a science fiction glossary? or book?

[Ray McCarthy]

In the simply-defined case of tachyons (a particle that must exceed c in all inertial reference frames)

Of course Tachyons are likely a mathematical artefact, like negative frequency (in DSP mathematics), with no actual existence.

and there are no logical limitations on how wormholes could interact with time

Yes there is. From a basis of simple logic we can regard maths opening Wormholes to the past as a mathematical artefact (like Quadratic Equation roots are + and - and usually the - answer has no physical implementation). It's also dubious that a wormhole can be instantly opened to future, except in sense that light from far end will take normal time to travel outside wormhole, or view of space via wormhole (if possible) end 10,000 LY away would not be the 10,000 year old direct view but view now.

or it could connect "Earth, year 2015" to "Galactic Core, year 1,000,000BC (Earth reference frame)". The latter would absolutely represent a time paradox, because you could then fire a photon torpedo at Earth and destroy the planet a million years before you were born.

I think even if wormholes are possible, opening one doesn't open a portal to the past. Or can't due to causality.
Um ... it's about 30,000 LY to Galactic core. Anyway if photon torpedo is light speed, so FIXED* Worm hole is opened, the other end of a 100,000 LY wormhole isn't 100,000 LY in the past, but now. So a photon torpedo would arrive here 100,000 years in the future.

Any kind of method to get from A to B WITHOUT travelling in normal space isn't subject to relativistic time dilation equation.

but their space-time reference frames would seem "infinitely finely-tuned" so that it is impossible to use wormholes to interact with your own past.

Yes, If a wormhole or Star gate or Jump drive is possible at all, it only folds or bypasses space (like a walkway across between top of two skscrapers), it's not FTL travel also it will not allow time travel.

[* If it was possible to move one end of an open wormhole, then you can create a temporal paradox, such a thing is probably impossible anyway.

Possibly the energy to keep a Wormhole open is so large that they can only exist for a fraction of a femto second or a Planck interval, if they are possible at all.
]

 

[SilentRoamer]

Ray McCarthy: Whether travelling through "normal" space or some other exotic measure we are not using time dilation as an artefact of time travel. The time dilation experienced is irrelevant in this context (only the distance matters) because to any external observer they Arrive at B prior to leaving A.

If there is no time travel involved and they travel to a Universal Timezone (humour me that) then essentially we are not talking about FTL travel because by this theory you could strap into a .99C spacecraft and make the same journey through physical space.

The necessity for some sort of either: Time independent special manifolds or time travel to same spacetime are a REQUIREMENT of FTL physics. I can show you how from a mathematical proof but it may be easier for me to link you to relevant papers. This is because instantaneous transfer of matter from any point A to any Point B violates causality IF you are using Universal Time. When I say violates causality I am not talking about causality in a sense of the Novikov Self Consistency theory but from a WorldLine perspective, any A to B instant travel enables someone to intersect their own observational WorldLine.

Piousflea84 when you say: "Any violation of c from any reference frame will, by definition, violate causality from that reference frame." This is correct - in relativity there is no such thing as relative motion, or to put it another way there is no way to measure motion without reference to other observers and no observer has precedence.

 

[Ray McCarthy]

because to any external observer they Arrive at B prior to leaving A.

No. that's not possible.

 

[psychotick]

Hi Silent,

I rather liked the last sentence of your previous post. It reminded me of a special relativity conundrum I came up with a while back.

Consider the twins paradox. So one twin is on a spaceship heading away from the Earth at close to the speed of light. Now according to special relativity people on Earth should see the people on the spaceship moving about much more slowly as time slows down for them. And in fact time has slowed down for them relative to time on Earth since the standard model has the twin returning to Earth and being a younger person having experienced less time than his twin on Earth.

However it occurred to me that we are talking about relative frames of reference - inertial / temporal. There is no absolute temporal / inertial frame of reference, it's all relative. If everything is relative and there is no absolute frame of reference, then it's logically incorrect to say that the spaceship is leaving Earth at nearly the speed of light. In actual fact since there are only two frames of reference to consider in space, the correct interpretation is that the Earth and the spaceship are leaving each other with the distance between them increasing at nearly light speed.

If that's correct, and according to what I can tell of the theory as a novice it is - then the paradox is resolved - sort of. Because the twin on the spaceship must be able to look back at Earth and see everything their moving much more slowly as time again has slowed down there.

But if time has slowed on Earth at exactly the same rate as time has slowed on the spaceship, neither twin should notice the slightest difference in the rate of time experienced by the other - thus negating the paradox.

So how does it work that experimentally we have seen with the atomic clocks on planes etc, that time slows only for one of the objects in motion? Are we claiming that there is actually an external absolute time / space against which all velocity / movement is compared? And that therefore the spaceship is leaving the Earth but the Earth is not leaving the spaceship? If so the basic premise of relativity is gone.

