5 ms·

That's a pretty huge experimental success: quantum mechanics is truly probabilistic, not just deterministic but based on some hidden variable we haven't (or can

That's a pretty huge experimental success: quantum mechanics is truly probabilistic, not just deterministic but based on some hidden variable we haven't (or cannot) found. Have I understood it correctly?

GolDDranks 4y ago
You understood correctly that quantum mechanics cannot be based on some hidden variable we haven't or cannot find. (Edit: oops, I re-read your comment and it seems you say the exact opposite thing? The point is that Bell's theorem rules hidden variables OUT. Here's an easily digestible video about this: https://www.youtube.com/watch?v=ZuvK-od647c https://www.youtube.com/watch?v=ZuvK-od647c ) About probability: no one knows. It might be that there is a "wave function collapse" that has a probabilistic outcome. But it might be that there is no such a thing. Quantum mechanics that remain in the "quantum" realm are not probabilistic, it's only when you cross over to the classical world. So it might be equally well, that the Everett interpretation (so-called "many worlds interpretation") is true, and the probability is something physicist Sean Carroll calls "self-locating uncertainty": https://www.preposterousuniverse.com/blog/2014/07/24/why-probability-in-quantum-mechanics-is-given-by-the-wave-function-squared/comment-page-3/ https://www.preposterousuniverse.com/blog/2014/07/24/why-pro... That is, there are multiple "yous" that experience different outcomes, and you don't know which branch of the wavefunction you find "yourself" in, which "you" you are.
- twawaaay 4y ago
  > You understood correctly that quantum mechanics cannot be based on some hidden variable we haven't or cannot find. That's not true. The only thing we know is that the above appears to be true, but since we do not actually know the mechanism behind quantum mechanics we will be in this limbo until (if ever) we find the actual rules.
  - n4r9 4y ago
    Actually, the power of Bell's theorem is that it applies to any physical theory which attempts to explain observed correlations in experiments on entangled particles. It really does say "No matter what's behind quantum theory, we know it isn't like this". I do have a small gripe with the above comment, in that Bell's theorem only rules out local hidden variables. Some take the view that Bohmian mechanics is an formulation of quantum theory which employs hidden variables, just explicitly non-local ones.
    - q-big 4y ago
      > I do have a small gripe with the above comment, in that Bell's theorem only rules out local hidden variables. Some take the view that Bohmian mechanics is an formulation of quantum theory which employs hidden variables, just explicitly non-local ones. Superdeterminism also allows local hidden variable theory without violating Bell's theorem: > https://en.wikipedia.org/wiki/Superdeterminism https://en.wikipedia.org/wiki/Superdeterminism A 2013 interview with the Nobel Laureate Gerard 't Hooft on this topic: > https://spookyactionbook.com/2013/10/07/does-some-deeper-level-of-physics-underlie-quantum-mechanics-an-interview-with-nobelist-gerard-t-hooft/ https://spookyactionbook.com/2013/10/07/does-some-deeper-lev... A paper by Sabine Hossenfelder and Tim Palmer: Sabine Hossenfelder and Tim Palmer; Rethinking Superdeterminism > https://www.frontiersin.org/articles/10.3389/fphy.2020.00139/full https://www.frontiersin.org/articles/10.3389/fphy.2020.00139... In 2016, 't Hooft published a textbook on some specific points of superdeterminism: Gerard 't Hooft; The Cellular Automaton Interpretation of Quantum Mechanics > https://link.springer.com/book/10.1007/978-3-319-41285-6 https://link.springer.com/book/10.1007/978-3-319-41285-6
