance of winning the bet.)

2.The bet is this.  Within 20 years, the wealthy bettor bets that _none_ of the following will have occurred.

a.The discovery of certain evidence of life, convincing to the scientific community, other than microscopic, originating anywhere in the universe other than on this planet.
b.A manned mission to Mars that reaches the planet and returns to Earth.
c.Certain proof that FTL travel is possible, i.e. the physics are worked out even if the application will take some years yet; but the scientific community affirms that it can be done.
d.Certain proof that time travel into the past or into the future may be done, i.e. the physics are worked out even if the application will take some years.

If one or more of these occurs at any time before the 20 years are up, the bettor will pay the physicist $10 million.


----------



## Swank (Aug 24, 2022)

Extollager said:


> a.The discovery of certain evidence of life, convincing to the scientific community, other than microscopic, originating anywhere in the universe other than on this planet.
> b.A manned mission to Mars that reaches the planet and returns to Earth.
> c.Certain proof that FTL travel is possible, i.e. the physics are worked out even if the application will take some years yet; but the scientific community affirms that it can be done.
> d.Certain proof that time travel into the past or into the future may be done, i.e. the physics are worked out even if the application will take some years.


a. Lift a Buick over your head.
b. Warm up soup.
c. Memorize Wikipedia.
d. Hold your breath for 1 hour 35 minutes.

We could go to Mars in 2 years if we broke the nuclear weapon space treaty, or sunk a couple trillion into it. It isn't really a technical problem as much as a political one. The other ones range from unpredictable to scientifically unlikely. All of which are out of the control of scientists.


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## Christine Wheelwright (Aug 24, 2022)

I'd take that bet, although I'm not a physicist.  d) may need some rephrasing.  Technically space station crews have experienced less time than folks on earth (by the merest fraction of a second) due to time dilation.  This could be argued to be a small jump forwards in time.  But certainly not what most people would define as significant time travel. c) and d) are kind of related.  They would come as a package I think.

The only problem is that in 20 years I'll be a little too old to spend all that money on partying and loose boys.  Can I get an advance?


----------



## Swank (Aug 24, 2022)

Christine Wheelwright said:


> I'd take that bet, although I'm not a physicist.  d) may need some rephrasing.  Technically space station crews have experienced less time than folks on earth (by the merest fraction of a second) due to time dilation.  This could be argued to be a small jump forwards in time.  But certainly not what most people would define as significant time travel. c) and d) are kind of related.  They would come as a package I think.
> 
> The only problem is that in 20 years I'll be a little too old to spend all that money on partying and loose boys.  Can I get an advance?


I might be able to find you some loose boys. Got pics?


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## Ursa major (Aug 24, 2022)

Swank said:


> That depends. Iron Man or Guardians of the Galaxy are pretty much SF, and the Matrix straddles the line.


Iron Man does not have superpowers (he has technology)... which means that he fits the exception I implied:


Ursa major said:


> Whatever they travel about in, their superpowers *(well, the superpowers of those that have them) *are pure fantasy.


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## Serendipity (Aug 24, 2022)

Foxbat said:


> Maybe we are experiencing them but just aren’t aware that we are.
> 
> After all, our bodies are subjected all the time to things we aren’t aware of (at least without measuring equipment). Example… Radon gas daughter product particles that often fill our homes without us realising that they are there. They can produce alpha particles that  enter our lungs and potentially irradiate soft tissues but we just don’t experience any of that on a conscious level.
> 
> Edit, I don’t actually believe that we are experiencing FTL without awareness but, as it’s a thought experiment then I thought I’d add a thought alternative.


Hm... so if something is travelling faster then the speed of light relative to the observer, then they would go right through the observer without the observer feeling a thing?


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## Serendipity (Aug 24, 2022)

Wayne Mack said:


> Okay, I'll play. The part about Albert confused me, so I'll omit him. Assuming the frame of reference accelerates to the speed of light and then goes past it, the observer would see time slow and then stop. Assuming negative time, the observer would move back to earlier times. One cannot assume the observer both moves forward in time and backwards in time, so the observer cannot create new events. The observer would be walking back through past events.
> 
> From an external frame of reference, when the moving object starts going backwards in time, then it no longer goes forward in time. From an external point of view, the object would hit the speed of light and then cease to exist. From an external point of view, the speed of light was not violated, though there is the pesky matter of conservation of matter and energy.


Hm... interesting... hm... If the obverse in their own frame reference accelerates away from another frame of reference (I believe it had a clock tower in the original correspondence - so let's put a clock tower in this frame of reference), then indeed the time as measured by the clock tower would appear to slow down. If the observer travels at the speed of light away from the clock tower, then the clock tower would always show the same time. If the observer exceeds the speed of light, then it would show the clock tower before the the observer left because the observer would only see the light that was sent earlier. (I think we're agreed so far!)

Now if the observer returns to the clock tower after having accelerated to beyond the speed of light from the clock tower, the observer would go back through all the light signalling until the observer reaches the clock tower at a time later than the observer started out where that time difference is due to the time it takes the observer to travel away from and back to the clock tower. So by this 'logic' the observer could not return to the clock tower before the observer left. (Which is different from the example I cited earlier - mea culpa).

Does this make sense to you?


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## Astro Pen (Aug 24, 2022)

AllanR said:


> Like India launching a probe to Mars the same year Interstellar came out, and they did it cheaper than the cost of the movie. $57 million vrs $165 million


Meanwhile, Neymar (a football player) transfer fee to Barcelona  - 222 million euros! 
What hope is there for the future of mankind with societal priorities like that?


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## Wayne Mack (Aug 24, 2022)

Serendipity said:


> Hm... interesting... hm... If the obverse in their own frame reference accelerates away from another frame of reference (I believe it had a clock tower in the original correspondence - so let's put a clock tower in this frame of reference), then indeed the time as measured by the clock tower would appear to slow down. If the observer travels at the speed of light away from the clock tower, then the clock tower would always show the same time. If the observer exceeds the speed of light, then it would show the clock tower before the the observer left because the observer would only see the light that was sent earlier. (I think we're agreed so far!)
> 
> Now if the observer returns to the clock tower after having accelerated to beyond the speed of light from the clock tower, the observer would go back through all the light signalling until the observer reaches the clock tower at a time later than the observer started out where that time difference is due to the time it takes the observer to travel away from and back to the clock tower. So by this 'logic' the observer could not return to the clock tower before the observer left. (Which is different from the example I cited earlier - mea culpa).
> 
> Does this make sense to you?


The issue is not observation of light, but time dilation in different frames of references. Time dilation is already an observed phenomenon and satellites orbiting the Earth require periodic time clock resynchronization. This time dilation, however, is due to the effects of gravity not speed. Time runs faster in space. Take two clocks, leave one on Earth and take the other up to space and then back down and the clock on Earth will record less time elapsed than the one that traveled into space.

At velocity, the opposite occurs. The object in motion experiences time passing slower. At the speed of light, time ceases to pass. Someone who traveled for a light year out and a light year back would experience no passage of time, while two years have passed at the origin point. The concept of variable time is pretty strange.

If an object exceeds the speed of light, it would seem to enter the realm of negative time, which is an even more bizarre concept. My extrapolation was that time moving in a negative direction meant that the object would regress back to an earlier state. I had also assumed that this would mean the object regressed to an earlier position. If so, the object would no longer be externally observed. This seems to be a rather strange outcome from an external observation point, but it avoids the consequences of experiencing reversal of interaction. One such interaction would be emitting the light of previously viewed objects, but from a different location in space.

Another way of viewing this would be to look at the speed of light as a wrap point. Some of the computer scientists may get this, but essentially C + 1 = -C + 1. Continued acceleration in the original direction becomes deceleration in the opposite direction.


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## Serendipity (Aug 26, 2022)

Wayne Mack said:


> The issue is not observation of light, but time dilation in different frames of references. Time dilation is already an observed phenomenon and satellites orbiting the Earth require periodic time clock resynchronization. This time dilation, however, is due to the effects of gravity not speed. Time runs faster in space. Take two clocks, leave one on Earth and take the other up to space and then back down and the clock on Earth will record less time elapsed than the one that traveled into space.
> 
> At velocity, the opposite occurs. The object in motion experiences time passing slower. At the speed of light, time ceases to pass. Someone who traveled for a light year out and a light year back would experience no passage of time, while two years have passed at the origin point. The concept of variable time is pretty strange.
> 
> ...


