Few words stir upwards a hornet’s nest on TRF every bit reliably every bit “nonlocality,” together with hence it is alongside roughly trepidation that I offering a few thoughts on the subject. To roughly extent, I retrieve terminology has sown confusion. Different people work the intelligence “nonlocality” inwards unlike ways, together with if nosotros tin forcefulness out care on our terms, much of the dispute volition evaporate. But non all of it.
Luboš defines nonlocality every bit a violation of relativistic causality—an powerfulness to signal at spacelike separation. (See here together with here.) In our nowadays understanding of physics, that is impossible, although, every bit Luboš has every bit good explained, nosotros may legitimately await for such nonlocal effects inwards black-hole physics together with string-theoretic dualities. At times, physicists together with popularizers of physics receive got been guilty of leaving the impression that quantum correlations are nonlocal inwards this sense, together with Luboš is correct to receive got them to line of piece of work (for instance, here, here, together with here). But nosotros involve to distinguish incautious presentation from bad physics. No ane actually thinks signaling tin forcefulness out occur across spacelike separation. Not fifty-fifty advocates of Bohmian mechanics produce (although they produce retrieve at that spot is a type of Lorentz-violating nonsignaling causation). When Einstein spoke of spukhafte Fernwirkung, he was putting it frontward non every bit an actual physical process, but every bit the scandalous outcome of claims that Bohr together with others had been making.
When I together with many other people work the term “nonlocality,” nosotros receive got inwards hear a broader Definition that includes the nonseparability of entangled states, which violate what Einstein called the Trennungsprinzip. We likewise utter of nonlocality inwards patently gauge-invariant formulations of Yang-Mills theory together with inwards string theory. If nosotros are attuned to these varied usages, I retrieve nosotros volition divulge wide understanding on the physics.
Where nosotros produce disagree is the significance of quantum correlations, together with hence allow us focus our energies on that. Does the disagreement reverberate an outright mistake or simply a query on which nosotros tin forcefulness out care to disagree? Regarding a duad of electrons inwards the singlet state, Luboš draws a comparing to Bertlmann’s socks:
When yous mensurate the colors of his socks, at that spot is naught mysterious most the anticorrelation. It was guaranteed past times pattern because the same encephalon decided most the 2 socks inwards the morning.Remember, when John Bell introduced Bertlmann’s socks, his indicate was that entangled particles produce not demeanour similar socks. Yes, the electrons are correlated past times virtue of their articulation grooming inside the past times low-cal cone. But the sock metaphor is realist. We tin forcefulness out assign definite colors to the socks, together with hence nosotros receive got a straightforward explanation of how they develop, maintain, together with exhibit their correlation. We know from Bell-inequality violations that nosotros cannot produce anything analogous alongside the electrons. One mightiness yet struggle that this is non mysterious together with that quantum mechanics only enlarges our project design of the types of objects that populate our world—objects that need non follow classical logic. But yous cannot appeal to people’s intuition most matching socks.
The province of affairs is nonlocal inasmuch every bit nosotros are speaking of articulation properties of spatiotemporally separated objects. We know the singlet electrons receive got a full spin of zero, but nosotros cannot ascribe either particle a definite spin inwards advance of measurement. If yous object to the intelligence “nonlocal” inwards this context, fine. I would every bit good last happy alongside “nonseparable,” “delocalized,” or “global.”
The existent number is how to explicate the phenomenology of correlations. I know that Luboš does non retrieve highly of the EPR newspaper (neither did Einstein), but it is the green starting indicate for this discussion, together with hence allow us focus on the most corporation travel of that paper: the dilemma it presents us with. Given certainly assumptions, to explicate correlated outcomes, nosotros must either assign roughly preexisting values to the properties of entangled particles or nosotros must imagine activity at a distance. Einstein recoiled from the latter possibility—he was committed to (classical) acre theory. The quondam possibility was afterward ruled out past times Bell experiments. So, presumably nosotros involve to query ane of the assumptions going into the argument, together with that’s where nosotros become downwardly the interpretive rabbit hole of superdeterminism, Everettian views, together with and hence forth, none of which is exclusively satisfactory, either. We appear to last stuck. I personally await to emergent-spacetime models for roughly help, since those models propose that the degrees of liberty nosotros run into arrayed inwards infinite are non fundamental.
Luboš has written:
An activity at a distance would last needed inwards a classical model that would endeavor to mimic the predictions of quantum mechanics.True, but quantum mechanics does non render a physical picture, either. It tell us that objects should last correlated, but does non tell us how, together with it creates a serious tension betwixt correlations together with indeterminism. If yous disagree, fine. Tell me what is going on. Give me a step-by-step explanation of how particle spins demo the observed correlations fifty-fifty though neither has a determinate value inwards advance of existence measured.