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I am writing a Sci-fi/detective story and I'm wondering if Quantum Entanglement is a feasible means of FTL travel. (I know very little on the subject so if no is the answer please suggest a possible alternative.)

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Okay, so now I know that this is not possible, are there any ways of FTL travel that are feasible?

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  • $\begingroup$ Could you please describe how you want to use entanglement for FTL travel, or even for slower-than-light travel? I seem to have a temporary loss of imagination, because I just cannot see this. Entanglement is a property of pairs of particles; all right, you make entagled twins of all the particles in your body and send them ahead of time to the destination, and then? What? $\endgroup$
    – AlexP
    Commented Sep 16, 2017 at 20:18
  • $\begingroup$ @AlexP You could build two machines, send one of them far away and then transmit the information needed to reconstruct your body at its location using the one you have at home. Basically FTL teleportation. Well.. Atleast you could do this if it didn't violate the no communications theorem. $\endgroup$
    – AngelPray
    Commented Sep 16, 2017 at 20:29
  • $\begingroup$ @AngelPray: But ... but ... but ... that's not travel, it's communication. Travel means taking some stuff from here and moving it there. What you described is a way to make copies very quickly; even without the FTL aspect, the ability to copy humans may be of great use, so that would be important element in the story. $\endgroup$
    – AlexP
    Commented Sep 16, 2017 at 20:32
  • $\begingroup$ @AlexP Well you wouldn't be able to create a perfect copy without destroying the first (see No-Cloning theorem). Basically star-trek transporters. Transportation, a.k.a. "a method of travel". $\endgroup$
    – AngelPray
    Commented Sep 16, 2017 at 20:39
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    $\begingroup$ LordofTheNerds please know that it is very frowned upon on this forum to edit a question to ask a completely new query instead of simply creating a new thread, as you just did. Also please be aware that you are obviously not going to be the first person who asked if there are methods of plausible FTL travel on this website, as such even if you did create a new thread it would be closed for being a duplicate. I suggest you look at the answers to this question. $\endgroup$
    – AngelPray
    Commented Sep 16, 2017 at 20:47

2 Answers 2

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Unfortunately no.

Quantum entanglement works like this: You have 2 particles, let's say photons, which are entangled. When you observe the spin of one of the photons and find that it is +1, then you also know that the spin of the other one must be -1. If instead when you observe it, it turns out to be -1 than in the same way the other one will be +1.

Somehow, the spins of these two photons are intrinsically linked. Linked in such a way that at the very moment (and I mean that literally) that you observe the state of one of the photons, the state of the other photon (no matter where it is in the universe) can be predicted with total accuracy based on the measurement taken from the first.

Now at this point it might seem as if this has all you need for faster than light teleportation: you could build two machines with a bunch of entangled particles between them, send one of them far away, and use the machines to transmit the quantum state of whatever you want to teleport to the other so that the thing can be rebuilt. Sadly this won't work.

The problem lies here:

Until you make the measurement on one of the particles than their states are completely indeterminate (a phenomena that's called quantum superposition). You can't know what will be the photon's spin until you check it. And you can't do anything but measure the particle if you want to keep the entanglement intact. If you force the particle to be in the state you want it to be, than the entanglement will instantly break.

So you're left with a weird situation where you can know exactly what the state of a particle right across the universe is but not be able to use it to transmit information.

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No, this is not possible. It would violate the "No communications theorem", which says that while two observers may simultaneously measure two different entangled particles, they cannot exchange information. Information cannot travel faster than light, not even with entangled particles.

Wikipedia can explain this much better than I can: No communications theorem.

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