If an object exceeds the speed of light, that object would observe the universe around it as if it were travelling back in time. The object itself does not become younger because it remains in its own frame of reference. This applies even when gravity affects the speed of light as in Einstein's theory of general relativity.


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## Wayne Mack (Aug 26, 2022)

Serendipity said:


> If an object exceeds the speed of light, that object would observe the universe around it as if it were travelling back in time. The object itself does not become younger because it remains in its own frame of reference. This applies even when gravity affects the speed of light as in Einstein's theory of general relativity.


I will freely admit that I do not grasp the concept of negative time or whether it exists. I even struggle with the idea of zero time. For my model, I tend to rely on the idea of someone on a moving object with a flashlight.

Suppose there is an object traveling at 0.9 C and someone (the internal observer) turns on a flashlight. An external observer will see the light from the flash traveling at C and the object traveling at 0.9 C. In one second, the light will travel 1.0 light-seconds and the object will travel 0.9 light-seconds and the two will be 0.1 light-seconds apart. Now where is starts to get strange, for the internal observer, the light from the flashlight still travels away from him at C. After 1 second, the light will be 1 light-second distant. One explanation for this is the rate of time has reduced for the internal observer (another is that distance has expanded, but that becomes even weirder).

Now, what if the object reaches the speed of light. When the flashlight is turned on, the light cannot move faster than the object and remains at the emitting bulb. After 1 second, both would travel 1.0 light-seconds. For the internal observer, the speed of light is still a constant. The light from the flashlight would need to move away at the speed of light. After 1 second, the light would need to be 1.0 light-seconds away. This can be explained by the rate of time internal to the object having gone to zero and introduces all sorts of divide by zero issues. I assume that this means that time fails to pass for the internal observer.

Now, suppose the object gets to 1.1 C. For an external observer, after 1 second, the light from the flashlight would be 0.1 light-seconds behind the object. For the internal observer, however, after 1 second, the light would be 0.1 light-seconds in front of the object. Or perhaps the internal observer experiences -1 seconds to a time 1 second before the flashlight was turned on. If time is truly reversed, wouldn't the internal observer be emitting light from his or her eyes that is traveling back towards its source? If moving backwards in time, wouldn't the object be returning to an earlier state? Wouldn't any particles shed by the object be re-merging with it? If so, how would these shed particles now be a a different location? The only way I see to resolve this is that when time goes negative, so does distance. Which would put the object overlaying its previous location, effectively doubling its mass. To the external observer, the moving object would wink out of existence as it passed the speed of light.

I am not qualified to say any of this is true, but I do have a hard time apply negative numbers to most physical phenomena.


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## Ursa major (Aug 26, 2022)

I recall reading, more than four decades ago, at least some of a small (library) book by Albert Einstein (which he started writing at the end of 1915) aimed at "a popular audience". I thought I'd look it up online. There's been an update to it, but I thought I'd see if the original was available... and it was (and for *45p* as a Kindle book).

Don't expect this to enable me to explain anything raised here, but some of you might find it worthwhile looking at, what with such a bargain price and a relatively well-informed author.


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## Lumens (Aug 26, 2022)

Did you mean a relativitivly well informed author...?

Is it this one?





						Relativity: The Special and the General Theory: Amazon.co.uk: Einstein, Albert: 9781891396304: Books
					

Buy Relativity: The Special and the General Theory Translation by Einstein, Albert (ISBN: 9781891396304) from Amazon's Book Store. Everyday low prices and free delivery on eligible orders.



					www.amazon.co.uk
				




Edit: also available for free here: 
Relativity : the Special and General Theory by Albert Einstein


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## Ursa major (Aug 26, 2022)

I didn't look "on gutenberg", as I assumed it was still in copyright here, given that Einstein lived until 1955.


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## StilLearning (Aug 27, 2022)

I don't know if this has been mentioned (almost certainly), but general relativity theory (theory!) predicts any number of natural scenarios where a person in one reference frame can look towards a person in a different reference frame and view them as moving faster than the speed of light. A trivial example would be a spinning reference frame (special relativity doesn't explicitly deal with this situation, oddly enough, although you can hack it to do so by dividing time into infinitesimal slices!). Others include the ergosphere around a spinning black hole and regions of the universe beyond our hubble volume.

Now... nobody jump me. I've had people get really mad and insist on long and 'passionate' arguments just from hearing someone say these things. They're usually especially offended by the more trivial examples because _of course, _in a scenario where you spin with your finger out, the direction you're pointing changes at a rate faster than the speed of light - that's not FTL movement, it's a trick - it's conflating angular motion with linear motion. I'm happy to talk about the reasons why GR _does_ count such things as more than just a trick (e.g. everyone is stationary in their own reference frame, FTL motion is only actually forbidden locally wrt to the observer etc etc), but can I be clear: I'm not being a smartass and trying to trick anyone.

Disclaimer made...
While there are natural examples of something like FTL motion predicted by GR, it's unclear at best whether these might translate into actual travel, even in principle. I think guys like Alcubierre are akin to 17th century mathematicians calculating a the orbits needed to reach the Moon. Sure they can calculate what would need to be done, but there's literal lifetimes of other stuff that would need to be overcome before it was anything more than a theoretical curiosity.


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## Swank (Aug 27, 2022)

StilLearning said:


> They're usually especially offended by the more trivial examples because _of course, _in a scenario where you spin with your finger out, the direction you're pointing changes at a rate faster than the speed of light - that's not FTL movement, it's a trick - it's conflating angular motion with linear motion.


That sounds like my example of moving your gaze from star to star.


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## Brian G Turner (Aug 27, 2022)

StilLearning said:


> it's conflating angular motion with linear motion


I think this is what I was trying to reference when I mentioned synchrotrons.


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## StilLearning (Aug 27, 2022)

Swank said:


> That sounds like my example of moving your gaze from star to star.


That's the one - it's all the same issue of an observer being stationary in their own reference frame, whether it's a rotating reference frame, an accelerating reference frame, or an inertial (moving at constant speed/ stationary, which are treated as the same thing) reference frame. 
If you guys have already beaten this into the ground I'll leave it alone - I've seen some names here that I know from experience are knowledgeable wrt general relativity.


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## hitmouse (Aug 28, 2022)

Astro Pen said:


> Meanwhile, Neymar (a football player) transfer fee to Barcelona  - 222 million euros!
> What hope is there for the future of mankind with societal priorities like that?
> 
> View attachment 92437


Thats not a societal priority. Nor is it Neymar’s salary, astronomical as that may be. It is simply a commercial bet by one of the biggest clubs in the world. It may be ridiculous, but it has to looked at in terms of international sports business and marketing in the same sense as the Olympics, NFL, Fifa, F1, 20-20,etc.


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## StilLearning (Aug 29, 2022)

It's probably worth mentioning that the use of near-Earth-space as a resource to do things here on Earth - the off-world portion of the global economy, so to speak - is worth between $400 billion and $150 billion annually, depending on where you draw its boundaries. That is almost entirely unmanned satellites, with a little smidge of space tourism and commercial space experiments tended to by humans on the ISS and the Chinese space stations (in more recent times). The combined manned spaceflight budgets of NASA, ESA and Roscosmos don't top $10 billion a year most years _I_IRC.

It seems likely that, without the need to demonstrate technological prowess (if our goals in space were simply it's use as a resource and for-knowledge-only exploration), humanity would probably have given up on manned spaceflight back in the 70's. The US military space program did exactly that. 

