4 ms·

Experiments upholding Bell's inequalities imply it is.

dclowd9901 4y ago
So couldn’t you send a bunch of entangled particles somewhere and collapse the wave function on them in sequence in some way as to communicate faster than the speed of light?
- roywiggins 4y ago
  All you can do with your half of the pair is observe its state after the wave function collapsed. Whether it collapsed because you just poked it or because the other half of the pair was poked first can't be known without comparing notes afterward using classical means. https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem
  - GoblinSlayer 4y ago
    An interferometer can differentiate that. If a photon is in superposition, it exits interferometer on a certain path, if it's collapsed, it exits on a random path. If you send 100 such photons, you can send 1 bit this way with good precision.
    - Workaccount2 4y ago
      Although not informed enough to comment on this, I do know that if it was true, it would break relativity and that would have come across my feed at some point. So I would say you are missing something.
      - GoblinSlayer 4y ago
        I made it up. Any nonlocality breaks relativity, this doesn't break it further. You can still say the same thing - it's okay because why not. Or you mean it will be a paradox if they receive a message in the past? I guess it can be prevented if the entangled photon doesn't interfere with itself.
        Workaccount2 4y ago
        Information cannot move faster than the speed of light. If the non-locality has a random output, then it doesn't violate relativity because random noise cannot carry information (by definition it's no longer random if it does).
        GoblinSlayer 4y ago
        That's the trick - to replace random process with deterministic process which is still sensitive to collapse. Or rather make collapse switch from deterministic to random process.
        Workaccount2 4y ago
        Whether or not the photon is collapsed isn't the process that makes entangled particles "spooky" though. (Sorry I should have originally stated this) Its that they have opposite states when you collapse them. So collapsing one doesn't collapse the other. Its just that when you collapse one (by measuring it) you can know the state of the other (even if it's on the other side of the universe). The real "spookiness" is that the particles don't have a predetermined state "underneath" their superposition. When you collapse one its odds of being heads or tails are 50/50 up to the moment you collapse it. And when you collapse it you know what reading you will get when you collapse the other one.
        GoblinSlayer 4y ago
        Did you try to describe Everett's interpretation? There observation of one particle doesn't change the state of the other indeed. If everything is local, then no FTL is ever implied. In copenhagen collapse is nonlocal and happens instantaneously across the universe, so FTL actually happens.
        Workaccount2 4y ago
        >In copenhagen collapse is nonlocal and happens instantaneously across the universe, so FTL actually happens. I don't know if this is a mathematical deduction or something empirically verified. Technically when you measure one particle the wave function of both collapses, because now you know what the properties of the other particle are. But it could be like a pair of dice that always land on opposite faces. When the first die lands, the fate of the second die is sealed and it's no longer in a "superpostion" despite the second die still tumbling around in the air. I strongly suspect this is the case, because otherwise, like you said, you could transmit information faster than light, breaking relativity.
- cycomanic 4y ago
  No, because the only way to determine "who collapsed the wavefunction first" is to communicate subluminal. In other words you can't detect the event of the wavefunction collapsing.
- dreamcompiler 4y ago
  Think of the two entangled particles as telegraph operators that can communicate with each other infinitely fast -- the speed of light is no obstacle for them. But you cannot hand one of them a message to be transmitted because they simply ignore you.* You can ask either of them if they recently sent or received a message from the other, and what that message was, and they will tell you the truth. But they will only tell you this over subluminal channels, and they will not accept a message to be transmitted superluminally. We can prove they are communicating superluminally because of the Bell inequality, but we cannot control what they are communicating. *More precisely, the act of handing one of them a message causes that one to communicate some random message to the other.
  - dclowd9901 4y ago
    Thanks for the explanation, I think I understand better the underlying theory

So couldn’t you send a bunch of entangled particles somewhere and collapse the wave function on them in sequence in some way as to communicate faster than the speed of light?

roywiggins 4y ago
All you can do with your half of the pair is observe its state after the wave function collapsed. Whether it collapsed because you just poked it or because the other half of the pair was poked first can't be known without comparing notes afterward using classical means. https://en.m.wikipedia.org/wiki/No-communication_theorem https://en.m.wikipedia.org/wiki/No-communication_theorem
- GoblinSlayer 4y ago
  An interferometer can differentiate that. If a photon is in superposition, it exits interferometer on a certain path, if it's collapsed, it exits on a random path. If you send 100 such photons, you can send 1 bit this way with good precision.
  - Workaccount2 4y ago
    Although not informed enough to comment on this, I do know that if it was true, it would break relativity and that would have come across my feed at some point. So I would say you are missing something.
    - GoblinSlayer 4y ago
      I made it up. Any nonlocality breaks relativity, this doesn't break it further. You can still say the same thing - it's okay because why not. Or you mean it will be a paradox if they receive a message in the past? I guess it can be prevented if the entangled photon doesn't interfere with itself.
      - Workaccount2 4y ago
        Information cannot move faster than the speed of light. If the non-locality has a random output, then it doesn't violate relativity because random noise cannot carry information (by definition it's no longer random if it does).
        GoblinSlayer 4y ago
        That's the trick - to replace random process with deterministic process which is still sensitive to collapse. Or rather make collapse switch from deterministic to random process.
        Workaccount2 4y ago
        Whether or not the photon is collapsed isn't the process that makes entangled particles "spooky" though. (Sorry I should have originally stated this) Its that they have opposite states when you collapse them. So collapsing one doesn't collapse the other. Its just that when you collapse one (by measuring it) you can know the state of the other (even if it's on the other side of the universe). The real "spookiness" is that the particles don't have a predetermined state "underneath" their superposition. When you collapse one its odds of being heads or tails are 50/50 up to the moment you collapse it. And when you collapse it you know what reading you will get when you collapse the other one.
        GoblinSlayer 4y ago
        Did you try to describe Everett's interpretation? There observation of one particle doesn't change the state of the other indeed. If everything is local, then no FTL is ever implied. In copenhagen collapse is nonlocal and happens instantaneously across the universe, so FTL actually happens.
        Workaccount2 4y ago
        >In copenhagen collapse is nonlocal and happens instantaneously across the universe, so FTL actually happens. I don't know if this is a mathematical deduction or something empirically verified. Technically when you measure one particle the wave function of both collapses, because now you know what the properties of the other particle are. But it could be like a pair of dice that always land on opposite faces. When the first die lands, the fate of the second die is sealed and it's no longer in a "superpostion" despite the second die still tumbling around in the air. I strongly suspect this is the case, because otherwise, like you said, you could transmit information faster than light, breaking relativity.
cycomanic 4y ago
No, because the only way to determine "who collapsed the wavefunction first" is to communicate subluminal. In other words you can't detect the event of the wavefunction collapsing.
dreamcompiler 4y ago
Think of the two entangled particles as telegraph operators that can communicate with each other infinitely fast -- the speed of light is no obstacle for them. But you cannot hand one of them a message to be transmitted because they simply ignore you.* You can ask either of them if they recently sent or received a message from the other, and what that message was, and they will tell you the truth. But they will only tell you this over subluminal channels, and they will not accept a message to be transmitted superluminally. We can prove they are communicating superluminally because of the Bell inequality, but we cannot control what they are communicating. *More precisely, the act of handing one of them a message causes that one to communicate some random message to the other.
- dclowd9901 4y ago
  Thanks for the explanation, I think I understand better the underlying theory