Compatibility of Quantum Mechanics and Special Relativity

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  • #26
zonde
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As indeed no physical effect can propagate faster than light,
As I see experiments have demonstrated results that falsify this statement.
I assume you attribute speed and propagation to entanglement.
No. Your statement is sloppy. Entanglement is joined statistical property of two particle state. To speak about speed or propagation we have to speak about individual particles in entangled pairs. It does not make sense to say that two particle property propagates from one particle to the other one.
Entanglement is a well define process that occurred at one single event. The firther detection space/time separations events are irrelevant.
The whole point of Bell inequality violation is to demonstrate that this can not be the case.
 
  • #27
martinbn
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As I see experiments have demonstrated results that falsify this statement.

Like what?
 
  • #28
zonde
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Like what?
Loophole free violations of Bell inequalities.
 
  • #29
martinbn
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Loophole free violations of Bell inequalities.

What propagates there?
 
  • #30
zonde
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What propagates there?
Whatever it is that can affect measurement result of individual photon (or electron).
 
  • #31
martinbn
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Whatever it is that can affect measurement result of individual photon (or electron).

That is very vague. Your claim was that there is something that propagates. I asked what it was. Your answer is whatever it is. Very unsatisfying. Let me ask the question this way. How do we know that there is something at all that propagates faster than light?
 
  • #32
Boing3000
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As I see experiments have demonstrated results that falsify this statement.
Your respond to martinbn is more than vague, it is incorrect. What affect measurement of individual photon is a polarization filter. Have we observed such a filter goes faster than light ? As far as effect is concerned what is that effect exactly and what speed does it have ? A number will do (**).

No. Your statement is sloppy. Entanglement is joined statistical property of two particle state. To speak about speed or propagation we have to speak about individual particles in entangled pairs. It does not make sense to say that two particle property propagates from one particle to the other one.
My statement was clear, but apparently incorrect. But then you've just make a new statement totally contradictory to what you stated previously. Now we agree completely. Although I would state "one property shared by (non-local to any of) two particles"

The whole point of Bell inequality violation is to demonstrate that this can not be the case.
Unless I am mistaken, Bell's inequality violation are tested on particle created at one single event. The demonstration tells which side off two possibilities must be true when tested elsewhere (detection space/time separations events are irrelevant whatever the effort of experimenters (delay choice etc etc))
Thus experiments show that the correlation appears to be instantaneous. (**) The number you may have mistaken for a speed is this bound.
As far as I know "instantaneous" would be synonymous to infinite speed. But infinite is not a number. By logic alone, if something (like a polarization property value) is at two places at the "same instant" it is the same thing, and don't move.
 
  • #33
zonde
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That is very vague. Your claim was that there is something that propagates. I asked what it was. Your answer is whatever it is. Very unsatisfying.
As I understand that you need a name for it. Unfortunately I can't help with that. Pick one yourself.
Let me ask the question this way. How do we know that there is something at all that propagates faster than light?
Well, we can not know that in some absolute sense. In science what we know is that certain approaches don't work. And we know approaches that work for now or work FAPP in their domains of applicability.
So from Bell inequality tests we know what approaches are not going to work. So we can look what is left when we exclude these that wont work. And then we can look which ones of these remaining approaches are consistent with scientific approach. And there are two: unbelievable coincidence and physical effect that propagates FTL.
 
  • #34
PeterDonis
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from Bell inequality tests we know what approaches are not going to work

No, from Bell inequality tests we know what kinds of theoretical models are not going to work. Theoretical models are not reality.

Even if we talk about theoretical models, however, your apparent belief that the only viable ones given the Bell inequality tests are ones with FTL propagation is incorrect. Quantum field theory predicts violations of the Bell inequalities, and it is perfectly consistent with SR and has no FTL propagation.
 
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  • #35
zonde
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Your respond to martinbn is more than vague, it is incorrect. What affect measurement of individual photon is a polarization filter. Have we observed such a filter goes faster than light ? As far as effect is concerned what is that effect exactly and what speed does it have ? A number will do (**).
So you are saying I can't claim that certain theoretical models won't work without providing detailed alternative model, right?
But then you've just make a new statement totally contradictory to what you stated previously.
I am fairly sure I didn't.
By logic alone, if something (like a polarization property value) is at two places at the "same instant" it is the same thing, and don't move.
That logic would require totally novel structure of spacetime. And this would go outside philosophical basis of scientific approach.
 
