4 ms·

While I disagree (quite strongly) with the claim that non-locality is a problem with QM (on the contrary it seems like an extremely interesting and useful prope

While I disagree (quite strongly) with the claim that non-locality is a problem with QM (on the contrary it seems like an extremely interesting and useful property), I would like to know why you think this paper has anything specifically interesting for Bohemian mechanics rather than any other interpretation.

naasking 4y ago
It's a problem for QM because it establishes an obvious tension with relativity that can't be ignored. The reason this has more relevance for Bohmian mechanics is because that interpretation makes the non-locality explicitly manifest in the core ontology, where other interpretations try to eliminate the non-locality via other means, eg. Copenhagen eliminates counterfactual definiteness, many worlds eliminates collapse, etc. Edit: This means Bohmian mechanics has an unresolved tension with relativity, which is why it hasn't yet been extended to a field theory.
- raattgift 4y ago
  > obvious tension with relativity Quantum nonlocality is perfectly compatible with special relativity. The spacetime of the standard model of particle physics is exactly the flat spacetime of special relativity. Far from being ignored, the compatibility between special relativity and quantum mechanics has been investigated and demonstrated experimentally over the past century. In modern graduate courses this is best seen by studying the relevant group theory. You can read more about the SO(3,1)+ Lorentz group (which also applies to the Maxwell-Heaviside field equations for electromagnetism and the Dirac equation) at e.g. <https://en.wikiversity.org/wiki/Representation_theory_of_the_Lorentz_group#Non-technical_introduction_to_representation_theory https://en.wikiversity.org/wiki/Representation_theory_of_the...>. These are also excellent lecture notes: <https://arxiv.org/abs/math-ph/0602018 https://arxiv.org/abs/math-ph/0602018> and <https://www.ippp.dur.ac.uk/~krauss/Lectures/StandardModel/StandardModel.pdf https://www.ippp.dur.ac.uk/~krauss/Lectures/StandardModel/St...>
  - naasking 4y ago
    > Quantum nonlocality is perfectly compatible with special relativity... ...if you accept the ontology of certain interpretations of QM. Bohmian mechanics is based on a different ontology, which is why Bohmian mechanics currently has to posit a preferred foliation of spacetime in order to square with relativity. This is a little ugly, to put it mildly. Edit: and the point I was making re:non-locality being the real problem, is because there are still plenty of unresolved issues between QM and general relativity, and I think these will come down to ontological incompatibilities, and so a different ontology may provide the insight needed to make a breakthrough.
    - eigenket 4y ago
      Quantum interpretations all generally predict the same stuff (or very close to the same stuff) that "normal" quantum mechanics does. If you have something which has substantially different predictions then it isn't really an interpretation, its a whole different theory. The problems between general relativity and quantum mechanics are not at this subtle interpretational layer. They're actual calculations you do, predictions you make, where the results you get make no sense. In any case if the nonlocality of quantum mechanics was the problem then we should see issues already when trying to connect special relativity with quantum theory, and that seems to work pretty well (e.g. quantum electrodynamics seems fairly legit).
    - raattgift 4y ago
      If you want to write, "Bohmian mechanics is incompatible with special relativity", then I will agree with you. If you want to write, "therefore special relativity is wrong", then do so, and we'll have a lot less to talk about given how well-supported special relativity is by direct in-solar-system evidence. In a previous edit up-thread you added that [de Broglie]-Bohmian mechanics has not been turned into a field theory. Incorrect. It is easy to do turn it into a field theory, but that field theory will not be relativistic. One can add extra structure on the spacetime of special relativity and get a quasi-relativistic field theory. As you note in your second paragraph above, one can do this by picking out a universally true time axis and demoting the infinity of others to pseudo-time. However, in "Can Bohmian mechanics be made relativistic?" <https://arxiv.org/abs/1307.1714v2 https://arxiv.org/abs/1307.1714v2> the authors take seriously the idea that the distribution of matter (and its dynamics) picks out a particular foliation. As a relativist this doesn't bother me: the distribution of matter at cosmological scales (i.e., ignoring "local stuff" it's effectively homogeneous and isotropic from all vantage points) and its dynamics picks out the cosmological frame, after all, and we use that to talk about things happening billions of years ago. However, it's hard to grind this kind of matter-picks-out-a-frame thinking down to the scale of a terrestrial particle-collider experiment or to natural astrophysical "experiments" like magnetars. (The second-last paragraph of the Discussion section of the paper is provocative, however.) Also, I am cautious about predicting whether one can successfully "comma-goes-to-semicolon" a possibly-relativistic frame into a properly covariant theory. Often attempting to do so shows that one has what one might roughly call a surplus of long-distance forces that vanish only in the possibly-relativistic frame (or some family of related frames) but can be made incredibly strong in some other frame (or set of families of frames). The authors above are similarly cautious, and cannot answer their own question. Finally, > general relativity if you are incompatible with special relativity at every point then you are also automatically incompatible with general relativity, because that guarantees SO(3,1)+ at every point and in its ultra-local neighbourhood even if you abolish it as a global symmetry. So your qualification of "relativity" as "general relativity" is unhelpful; SR, after all, just a special case of general relativity which is much closer to everywhere in the solar system than anything with strong enough curvature to make a difference in a beta- decay or relativistically smashing together two lead nuclei.

