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Pretty much as my title says... are Superdeterminism and Many Worlds compatible quantum interpretations? It seems to me that they might be compatible, or close to it, maybe even the stronger statement that they are essentially equivalent? But I feel like I am missing some important differences between the two.

Qmechanic
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Mooks
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  • See my comment on alanf's answer. Also, MWI is bogus but superdeterminism cannot be ruled out. After all, if a particle's wavefunction actually represents the non-local reality of the particle (rather than being a calculation tool), then it's not inconsistent to have superdeterminism. On the other hand, there's no way to rule out non-determinism either, as we simply cannot physically analyze non-physical aspects of the world (if any). – user21820 Apr 28 '22 at 13:03

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Superdeterminism is the idea that measuring devices and the systems they measure are somehow correlated in advance of the measurement. Advocates of this theory say it would account for the results of EPR type experiments and that this theory could be local. I have explained some problems with this idea in another answer.

The many worlds interpretation (MWI) doesn't require superdeterminism and isn't equivalent to it. The MWI just claims that quantum mechanics is an accurate description of how the world works and that it implies the existence of a structure called the multiverse that looks like a collection of parallel universes in some approximations. The MWI is local since quantum systems are described in terms of local equations of motion so that changes in quantum observables propagate at or below the speed of light. This doesn't require that measuring instruments are correlated with the systems being measured in advance. For more on the explanation for EPR type correlations see this answer.

alanf
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  • Thanks. I think my point is that MWI posits a single universal wavefunction that evolves unitarily with time. Isn't that compatible with SD given it could potentially (I think???) lead to said system-measuring device correlations as posited by SD? – Mooks Mar 29 '22 at 10:49
  • @Mooks In principle the states of systems could have loads of pre-existing correlations in the MWI, but no such correlations are required and explaining their existence produces more problems. – alanf Mar 29 '22 at 10:58
  • Ah yes. So MWI doesn't require these correlations, but these correlations aren't inconsistent with it. So I guess the answer is that they are (potentially) compatible but not necessarily equivalent? (Glossing over those other problems you mention, of course). Thank you. – Mooks Mar 29 '22 at 10:59
  • Our comments got deleted for no good reason. My response to you was that I do not have time to write obvious stuff about hundreds of bogus hypotheses out there. At the same time, since most physicists are strongly emotionally attached to either Copenhagen or MWI, they won't say what I say either (which is that both are wrong). In case my latest comment gets deleted, I'll reproduce it here: – user21820 Apr 28 '22 at 12:54
  • Both CI (Copenhagen interpretation) and MWI variants arise from the plain refusal to accept that particles are intrinsically non-local. If one does not make the philosophically silly assumption that a particle must have a specific position upon a measurement, then one will not need any kind of collapse or multiple worlds. A measurement device simply causes a measured particle's wavefunction to evolve to localize for the measured quantity. – user21820 Apr 28 '22 at 12:59
  • @user21820 The MWI doesn't assume a particle must have a specific position upon measurement https://arxiv.org/abs/1111.2189. Also, theories that try to make the wavefunction localise are variants of quantum theory that have unsolved problems https://arxiv.org/abs/1407.4746. – alanf Apr 29 '22 at 19:14
  • @alanf: I shouldn't have said "upon a measurement". All I meant to say was that both CI and MWI assume that particles have specific position (which in the case of CI is revealed upon measurement of position). I do not agree with the abstract of the first paper. ZFC is a widely touted FOL theory that proves lots of empirically verifiable arithmetical sentences, but that means nothing in itself because if one believes ZFC is meaningful one must believe Con(ZFC) and hence also that ZFC' = ZFC+¬Con(ZFC) is consistent, and look, ZFC' proves all those verifiable sentences too! What went wrong? – user21820 Apr 29 '22 at 19:24
  • Empirical evidence so far has only provided justification for a miniscule fragment of SOA (second-order arithmetic; not even anywhere near set theory) called ACA0. It is possible to argue on seemingly cogent conceptual grounds that if ACA0 is meaningful then so is ATR0 (another well-known subsystem of SOA), but it is difficult to philosophically justify much more than that, due to simply circular impredicativity. And it remains a fact that no known application of mathematics requires theorems beyond the reach of just ACA0. – user21820 Apr 29 '22 at 19:30
  • This fallacy of ascribing meaning to a bigger system based on evidence for only a miniscule fragment of it is extremely common in 'philosophy of mathematics' and 'philosophy of science'. The second paper your linked seems to be equally hand-wavy philosophy as well, so I won't bother commenting on it. I also don't know why you thought I support collapse theories, since I explicitly stated that one will not need any kind of collapse if one doesn't assume particles have specific position. – user21820 Apr 29 '22 at 19:40
  • To make that clear, what I mean is that we should not attempt to impose collapse of any form. When a measuring apparatus causes a particle's wave-function to localize for that measured quantity, it does not collapse at all. CI collapse should be viewed as just an approximation trick that works when you happen to choose by experience or luck a collapse point that roughly agrees with the localization point. The Schrodinger-cat is never in the kind of superposition that popular accounts portray. I'll give a brief sketch of what really happens in that situation. – user21820 Apr 29 '22 at 19:51
  • The very presence of the macroscopic detector forces the radioactive atom to be highly localized to not-decayed or decayed at almost all points in time, with a very sharp transition period. Thus after the experiment you do not have a half-alive half-dead quantum cat; the detector simply physically precludes (i.e. constrains to astronomically low probability) the possibility of a superposed detector state. So CI is wrong, and Copenhagen's original intuition that it is absurd was right. MWI is also wrong, because ontological fictions are not real. Anyway thanks for replying! – user21820 Apr 29 '22 at 19:59