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Is there any known, verifiable way to transfer classical information faster than light, using quantum entanglement or other phenomenon?

Does quantum teleportation, or other known phenomenon, allow FTL transfer of information (not "quantum state", but true classical information)?

A friend and I have a few $$$ riding on this ... I know I'm right, and I need some answer he will accept as irrefutable evidence one way or the other. (The evidence would be not that it's physically impossible, but that the general consensus in the physics community is that it's impossible)

I saw some duplicate questions, but nothing that asks this simple, generic question.

Edit - I need a straight "Yes" or "No" answer, and so far I haven't seen it.

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Related: physics.stackexchange.com/q/15282/2451 and links therein. –  Qmechanic Jan 27 '13 at 18:20

5 Answers 5

up vote 8 down vote accepted

Short answer: No.

Short answer as a complete sentence: We have no reason to believe that there is any way that teleportation (or any other quantum mechanical effect, or any other physical phenomenon which we believe occurs) allows you to send superluminal signals.

Detailed answer:

Quantum teleportation can only be used to transfer quantum states. Those quantum states may encode classical information, but they are still quantum states. (Of course, the world being quantum mechanical, even "classical information" is represented by quantum states, albeit those of a very large number of particles at once — but never mind.)

Teleportation requires open classical communication to work anyway; so teleporting the information classically won't save you any work, and in fact is totally unhelpful — except as a quantum mechanical version of a Vernam cipher (i.e. a one-time pad).

Whether anything is secretly happening in quantum mechanics faster than the speed of light is actually a matter of philosophical debate in the foundations of physics. There are people who say that there is (such as advocates of de Broglie–Bohm theory), and people who say that there isn't (advocates of the Many Worlds Interpretation, Consistent Histories, and some Bayesians). What people mostly agree on is that quantum mechanics allows you to realise correlations in probability distributions which are not possible in slower-than-light local hidden variable theories; but that even if there is anything happening faster than the speed of light, you'll not going to be able to use it to transmit signals, because everything looks like correlated but uncontrollable random outcomes.

Related question: Why can't quantum teleportation be used to transport information?

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This answer will definitely be open to interpretation. ELI5 - can quantum phenomenon be used to transport the ASCII encoding of this question faster than light? The answer you linked to implies no, but I need a conclusive answer, not just implications. –  ripper234 Aug 22 '12 at 14:35
@ripper234: not really. While "Is something happening faster than the speed of light in QM?" is open to interpretation (with the majority answering either 'no' or 'shut up and calculate'), the question "Can quantum phenomena be used to signal faster than light" has a very strong majority opinion of "no". If you want anything more certain than that, then what you want is not a consensus opinion, but to have absolute certainty; and science isn't in the business of giving people absolute certainties. –  Niel de Beaudrap Aug 22 '12 at 14:53
Thanks. I'll be expecting my payout now... –  ripper234 Aug 22 '12 at 22:06
Deduction can travel faster than light. If I measure event A from some star 10 LY away and event B from another, and knowing the properties and nature of those events I can then deduce event C, which is 40 LY away... information about C has just traveled faster than light, via deduction. Certain information cannot travel faster. But probabilities certainly can. Even 99.9999% certain probabilities can travel FTL. –  Erik Aronesty Feb 12 at 17:00
@ErikAronesty: But probabilities are not signals. An event at A does not reveal anything about a joint event on (A,B), except of course for the part which has to do with what happened at A. As for the deduction: that is happening entirely within your head based on what you have observed from light-like signals --- your deduction does not go forth and impose structure upon the world: you are merely swept into a contingency (corresponding to a "possible world"), the partial knowledge of which spreads outward at light speed from those sources which have been swept into the same contingencies. –  Niel de Beaudrap Feb 12 at 21:03

According to special relativity, faster than light (FTL) means backwards in time, ie FTL communication would violate causality, which is generally believed to hold.

Depending on your choice of interpretation of quantum mechanics, measurement of entangled states does lead to 'spooky action at a distance' (which can be FTL) or a limited form of retrocausality. However, as such experiments just correlate random results of measurements and you can't force a quantum system to give you the particular result you want, there's no way to use this for direct communication.

A second class of seemingly FTL effects has been seen in experiments with quantum tunneling (eg with electrons) or evanescent wave coupling (eg with microwaves). When I last looked into this, the majority vote was that causality holds, but no consensus had been reached as to why, ie there were several different explanations. Might be interesting to revisit the issue...

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Let's be clear. At the present time, you cannot go back in time and you cannot send a grocery list faster than light and there is little chance it will ever be true. Unless it's been done, the answer remains a very clear NO. Also, Einstein never meant his relativity formula to indicate that you could go back in time. The formula was only meant for velocities less than the speed of light - why? Because the energies required to reach or exceed the speed of light exceed all the energy in the universe. If that's not enough, the mass of the object would be infinite at the speed of light - another impossibility. This is all in the actual understanding of the theory which includes the math as well. One should not be embarrassed to admit that they cannot understand the math. It's currently been shown that without some unusual connections in the brain, that level of mathematical understanding cannot be achieved.It does not mean your are not smart or less than. We all have our own talents.

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Short Answer: NO

Just because we can't control the outcomes of experiments doesn't mean there isn't transfer of information between entangled particles. Bell's theorem once and for all proved spooky action. Consider the following example:

If you gave Alice and Bob each a quarter and separated them by a large distance and tasked them with choosing heads or tells, and they always came back to you with one choosing heads, the other choosing tails, what might you think? Maybe they talked to each other on a phone and coordinated their results?

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The question is simple: Can these phenomenon be used to transfer good ol' bits from point A to point B FTL. –  ripper234 Aug 22 '12 at 5:06
No, you cannot transfer classical information using entanglement. However, there is a transfer of information between entangled particles. –  user7348 Aug 22 '12 at 14:19

Simple answer: Yes.

experimental proof: the cosmic microwave background radiation has the same temperature from all directions, including from regions that are not causally connected, i.e. that are farther apart than a light ray might have traveled from the beginning of the universe until now. The only known explanation for this is that these points once were separating faster than the speed of light. The best current hypothesis is that this happened during an early inflationary phase of our universe where basically a large cosmological constant was driving this separation.

edit: well, it seems necessary to correct some anthropocentric misconceptions. the question was whether a classical bit of information can be transferred faster than light. the clear answer is yes, as the CMB shows. this should settle the bet.

now some people confuse this simple fact with the possibility of constructing some useful device to send information faster than light from any one point to any other. that is another question. if the reason for the faster than light information transfer that we observe in the CMB was indeed inflation, it does not help in constructing some useful device because any potential recipient of the message is removed from the sender at similar speed. this is all true, but again, this was not the question.

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That's not transmitting information faster than light - anymore than light emitted form a galaxy that is now outside the observable universe is telling us anything about the galaxy now. –  Martin Beckett Aug 22 '12 at 15:28
inflation doesn't help with getting a signal from A to B - in fact, it's harmful because of increase in distance and cosmological redshift –  Christoph Aug 22 '12 at 15:34
i send information from point A to point B. then inflation sets in, and A and B are moved apart faster than light. sorry guys, this is possible and has happened. –  Chris Aug 22 '12 at 15:48
@Chris: THEN inflation sets in - the signal has already been transmitted at that point –  Christoph Aug 22 '12 at 15:52
transfer of information faster than light == causal relationship across space-like separation; the whole point of inflation is that it can explain the uniformity of the CMB without violating Einstein causality –  Christoph Aug 22 '12 at 18:27

protected by Qmechanic Dec 11 '14 at 21:38


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