Who thinks Faster Than Light travel is possible?

[Swank]

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

6:53 on this one

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?)

 

[LordOfWizards]

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.

 

[Swank]

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.

 

[Wayne Mack]

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?

 

[LordOfWizards]

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.

 

[Swank]

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.

 

[Wayne Mack]

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.

 

[Swank]

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.

 

[SilentRoamer]

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.

 

[LordOfWizards]

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?

 

[Swank]

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?

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

 

[LordOfWizards]

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.

 

[Vertigo]

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.

 

[Ursa major]

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).

 

[Venusian Broon]

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

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....

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.

 

[AE35Unit]

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

 

[Wayne Mack]

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.

 

[Robert Zwilling]

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.

 

[Christine Wheelwright]

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.

 

[Venusian Broon]

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.)

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?

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.

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...!