Open to all to answer.

Cheers, Greg.

 

[Piousflea84]

Here's teleportation causality violation in a nutshell:

Let's say Kurt teleports instantly from the Earth to the Moon, approximately 1 light-second apart. Xavier is standing on the Moon and he sees Kurt arrive 1 second before he left. Logan is standing on the Earth and sees Kurt arrive 1 second after he left. By itself, this isn't a violation of causality because Logan and Xavier are 1 light-second away. They can easily subtract the lightspeed delay and calculate that Kurt "entered" and "exited" the teleport at exactly the same time coordinate - the two events were simultaneous. Technically speaking, Kurt traveled through space while staying on a simultaneous hyperplane relative to himself, Logan and Xavier.

At the same time, Scott is flying in the same direction at 0.5c. Because he is moving relative to Kurt, his simultaneous hyperplane is different from Kurt's... this is a typical Lorentzian traincar experiment where events that are simultaneous to one observer are not simultaneous to a second observer. Scott will see Kurt arrive on the Earth a fraction of a second before he left, even accounting for lightspeed travel time. Technically speaking, Kurt's entry and exit points were non-simultaneous relative to Scott's frame of reference.

Now if Scott flew in the opposite direction, he would actually see Kurt arrive a fraction of a second after he left. His teleportation is no longer instant, it has a finite and measurable speed.

Now all this is really bad because Einstein's theory of special relativity says that no inertial reference frame is preferred over any other. Kurt, Xavier and Logan perceived that the teleport took zero time, but Scott either saw that it took a finite amount of time, or a negative amount of time. This is bad! In order to resolve the paradox you would have to say that Kurt's reference frame is "right" and Scott's reference frame is "wrong" - but this would really muck up a lot of physics as we know it.

Now Scott is mad because he doesn't like to be wrong. The next time he sees Kurt arriving on the Moon a split second "before" he leaves Earth, Scott teleports back to the Earth and punches Kurt in the face. This prevents him from teleporting in the first place, causing a "grandmother paradox" and blowing up the entire universe. Oops!

****

The logical conclusion of this thought exercise is that indiscriminate use of FTL travel can very easily cause time paradoxes. However, FTL doesn't necessarily cause a time paradox. If there is only one wormhole in the universe, and its entry and exit terminii do not have dramatically different planes of simultaneity, one can show that no particle history can possibly use the wormhole to interact with its own past.

Going back to the previous example; if Kurt leapt through a wormhole to get to the Moon: Scott would percieve Kurt as arriving a split-second earlier than he left, but he would also perceive the two ends of the wormhole as existing in slightly non-simultaneous planes. If Scott jumped into the wormhole as soon as Kurt popped out, it would send him "forward in time" by the same split-second that it sent Kurt "back in time". So he would not be able to interact with Kurt's past-self.

In order to keep this universe non-paradoxical, the only constraint you need is that the wormhole's terminii are "simultaneous" according to the hyperplane of someone's slower than light worldline. It could be simultaneous with regards to the Earth (<1sec difference according to Scott), or simultaneous with regards to Scott (<1sec difference according to the Earth), or simultaneous with regards to a far-away alien (<1sec difference for both Earthlings and Scott). Any particle that attempts to follow a "looping" worldline that uses the wormhole to interact with its own past will find that there's not enough of a time difference to allow its post-wormhole light cone to intersect with its pre-wormhole light cone.

The constraints become much more difficult if you are dealing with multiple wormholes in close proximity... You could jump into one wormhole after another, and if their entry-exit time coordinates existed on different hyperplanes then you could very easily travel "back in time".

 

[Piousflea84]

Open to all to answer.

Cheers, Greg.

Here's an explanation of the Twin Paradox:

First, we look at the physics of observing a moving object, without any time dilation at all. Let's say you're at an airshow. A jet fighter zooms past you at 99.5% the speed of sound, spends 10 seconds flying away, then turns around and comes toward you at 99.5% the speed of sound.

How much time do you get to hear the jet flying away? Well, it takes 10s for it to fly, but it takes an additional 9.95s for its sound to reach you. So you will hear the "flying away sound" for 19.95s. In addition, since it takes you ~20s to hear 10 seconds of sound, that sound will be "stretched out" by a factor of ~2x. This is the Doppler shift that makes things low-pitched when they move away from you.

How much time do you get to hear the jet coming toward you? Well, it took the jet 10s to fly toward you, but it takes the jet's sound 9.95s just to reach you. So you only get to hear its sound for 0.05s, 200x less time than it took for the jet to make the sound! The sound is compressed and amplified by 200x, turning into a ferocious sonic boom!