naasking 4y ago

It's a problem for QM because it establishes an obvious tension with relativity that can't be ignored. The reason this has more relevance for Bohmian mechanics is because that interpretation makes the non-locality explicitly manifest in the core ontology, where other interpretations try to eliminate the non-locality via other means, eg. Copenhagen eliminates counterfactual definiteness, many worlds eliminates collapse, etc. Edit: This means Bohmian mechanics has an unresolved tension with relativity, which is why it hasn't yet been extended to a field theory.

raattgift 4y ago
> obvious tension with relativity Quantum nonlocality is perfectly compatible with special relativity. The spacetime of the standard model of particle physics is exactly the flat spacetime of special relativity. Far from being ignored, the compatibility between special relativity and quantum mechanics has been investigated and demonstrated experimentally over the past century. In modern graduate courses this is best seen by studying the relevant group theory. You can read more about the SO(3,1)+ Lorentz group (which also applies to the Maxwell-Heaviside field equations for electromagnetism and the Dirac equation) at e.g. <https://en.wikiversity.org/wiki/Representation_theory_of_the_Lorentz_group#Non-technical_introduction_to_representation_theory https://en.wikiversity.org/wiki/Representation_theory_of_the...>. These are also excellent lecture notes: <https://arxiv.org/abs/math-ph/0602018 https://arxiv.org/abs/math-ph/0602018> and <https://www.ippp.dur.ac.uk/~krauss/Lectures/StandardModel/StandardModel.pdf https://www.ippp.dur.ac.uk/~krauss/Lectures/StandardModel/St...>
- naasking 4y ago
  > Quantum nonlocality is perfectly compatible with special relativity... ...if you accept the ontology of certain interpretations of QM. Bohmian mechanics is based on a different ontology, which is why Bohmian mechanics currently has to posit a preferred foliation of spacetime in order to square with relativity. This is a little ugly, to put it mildly. Edit: and the point I was making re:non-locality being the real problem, is because there are still plenty of unresolved issues between QM and general relativity, and I think these will come down to ontological incompatibilities, and so a different ontology may provide the insight needed to make a breakthrough.
  - eigenket 4y ago
    Quantum interpretations all generally predict the same stuff (or very close to the same stuff) that "normal" quantum mechanics does. If you have something which has substantially different predictions then it isn't really an interpretation, its a whole different theory. The problems between general relativity and quantum mechanics are not at this subtle interpretational layer. They're actual calculations you do, predictions you make, where the results you get make no sense. In any case if the nonlocality of quantum mechanics was the problem then we should see issues already when trying to connect special relativity with quantum theory, and that seems to work pretty well (e.g. quantum electrodynamics seems fairly legit).
  - raattgift 4y ago
    If you want to write, "Bohmian mechanics is incompatible with special relativity", then I will agree with you. If you want to write, "therefore special relativity is wrong", then do so, and we'll have a lot less to talk about given how well-supported special relativity is by direct in-solar-system evidence. In a previous edit up-thread you added that [de Broglie]-Bohmian mechanics has not been turned into a field theory. Incorrect. It is easy to do turn it into a field theory, but that field theory will not be relativistic. One can add extra structure on the spacetime of special relativity and get a quasi-relativistic field theory. As you note in your second paragraph above, one can do this by picking out a universally true time axis and demoting the infinity of others to pseudo-time. However, in "Can Bohmian mechanics be made relativistic?" <https://arxiv.org/abs/1307.1714v2 https://arxiv.org/abs/1307.1714v2> the authors take seriously the idea that the distribution of matter (and its dynamics) picks out a particular foliation. As a relativist this doesn't bother me: the distribution of matter at cosmological scales (i.e., ignoring "local stuff" it's effectively homogeneous and isotropic from all vantage points) and its dynamics picks out the cosmological frame, after all, and we use that to talk about things happening billions of years ago. However, it's hard to grind this kind of matter-picks-out-a-frame thinking down to the scale of a terrestrial particle-collider experiment or to natural astrophysical "experiments" like magnetars. (The second-last paragraph of the Discussion section of the paper is provocative, however.) Also, I am cautious about predicting whether one can successfully "comma-goes-to-semicolon" a possibly-relativistic frame into a properly covariant theory. Often attempting to do so shows that one has what one might roughly call a surplus of long-distance forces that vanish only in the possibly-relativistic frame (or some family of related frames) but can be made incredibly strong in some other frame (or set of families of frames). The authors above are similarly cautious, and cannot answer their own question. Finally, > general relativity if you are incompatible with special relativity at every point then you are also automatically incompatible with general relativity, because that guarantees SO(3,1)+ at every point and in its ultra-local neighbourhood even if you abolish it as a global symmetry. So your qualification of "relativity" as "general relativity" is unhelpful; SR, after all, just a special case of general relativity which is much closer to everywhere in the solar system than anything with strong enough curvature to make a difference in a beta- decay or relativistically smashing together two lead nuclei.