4 ms·

It is not absolutely certain. Quantum theory is an incomplete description of the physical laws of our universe, and the mechanism behind quantum teleportation i

by darawk 10y ago

It is not absolutely certain. Quantum theory is an incomplete description of the physical laws of our universe, and the mechanism behind quantum teleportation is not even fully understood within the framework of that theory. So, it is most certainly not absolutely certain that FTL communication by this means is impossible, though it would be fairly surprising. The premise upon which the idea that it is impossible is based is an axiom: https://en.wikipedia.org/wiki/Wightman_axioms#W3_.28local_commutativity_or_microscopic_causality.29 https://en.wikipedia.org/wiki/Wightman_axioms#W3_.28local_co... Not a conclusion from data or other, simpler premises. It is an axiom that has nice consequences and is generative of much that describes our observations, but it remains an untestable assumption.

lisper 10y ago
It is as certain as anything in science. Yes, QM is incomplete, but it places hard constraints on the space of possible completions, and none of them allow FTL communications. FTL would break not only QM and relativity, but causality: it would allow you to send information backwards in time.
- bostonpete 10y ago
  It seems to me that's exactly what an alien trying to keep us in the dark would say...
  - zeveb 10y ago
    > It seems to me that's exactly what an alien trying to keep us in the dark would say... Well, Lisp is secret alien technology: http://lispers.org/ http://lispers.org/
- johncolanduoni 10y ago
  > Yes, QM is incomplete, but it places hard constraints on the space of possible completions, and none of them allow FTL communications. This is entirely incorrect. All of the proofs about broken causality (all of which stem from special relativity, since non-relativistic QM doesn't put the speed of light on a pedestal) assume that the laws of special or general relativity hold everywhere. What you're saying is the equivalent of claiming in 1914 that the theory of special relativity proves that physics cannot operate without an intertial reference frame.
  - lisper 10y ago
    Yes, I am assuming that relativity holds everywhere. There is zero evidence that this is not the case. This is what it means to be "as certain as anything in science."
    - johncolanduoni 10y ago
      That's not a "hard constraint on the space of possible completions". That's assuming the answer to begin with.
      - lisper 10y ago
        No, it isn't. The mathematical formalism of QM is fully compatible with SR. QM can only be completed within the constraints of SR. To get FTL you would not have to complete QM, you would have to overthrow it and SR and GR and replace them all with something completely different. Not just that, but whatever you replaced it with would still have to account for the observed invariance in the speed of light in all reference frames. QM and entanglement are really red herrings with respect to the FTL question. The impossibility of FTL is a direct logical consequence of the fact that there exists a universal speed reference in space-time. Entanglement only appears to violate this because people don't understand what entanglement actually is and how it works. When you make a measurement on one member of an EPR pair, nothing happens to the other particle. It's still in exactly the same state it was in before the measurement. So there is absolutely no reason whatsoever to believe that FTL could be possible, and a lot of reasons to believe that it's not. Granted, this is not "absolutely certain" (nothing in science ever is) but it's as certain as it gets.
        johncolanduoni 10y ago
        > QM can only be completed within the constraints of SR. This is not true. QM theory in general (without talking about particular Hamiltonians, field or otherwise or not) has no reliance on special relativity; it doesn't even have a reliance on positions in three-dimensional space (physicists who work in quantum information routinely work with QM at this level)! So again, you're already specifying QFT (e.g. by something like the Wightman axioms), which includes special relativity as an assumption. > The impossibility of FTL is a direct logical consequence of the fact that there exists a universal speed reference in space-time. This is what special and general relativity say. Not only are you begging the question again, but GR doesn't rule out violations of causality: there's a bunch of known models within GR that violate it[1]. Since GR is in fact more certain than SR (in that SR has strictly less explanatory power than GR since it's a special case of it), you must believe that it is as certain as anything else in science that causality violations are real! [1]: https://en.wikipedia.org/wiki/Closed_timelike_curve https://en.wikipedia.org/wiki/Closed_timelike_curve

by darawk 10y ago

lisper 10y ago

It is as certain as anything in science. Yes, QM is incomplete, but it places hard constraints on the space of possible completions, and none of them allow FTL communications. FTL would break not only QM and relativity, but causality: it would allow you to send information backwards in time.

bostonpete 10y ago
It seems to me that's exactly what an alien trying to keep us in the dark would say...
- zeveb 10y ago
  > It seems to me that's exactly what an alien trying to keep us in the dark would say... Well, Lisp is secret alien technology: http://lispers.org/ http://lispers.org/
johncolanduoni 10y ago
> Yes, QM is incomplete, but it places hard constraints on the space of possible completions, and none of them allow FTL communications. This is entirely incorrect. All of the proofs about broken causality (all of which stem from special relativity, since non-relativistic QM doesn't put the speed of light on a pedestal) assume that the laws of special or general relativity hold everywhere. What you're saying is the equivalent of claiming in 1914 that the theory of special relativity proves that physics cannot operate without an intertial reference frame.
- lisper 10y ago
  Yes, I am assuming that relativity holds everywhere. There is zero evidence that this is not the case. This is what it means to be "as certain as anything in science."
  - johncolanduoni 10y ago
    That's not a "hard constraint on the space of possible completions". That's assuming the answer to begin with.
    - lisper 10y ago
      No, it isn't. The mathematical formalism of QM is fully compatible with SR. QM can only be completed within the constraints of SR. To get FTL you would not have to complete QM, you would have to overthrow it and SR and GR and replace them all with something completely different. Not just that, but whatever you replaced it with would still have to account for the observed invariance in the speed of light in all reference frames. QM and entanglement are really red herrings with respect to the FTL question. The impossibility of FTL is a direct logical consequence of the fact that there exists a universal speed reference in space-time. Entanglement only appears to violate this because people don't understand what entanglement actually is and how it works. When you make a measurement on one member of an EPR pair, nothing happens to the other particle. It's still in exactly the same state it was in before the measurement. So there is absolutely no reason whatsoever to believe that FTL could be possible, and a lot of reasons to believe that it's not. Granted, this is not "absolutely certain" (nothing in science ever is) but it's as certain as it gets.
      - johncolanduoni 10y ago
        > QM can only be completed within the constraints of SR. This is not true. QM theory in general (without talking about particular Hamiltonians, field or otherwise or not) has no reliance on special relativity; it doesn't even have a reliance on positions in three-dimensional space (physicists who work in quantum information routinely work with QM at this level)! So again, you're already specifying QFT (e.g. by something like the Wightman axioms), which includes special relativity as an assumption. > The impossibility of FTL is a direct logical consequence of the fact that there exists a universal speed reference in space-time. This is what special and general relativity say. Not only are you begging the question again, but GR doesn't rule out violations of causality: there's a bunch of known models within GR that violate it[1]. Since GR is in fact more certain than SR (in that SR has strictly less explanatory power than GR since it's a special case of it), you must believe that it is as certain as anything else in science that causality violations are real! [1]: https://en.wikipedia.org/wiki/Closed_timelike_curve https://en.wikipedia.org/wiki/Closed_timelike_curve