*****

Now what changes when we are no longer observing things with sound? Well, going near lightspeed introduces something called a Lorentz factor, which governs both time dilation and length contraction. A ship leaving the earth at 99.5%c will have a Lorentz factor of ~10.

If an Earth Twin and Ship Twin observe each other, they will both see the same thing - the other twin ages very, very slowly. At ~99.5%c they will experience a ~20x relative time dilation. (~2x Doppler factor, ~10x Lorentz factor) It is impossible to determine which one is "moving" and which one is "stationary" as both twins will see the same factor.

However, thanks to time dilation the duration of this journey is different for the Earth twin and the Ship twin. If the twin set out on a "10 light-year journey", the Earth Twin will perceive the "outbound phase" as lasting 20 years. (10 years for the ship to get there, 10 years for light to come back from the ship) However, the Ship Twin will only perceive 1 year of outbound time - 10 light-years / 10x Lorentz contraction. During this time, the Earth Twin will see 'S' age by 1 year, while the Ship Twin will see 'E' age by 18.25 days.

Once the starship turns around, both twins will see their counterpart age very rapidly - 200x Doppler factor / 10x Lorentz factor = 20x acceleration in apparent time. The Ship Twin will perceive the "return phase" as lasting 1 year, exactly the same as the "outbound phase". During this year he will see his twin age by 20 years (1 year x 20). On the other hand, the Earth Twin will only perceive the "return phase" for 18.25 days (10 years / 200x Doppler factor) because the Ship Twin is traveling so fast that it arrives shortly after its own light. During this time, 'S' will appear to age by 1 year. (18.25d * 20)


**
The difference between the two twins is that the Ship Twin changed directions!

Under normal circumstances, something moving rapidly toward you will always appear to happen much faster than normal, while something moving rapidly away from you will always appear to happen much slower than normal. The Earth Twin's perception followed this pattern exactly; he saw the ship twin fly away for 20 years and come back in 18 days.

The fact that the Ship Twin changed directions meant that he perceived both legs of the journey as taking an equal amount of time. This means that he cannot possibly be a non-accelerating reference frame. The high travel velocity and the acceleration/reversal caused his personal worldline to experience much less time than his non-accelerating twin.

 

[psychotick]

Hi Pious,

A clever explanation but doesn't work as far as I can see. And it all hinges on the ship changing direction. But you have two reference points and nothing else. Therefore you can't say that ship A changed directions. It actually didn't. There is no absolute point of reference. Only point A (ship) with reference to point B (Earth). So actually A and B were separating at whatever speed. And then they were returning towards one another at whatever speed. It's equally fair to say they both changed directions. It's purely a matter of symetry.

Cheers, Greg.

 

[SilentRoamer]

No. that's not possible.

Hi Pious,

A clever explanation but doesn't work as far as I can see. .

I appreciate this is a pretty non-intuitive branch of mathematics/thinking. However just because you deny the logic it does not make it less so. Time dilation in special relativity is a "proven" branch of science. See: http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

Taking this to the logical extreme and exceeding C violates causality - whether or not any paradoxes occur because of the violation is irrelevant the fact is cause and effect are no longer in effect. Modes of travel and whether or not we are physically moving through space is irrelevant - otherwise the Point B location arrival date must be the same Universal Time as Point A in which case there is never any FTL to violate causality.

 

[Ray McCarthy]

Let's say Kurt teleports instantly from the Earth to the Moon, approximately 1 light-second apart. Xavier is standing on the Moon and he sees Kurt arrive 1 second before he left. Logan is standing on the Earth and sees Kurt arrive 1 second after he left. By itself, this isn't a violation of causality because Logan and Xavier are 1 light-second away.

Yes.

Scott will see Kurt arrive on the Earth a fraction of a second before he left, even accounting for lightspeed travel time.

No. That's flawed logic.

The constraints become much more difficult if you are dealing with multiple wormholes in close proximity... You could jump into one wormhole after another, and if their entry-exit time coordinates existed on different hyperplanes then you could very easily travel "back in time".

No. logically impossible.

 

[Phyrebrat]

I feel a bit cleverer after semi getting through this terrifying physics pious flea. Thanks. my brains are bleeding tho

pH

 

[Piousflea84]

Hi Pious,

A clever explanation but doesn't work as far as I can see. And it all hinges on the ship changing direction. But you have two reference points and nothing else. Therefore you can't say that ship A changed directions. It actually didn't. There is no absolute point of reference. Only point A (ship) with reference to point B (Earth). So actually A and B were separating at whatever speed. And then they were returning towards one another at whatever speed. It's equally fair to say they both changed directions. It's purely a matter of symetry.

Cheers, Greg.

