Is Faster than Light Time Travel Possible?

[BruceW]

I would assume so. The problem about tachyons, is we really don't know how they would act (whether they are too unstable to be called particles, or whether they will allow causality reversal). Wikipedia's page is pretty good.

 

[CJames]

Wrt the highlight ...

Causality would be violated given superluminal motion from the vantage of our sub-c POV. However, it seems to me that one should expect casuality to be reversed given tachyon speeds, since time should run in reverse for the tacheon relative to our own sub-c POV. From the POV "of the other (tachyon) side" it deems itself sub-c, and causality should seem normal from its own sub-c POV. Yes?

GrayGhost

Tachyon's have an imaginary rest mass. Like a beam of light, they can't be at rest. I don't know if it's actually possible to try to construct an inertial reference frame from the POV of a tachyon.

 

[GrayGhost]

Tachyon's have an imaginary rest mass. Like a beam of light, they can't be at rest. I don't know if it's actually possible to try to construct an inertial reference frame from the POV of a tachyon.

Hmmm, interesting. I did just take a look at Wiki. I had never assumed "imaginary mass" of superluminal particles to mean "effective mass" as in the photon. I figured an imaginary mass could be at rest. Speed c exists "at the cosmic speed limit", but superluminal speeds do not. I had assumed that the imaginary spacetime would be "orthogonal" to our spacetime, since neither side can have a particle accelerate to c.

GrayGhost

 

[jiohdi]

FTL travel is still forwards in time not backwards... by definition you are traveling some distance in some forward unit of time. Just because you are outside a light cone does not mean you are traveling backwards in time... one part of the equation that seemingly gets ignored is the mass... if you could in theory travel your mass to a prior spacetime coordinate what do you suspect you would find? what is missing is the rest of the universes mass... your traveling to a prior spacetime coordinate would not drag that mass back with you... you would undoubtedly find yourself in hyperspace alone or with some other hyperspacial objects but the past you were looking for would not be there... that only exists in records.

 

[CJames]

Hmmm, interesting. I did just take a look at Wiki. I had never assumed "imaginary mass" of superluminal particles to mean "effective mass" as in the photon. I figured an imaginary mass could be at rest. Speed c exists "at the cosmic speed limit", but superluminal speeds do not. I had assumed that the imaginary spacetime would be "orthogonal" to our spacetime, since neither side can have a particle accelerate to c.

GrayGhost

I don't know enough about tachyons to really say for sure. The only way that I could imagine picturing a tachyon's reference frame would be if you were to say that the x-axis for matter is the t-axis for a tachyon. If that were the case then all normal matter would look like tachyons, some of which would appear to be traveling backward in time.

 

[CJames]

FTL travel is still forwards in time not backwards... by definition you are traveling some distance in some forward unit of time. Just because you are outside a light cone does not mean you are traveling backwards in time...

The point is that different observers would disagree about the order of events. Some observers would say that the tachyon was present at all points along the trajectory simultaneously. Others would say that it traveled from event A to event B, and still others would say that it traveled from event B to event A.

one part of the equation that seemingly gets ignored is the mass... if you could in theory travel your mass to a prior spacetime coordinate what do you suspect you would find? what is missing is the rest of the universes mass... your traveling to a prior spacetime coordinate would not drag that mass back with you... you would undoubtedly find yourself in hyperspace alone or with some other hyperspacial objects but the past you were looking for would not be there... that only exists in records.

I'm not sure what you're getting at here.

 

[jiohdi]

The point is that different observers would disagree about the order of events. Some observers would say that the tachyon was present at all points along the trajectory simultaneously. Others would say that it traveled from event A to event B, and still others would say that it traveled from event B to event A.



I'm not sure what you're getting at here.

anyone who could measure a tachyon as moving faster than light would be measuring a forwards time by definition... otherwise it would not make any sense to say it was faster than light... a major point of relativity theory is the ability to normalize any frame of reference ot any other by means of the lorenz transformations and come to an understanding of a true order of how reality unfolded.

 

[DaveC426913]

anyone who could measure a tachyon as moving faster than light would be measuring a forwards time by definition...

The point is that, because it could be arranged such that event B preceded event A, it is possible that effect can precede cause i.e. violating causality, i.e. a form of time travel.

 

[CJames]

anyone who could measure a tachyon as moving faster than light would be measuring a forwards time by definition... otherwise it would not make any sense to say it was faster than light... a major point of relativity theory is the ability to normalize any frame of reference ot any other by means of the lorenz transformations and come to an understanding of a true order of how reality unfolded.

Except that this isn't the case if trajectories outside of the light cone are allowed. The ability to travel between two events with spacelike separation is the ability to travel between two events that should not be causally connected to one another. This is one of the main reasons why they are suspected not to exist.

 

[abaio]

Thanks for the information.

 

[CJames]

Thanks for the information.

You're welcome.