- #1
TrickyDicky
- 3,507
- 27
Are many-particles systems theories like the Standard model of particle physics examples of local hidden variable theories?
I understand that to the extent they follow Quantum theory mathematically they can'tatyy said:The many-particle theories of condensed matter physics and the standard model of particle physics are not local hidden variable theories. They obey the standard axioms of quantum mechanics such as a state being a ray in a vector space, unitary evolution between measurements, and state reduction upon measurement. This is stated clearly in Weinberg's QFT text.
The standard model of particle physics is local in a different sense: it does not allow superluminal communication of classical information. The distinction between these two definitions of locality can be found in Susskind's quantum mechanics text, part of the Theoretical Minimum series.
TrickyDicky said:I understand that to the extent they follow Quantum theory mathematically they can't
be(per Bell's theorem). But the idea of a
discrete particle structure of matter and
interactions that seems to lie beneath as ontology would clearly be an LHV theory, no? Or is it more correct to just consider there is simply no ontology behind the SM or condensed matter physic( or any Quantum theory in general) to avoid the issue altogether?
Yes, I was referring only to (3) and the ontology of any theory based on a discreteatyy said:Take a look also at bhobba's remark on cluster decomposition at https://www.physicsforums.com/threa...no-spooky-no-nonlocality.792088/#post-4974680.
So relativistic QFT is local or nonlocal depending on the definition of locality one uses:
(1) no superluminal transfer of classical information (spacelike observables commute) YES
(2) cluster decomposition YES
(3) locally causal NO
TrickyDicky said:Yes, I was referring only to (3) and the ontology of any theory based on a discrete
structure of matter, as in quarks and leptons, is by definition local in that third sense, is there maybe some disconnect between the math and the narrative of quantum many-particle theories? because it makes no sense to use the concept of microscopically fine-grained collections of many particles if they are not locally causal, and yet correlation experiments rules this out.
Not only the simplest narratives, also many textbooks descriptions specially on particle physics. I mean for matter one has the notion of quasiparticles or collective excitations but it would have to be applied to the vacuum, to what is described as "elementary particles" of the SM for them to avoid being locally causal.atyy said:The standard model of particle physics with electrons, photons and quarks etc is not locally causal. There is no locally causal theory that reproduces the prediction of quantum mechanics that the Bell inequalities are violated at spacelike separation. So yes, there is a disconnect between the mathematics and the simplest narratives about these particles. It is especially clear in the Schroedinger picture, where the wave function is the Schroedinger functional (I don't know if this rigourously exists, but the standard model is not rigourous). The wave function is clearly not any wave on "spacetime", but a wave on field configurations, eg. http://arxiv.org/abs/hep-lat/9312079 (see Eq 3.2).
TrickyDicky said:Also the whole interpretation of experiments(like inelastic scattering, etc) as substructure in the form of particles is a purely locally causal interpretation.
Well, the problem is that they can't be ignored after all the experiments confirming them. But the fact is that all the particle descriptions that sustain the modern scientific atomic theory from Thomson's electron to SLAC 1968 experiments, or the Rutherford one you mention ignore those predictions even nowadays with the evidence from 1982 Aspect's first experiments and subsequent confirmations.atyy said:A tricky question is whether if one ignores the prediction that the Bell inequalities are violated, and restricts oneself to a subset of quantum phenomena, whether a locally causal explanation exists.
An analogy is that in quantum mechanics, we always say that particles do not have trajectories with simultaneously well defined position and momentum. Interestingly, if one makes the restriction to free particles and Gaussian wave functions, a quantum mechanical particle can have simultaneously well defined position and momentum.
Or the case of Rutherford scattering where the classical calculation gives the same result as the quantum calculation - that's how Rutherford discovered the nucleus, based on Geiger and Marsden's experiments.
TrickyDicky said:Well, the problem is that they can't be ignored after all the experiments confirming them. But the fact is that all the particle descriptions that sustain the modern scientific atomic theory from Thomson's electron to SLAC 1968 experiments, or the Rutherford one you mention ignore those predictions even nowadays with the evidence from 1982 Aspect's first experiments and subsequent confirmations.
Local hidden variable theories are a class of theories in physics that propose the existence of hidden variables that determine the outcomes of quantum mechanical experiments. These theories attempt to explain the apparent randomness of quantum phenomena by suggesting that there are underlying, local variables that we are not aware of.
Local hidden variable theories differ from other interpretations of quantum mechanics, such as the Copenhagen interpretation, by proposing that the randomness observed in quantum experiments is not inherent to the system itself, but rather due to our lack of knowledge about the hidden variables that determine the outcome. This is in contrast to the Copenhagen interpretation, which suggests that the randomness is a fundamental aspect of quantum systems.
Yes, local hidden variable theories can be tested experimentally. Several experiments have been conducted to test the predictions of these theories, but they have all been found to be inconsistent with the results of quantum mechanical experiments. This has led to the rejection of local hidden variable theories by the scientific community.
Local hidden variable theories were proposed in an attempt to reconcile the apparent randomness of quantum phenomena with the determinism of classical physics. They were also seen as a way to explain certain correlations observed in quantum experiments that seemed to violate the principle of locality.
No, there are currently no practical applications of local hidden variable theories. They have been largely rejected by the scientific community and are not considered to be a valid interpretation of quantum mechanics. However, the study of these theories has contributed to our understanding of quantum mechanics and the limitations of classical physics.