No, it's not fair to say that the Earth and Ship are equivalent:

The Earth's reference frame sees the ship leave (for 20 years), then it sees the ship come back (for 18 days). People on the Earth can correctly determine that the Earth did not accelerate because its reference frame stayed the same, which means that "objects leaving" are visible for a much longer time than "objects coming back". (see jet airplane analogy for why is always true)

The ship's outbound reference frame sees the Earth 'leave' (for 1 year). Then the ship turns around and accelerates back toward the Earth. This acceleration changes its reference frame. It then sees the Earth 'come back' (for 1 year). Passengers on the ship can correctly determine that the ship accelerated because their reference frame shifted. They were able to observe the Earth 'leaving' for exactly the same amount of time as they were able to observe the Earth 'coming back', a phenomenon that is impossible in a non-accelerating reference frame.

Einsteinian Relativity states that any two inertial reference frames are equally "correct" and indistinguishable. As soon as you accelerate, you change your own reference frame and so you are no longer an equally valid observer.

***
A non-accelerating observer in the ship's outbound frame (99.5%c away from Earth) would see the following:

Ship's Outbound Phase: Ship stays perfectly still for "1 year", aging "1 year". Earth moves away for "1 year" (2x Doppler, 10x Lorentz), aging "18 days" and moving ~0.995 light-years away.

Ship's Turnaround: Ship suddenly goes from "stationary" to "Moving at 99.9987%c away from outbound frame". (Relativistic summation of velocities) The ship is now time-dilated by a factor of 200x.

Ship's Return Phase: This lasts for just under "400 years" - ~200 years for the Ship to catch up with the Earth, and ~200 years for the light from the Earth/Ship to reach the outbound observer.

At the moment that the ship reaches Earth, the Earth (~99.5%c) has moved just under 199 light-years from the outbound frame. Due to time dilation, the Earth has only aged 20 years. (400/(2x10))

At the same moment, the Ship (~99.9987%c ) has moved just under 199.995 light-years, barely enough to catch up with the Earth (which was ~0.995 light-years away). Due to time dilation, the Ship has aged 1 year. (400/(2x200)

Note that the non-accelerating Outbound Reference Frame sees "movement away from observer" as taking a much longer time than stationary objects or movement toward the frame... this is exactly what you expect from an inertial observer.

 

[chrispenycate]

And you experience a force in your handbrake turn round the star at the other end - actually, at better than 99% c, probably a good idea to make it a neutron star - you're going to have to get awfully close. Actually, you're going to experience tidal forces, but the one I was worrying about, cancelling out the star's attraction, is the one that changes time.

 

[Danny McG]

After slowly reading my way through all this and getting my head around the different concepts here I can only make one assumption.
That the OP for the question about basic sci fi terms (I think it was Shamguy4) went away and wrote a nice story about a magic duck instead.

 

[shamguy4]

lol.
Nope im still grinding at the same book. The story has grown a lot!!! Writing a book is really hard and frustrating.... Maybe the duck idea isn't so bad.

 

[tinkerdan]

I think this thread demonstrates why a serious number of novels fail to give in-depth explanations for how their science works. No matter what you come up with there will be someone who comes around, who sounds logical and kicks your sandcastle down maliciously. When the truth is that no one knows how it all works because we haven't done it yet and until we do it is too difficult to wrap our heads around.

I once listened to someone use present physics to demonstrate why airplanes can't possibly fly. Since then I've not been able to board a plane. Once you know how physics works that old magic won't support you anymore so best to bow out before the great fall.

The best idea is to use lots of hand-wavium or at the very least write something totally ridiculous so that the most that can be said about it is that the science is inscrutable.

Either way I'm no physicist; however I find it hard with my limited capacity to accredit even one so far in this discussion. Perhaps someone could enlighten us with their credentials and shed some light, however I'm not sure how much that will help the OP's query.

But let's get back to the original poster.
Read this book.

All the Windwracked Stars (Sci Fi Essential Books) Hardcover – 6 Dec 2008
by Elizabeth Bear (Author)

All the Windwracked Stars (Sci Fi Essential Books): Amazon.co.uk: Elizabeth Bear: 9780765318824: Books

It is Myth Magic and Technology and look it calls itself a Sci Fi Essential book.
Beautiful prose. Fantasy and Science Fiction

 

[psychotick]

Hi,

Meanwhile I'm now thinking to myself how wonderful it would be to include a magic duck in my current WIP!

Cheers, Greg.

 

[Danny McG]

Hi,

Meanwhile I'm now thinking to myself how wonderful it would be to include a magic duck in my current WIP!

Cheers, Greg.

Greg, don't hesitate, go for it right now.
There is a massive untapped market for 'hard sci fi but with a magic duck' novels.
People aren't consciously aware of it but they are inwardly yearning for such tales

 

[Danny McG]

And if 'hard sci fi with a magic duck' isn't a theme for the next writing challenge then indeed we are in a pocket universe