Physics SE and Space Exploration SE thought this was off-topic for them, so I'm trying it here. Sorry if I'm doing it wrong.

As I understand, within an event horizon, spacetime gets rotated so that the singularity is in the future, rather than in the distance. This is because every radial path is spacelike.

So could it be that on a superluminal vessel, the destination seems to be in the future to those on board? Maybe the only way for the trip to seem instantaneous is to go lightlike?

Maybe it depends on whether or not you carry your arrow of time with you when you go superluminal? Maybe that's the core of the question.

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    This question appears to be off-topic because it is about physics; it's unfortunate that this is too outside the mainstream for that SE. – Dave Nov 24 '14 at 18:42
  • Gah! Can't win! :) – MackTuesday Nov 24 '14 at 18:44
  • This question strikes the point where the mathematics of physics makes people think the impossible is possible. Rather like Nietzsche's eternal recurrence makes people think of many-worlds theories. Although the OP does not speak of tachyons, I suspect the physics of super luminosity is beyond physics, and dare I say meta-physical. – Chris Degnen Nov 24 '14 at 21:31
  • I suggest this is why Physics SE referred the OP to ask here. – Chris Degnen Nov 24 '14 at 21:49
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    There is an interesting book I just came across you may be interested in. It is "Time Reborn: From the Crisis in Physics to the Future of the Universe" by Lee Smolin – Swami Vishwananda Nov 25 '14 at 5:39

For me, the problem with going the speed of light is that you are then outside of time. Once you were How would you slow back down when you got where you wanted?

So there is the other side if the speed of light, but you can't get there from here, you have to go somewhere else first. And the 'somewhere else' is a place where all material objects have infinite mass.

Theoretically, the only way to get 'superluminal' would be to translate yourself via CPT reversal, or some other translation mechanism that turns "you" into something that is already "tachyonic antimatter". But that is in some sense not travel, just some sort of information re-encoding.

And it may happen spontaneously all the time. (Yes, I am going where I always go with time questions, time either equals or does not equal entropy accumulation.) If entropy does not accumulate in a perfectly linear way throughout the universe, then you occasionally go back in time, but you cannot experience the reversal, because memory is an exothermic process.

So to my mind, the way to get somewhere yesterday is not to pass the speed of light, it is to manipulate entangled states. If time really is subjective, and flows both ways, you should be able to make something in the past that must match a given state in the future or keep some other event un-collapsed forever. Since the odds of the latter are so low, a copy of you would have appeared there, then, to prevent it from needing to happen.

We think we know how to set up quantum states that can only be observed if they meet a given set of conditions. This is the basis of quantum computing: if the bizarre combination of factors that formulate the problem were not met, the computer would have to stay 'uncollapsed' for way too long. So just stating the question forces a solution to happen relatively quickly.

If time really has no implicit direction (or if any kind of paradox prevention is automatic) then creating a causal loop constitutes causation. So stating a problem, and locking it away unobserved means that its outcome is not determined until we observe it. I think we could, if fiendishly clever, force the conditions to be that the solution should match what we are going to put into a given box later.

Then we put you in the box. And you are the unobserved solution, which means you exist shortly after the problem was stated. But now you are observed. The causal loop constitutes a cause of you being instantly duplicated at an earlier time at a given location, which may be arbitrarily far away from where you are now.

Of course, we cannot do that kind of thing now, and you may only ever be able to manage that state at the level of an individual quantum particle. But if you could do it to something with history, it would prove that time's arrow is not a physical reality, but an aspect of perception.

  • Hey, whatever gets you there. If you can be "decoded" at your destination, great. One problem is that tachyons, as they're conventionally understood, don't do what we want. They're unstable and can't transmit information faster than light. :-( – MackTuesday Nov 25 '14 at 17:36
  • Sorry, I came back to add more while you were reading. I think you do not need to use them as pawns, since we cannot hold onto them, but there is a framing of time in which we can profit from their existence nonetheless. – user9166 Nov 25 '14 at 17:43
  • Could you elaborate on your fifth paragraph, the one on entangled states? It sounds fascinating but I don't see the truth of it. Oh and while you're editing, you might want to fix "peed" in your first paragraph. Hehe. – MackTuesday Nov 25 '14 at 17:49
  • The comment was too long, I put it in the answer. – user9166 Nov 25 '14 at 19:48

