FTL equals time travel

I keep seeing and hearing that said, but no one has ever demonstrated it. They just assert it.

I don’t see how warp travel lets me go back in time. Can anyone explain this other than “it is what the math says”

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Author: Bryan G. Stephens

Bryan G. Stephens is a former executive on a mission to transform the workplace. He is the founder and CEO of TalkForward, a consulting and training company, utilizing Bryan’s clinical and management expertise to develop managers and teams in a corporate environment. As a licensed therapist with strong understanding of developing human potential, he is dedicated to the development of Human Capital to meet the needs of leaders, managers, and employees in the 21st Century workplace. Bryan has an Executive MBA from Kennesaw State University, Coles School of Business, and both a Master’s and Bachelor’s degree in Psychology.

9 thoughts on “FTL equals time travel”

1. It is all a scam to sell old DeLoreans, Bryan. Get one with a stock 1992 Flux Capacitor. The others are junk.

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2. I advocate the SuperStar drive.  As it goes forward in space it goes backward in time.  (Unitary matrix – what’s not to like?)  You can then go anywhere in the universe, instantly, at a stately Nixonian 55 mph, getting maximum spacetimeage.  The only drawback is that if two beings do it simultaneously…kaput.

https://www.physicsforums.com/attachments/14mye5-jpg.222621/

An Alcubierre drive bubble does it, but…as with supercavitating torpedoes, the interior of the bubble may not communicate with the medium.  How does one steer and know when to brake?

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3. The notion that faster than light travel allow you to go back in time depends upon Einstein’s definition of simultaneity in special relativity.  Basically, it is not possible to define a unique time for objects which are separated in space and moving relative to one another.  But you can define what is called a “spacetime interval” based upon the distance between two locations and events which occur at them.  This interval is called null if the two events could be connected by a pulse of light from one to another, timelike if a pulse of light would arrive before the second event, and spacelike if it would arrive after.  If the separation of events is spacelike, then the first event cannot have any effect on the second, since nothing can propagate faster than light.

Now, if you had the ability to travel (or send a signal) faster than light, you would be able to causally effect distant events before a light signal would arrive, and hence, by the definition of interval, arrive in the “past”.  But this does not mean you could travel into your own past (for example, to go back and have a conversation with your distant ancestors).

There are solutions of general relativity (for example, Gödel universe) in which “closed timelike curves” exist, where by travelling slower than light it would be possible to go back into your own past.  But the Gödel universe is an extremely contrived solution to Einstein’s equations that models a globally rotating homogeneous space filled with dust and a cosmological constant, and there is no evidence whatsoever that our actual universe is described by that model or that it contains closed timelike curves.

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4. So John,  it does not sound like actual time travel then. It is just calling it the past because you went fater than light

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5. Bryan G. Stephens:
So John,  it does not sound like actual time travel then. It is just calling it the past because you went fater than light

In special relativity, you can’t speak of “past” and “future” because there is no universal clock—every observer has their own clock, and depending upon their motion and location they may observe distant events to occur in different orders.  What you can speak of is causality: can something here affect something there.  This is governed by the spacetime interval.  If faster than light travel (or signalling) were possible, this would break down, and it would be possible for an action here to have an effect there faster than a ray of light could travel between the two events.  There us no evidence that this occurs in our universe.

Special relativity does, of course, allow time travel into the future.  You do it all the time when you jog or drive in your car, albeit by a small (but measurable) amount.  Go fast, stay young.  GPS satellites have an explicit correction for this effect: because they’re moving rapidly, the clocks on board run slower than those on the Earth.

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6. Bryan G. Stephens:
So John,  it does not sound like actual time travel then. It is just calling it the past because you went fater than light

In special relativity, you can’t speak of “past” and “future” because there is no universal clock—every observer has their own clock, and depending upon their motion and location they may observe distant events to occur in different orders.  What you can speak of is causality: can something here affect something there.  This is governed by the spacetime interval.  If faster than light travel (or signalling) were possible, this would break down, and it would be possible for an action here to have an effect there faster than a ray of light could travel between the two events.  There us no evidence that this occurs in our universe.

Special relativity does, of course, allow time travel into the future.  You do it all the time when you jog or drive in your car, albeit by a small (but measurable) amount.  Go fast, stay young.  GPS satellites have an explicit correction for this effect: because they’re moving rapidly, the clocks on board run slower than those on the Earth.

OK, I understand I move faster than causality. I get there before information could, and as such I make a change that can happen before light catches up to me. Heck, I can go there, make a change and come back and watch myself show up and make the change.

But.

Time Travel into the “past” (scare quotes) means, to normal people (not to people who think math is real) I can change past events. That is what everyone outside (it would seem) scientists. How does FTL travel along the lines of a warp drive, imply I can change the past. You have said:

John Walker:
Now, if you had the ability to travel (or send a signal) faster than light, you would be able to causally effect distant events before a light signal would arrive, and hence, by the definition of interval, arrive in the “past”.  But this does not mean you could travel into your own past (for example, to go back and have a conversation with your distant ancestors).

If I am understanding this correctly, in any normal understanding of time travel, in fact, FTL does not automatically mean you can go back in time, because it does not let you visit your past.

Now, I can see how wormholes would allow this. If you had your pair, and you sent one on a .999999 c trip around the sun and brought it back home, the end that traveled would have had different time pass than the end that stayed put. It would be now we side by side with its exit, but, looking through it would be looking into the past. That I get.

But doing the warp thing, it seems to me does not let you step into your past, so it is not, by any normal understanding of things, “Time Travel into the Past”.

Am I right on this?

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7. Bryan G. Stephens:
But doing the warp thing, it seems to me does not let you step into your past, so it is not, by any normal understanding of things, “Time Travel into the Past”.

Physicists prefer the more precise phrase “closed timelike curve” (CTC) to “time travel into the past”, which means different things to different people and in different contexts.  A closed timelike curve is a path through a Lorentzian manifold which, if followed at a speed less than that of light, allows returning to its starting point (and hence in the past of the traveller).

This is only possible in a spacetime with certain forms of curvature (of which a wormhole is an extreme example) or rotation (such as the Tipler cylinder or Gödel universe).  According to the equations of general relativity, closed timelike curves are possible in spacetimes such as these, but there is no evidence they exist within the universe we actually inhabit or could be made.  Stable wormholes, for example, appear to require exotic matter with negative energy, of which there is no evidence for existence.

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8. Bryan G. Stephens:
But doing the warp thing, it seems to me does not let you step into your past, so it is not, by any normal understanding of things, “Time Travel into the Past”.

Physicists prefer the more precise phrase “closed timelike curve” (CTC) to “time travel into the past”, which means different things to different people and in different contexts.  A closed timelike curve is a path through a Lorentzian manifold which, if followed at a speed less than that of light, allows returning to its starting point (and hence in the past of the traveller).

This is only possible in a spacetime with certain forms of curvature (of which a wormhole is an extreme example) or rotation (such as the Tipler cylinder or Gödel universe).  According to the equations of general relativity, closed timelike curves are possible in spacetimes such as these, but there is no evidence they exist within the universe we actually inhabit or could be made.  Stable wormholes, for example, appear to require exotic matter with negative energy, of which there is no evidence for existence.

As does the Warp Drive.

Also, a theroetical wormhole you can go through needs the mass of Jupiter of the stuff, so there is that.

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