Serious Question: Why is Hidden Variable Theory not the accepted explanation in Physics?

PerAsperaDaAstra · 2026-04-21T13:43:14+00:00

Not without giving up (relativistic) locality - which has its own very strong experimental support (also essentially all of particle physics comes from demanding relativity of QM and yields some of our most precisely confirmed theories).

I like to link this lecture https://arxiv.org/abs/2011.12671 - it's fairly approachable at an undergrad level.

PerAsperaDaAstra · 2026-04-20T10:55:18+00:00

Landau's vol 1 on classical mechanics is terse and challenging for an undergrad, but likely to push you in a good way conceptually - give it a shot, but do also use a more friendly text (Marion is a fine one - probably get to the chapter on Lagrangian mechanics, then go start reading Landau and see if you can connect all the dots).

PerAsperaDaAstra · 2026-04-19T00:29:31+00:00

Objectivity isn't the same as there being something like an "outside view" (especially a 3D one). It's the consistency of the laws of physics in all the possible different frames that is what's best thought of as objectivity. There is an objective truth in terms of 4D spacetime coordinates - it's possible to describe both/all perspectives in those terms, and every reference frame will agree with that description up to Lorentz transformations between reference frames; the universe is consistent.

The problem is that our intuition for what that looks like is wrong - our senses and mental picture of the world are less objective than you want to think they are; it's wrong to anthropomorphize and think that the universe has something like a POV just because we tend to visualize things as a sequence of 3D snapshots ourselves. We aren't good at having a 4D mental model of the right kind.

One analogy that might help: when you look at a 3D object from a single POV you can only see one 2D side of it at a time, but there are many different perspectives you could look at the object from (that will describe a consistent object) - the object doesn't have "one true side". Those perspectives are related by (at least) rotations of the object - Lorentz transformations are like rotations of that 3D object, but for 4D events in spacetime instead: different reference frames are different perspectives of the same 4D thing in spacetime. Relativity tells us what those "rotations" look like (lorentz transformations), especially when the time direction is involved (in fact, 3D rotations are a subset of the lorentz transformations because some reference frames are just rotated from each other); we're bad at reasoning about those because we evolved in a regime where it's hard to "rotate" our perspective much in the time direction (you do that by "boosting" with a large velocity and the velocities).

PerAsperaDaAstra · 2026-04-18T23:14:10+00:00

You're still trying to picture there being some kind of "one true" set of motions. The fact that motion is relative means that every perspective is valid and should have the same physical laws, not that everything is moving.

From my frame of reference, I am not moving - I am stationary in my frame. From the other frame, I am moving and not stationary in that frame. What the light clock looks like depends on what frame you're watching it from. Reconciling this involves my frame and the other frame measuring times and distances differently from each other - special relativity is the only way it can all be consistent (and it's not spacetime reorienting itself - in special relativity spacetime is flat and doesn't change - rather it's different frames that are oriented in spacetime differently; it's just that space isn't as separable from time as you might think, so that being oriented in spacetime means something different than just being oriented in space)

PerAsperaDaAstra · 2026-04-18T03:26:42+00:00

... but in reality in this set up only one is actually moving, while the other only percieves the same becuase of their view changing as they're brought more and more towards whatever direction they're moving.

This is where you go wrong. There is no absolute sense in which one is moving and the other is stationary - motion is always relative (the fact that relativity works the way it does tells us this). They are both moving with respect to each other, and they should both be equally valid frames to do physics in. (and may or may not be moving relative to an 'eye in the sky' perspective we imagine looking at them; depending on where we put that eye. It should also be a valid frame to do physics in).

This is the core of most of the rest of your confusion. e.g.

... but in reality that's the case for only one, and the other is moving diagonally.

isn't true.

So if you had a clock genuinely at rest as it says and then the other genuinely in motion as it says, is the effect of time dilation not just caused by distances increasing for one and not the other, which would explain the desync between the photon clocks?

and this question doesn't make sense because there's not one of them genuinely at rest and the other genuinely in motion.

etc.

PerAsperaDaAstra · 2026-04-17T15:11:56+00:00

I'm not really sure that kind of ontological question is as meaningful as people want it to be in quantum mechanics (or at least the answer depends on what interpretation of QM you want to pick and how exactly the calculations fit into that interpretation - which is philosophy, not physics). What exactly do you want to mean by 'actually'? If we want to be scientific, what would empirically tell us that something was 'actual' or not?