That need of different nations and cultures to demonstrate technological prowess is, in a lot of ways, fuelled by the same need to demonstrate international physical and cultural prowess via sport. So, in a way, I suspect that Neymar's insane seeming worth might come as a parcel with the things that have driven us to have ongoing manned space programs at all. That has changed a bit with space tourism ( a welcome change IMHO) - it's worth noting that Blue Origin's next flight will be a purely science oriented one (Blue Origin to launch next space flight on Aug 31, no tourists this time ) - but not a lot. The field has just been opened to the merely wealthy, rather than the world-dominatingly-wealthy.




			https://space-economy.esa.int/article/33/what-is-the-space-economy
		






						The Space Economy in Figures: How Space Contributes to the Global Economy | en | OECD
					

The space economy is expanding and becoming increasingly global, driven by the development of ever-more governmental space programmes around the world, the multiplication of commercial actors in value chains, durable digitalisation trends, and new...




					www.oecd.org
				











						Biden proposes $24.7 billion NASA budget in 2022 to support moon exploration and more
					

It's a $1.5 billion increase over NASA's 2021 budget.




					www.space.com


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## alai (Aug 30, 2022)

StilLearning said:


> So, in a way, I suspect that Neymar's insane seeming worth might come as a parcel with the things that have driven us to have ongoing manned space programs at all.


Neymar's _personal_ wealth -- coincidentally reportedly in the same sort of range as his transfer value, in principle a very distinct concept -- isn't insane in the global scheme of things.  The numbers of people with that sort of net worth is likely in the tens on thousands.  Though I suspect it might be a resonant one on this forum, where a hectomillionaire sportsballer is more appalling than that of -- say! -- an author with that much loot.  OTOH Neymar really is objectively one of the world's very best players.  Are JK Rowling, Jeffrey Archer, Danielle Steel and Dan Brown the world's _best writers_?  De gustibus!

But is it sane world?  All indications point to 'no'.



Wayne Mack said:


> This can be explained by the rate of time internal to the object having gone to zero and introduces all sorts of divide by zero issues. I assume that this means that time fails to pass for the internal observer.


It means "this theory has broken, bring me another one!"  Or failing such, "please don't ask that..."  But more usefully it predicts that for any finite amount of kinetic impulse, you're still going less than c, so you need some method of getting there other than 'just keep accelerating'.



Serendipity said:


> Hm... so if something is travelling faster then the speed of light relative to the observer, then they would go right through the observer without the observer feeling a thing?


It's possible -- who knows!  Tachyons are an entirely hypothetical class of particles, so their properties are likewise entirely (or doubly?) hypothetical.  And certainly some conventional particles with high (but not certain) probability behave like this this:  neutrinos, notoriously.

One idea is that if they did exist, it wouldn't be possible to interact with them.  Partly because they would be a wholly distinct class of particle -- you couldn't 'flip' states between the two in any model that allows them -- and partly by way of a causality cope.  Physicists, always opening cans of worms, and then complaining that they need bigger cans to cram them back into!



Foxbat said:


> After all, our bodies are subjected all the time to things we aren’t aware of (at least without measuring equipment). Example… Radon gas daughter product particles that often fill our homes without us realising that they are there. They can produce alpha particles that  enter our lungs and potentially irradiate soft tissues but we just don’t experience any of that on a conscious level.


Sure, but those are still interactions -- and even 'observations', with the usual 'not really properly defined as a concept' caveats -- in the physics sense.  If there are interactions that are occurring that aren't detectable with current experimental apparatus, or even there are particles that exist that don't interact even in principle with normal matter...  than that's very much another day's work.  @.@



Swank said:


> We could go to Mars in 2 years if we broke the nuclear weapon space treaty, or sunk a couple trillion into it. It isn't really a technical problem as much as a political one.


"Make bricks without straw" is a _sort_ of technical problem.  Politically, there's been by my count 5.5 manned missions to Mars that have been _politically announced_ already.  Now, you might point out that none of them have been planned to happen within the current terms of the administrations of any of the polities involved (insofar as some (soon to be all?) of them really have 'administrations' and 'terms' in any politically meaningful way).  And the funding and the planning may be inadequate to the task as set out...



Robert Zwilling said:


> That's the old science fiction vs fantasy discussion which never has a definite solution. If you want to get technical about it, 99 percent of what passes for science fiction is science fantasy. Might as well drag Speculative Fiction back out into the spot light.


You're giving me distinctly Atwoodesque twitches here!


Robert Zwilling said:


> Anything with space travel past the asteroid belt is pure fantasy, within the belt that's science fiction so long as it is done in tiny ships and not giant massive dreadnaught size ocean liners.





Robert Zwilling said:


> Perhaps life can never be accelerated past the speed of light without becoming a monument to its previous existence.


Wow, that escalated quickly!  There's a whole middle you're excluding there between "current engineering" and "current physics".  (Crewed -- clearly uncrewed exploration has already occurred) space travel beyond the 'Belt is perfectly possible, would just need time and (a lot of!) money.  Don't see how that's remotely in the realm of fantasy, unless it's described in a gratuitously Buck-Rogers manner.

Never mind a return trip to Mars, there's no deep physics reason, in any "there's a strong basis to believe this is literally impossible" sense, you couldn't have a return trip to _α-Cent _by 2042.  Never mind this mere Mars bagatelle!  Indeed there's no _deep_ reason I couldn't be there this time tomorrow, subjectively speaking, if we handwave away a few more mere technical and squishy biology problems.

OTOH FTL travel is _vastly_ more problematic.  I don't think it _automatically_ qualifies as works including it as fantasy, but very often it might as well be.  Or it's "soft" SF, or "overwise putatively hard SF but we're giving ourselves the standard pass on that".  _Very_ occasionally it's some sort of actually-making-it-a-meaningful-part-of-the-SF (like addressing the causality implications, say).


Robert Zwilling said:


> Sometimes [Vikings] dragged the ships over land to get to the other side.


Indeed so;  witness all the places in Scotland and Ireland with names like "Tarbe(r)t"!


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## StilLearning (Aug 30, 2022)

alai said:


> OTOH FTL travel is _vastly_ more problematic.  I don't think it _automatically_ qualifies as works including it as fantasy, but very often it might as well be.  Or it's "soft" SF, or "overwise putatively hard SF but we're giving ourselves the standard pass on that".  _Very_ occasionally it's some sort of actually-making-it-a-meaningful-part-of-the-SF (like addressing the causality implications, say).


I'll point out, in an openly self serving fashion because it's the subject of what I'm currently writing  , that you can have star systems where the planets (including habitable ones) are comparable distances apart to the Earth and Moon, and that double, triple and quadruple star systems are well documented - where each star has room for it's own system of planets and habitable zone, and the systems are each a matter of light hours or days apart. (Alpha Centauri is such a system). Although they are rare, even septuple star systems have been found. Lastly there are parts of the galaxy, e.g. older open clusters, where the average separation between stars is less than a light year.

So, for the purpose of writing fiction, FTL isn't needed to create a setting where spacecraft travel to many different planets, between star systems, in relatively short periods of time. George Lucas didn't ever actually need hyperdrive for Star Wars. FTL only really becomes a needed plot device if you're wedded to the idea of Earth as a main location in said setting. And even then, there are still other approaches to make the transit times effectively shorter, such as the technology for functional immortality being discovered (this may bother biologists as much as FTL bother physicists, but it's just an example).

As a little bit of an example, here's a not-to-scale map of the septuple star system Nu Scopii:




​If you took that as your starting point, gave each star 4 rocky planets (one naturally habitable orb apiece) and 4 giant planets with an average of 4 large & varied moons each (as Jupiter has - including 2 ice-covered ocean moons and a volcano moon), you have a setting with homes for 7 space faring civilisations, encompassing a total of 140 large solid-surfaced worlds and 28 gas-giants (and as many dwarf planets and large asteroids as you want). All within weeks or at most months of travel of each other, if your ships can hit 50% of lightspeed.

All that said FTL _is_ a fascinating thought experiment, it's just not as vital to building a workable sci-fi setting as its prevalence would have it seem.


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## alai (Sep 1, 2022)

StilLearning said:


> I'll point out, in an openly self serving fashion because it's the subject of what I'm currently writing  , that you can have star systems where the planets (including habitable ones) are comparable distances apart to the Earth and Moon, and that double, triple and quadruple star systems are well documented - where each star has room for it's own system of planets and habitable zone, and the systems are each a matter of light hours or days apart.


I wouldn't worry too much about serving yourself.  It's not as if this is a salaryman drinking night-out! 