As far as I know you cannot go superluminal. It just seems that if the speed of light is 299,792 km/s then you just have to go a bit faster to go superluminal. If you are a photon travelling from the sun at the speed of light then your 'matter' is frozen against the speed-of-light limit, and your local time is stopped. Even though an observer on earth has to wait 8 minutes to see you, you are zipping across the universe in no time as all as far as you are concerned. Your arrow of time disappears at light-speed, (and certainly doesn't reverse if you go faster -- which you can't anyway).

  • I was hoping to find some interesting speculation on how things would work if, by some magic, superluminal travel were possible. The speculation would depend on the nature of the magic, but I figured it would still be illuminating. – MackTuesday Nov 25 '14 at 17:18

The concept of proper time in relativity corresponds to the duration of a journey as measured by the observer who is performing the journey. For an observer going at the speed of light, proper time is always zero, which means that any travel is felt as instantaneous.

EDIT (sorry I hadn't understood your question)

I think this question is metaphysical, and has its place on the philosophy SE. However the question is not very clear: is it about the duration experienced by the observer, or is it about where they locate distant objects in their referential? If the latter, we should talk of events rather than objects, or specify a time and a referential or the question does not have sense. Also, are you assuming that the vessel is superluminal relatively to inertial observers or by its own standards?

If you mean by its own standards (the vessel takes a space-like path in its own referential) then the question is meaningless for several reasons:

  • If you look at the formalism, it seems that the proper time of a space-like path would be an imaginary number (the square root of a negative number). The formalism does not come with an interpretation of what an imaginary duration would be, but at first sight, it seems to make no sense.
  • If you view relativistic space-time as a causal structure, the question is meaningless because you cannot cause an event which is not in your future light cone, and thus there cannot be a continuous experience following a space-like path.
  • there is no absolute direction of a space-like path (whether the 'origin' is before or after the destination is relative).
  • Another observation is that there seem to be something tautological in the sentence "the destination seems to be in the future". If you are travelling, then of course your destination is in your future (by definition of destination).
  • What you seem to mean in this sentence is that the location of the destination at a simultaneous time is actually in the future of the observer. But this location cannot be both at a simultaneous time and in the future (or you have to specify two different observers). If by "location" you mean location in space, then "in the future" is definitely not the answer (unless, again, you consider two observers).
  • What exactly should we expect? An experience that "rewinds" seems nonsensical.

Another possibility is that the vessell is superluminal relatively to inertial observers, because of a distorsion of space-time. This case is analogeous to the one behind a singularity, and indeed the vessell will have to pass through a singularity to reach this situation. Then the question is meaningful. The answer can be given by physics.

Regarding experienced time, if assimilated with proper time, it will always be positive (for the reasons given above). About the way they locate objects: they have to go through a singularity, so you cannot compare directions of inertial obervers and the vessel (it is like trying to keep track of relative directions at the surface of earth: it depends which path you take. If you travel to the pole, your inital "north" direction will no more point to the north).

However there might be a sense in which their time direction corresponds to one of our space direction, and conversely, wich allow them to travel to our past, but the the question if they locate their destination in their future is either trivial or meaningless, as already noted.

  • But the observer also sees distances modified, so it doesn't actually look like he or she or it is travelling very far. By comparing the distance you see yourself to be travelling with the time it takes you, you will never measure your own speed to be beyond the speed of light. – gnasher729 Nov 25 '14 at 14:19
  • Yes, I believe I established this with the question, "Maybe the only way for the trip to seem instantaneous is to go lightlike?" – MackTuesday Nov 25 '14 at 17:15
  • Right, but it does not matter whether you get everywhere at once, or whether everything, subjectively comes to you. Once you exit time, you have exitted time. How would you "then" slow down when you get where you wanted to be? "Felt as instantaneous" requires feeling, which requires experience, which requires time. – user9166 Nov 25 '14 at 17:16
  • @MackTuesday sorry I hadn't well understood your question. I will edit my answer. – Quentin Ruyant Nov 25 '14 at 23:27

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