      - n4r9 4y ago
        It's true in a sense that you can get around Bell's theorem by supposing that Alice and Bob's mesasurement choices are strongly pre-correlated in a specific way. But then I feel you end up with this sort of bizarre universal conspiracy set up just to make humans believe in quantum theory.
        q-big 4y ago
  - heckerhut 4y ago
    But there are constraints on those hidden mechanics as well. Not sure hidden variables theory survives these constraints. Can someone more knowledgeable talk on this?
- DebtDeflation 4y ago
  QM can't be based on LOCAL hidden variables. Hidden variables theories that are explicitly nonlocal are not ruled out. Separately, Superdeterminism eliminates both the requirement for nonlocality and the result that QM is inherently probabilistic.
  - q-big 4y ago
    > QM can't be based on LOCAL hidden variables. ... as long as we assume that the system being measured is uncorrelated with the choices of which measurements to make on it. :-)
  - rmu09 4y ago
    Superdeterminism eliminates any requirement(s).
  - GolDDranks 4y ago
    Oh, you are definitely correct. Pardon the inaccuracy.
deleted 4y ago
[deleted]
hackandthink 4y ago
I like the essence of Quantum Strangeness here: "To be more precise, what we shall show is that the particles’ response∗ to a certain type of experiment is not determined by the entire previous history of that part of the universe accessible to them." John Conway, Simon Kochen: Free Will Theorem https://arxiv.org/abs/quant-ph/0604079 https://arxiv.org/abs/quant-ph/0604079
- shellac 4y ago
  That is a lovely way of putting it. (I wish they'd never mentioned 'Free Will' since people get hung up on that) Always keep in mind that Bell himself was quite a fan of Bohm's theory, which is the canonical hidden variable theory really. The question becomes one of characterising that 'strangeness': is it the violation of locality ('that part of the universe accessible to them'), is violating outcome independence palatable, but not parameter independence (this was Shimony's idea originally)? Lots of curious stuff.
- zmgsabst 4y ago
  > Why do we call this result the Free Will theorem? It is usually tacitly assumed that experimenters have sufficient free will to choose the settings of their apparatus in a way that is not determined by past history. […] > We consider experimenters A and B performing the pair of experiments described in the TWIN axiom on separated twinned particles a and b, and assert that the responses of a and b cannot be functions of all the information available to them. I don’t get it — this sounds like they assumed their conclusion. There’s also a couple places they make strong assumptions about information geometry I’m not sure I agree with — namely, if you want to refute modern Bohm-inspired models, you need to account for radically non-Euclidean spacetime. (Where you have a much harder time with “space like separated”.) > FIN is not experimentally verifiable directly, even in principle (unlike SPIN and TWIN3).Its real justification is that it follows from relativity and what we call “effective causality,” that effects cannot precede their causes. […] > Not all information in the universe is accessible to a particle a. In the light of FIN, information that is space–like separated from a is not accessible to a. The information that is accessible to a is the information in the past light cone of a.
lucozade 4y ago
As I understand it, Bell showed that, if quantum mechanics is correct, then any deterministic hidden variable theory would either have to be non-local or non-causal. Aspect et al demonstrated experimentally that quantum mechanics is correct in the Bell sense.