I'd add the small cautionary note that there's maybe a question mark about whether such system are _as_ likely to have habitable planets, much less having one each.  OTOH current thinking seems to be leaning in the direction of "dunno, but seems no reason why not".  Extreme cases of this, like the Fireflyverse, are _highly_ unlikely... but if we're only going to limit ourselves to what's possible, then we could even have Klemperer rosettes of planets all within an especially easy commute of each other!



StilLearning said:


> So, for the purpose of writing fiction, FTL isn't needed to create a setting where spacecraft travel to many different planets, between star systems, in relatively short periods of time. George Lucas didn't ever actually need hyperdrive for Star Wars. FTL only really becomes a needed plot device if you're wedded to the idea of Earth as a main location in said setting.


George Lucas very much _did_ need it, as the style of exposition was very much, we're in one star system, clock wipe, we're in another.  It's almost an anti-plot-device:  we're brushing it under the carpet so much it might as well be "a little later in another town down the road after a brisk horse-ride by the posse."  If you were rewriting the story to keep the same plot structure, but to tweak the "tech" elements, it'd be a darn sight easier to just say "actually not happening in space at all" rather anything else.



StilLearning said:


> And even then, there are still other approaches to make the transit times effectively shorter, such as the technology for functional immortality being discovered (this may bother biologists as much as FTL bother physicists, but it's just an example).


I'd doubt it, as we already know of organisms that are much more longer-lived than humans, others that can survive cryogenic freezing, etc.  So unless we're quibbling on "how many tech levels higher", or have some vitalist or essentialist belief that humans are some special unique case in some way, it's hard to imagine why anyone would think this is impossible, rather than "we dunno how to do that yet".

Also recall that relativity itself has exactly this effect, from the PoV of the crew.  Which really _is_ a SF plot point in any number of cases.  (_Forever War_ and _Revelation Space_ spring immediately to mind.)



StilLearning said:


> If you took that as your starting point, gave each star 4 rocky planets (one naturally habitable orb apiece) and 4 giant planets with an average of 4 large & varied moons each (as Jupiter has - including 2 ice-covered ocean moons and a volcano moon), you have a setting with homes for 7 space faring civilisations, encompassing a total of 140 large solid-surfaced worlds and 28 gas-giants (and as many dwarf planets and large asteroids as you want). All within weeks or at most months of travel of each other, if your ships can hit 50% of lightspeed.


That's a fair-sized "if", mind you!  I know it seems very modest in the context of this thread -- "let's compromise between what's currently technologically feasible, ~0.001c, and relativistic velocities of ~0.999c, and say 0.5c!" -- attaining such speeds are pretty challenging.  If we imagine "lighthugger"-type ships that can pull 1g at their discretion and at length (already fairly maguffinesque), then it takes about six months just to accelerate to such speeds -- you'd never actually get that fast even in systems as large as Nu Scopii.  And thus far it's only Newton that's spoiling our fun, not Einstein.  You could of course merrily make that on the order of a 10g acceleration if you're thinking of the crew being in not so much cruise-liner grade accommodation as jet-fighter cockpit.  Much beyond that we'd be assuming reactionless drives or artificial gravity, or an extremely post-human sort of crew.



Swank said:


> I don't think FTL exists, I just don't think it should be ruled out at this stage. Especially by SF writers. Along with all the other unlikely but not actually disprovable stuff that they might dote upon.


I don't think physicists (or indeed SF 'purists') are organising boycotts of woolly space-fantasy movies or book -- or if they are, I've missed the pickets, and so on.  But it's about as "disproved" a possibility as anything really gets in physics.  And way more than any (for example) legal standard of proof.



Mon0Zer0 said:


> Physicists don't assume dark matter exists, they posit as a potential solution to the evidence of inflation. There's a high probability they're wrong.


That's more to do with dark energy, as I understand, which is a waaaay more vague and speculative a concept.  If it even qualifies as a concept!  Dark matter there's quite a lot of evidence for, all basically to do with the medium-scale gravitational structure of the universe.  But it's also possible that (say) a whole series of observations are spectacularly wrong, or that gravity behaves in a non-uniform manner.  Those just seem less likely, and less satisfactory as explanations.


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## StilLearning (Sep 1, 2022)

EDIT: Fair enough about Star Wars too - it is openly taken right from Samurai films and westerns. I suppose it'd be more accurate to say you could do that kind of multi-world, multi civilization worldbuilding without hyperdrive. END EDIT



alai said:


> I'd add the small cautionary note that there's maybe a question mark about whether such system are _as_ likely to have habitable planets, much less having one each.  OTOH current thinking seems to be leaning in the direction of "dunno, but seems no reason why not".  Extreme cases of this, like the Fireflyverse, are _highly_ unlikely... but if we're only going to limit ourselves to what's possible, then we could even have Klemperer rosettes of planets all within an especially easy commute of each other!


A fair point, but as the object of the exercise is SF worldbuilding I figure we can tolerate a some divergence from what the most _likely_ scenarios are, as long as we stay well within the possible. It's also worth considering the possibilities of terraforming, and that for around a billion years our own solar system boasted both Earth and Mars as potentially life supporting planets (https://www.science.org/doi/10.1126/sciadv.abl7497), and possibly Venus as well (Venus May Once Have Been Habitable). So... if we're building SF settings... there's some room to maneuver, for that purpose.

EDIT: The underlying thing is that I want to be offering people a fairly realistic setting in which to set their story, but I absolutely don't want to be dictating to anyone what that story should be like, even by the default of setting too tight a bounds on what I'll consider 'realistic'. So the setting guide should be equally useful tool to someone wanting to write outright science fantasy but with a realistic backdrop, someone writing about a human colony with hyper-tech limited only by fundamental physical laws, someone writing about an alternate 1970's Earth with a nearby stellar neighbor, and all points between. END EDIT

IIRC in Firefly the majority of the inhabited worlds were terraformed by colonists from Earth (possibly all - it's not clear from the lore). Something similar is true for the 12 colonies of Kobol from Battlestar Galactica, which were located in quadruple star system.
The most extreme version of the constructed rosette of planets - the ultimate solar system (The Black Hole Ultimate Solar System: a Supermassive Black Hole, 9 Stars and 550 Planets) - is going to feature in a future book - you wouldn't even need a spaceship to commute between planets in the same orbital ring, you could build space elevators between them! I also plan to cheekily shoe horn in an 800km diameter artificial world made of Osmium, which would have close to Earth-like gravity .



alai said:


> Also recall that relativity itself has exactly this effect, from the PoV of the crew. Which really _is_ a SF plot point in any number of cases. (_Forever War_ and _Revelation Space_ spring immediately to mind.)


You really _do_ have to snuggle up to lightspeed to get the effect -  85% of lightspeed for a 50% change in the perceived passage of time. Just for me, I'd prefer the option of extended lifespan over time dilation, especially since you stand a better chance of coming home to find some people who remember you.



alai said:


> I know it seems very modest in the context of this thread -- "let's compromise between what's currently technologically feasible, ~0.001c, and relativistic velocities of ~0.999c, and say 0.5c!" -- attaining such speeds are pretty challenging. If we imagine "lighthugger"-type ships that can pull 1g at their discretion and at length (already fairly maguffinesque), then it takes about six months just to accelerate to such speeds -- you'd never actually get that fast even in systems as large as Nu Scopii. And thus far it's only Newton that's spoiling our fun, not Einstein. You could of course merrily make that on the order of a 10g acceleration if you're thinking of the crew being in not so much cruise-liner grade accommodation as jet-fighter cockpit. Much beyond that we'd be assuming reactionless drives or artificial gravity, or an extremely post-human sort of crew.


Actually, in this thread, we're specifically talking about faster than light travel, and people are throwing around ideas like Alcubierre metrics and wormholes, so it's a big compromise (almost going off topic!) just by insisting we stay below lightspeed  ! But, again, that's a fair point, and obviously there are massive engineering problems beyond the engine and acceleration, such as even tiny particles of space dust striking a vehicle's leading edge and going BANG like an anti-tank mine.

