I know this has been asked many times, but I have a hard time "crystallising" it in my mind.

  1. First: let's say we teleport a DVD (with quantum teleportation). Isn't this FTL communication?

  2. Second: would it be possible to create 2 quantum computers fully entangled?

  3. If we assume that it would be possible (with the computers in separate locations) then "asking" the first one a question to which we already know the answer, then observe that answer, would the answer appear on the second computer? Would this be FTL communication?

Now I know someone will say, "but the one with the second computer has no way to know if the first one has already been 'observed'", to which I'll respond: if we do systematic observation on the computer, like every x period of time, each one of them is always in sync with their readings.

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    $\begingroup$ Is it communication if you and I, several light years apart, each click our heels every hour on the hour, having agreed to do so in advance? $\endgroup$
    – WillO
    Jun 25, 2016 at 2:43
  • $\begingroup$ That's not the point, the heels clicking is just a mean to observe the computers state at the right time. $\endgroup$
    – Nick
    Jun 25, 2016 at 2:49
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    $\begingroup$ So if you and I, two light years apart, simulateneously observe an event that occurs halfway between us at time 0, so that our observations occur just one light year after the event, have we just "communicated" faster than light? $\endgroup$
    – WillO
    Jun 25, 2016 at 2:52
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    $\begingroup$ 1) quantum teleportation isn't FTL 2) There is a no-cloning theorem that forbids that quantum states can be copied 3) This is physics and not creative writing - we don't assume things around here that nature doesn't do. We merely observe and describe what nature actually does. $\endgroup$
    – CuriousOne
    Jun 25, 2016 at 6:12
  • 1
    $\begingroup$ Obligatory comic link: xkcd.com/1591 $\endgroup$ Jun 25, 2016 at 14:52

2 Answers 2


Teleportation and entanglement do not involve FTL communication of any kind. There is a local description of the evolution of any given quantum system in terms of its Heisenberg picture observables. The observables change only when the system changes by itself or through a local interaction with another system.

Entanglement and teleportation can be explained by quantum information being transported locally through decoherent channels. The information is contained in the observables of the channels, but it does not affect their expectation values: locally inaccessible information. This locally inaccessible information can only be unlocked by using it in conjunction with information from the other entangled system:


The computer preparation protocol you describe would not give you faster than light answers because in order to get the relevant information out, you would have to combine the locally inaccessible information from the two computers.


"Agreeing" to engage in a mutual activity at a predetermined time is not "ftl" . Not even close. That's simply a "coordinated simultaneous event". For it to truly be FTL the "clicking of the heels" would need to be observed BEFORE the stimulus that caused the clicking took place. In other words the other guy would have to SEE OR HEAR the clicks before the other guy moved his feet. The above examples ARE GREAT for helping to conceptualize a rather abstract topic but none of them meet the criteria in terms of physics. True "ftl" can only be achieved by something moving AT OR NEAR the speed of light. So that eliminates ANY HUMAN experiments. There is however, one mechanism, solidly within our grasp, that can move that fast; thought! The speed of a "thought " is probably the closest organic experience we have to lightspeed. However we cannot control the speed of our thoughts. So in order to really experiment we must use a computer, which essentially is a nonhuman "thinker". Theoretically speaking, as Moore's law takes effect, and data speeds increase, we MUST (HOLDING WITH MOORE'S LAW) one day reach a point when processing speeds are sooooo fast that it would be possible for a user to receive an answer to an inquiry prior to even typing it. However, let's not celebrate yet because although this ia theoretically possible the challenge would be to cause the computer to both "Ask and answer " without user input. User input (since we're limited to normal speeds) would slow the process down and bring the speeds back down to "normal" levels. For this experiment to truly take place it would need to be totally independent of human tampering. In that case how would the computer "know" what questions to initially Ask? And so it seems, that at least for now, it's a totally hypothetical situation that can only occur within the confines of our minds. Perhaps the secret lies in "cyborg" technology. A computer- human hybrid could possibly accomplish this. Then again that seems almost as unlikely as the first scenario. I digress.


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