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I'm not a Physicist. From what I understand, Bell's theorem only covers local hidden-variables and that this can still be explained using non-local theories lik

by kovac 5y ago

I'm not a Physicist. From what I understand, Bell's theorem only covers local hidden-variables and that this can still be explained using non-local theories like Bohm's. Can someone shed a bit of light on the non-local theories and if Bell's theorem addresses those as well?

GoblinSlayer 5y ago
Bell's theorem is a mathematical theorem and has narrow scope, it addresses local hidden variables theories and says they won't fly, it does nothing else, and doesn't prove spooky action at a distance either - that's author's addition.
jostylr 5y ago
Bell was inspired by Bohm's theory. Having seen that a rational theory of existence was compatible with QM, Bell wanted to know if the nonlocality could be removed. Bell's work showed that it could not be removed. Bell was a proponent of Bohm's work. Bohmian mechanics is a perfectly sound theory, proven to be consistent and in agreement with quantum mechanics results whenever QM has results. EPR (and more relevantly, Bohm's version of it involving spin entangled particles) showed that either one has hidden variables or nonlocality. Bell's work showed that local hidden variables is not possible. Hence, nonlocality is the conclusion and the argument to demonstrate the incompleteness of quantum mechanics falls apart. The Many Worlds interpretations kind of gets away from this by exploiting another assumption in that work: that results from experiments actually happen in the sense that the other outcomes don't. Most people at the time would have just assumed that, but MW points out that experiments need not have definitive results, instead we have multiple results of experiments correlated with multiple versions of experimenters who think they have results. Thus, the correlations we see only need to be reconciled when the two groups of experimenters get together to compare notes, a perfectly local notion. Of course, some descriptions of MW, with branching of the universe, is rather nonlocal, but a proper formulation of MW is possible without any of that. By the way, a key feature of Bohmian mechanics is the reliance on position as the "hidden variable". The spin of a particle is not an aspect of the particle itself, but rather of the wave function guiding the particle. In the spin experiments, the correlation with the environment once measurement has happened, separates the overlapping spin parts of the wave function and the particle is then being guided by that singular spin. Hence the appearance of the particle behaving as if it had that spin, but the particle is not actually spinning, whatever that would mean for a point particle.

by kovac 5y ago

GoblinSlayer 5y ago

Bell's theorem is a mathematical theorem and has narrow scope, it addresses local hidden variables theories and says they won't fly, it does nothing else, and doesn't prove spooky action at a distance either - that's author's addition.

jostylr 5y ago

Bell was inspired by Bohm's theory. Having seen that a rational theory of existence was compatible with QM, Bell wanted to know if the nonlocality could be removed. Bell's work showed that it could not be removed. Bell was a proponent of Bohm's work. Bohmian mechanics is a perfectly sound theory, proven to be consistent and in agreement with quantum mechanics results whenever QM has results. EPR (and more relevantly, Bohm's version of it involving spin entangled particles) showed that either one has hidden variables or nonlocality. Bell's work showed that local hidden variables is not possible. Hence, nonlocality is the conclusion and the argument to demonstrate the incompleteness of quantum mechanics falls apart. The Many Worlds interpretations kind of gets away from this by exploiting another assumption in that work: that results from experiments actually happen in the sense that the other outcomes don't. Most people at the time would have just assumed that, but MW points out that experiments need not have definitive results, instead we have multiple results of experiments correlated with multiple versions of experimenters who think they have results. Thus, the correlations we see only need to be reconciled when the two groups of experimenters get together to compare notes, a perfectly local notion. Of course, some descriptions of MW, with branching of the universe, is rather nonlocal, but a proper formulation of MW is possible without any of that. By the way, a key feature of Bohmian mechanics is the reliance on position as the "hidden variable". The spin of a particle is not an aspect of the particle itself, but rather of the wave function guiding the particle. In the spin experiments, the correlation with the environment once measurement has happened, separates the overlapping spin parts of the wave function and the particle is then being guided by that singular spin. Hence the appearance of the particle behaving as if it had that spin, but the particle is not actually spinning, whatever that would mean for a point particle.