While I picked Nu-Scorpii  and 50% of C arbitrarily as examples, my main criteria when writing have been speed-of-light travel time between potentially habitable planets, and travel times by chemical rockets: Speed of light time between worlds, since that sets the time limit for sending any kind of message, and without being able to _at least_ send and receive information in a fairly timely fashion any civilization, however post-human and advanced, is arguably not a civilization at all. And chemical rockets because that's probably the absolute lower bound for getting into space from an Earth-like planet and moving between the hypothetical planetary systems of two binary stars - using the more likely example of Alpha Centauri (if the 'A' and 'B' stars had planets): The average separation between the 'A'  and 'B' stars is similar to the distance between Earth and Saturn, so you could imagine the inhabitants of star system A sending probes into the B system with cold-war technology.

There's a helluva lot to talk about regarding what might actually be possible in terms of star drives, but going into the details of stardrives for hard SF is another separate booklet in the series. Probably two. However it's a great idea (so thank you @alai ) to include a few paragraphs on how the survivable accelerations for a human being will limit the effective speed for any vehicle crewed by conventional humans, as well as what kinds of accelerations unmanned craft might hit.

Some moderately serious studies have suggested speeds of 20% of C, and accelerations of 1000's of g, might be achievable for an ultra-lightweight robot probe using fairly near-term technology (Breakthrough Starshot: A voyage to the stars within our lifetimes), so Nu Scorpii civilizations a bit further ahead than us might trade big chunks of information regularly enough, via vehicles that are like space-faring flash drives, but still find sending actual biological citizens from one end of their 7-star system to the other utterly impractical


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## LordOfWizards (Oct 7, 2022)

Hi All, Sorry just now catching up. Been gone for a spell.

Wow!  Those were some serious tangents taken from "Who thinks Faster Than Light travel is possible?"
It could have just been a series of posts: Me | Not Me | Not Me ... instead, 9 pages later I'm not sure we have an answer. 

Off the top, I'll mention a book by Michi Okaku called "The Physics of the Impossible" with an entire chapter on FTL. Some knowledge of physics is required. 

I'd love to address some of the ideas put forth here, but can't do all at once. 

Here's one that caught my eye early on.


AllanR said:


> Lets say I have a shinny new FTL ship and I go for lunch at Alpha Centarie.  Say I get there in just a few hours (by my watch).... when I am at Alpha Centarie, the light I see from the Sun left 4 years before I did. The light being emitted by the Sun is still another 4 years further behind that.
> After lunch I decide to go home right away. Again lets say this takes just a few hours.
> When I get back to Earth it will be 8 years before I left.



If I'm not mistaken (don't shoot!) it will be 8 years later on Earth, but for you only about 8 hours have passed. That is usually the depiction made in SF novels and film. Like someone mentioned earlier this is known as time dilation. Two types of time dilation exist; time dilation onset by a near light speed relative velocity, and time dilation brought about by the effect of gravity. Interstellar depicted an example of the second type (gravity).

I am not a physicist per se, but it is among my very top favorite subjects. I have done the maths of special relativity (which are easier than general relativity). So give me a percent of the speed of light and I'll tell you the difference in the rate of time between "stationary" and the speeding object's reference frame.

I think that one day we may be shocked to look back and see how primitive we still were in the twenty first century. Yes one day FTL will be possible but we have a looooooong way to go.


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## Swank (Oct 7, 2022)

LordOfWizards said:


> If I'm not mistaken (don't shoot!) it will be 8 years later on Earth, but for you only about 8 hours have passed. That is usually the depiction made in SF novels and film.


I believe you're mistaken. FTL doesn't exist (as far as we know), but the point of it is that it doesn't take 8 years but much less. Like the same 8 hours. 

What you're describing is travel at speeds approaching the speed of light.


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## Vertigo (Oct 7, 2022)

Swank said:


> I believe you're mistaken. FTL doesn't exist (as far as we know), but the point of it is that it doesn't take 8 years but much less. Like the same 8 hours.
> 
> What you're describing is travel at speeds approaching the speed of light.


Which brings you to the whole (unanswerable*) question of whether an FTL drive will involve time dilation at all. If it doesn't then the previous post is still wrong as it will be 8 hours objective and subjective each way so no your won't have travelled back in time. Although you will get back before the light of your departure has arrived.

Unanswerable because we still don't have a working FTL mechanism. I think the Alcubierre drive avoids time dilation as you aren't technically moving but space is moving around you.


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## LordOfWizards (Oct 8, 2022)

Swank said:


> I believe you're mistaken. FTL doesn't exist (as far as we know), but the point of it is that it doesn't take 8 years but much less. Like the same 8 hours.
> 
> What you're describing is travel at speeds approaching the speed of light.



I was responding to the post I quoted. I never said FTL exists. I am trying to correct the perception that AllanR seemed to have. But you are correct. I was conflating FTL with near light speed effects. I was pretty tired when I wrote that. I had just read 9 pages of conjecture!


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## Swank (Oct 8, 2022)

Vertigo said:


> Which brings you to the whole (unanswerable*) question of whether an FTL drive will involve time dilation at all. If it doesn't then the previous post is still wrong as it will be 8 hours objective and subjective each way so no your won't have travelled back in time. Although you will get back before the light of your departure has arrived.
> 
> Unanswerable because we still don't have a working FTL mechanism. I think the Alcubierre drive avoids time dilation as you aren't technically moving but space is moving around you.


There is no reason to believe there is FTL, but if it is possible, the rules it would operate under are as unknowable as its mechanism.

There could be extreme time dilation - making the trip much faster than the scant external time. Or the lack of acceleration (the seeming mechanism of dilation, given gravity dilation) might mean no dilation at all.

Causality is really the big question. Will it prevent FTL? Is causality only a factor if something is going to cause a noticeable paradox? Will travel in pro-paradox directions be prevented, but everywhere else is okay? The universe seems to function on the basis of information - like Heisenberg's Principle. With FTL the prevention of paradox might be a fairly interactive process with travelers.


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## LordOfWizards (Oct 8, 2022)

Swank said:


> With FTL the prevention of paradox might be a fairly interactive process with travelers



Could you please explain what this sentence means?


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## Swank (Oct 8, 2022)

LordOfWizards said:


> Could you please explain what this sentence means?


They might find that the calculation of causality conflict is important to successfully travel to certain locations at FTL speeds. Do it wrong and the ship doesn't move, disappears, ends up somewhere else or takes as long as light to arrive. Understand and avoid conflicts and the crossing might be instantaneous.


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## Swank (Oct 8, 2022)

Another factor in FTL (and dear to SF writers) is the manner that the ship moves. Off the top of my head, we have warp (where space changes shape to make normal velocities cover larger distances), hyperspace (a realm in our universe that has different laws), wormholes or other interconnected places in the universe, quantum coupling allowing matter to turn into information and return to matter elsewhere, moving between near identical universes (might be the same as the previous example), translation into particles that only exist above light speed (the hypothetical tachyon), and teleportation.

The move between similar universes is my idea, and avoids paradox.


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## LordOfWizards (Oct 8, 2022)

> When I get back to Earth it will be 8 years before I left.


This is the statement that messed me up. I don't think FTL introduces this kind of paradox. In fact the statement violates the law of Entropy. I suspect the jump in logic he took was that the light took 8 years (4 LY each way) so if he got back in 8 hours he would back in our system before the light got very far. It's an interesting observation, but I don't think FTL would mess with your time like that. 

Every depiction I've seen of FTL (and wormholes) sends you to the destination without any distortion of time on either end. It seems to me the whole point of FTL is to have a shortcut through space. FTL should allow us to go back and forth light year distances without any effect on local time.


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## StilLearning (Oct 11, 2022)

According to this Scientific American article ( Star Trek ’s Warp Drive Leads to New Physics ) , because powerful space warps mean/are powerful gravitational fields, you could expect time on a ship being 'propelled' by an Alcubierre-type arrangement of space time to, in effect, run slower for the occupants, who could exert some control over the flow of time by adjusting the exact geometry of their 'warp bubble'.


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## AllanR (Oct 11, 2022)

here are a couple good videos on why FTL means time travel.
explanation starts at 8:30   



6:53 on this one


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## Swank (Oct 11, 2022)

AllanR said:


> here are a couple good videos on why FTL means time travel.
> explanation starts at 8:30
> 
> 
> ...


I am not at peace with Minkowski diagrams. Any reference frame can be represented by them, including that of a ship traveling at the speed of light. For that ship's crew, dilation is total - there is no passage of time. To diagram that from their frame, you either have to draw the travel line horizontal, or you have to make the distance traveled zero (which might make sense, given length compression). 