  • #36
zonde
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No, from Bell inequality tests we know what kinds of theoretical models are not going to work. Theoretical models are not reality.
Of course. Map is not the territory. Experiments can falsify only theoretical models and not reality itself.
Even if we talk about theoretical models, however, your apparent belief that the only viable ones given the Bell inequality tests are ones with FTL propagation is incorrect. Quantum field theory predicts violations of the Bell inequalities, and it is perfectly consistent with SR and has no FTL propagation.
Well, I meant only category of models that could attempt to model entanglement phenomena at the level of spacetime events (individual clicks in detectors). Quantum field theory is describing entanglement at the level of statistics and does not fall in that category. I should have been more specific.
 
  • #37
Boing3000
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So you are saying I can't claim that certain theoretical models won't work without providing detailed alternative model, right?
Well this isn't the place for discussing alternative models. This is a thread about compatibility between SR and QM. Your claim (or was it ?) that there are inconsistencies is based on something that does not exist: "a propagating effect". There is no such thing in QM entanglement, and there is not such FLT thing in SR.

zonde said:
That logic would require totally novel structure of spacetime. And this would go outside philosophical basis of scientific approach.
Quite the opposite, spacetime is a well defined structure that doesn't need philosophy. The logic of Bell's theorem is quite simple. Polarization filters are quite simple objects. Photons with entangled polarization are a little more unusual, that's all.
 
  • #38
zonde
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This is a thread about compatibility between SR and QM. Your claim (or was it ?) that there are inconsistencies is based on something that does not exist: "a propagating effect".
My answer about compatibility of SR and QM was that they are compatible. That is my answer to the title of this thread.
But opening post has more context for this question with references to Bell inequalities. So my claim as related to this more broader context of the question is that there indeed is incompatibility. And that incompatibility is between popular interpretation of SR (not SR itself) and experimental results of loophole free Bell inequality tests (not QM's statistical description of entanglement). In particular my claim is that these experimental results can not be modeled with scientific spacetime events based model where any physical effect propagates no faster than speed of light in vacuum.
Quite the opposite, spacetime is a well defined structure that doesn't need philosophy. The logic of Bell's theorem is quite simple. Polarization filters are quite simple objects. Photons with entangled polarization are a little more unusual, that's all.
Maybe I misunderstood what you said. This is your statement: "if something (like a polarization property value) is at two places at the "same instant" it is the same thing"
Did you mean it's the same physical thing or more like it's two physical things that share the same description (in the sense of some kind of information)?
 
  • #39
Boing3000
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In particular my claim is that these experimental results can not be modeled with scientific spacetime events based model where any physical effect propagates no faster than speed of light in vacuum.
But that claim is false. Non-locality is a perfectly valid non-stochastic model for explaining the correlation, because there is no "propagating effect"

Did you mean it's the same physical thing or more like it's two physical things that share the same description (in the sense of some kind of information)?
Both. There are two local physical photons sharing one non-local physical property "polarization angle". I consider everything that can be measured as physical.
 
  • #40
zonde
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Non-locality is a perfectly valid non-stochastic model for explaining the correlation, because there is no "propagating effect"
I don't see non-locality (as I understand it from your posts) as perfectly valid model. For me it seems more like Matrix movie (solipsistic worldview) inspired hand waving. Sorry. Maybe I'm missing something.
 
  • #41
Boing3000
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I don't see non-locality (as I understand it from your posts) as perfectly valid model.
OK, but the fact you don't see it, does not make it an invalid model. Logic make it valid (like Bell's proof). Logic is quite the opposite of solipsistic.

In my book, what makes a model "hand wavy" it the use of undefined/uncalled for "action at a distance" or "propagating effect".
 
  • #42
zonde
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Logic make it valid
Logic gives rules for arguing. It does not make particular conclusion valid. Arguments do that.
 
  • #43
Boing3000
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Logic gives rules for arguing. It does not make particular conclusion valid. Arguments do that.
And the many logical argumentation of Bell (an others) have done that.

So unless you can argue otherwise, with some logically described phenomenon (like "a propagating effect") or by faulting Bell's proof (which I doubt greatly), there is no point in continuing that conversation.
 
  • #44
zonde
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there is no point in continuing that conversation.
Sure
 

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