GolDDranks 4y ago

You understood correctly that quantum mechanics cannot be based on some hidden variable we haven't or cannot find. (Edit: oops, I re-read your comment and it seems you say the exact opposite thing? The point is that Bell's theorem rules hidden variables OUT. Here's an easily digestible video about this: https://www.youtube.com/watch?v=ZuvK-od647c https://www.youtube.com/watch?v=ZuvK-od647c ) About probability: no one knows. It might be that there is a "wave function collapse" that has a probabilistic outcome. But it might be that there is no such a thing. Quantum mechanics that remain in the "quantum" realm are not probabilistic, it's only when you cross over to the classical world. So it might be equally well, that the Everett interpretation (so-called "many worlds interpretation") is true, and the probability is something physicist Sean Carroll calls "self-locating uncertainty": https://www.preposterousuniverse.com/blog/2014/07/24/why-probability-in-quantum-mechanics-is-given-by-the-wave-function-squared/comment-page-3/ https://www.preposterousuniverse.com/blog/2014/07/24/why-pro... That is, there are multiple "yous" that experience different outcomes, and you don't know which branch of the wavefunction you find "yourself" in, which "you" you are.

twawaaay 4y ago
> You understood correctly that quantum mechanics cannot be based on some hidden variable we haven't or cannot find. That's not true. The only thing we know is that the above appears to be true, but since we do not actually know the mechanism behind quantum mechanics we will be in this limbo until (if ever) we find the actual rules.
- n4r9 4y ago
  Actually, the power of Bell's theorem is that it applies to any physical theory which attempts to explain observed correlations in experiments on entangled particles. It really does say "No matter what's behind quantum theory, we know it isn't like this". I do have a small gripe with the above comment, in that Bell's theorem only rules out local hidden variables. Some take the view that Bohmian mechanics is an formulation of quantum theory which employs hidden variables, just explicitly non-local ones.
  - q-big 4y ago
    > I do have a small gripe with the above comment, in that Bell's theorem only rules out local hidden variables. Some take the view that Bohmian mechanics is an formulation of quantum theory which employs hidden variables, just explicitly non-local ones. Superdeterminism also allows local hidden variable theory without violating Bell's theorem: > https://en.wikipedia.org/wiki/Superdeterminism https://en.wikipedia.org/wiki/Superdeterminism A 2013 interview with the Nobel Laureate Gerard 't Hooft on this topic: > https://spookyactionbook.com/2013/10/07/does-some-deeper-level-of-physics-underlie-quantum-mechanics-an-interview-with-nobelist-gerard-t-hooft/ https://spookyactionbook.com/2013/10/07/does-some-deeper-lev... A paper by Sabine Hossenfelder and Tim Palmer: Sabine Hossenfelder and Tim Palmer; Rethinking Superdeterminism > https://www.frontiersin.org/articles/10.3389/fphy.2020.00139/full https://www.frontiersin.org/articles/10.3389/fphy.2020.00139... In 2016, 't Hooft published a textbook on some specific points of superdeterminism: Gerard 't Hooft; The Cellular Automaton Interpretation of Quantum Mechanics > https://link.springer.com/book/10.1007/978-3-319-41285-6 https://link.springer.com/book/10.1007/978-3-319-41285-6
    - n4r9 4y ago
      It's true in a sense that you can get around Bell's theorem by supposing that Alice and Bob's mesasurement choices are strongly pre-correlated in a specific way. But then I feel you end up with this sort of bizarre universal conspiracy set up just to make humans believe in quantum theory.
      - q-big 4y ago
- heckerhut 4y ago
  But there are constraints on those hidden mechanics as well. Not sure hidden variables theory survives these constraints. Can someone more knowledgeable talk on this?
DebtDeflation 4y ago
QM can't be based on LOCAL hidden variables. Hidden variables theories that are explicitly nonlocal are not ruled out. Separately, Superdeterminism eliminates both the requirement for nonlocality and the result that QM is inherently probabilistic.
- q-big 4y ago
  > QM can't be based on LOCAL hidden variables. ... as long as we assume that the system being measured is uncorrelated with the choices of which measurements to make on it. :-)
- rmu09 4y ago
  Superdeterminism eliminates any requirement(s).
- GolDDranks 4y ago
  Oh, you are definitely correct. Pardon the inaccuracy.

deleted 4y ago

[deleted]

hackandthink 4y ago

I like the essence of Quantum Strangeness here: "To be more precise, what we shall show is that the particles’ response∗ to a certain type of experiment is not determined by the entire previous history of that part of the universe accessible to them." John Conway, Simon Kochen: Free Will Theorem https://arxiv.org/abs/quant-ph/0604079 https://arxiv.org/abs/quant-ph/0604079

shellac 4y ago
That is a lovely way of putting it. (I wish they'd never mentioned 'Free Will' since people get hung up on that) Always keep in mind that Bell himself was quite a fan of Bohm's theory, which is the canonical hidden variable theory really. The question becomes one of characterising that 'strangeness': is it the violation of locality ('that part of the universe accessible to them'), is violating outcome independence palatable, but not parameter independence (this was Shimony's idea originally)? Lots of curious stuff.
zmgsabst 4y ago
> Why do we call this result the Free Will theorem? It is usually tacitly assumed that experimenters have sufficient free will to choose the settings of their apparatus in a way that is not determined by past history. […] > We consider experimenters A and B performing the pair of experiments described in the TWIN axiom on separated twinned particles a and b, and assert that the responses of a and b cannot be functions of all the information available to them. I don’t get it — this sounds like they assumed their conclusion. There’s also a couple places they make strong assumptions about information geometry I’m not sure I agree with — namely, if you want to refute modern Bohm-inspired models, you need to account for radically non-Euclidean spacetime. (Where you have a much harder time with “space like separated”.) > FIN is not experimentally verifiable directly, even in principle (unlike SPIN and TWIN3).Its real justification is that it follows from relativity and what we call “effective causality,” that effects cannot precede their causes. […] > Not all information in the universe is accessible to a particle a. In the light of FIN, information that is space–like separated from a is not accessible to a. The information that is accessible to a is the information in the past light cone of a.

lucozade 4y ago

As I understand it, Bell showed that, if quantum mechanics is correct, then any deterministic hidden variable theory would either have to be non-local or non-causal. Aspect et al demonstrated experimentally that quantum mechanics is correct in the Bell sense.