It seems like another solution to FTL paradox is to define how superluminal communication velocity is measured when transmitted by a dilated reference back to a low velocity one. The diagrams suggest it must be a straight line back, but that seems like an assumption.

(I realize I am not qualified to suggest new physics, but inserting FTL lines on a Minkowski diagram is like inserting hieroglyphs into an English sentence. Maybe FTL lines should curve, for instance?)


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## LordOfWizards (Oct 11, 2022)

Yes, The videos are fascinating. One consideration is that the theory cannot be tested. But It really is all theory. It's fun to examine the possibilities. I guess to some degree my concept of FTL has been partially populated by science fiction. I say partially because I like to keep an open mind. I don't assume any of it is reality, I just go along for the ride. Any portrayal of FTL is fiction for now. I love science.


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## Swank (Oct 11, 2022)

Just throwing this out: What if the production of an FTL signal was governed by the amount of relative time it takes to generate? In this scheme, a low dilation place (earth) would produce an FTL signal over the course of one minute. But the same sort of signal on a near light speed ship would take relative years for a one minute generation, and wouldn't be FTL at all to earth observers. 

With no ability to FTL signal back, no paradoxes.


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## Wayne Mack (Oct 19, 2022)

Wayne Mack said:


> I'm not sure if this is a direct answer, but this is an interesting tidbit I found in researching a story. The universe expands faster than the speed of light. My physics-fu isn't strong enough to understand the explanations, but here is one link: How Can the Universe Expand Faster Than the Speed of Light?


Resurrecting this because my question still puzzles me despite how many answers that I've read. To summarize, the Universe is estimated to be 13.8 billion years old while the most distant observed point in the universe is 46.1 billion light-years. The answer I keep finding is that the distance is expanding while the velocity is constant. I still cannot grasp the difference between something travelling a distance and the distance it travelled having expanded. Another reference: Does the expansion of the Universe break the speed of light?


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## LordOfWizards (Oct 19, 2022)

Wayne Mack said:


> Resurrecting this because my question still puzzles me despite how many answers that I've read. To summarize, the Universe is estimated to be 13.8 billion years old while the most distant observed point in the universe is 46.1 billion light-years. The answer I keep finding is that the distance is expanding while the velocity is constant. I still cannot grasp the difference between something travelling a distance and the distance it travelled having expanded. Another reference: Does the expansion of the Universe break the speed of light?


This may be the issue: 'velocity is constant.' Actually the expansion of the universe is speeding up. Same idea as a car increasing it's speed with acceleration. It keeps getting faster. Not only do scientists and physicists not know why, they are flummoxed, stuck, puzzled, stumped, floored, nonplussed, and perplexed about it. Others can explain better how space itself is expanding - so all of 'the stuff' in the universe keeps stretching further apart.


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## Swank (Oct 20, 2022)

Wayne Mack said:


> Resurrecting this because my question still puzzles me despite how many answers that I've read. To summarize, the Universe is estimated to be 13.8 billion years old while the most distant observed point in the universe is 46.1 billion light-years. The answer I keep finding is that the distance is expanding while the velocity is constant. I still cannot grasp the difference between something travelling a distance and the distance it travelled having expanded. Another reference: Does the expansion of the Universe break the speed of light?


If the distance gets bigger between things, that isn't the same as those things traveling. So IF the universe is expanding the way currently thought, it is not breaking lightspeed because nothing is traveling FTL - but the space things travel through is growing, essentially slowing down effective velocities because the distance to traverse is greater than when the travel started.

I suspect this will get disproved, but in the meantime it doesn't violate lightspeed because space is being added, not velocities increasing.


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## Wayne Mack (Oct 20, 2022)

Swank said:


> If the distance gets bigger between things, that isn't the same as those things traveling.


I appreciate the explanation, but (and this reflects more on me than on anyone else) I simply do not understand the meaning of the words. What does it mean, for instance, to have two object be stationary, yet have the distance between them increase? How does one distinguish in change in distance due to movement from change in distance just due to change in distance?

I sort of get the argument that the speed of light is preserved because distance expands after the light has travelled through it, but I still struggle to understand how to describe what is happening at the end points and how they fail to be moving at greater than the speed of light. I get the promise of warp drives to compress and expand distance, but I don't understand travelling a distance while simultaneously travelling a shorter distance.

I apologize if my frustration is showing; I don't want this to sound like a dispute with your explanation. It is merely a reflection of where my head is at and that I am not able to separate the idea of velocity from a change in distance over time.


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## Swank (Oct 20, 2022)

Wayne Mack said:


> I appreciate the explanation, but (and this reflects more on me than on anyone else) I simply do not understand the meaning of the words. What does it mean, for instance, to have two object be stationary, yet have the distance between them increase? How does one distinguish in change in distance due to movement from change in distance just due to change in distance?
> 
> I sort of get the argument that the speed of light is preserved because distance expands after the light has travelled through it, but I still struggle to understand how to describe what is happening at the end points and how they fail to be moving at greater than the speed of light. I get the promise of warp drives to compress and expand distance, but I don't understand travelling a distance while simultaneously travelling a shorter distance.
> 
> I apologize if my frustration is showing; I don't want this to sound like a dispute with your explanation. It is merely a reflection of where my head is at and that I am not able to separate the idea of velocity from a change in distance over time.


It really doesn't make any sense - it is the result of the way the current theories function, rather than an observable effect.

But it is most like the balloon example - which might be better illustrated by imagining a water world planet. The world has islands floating on its surface and submarine cities in its depths. Now suppose there is a process at the water world's core that makes vast amounts of water. As the new water mixes with what's already there, the water world will expand. It will have more volume, more circumference, more surface area and more diameter. As this happens any two island cities, static on the surface, are going to get further apart. And the submerged cities, even though they aren't sinking, are going to get further away from the floating cities above them. All cities get further apart.

This is what is supposedly happening to our universe - space is filling in between galaxies. But space is empty, so we call that expansion. Regardless, there is more vacuum between galaxies without the galaxies moving in relation to their grid location in the expanding map.

One thing that ought to be emphasized is that time dilation and velocity aren't observer neutral. The reason we have the twin paradox is because time dilation happens to objects under acceleration, not just anything that seems to have velocity. A spaceship zooming past a planet might observe that the planet is passing them at a high relative velocity, but only the spaceship has accelerated to a dilated reference frame while the planet remains at a 'faster' time rate. So it is really important to keep in mind that the weird things that happen around relativistic velocities only happen when there is some sort of acceleration of mass. The universe getting more vacuum is not acceleration of anything.


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## SilentRoamer (Oct 20, 2022)

Above is a good explanation.

Metric Scale Expansion is not the same as acceleration because each observer (lets say in this instance a Galaxy is an Observer) sees every other Galaxy moving away from it - however each Galaxy (in its own reference frame) is not moving through space. So two objects can be separating at what appears to be FTL but within their own reference frames they are not moving at all. 

Take the 2d balloon analogy, semi inflate a balloon, now draw on some spiral galaxies, then inflate the balloon fully - (where the surface of the 2d balloon is an analogy for 4d space) when inflating each galaxy is moving away from each other galaxy but only relative to each other, in their own reference frame they do not move.

It is very counter intuitive.


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## LordOfWizards (Oct 21, 2022)

Wayne Mack said:


> appreciate the explanation, but (and this reflects more on me than on anyone else) I simply do not understand the meaning of the words. What does it mean, for instance, to have two object be stationary, yet have the distance between them increase? How does one distinguish in change in distance due to movement from change in distance just due to change in distance?


The last question is a good one. 1) One doesn't distinguish. Can our current space telescopes measure differences in 2 distinct distant velocities?  I have no idea. But over time (many years) we can see things have moved out further than they should have if light speed was a limit.

Try this: You have an enormous pure black bowl. You start pouring raisin pudding into it. The pudding itself is what we call empty space. The raisins are everything with mass (Stars, planets, dust) You have an endless supply of pudding. You keep pouring at a constant rate and the pudding is expanding. As you pour the raisins start to get further apart. Then you start pouring faster and faster. Now the distance between the raisins is increasing faster than when you were pouring at a constant rate.