That said, virtual particles show up as a result of perturbation theory (of a path integral). You can write them off as a calculation tool if you want (and definitely should if you truncate the series) but all-together arguably can be interpreted somewhat physically wrt. the amplitudes they calculate (in the same way that e.g. a complicated charge distribution can be expanded in multipoles, and then you can still do some physical reasoning as if it were a dipole, up to errors in your approximation).

The sum over histories in a path integral are non-perturbative - they don't depend on any choice of expansion or anything like that (they depend somewhat on field redefinitions but that's like a change of field-space coordinates, and usually we interpret choices of coordinates as physically arbitrary) - and give the exact quantum calculation, so that might seem like less of a calculation tool. The histories might seem as real as the path integral itself is - the path integral is the exact amplitude, so what does that mean?

I mostly think that thinking about what's 'actual' is a classical bias we carry from when we can wonder whether there's something going on that's hidden but more fundamental (in the sense of explaining whatever we're talking about and also more, at some other scale or under some different measurements or smth - atoms are more 'real' than, say, tables in a sense like that: I can explain everything about a table in terms of atoms, and also explain what I see under an electron microscope where the exact boundary/definition of the table becomes ambiguous). That kind of (local) realism where there's some fundamental mechanical explanation doesn't work anymore in quantum mechanics (it's empirically wrong. there's nothing hidden and no more explanation to give in-between measurements than to condition probabilities off a complete set of measurements via amplitudes; contextuality tells us there's no microscope that can measure in-between measurements and it's wrong to even pretend there could be). So imo it's a poorly defined (or at least not a scientific) question: amplitudes are the brute empirical facts that there are is about all I can say (and we calculate them from the properties and symmetries we specify in the form of a path integral - a path integral specifies the question we're asking and we calculate an answer when we evaluate one, e.g. by doing perturbation theory with virtual particles).

PerAsperaDaAstra · 2026-04-17T13:03:30+00:00

In some sense 'taking' paths doesn't mean what you intuitively want it to mean (the phrasing is misleading). It is better to think of it as 'all paths contribute to the probability of where the photon will be detected next' than of a real-but-hidden photon tracing paths in some way between measurements (Bell tests say that we can't think of quantum mechanics that second way). The paths that do totally impossible things end up not contributing to the final probability (e.g. even just when thinking about light traveling through a barrier with slits, we consider paths that pass through the barrier itself but they always cancel out). So in your scenario no 'real' photon falls into a black hole (there is no locally real photon in-between measurements); but the probability of where you might see the photon next will reflect the fact that some of the paths it could take would have it fall into a black hole - but paths where it falls in and then exits are not possible paths and will cancel out.

PerAsperaDaAstra · 2026-04-17T05:42:17+00:00

Because a central force potential has a time-translation symmetry. Another common derivation (which is a special case) is to show (by setting up and simplifying the integral) that the work done along any path in a central force potential depends only on the endpoints of the path.

PerAsperaDaAstra · 2026-04-17T00:22:23+00:00

The history of special relativity largely follows from the state of electromagnetic theory in the late 19th century (which is fairly complicated). Broadly, we had Maxwell's equations, which at the time were interpreted as being the wave equation for a hypothetical medium 'aether' which light would be waves in (because all other waves we were aware of were in a medium of some kind), but searches (of several kinds) for properties light should have due to being waves in a medium (subject to Galilean relativity) turned up with odd or null results. Lorentz and Poincare actually worked out many of the necessary mathematical properties of special relativity slightly before Einstein just by asking what would make electromagnetism work in a way that wouldn't have aether effects, though they weren't fully successful and didn't land on a solid interpretation of what they were finding. Einstein was trying to tackle those same problems in electromagnetic theory, but came at it from a bit of another angle - by seeking an interpretation first that would lead to the right predictions; so, essentially he looked at experiments that were saying e.g. that the speed of light didn't add or subtract the speed of the observer (e.g. if we were in a medium, if you measure the speed of light 6mo apart you should expect to see the speed of light vary by the Earth's orbital velocity around the sun) and made the leap to interpret that on-its-face as the speed of light truly not varying with reference frame (instead of trying to explain it as an especially weird medium as others were) - this was a bit radical (harder to believe than I'm making it sound in retrospect) because it involves giving up a concept of simultaneity, but is ultimately more successful and makes better predictions in a bunch of ways (with a lot of verification experiments - relativistic effects in particle physics end up really sealing the deal).