Caveats:
We can't see where the pudding is entering.
 (the speed of light here would be some arbitrary fill rate into the bowl)
A fixed amount of raisins were poured in at the start.

Does that work?


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## Swank (Oct 21, 2022)

LordOfWizards said:


> The last question is a good one. 1) One doesn't distinguish. Can our current space telescopes measure differences in 2 distinct distant velocities?  I have no idea. But over time (many years) we can see things have moved out further than they should have if light speed was a limit.
> 
> Try this: You have an enormous pure black bowl. You start pouring raisin pudding into it. The pudding itself is what we call empty space. The raisins are everything with mass (Stars, planets, dust) You have an endless supply of pudding. You keep pouring at a constant rate and the pudding is expanding. As you pour the raisins start to get further apart. Then you start pouring faster and faster. Now the distance between the raisins is increasing faster than when you were pouring at a constant rate.
> 
> ...


If the raisins are stars, the expansion of the universe includes the introduction of more stars/raisins?


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## LordOfWizards (Oct 21, 2022)

Swank said:


> If the raisins are stars, the expansion of the universe includes the introduction of more stars/raisins?


 
Caveat #3 A fixed amount of raisins were poured in at the start. 

You may recognize the raisin pudding analogy from somewhere else.


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## Vertigo (Oct 21, 2022)

Wayne Mack said:


> I appreciate the explanation, but (and this reflects more on me than on anyone else) I simply do not understand the meaning of the words. What does it mean, for instance, to have two object be stationary, yet have the distance between them increase? How does one distinguish in change in distance due to movement from change in distance just due to change in distance?
> 
> I sort of get the argument that the speed of light is preserved because distance expands after the light has travelled through it, but I still struggle to understand how to describe what is happening at the end points and how they fail to be moving at greater than the speed of light. I get the promise of warp drives to compress and expand distance, but I don't understand travelling a distance while simultaneously travelling a shorter distance.
> 
> I apologize if my frustration is showing; I don't want this to sound like a dispute with your explanation. It is merely a reflection of where my head is at and that I am not able to separate the idea of velocity from a change in distance over time.



Maybe this might help (or maybe not!). One of the key elements in all of this is that information - whether data passed by electromagnetic waves or matter - cannot travel faster than the speed of light. So if we take your two stationary objects where space is expanding faster than the speed of light, there is no actual information passing between them and, indeed, it cannot pass between them as it can only travel at most at the speed of light. So nothing, matter or light, can pass between them so relativity is not broken by the expansion of space. They are not _travelling_ apart but the space between them is stretching.

Or maybe another way of looking at it is that space is expanding and it is convenient but meaningless to say that it is expanding faster than the speed of light. Speed is measure by in terms of distance covered and if the distance itself is expanding then how can that speed be measured? The space between you and I, for example, is not expanding so much that we are moving apart faster than the speed of light. However the space between us is indeed expanding, so although we might both be stationary we _are _moving apart. But, in cosmic terms, the amount of space between us is tiny so the expansion is tiny so the rate we are moving apart is tiny. However add that expansion up across vast cosmic distances and the the expansion accumulates to significant levels and eventually to a point where vastly distant objects are moving apart faster than the speed of light.


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## Ursa major (Oct 21, 2022)

Wayne Mack said:


> how they fail to be moving at greater than the speed of light.


A simple/simplistic view....

Setting aside all the other various issues (relativity, etc.), explanations about which are far above my pay grade, it seems to be because "movement" is "movement _through space_" (which is limited to the speed of light) and adding space does not involve movement (and so there's no speed to limit).

If more space is created between two points** that are stationary*** (i.e. they are not moving _through space_), they are in exactly the same locations _in space_ as they were before (they have not moved) but are now farther apart, as there is now more space between them.


** - The more problematic idea (for me) concerns not points (which can be considered to be dimensionless) but objects where additional space may have been created within them. So what has happened? 1) Have their volumes and surface areas become larger? 2) Have their volumes and exteriors remained the same size, with points on those exteriors having moved through space to maintain their relative distances? 3) Is there a law of nature that does not allow space to be created between two "points" in space that are "occupied" by matter/energy (i.e. space can only be created in a vacuum)? I favour (3)... which has the advantage that it would explain why the process might be accelerating faster than it would if the creation of space was constant across the universe: the more space between matter/energy that is created, the greater the ratio of space in which more space can be created to that where it can't.

*** - Obviously, the same is true whether the points are moving or not: their speed is measured by movement through the space that exists as they move through it (and so not _before_ they did, and not _after_ they did).


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## Venusian Broon (Oct 21, 2022)

LordOfWizards said:


> This may be the issue: 'velocity is constant.' Actually the expansion of the universe is speeding up. Same idea as a car increasing it's speed with acceleration. It keeps getting faster.


Correct



LordOfWizards said:


> Not only do scientists and physicists not know why, they are flummoxed, stuck, puzzled, stumped, floored, nonplussed, and perplexed about it.



Methinks you doth protest too much!  It's an observation of what's actually happening (although see below!). I'm still puzzled why *F = *m *a*, but I measure it and that's what always seems to happen. I don't know why. My god, just sitting down and thinking about it, I'm perplexed. 

We do science because we do not know. Better to be puzzled with the universe and try and work it out than just take beliefs that you've been told and do nothing.

But just to complicate things, as for the expansion of the universe, some others have suggested that the data is flawed and it is not accelerating (still expanding, but at a constant rate). They suggest the data has been misinterpreted. Others have constructed other scenarios where it _seems _we are in an accelerating expanding universe, but we are not.

And of course who is to say that this acceleration rate isn't variable but that it will evolve with time? Perhaps drop to zero. Or go negative and start reeling in the galaxies and give us a 'Big Crunch'. Or grow even more in magnitude and cause the 'Big Rip'. 

This is because....


LordOfWizards said:


> Others can explain better how space itself is expanding - so all of 'the stuff' in the universe keeps stretching further apart.



....currently no one can explain how space is expanding, other than it's an observation that has been experimentally verified. We have no theory*. In fact, going even more basic, never mind the expansion, why spacetime? General relativity just assumes a universe with this 'stuff' everywhere, a backdrop for all those galaxies, mass and ourselves. Why?

Anyway, it's much more fun to have mysteries to try to explain, the universe would be very dull otherwise. 

==================

EDIT: To be correct, we have some theories. But none of them have been verified or seem likely to ever be verified.


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## AE35Unit (Oct 21, 2022)

I'm not sure its possible to have negative mass, so therefore ftl would be impossible. Warp speed however, different kettle of fish


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## Wayne Mack (Oct 21, 2022)

Venusian Broon said:


> I'm still puzzled why *F = *m *a*


I'm not sure what the concern is with this one, but let me take a crack at it.

I'd say there are three questions. One, why the relationship between force and acceleration. Two, why is there a linear relationship with mass. Three, why is there a linear relationship with acceleration. (I do not have an answer as to why there is a relationship with mass).

One. If one accepts the proposition that a body in motion tends to stay in motion, then it can be restated as a body at a constant velocity does not require applied force. Applied force is needed to cause a body to change its velocity. Acceleration is simply change in velocity.

Two. If one imagines a body of mass M traveling at some velocity, then a certain force is required to stop it. If there are two bodies of mass M, twice the force is needed to stop both of them. If one moves the two bodies closer and closer together, the stopping force remains constant until the two bodies are combined. At twice the mass, twice the force is required.

Three. If one imagines accelerating a ball of mass M from zero to velocity V, there is a defined force F required. If that ball is on a moving train, the same force is required to give the ball an additional velocity V. If the ball is thrown in the direction of travel of the train, additional force beyond F is not needed to achieve a a total velocity of train velocity plus ball velocity. The change remains linear. One can also consider the ball thrown in the opposite direction of the train. The force to achieve a relative velocity of V remains constant. 

Does that make sense? 

Of course, solar sails seem to create a problem with this thought process. Massless photons exert force on sails generating propulsion.


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## Robert Zwilling (Oct 21, 2022)

The expansion is only happening between massive systems that have no gravity connection between them. This means that smaller systems are staying the way they are because gravitational attraction is holding them together. Simply put, the solar system is not expanding. The extra space showing up between massive systems with no gravity attraction is supposedly a pure vacuum with absolutely nothing in it. There might be some interesting things happening at the edges of the pure vacuum. This might also mean that the vacuums we create or know about in the solar system are actually chock full of interesting things because they exist in a place where there is gravitational attraction between masses and can not be pure vacuums because they at least have gravity and other forces running through them. Perhaps there is a different kind of physics in a pure vacuum and if a pure vacuum portal could be created on Earth, it would suck you right out to the closest pure vacuum out in space in the middle of nowhere in zero time.


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## Christine Wheelwright (Oct 21, 2022)

Venusian Broon said:


> I'm still puzzled why *F = *m *a*, but I measure it and that's what always seems to happen.


Probably worth noting that force is defined (its unit, the newton, is defined) in terms of mass, time and distance (which are units that would have pre-existed it).  Therefore, the only observation necessary for a 17th century scientist was that acceleration is proportional to force.  Hence F=ma (with F being a newly-defined unit).  As for why F=ma....I'm not sure we fully understand that.


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## Venusian Broon (Oct 21, 2022)

Wayne Mack said:


> I'm not sure what the concern is with this one,



A philosophical concern rather than a physical one. Why this particular relationship between Force, mass and acceleration? Why not *F = *m *a*^2, *F = *ln (m *a*) or *F*^2 = 1 / (m cosh (*a*) ) or any of the infinite number of different mathematical relationships I could posit? 

(Other than the reason that, 'Well, that's the way we observe it"! Which is an _answer_, true, but seems a bit of a cop out  )

Yes, the universe would look _very_ different to ours if such a fundamental law about force acting on an inertial mass, but who is to say that in the multiverse there are infinite numbers of such different universes with sentient creatures puzzling the very same thing about their own different laws. 

Is there a deeper reason why our laws of physics are the way they are? For example, the reason why we (seem?) to have inverse-square laws - Newtonian gravity and Coulomb's laws is that we have three space dimensions. If there are more or less dimensions then this square law changes. And it _might_ be the case that on certain scales - the very big and very small - space isn't quite three dimensional and these laws would change. (Experiments are being carried out on some of these issues to test this idea.) 



Wayne Mack said:


> One. If one accepts the proposition that a body in motion tends to stay in motion, then it can be restated as a body at a constant velocity does not require applied force. Applied force is needed to cause a body to change its velocity. Acceleration is simply change in velocity.



Sure this is Newton' s first law. Nice. And F = ma is Newton's 2nd law, and we have Newton's third: for every action there is an opposite and equal reaction. Yet some of the concepts used in all three are fundamentally axioms that I can still ask: why do we observe the universe seemingly applying these axioms? Are there deeper reasons? 



Wayne Mack said:


> Of course, solar sails seem to create a problem with this thought process. Massless photons exert force on sails generating propulsion.



Photons have a momentum through their energy. When they are absorb by the matter - say that on a solar sail - the photon has been stopped and its momentum is now zero, and by conversation of momentum the matter gains this momentum. 



Christine Wheelwright said:


> Probably worth noting that force is defined (its unit, the newton, is defined) in terms of mass, time and distance (which are units that would have pre-existed it).  Therefore, the only observation necessary for a 17th century scientist was that acceleration is proportional to force.  Hence F=ma (with F being a newly-defined unit).  As for why F=ma....I'm not sure we fully understand that.



The Newton was defined, as far as I can tell, by the equation F = ma, so it's kinda a circular argument! If Newton had found a different equation. say Force was proportional to mass _squared _and acceleration to the power of 1 and a half, then the Newton would be defined by those relationships. 

It is weird to think that, before Newton, humankind didn't really have a good grasp of the mathematics of how forces actually worked. They did have a good intuition of how it did work, of course - otherwise ancient cultures wouldn't have been able to put up big buildings, ships., catapults etc...!


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## Swank (Oct 22, 2022)

Venusian Broon said:


> A philosophical concern rather than a physical one. Why this particular relationship between Force, mass and acceleration? Why not *F = *m *a*^2, *F = *ln (m *a*) or *F*^2 = 1 / (m cosh (*a*) ) or any of the infinite number of different mathematical relationships I could posit?


It seems like this is part of living in a relativistic universe. With no set base velocity, how could you say how far into an acceleration curve you were in? You'd end up with situations where you could manufacture energy from the differential in the force required to put two objects in identical orbits via different acceleration. It would be an unbalanced mess.



Venusian Broon said:


> Sure this is Newton' s first law. Nice. And F = ma is Newton's 2nd law, and we have Newton's third: for every action there is an opposite and equal reaction. Yet some of the concepts used in all three are fundamentally axioms that I can still ask: why do we observe the universe seemingly applying these axioms? Are there deeper reasons?


While these make more sense stated as three laws, they really are the same law from different points of view. Take the linguistics out of it and it is one symmetrical law. 

Imagine a universe where two identical objects orbiting a planet a millimeter apart would need to change orbit if they touched and therefore doubled in mass. It doesn't seem like there are a lot of other options besides F=MA.



Broon, you are a physicist, correct? I was hoping someone could answer this:
Given that you can get to places in the universe with a high degree of local time dilation without needing to expend the force normally associated with high acceleration reference frames, how would you _know_ you weren't in a place with a greater degree of dilation? 

I'm thinking of the _Interstellar_ thing, where traveling to and from a world orbiting closely around a black hole can be accomplished without the kind of acceleration needed to get to a large percentage of lightspeed. Given that the dilation changes the way you observe the outside universe, would that change in observation hide the fact that the center of the galaxy's black hole is much, much bigger than we think, and the Milky way exists in a relatively high degree of dilation - affecting our observations about the rest of the universe's red shift?


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## LordOfWizards (Oct 22, 2022)

Venusian Broon said:


> The Newton was defined, as far as I can tell, by the equation F = ma, so it's kinda a circular argument!



 Yes. I always imagine scenarios/examples. To me theory can't be well understood without examples (or possibly thought experiments).

So, a mass is at rest in space where there is no gravity. _Something _pushes it. What? acceleration? There is no acceleration without force. And no force without acceleration. very circular.
F = ma doesn't mention what object is doing the pushing, but if nothing was pushing it would stay at rest. It doesn't need to mention where the force comes from. It is only modeling what happens as the result of the push.

Mathematics is useful because through experiment we can observe what occurs in this universe. I'm kind of glad Newton found the relationship to be this simple. Newton didn't invent the underlying laws. They were already here. Newton found a model for interactions between masses, and experiments proved him correct over time.

I doubt Newtons 'Theories' of Force and Gravity were immediately accepted.

I like Max Planck's statement on scientific theories: “A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.”


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## Ensign Shah (Oct 22, 2022)

Having looked at the science, examined the theories, agonised over the formulas, I can only conclude that my answer should be, erm, maybe


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## paranoid marvin (Oct 22, 2022)

I suppose it depends on what we mean by travelling faster than light. Can I - somehow - get from point A to point B faster than the light from (for example) a particle of light can? Yes I believe this is definitely possible. The answer doesn't lie in a straight line 'drag race', but in finding ways to circumvent this method of physical travel. 'Folding' space, teleportation, and natural or induced wormholes are just some of the possibilities, but I'm sure that there are plenty more.

As I have mentioned earlier in this thread, considering our position in the backwaters of the western spiral arm of the galaxy in the outer reaches of the universe, it seems incredible to me that we can say with any certainty how the universe works. I'm sure it was Douglas Adams who said (something along the lines of) our understanding of the universe is about the same as an ant's understanding of the workings of the Tokyo subway system. I wish I could find the exact quotation, but I don't think he's too far off the mark with this suggestion.


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## Wayne Mack (Oct 22, 2022)

LordOfWizards said:


> F = ma doesn't mention what object is doing the pushing, but if nothing was pushing it would stay at rest.


I feel that this may be confusing acceleration and velocity. Without force, an object in motion would stay in motion. I tend to find the concept of an object of being at rest to be a little bit confusing. When comparing two objects, we usually define one as being at rest because its frame of reference allows for the simpler description of the major forces acting on the two bodies. 

Without any force acting on it, an object retains is speed and direction.


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