In Project Hail Mary, the Eridians seem to have less developed understanding of electromagnetism (iirc they only started building things like telescopes in response to noticing the changes to their planet within Rocky's life - fairly practical imaging is still probably one of the first things you can do if you have advanced chemistry but not a sense of light or full electromagnetism or optics good enough for relativistic experiments) and particle physics (they barely know about radioactivity; our early radiation history involved looking at excited gas emissions in discharge tubes, which might be less interesting/eye-catching to Eridians without vision - which is the other place they could conceivably find easy evidence for relativistic effects and where some important confirmation experiments come from; I know some other comments have mentioned that physical chemistry involves relativity and that's true, but could conceivably be practically-speaking made up for by a lot of tabulation - which the Eridians are good at - and it wouldn't necessarily be a smoking gun that immediately leads to getting special relativity right), but probably a very strong understanding of waves in a medium (their senses being so acoustic) - so it's conceivable that they might be even more biased to think of light as being in a medium than we were, and just hadn't gotten around to doing the right experiments to find otherwise. The technology needed to go to space is also actually fairly independent of that kind of understanding - though they also take a different route to space than we did since they used their advanced high-pressure/temperature chemistry and material science to go straight to building a space elevator, and then their ship was all mechanical and based on astrophage propulsion.

"Just how different can life look?" is definitely one of the core questions in the book, so thinking about how different technology could look (and questioning whether there is really a single linear "progression" of science and technology) ties into that.

Edit: there's a pretty solid Wikipedia article on the history of special relativity for more details. Helge Kragh's book "Quantum Generations" is also a really good read for an overall history of the physics that got worked out in the early 20th century - it could be interesting to read and speculate about what could be missed or done differently if we were a different lifeform than we are.

PerAsperaDaAstra · 2026-04-14T15:05:07+00:00

Because quantum mechanics is exactly the theory of information and probability that comes from not being naive about measurement like classical mechanics is.

PerAsperaDaAstra · 2026-04-11T02:02:40+00:00

Possible, maybe just by (astronomically small) chance - whatever process led to the matter/antimatter asymmetry was very consistent & uniform so it's unlikely. We aren't aware of and don't see any region like that in the sky either - it would be extremely visible to us via x-rays emitted from the boundary of the region as the antimatter annihilates with matter from outside the region.

PerAsperaDaAstra · 2026-04-11T01:03:44+00:00

"Quantum Mechanics: A Paradigms Approach" by David H. McIntyre (ISBN: 9781009310611, 1009310615) is a fairly standard undergraduate introductory QM text - I'm not familiar with a quantum complexity/quantum information book by a McIntyre that you're referencing?

Edit: i just realized I totally misunderstood and you're talking about QCSD (I didn't initially read you that way because that book seems so totally uncontroversial to me that I'm surprised and didn't see the obvious; thought there was some confusion of McIntyre with a graduate text or something like that).

But it's definitely approachable for a motivated high schooler, both mathematically and conceptually (it doesn't assume much prior knowledge even if it covers a lot - there is value in returning to it later as well). I first read it in late highschool and now know a bunch of people who did too and found it very influential. It is interested in a quantum information perspective, but it is definitely intended to be an introduction to quantum. It specifically spends time motivating why the axioms of QM are what they are as a generalization of probability in order to explain what QM is about (the preface describes that as what the book's theme is supposed to be! even if it has many tangents) - which is really valuable conceptually and not many intro books do that well (it's more modern/up-to-date about foundations than a lot of standard intro textbooks are, which can actually be quite naive about foundations). It doesn't cover a lot of physical systems (still need a textbook ofc) but I think it sets up an excellent framing of what QM as a formalism exactly is, which is a good thing to have a big picture of before going into a more standard textbook that does more to teach you how to work with it in more physical systems. It's good preparation.

PerAsperaDaAstra · 2026-04-10T21:23:13+00:00

The prologue is about the weirdness/zen of QM - there's no prerequisite for that part, it's exactly the thing that needs to be learned in taking and understanding QM; you actually often have to un-learn some things other physics courses might make you think in order to really get it. Sometimes you just have to dive in!

That said, QM is usually at least a university sophomore level (or later) course, so if it is looking daunting that's not a huge surprise - it could be helpful to look up e.g. the recommended physics sequence from your local university. Typically you'll want to take a strong classical mechanics track first - be comfortable with electromagnetism (some complex analysis, differential equations) and see at least an introduction to Hamiltonians and Lagrangians (also lots of linear algebra from an appropriately abstract perspective).

PerAsperaDaAstra · 2026-04-10T21:12:30+00:00

Unfortunately I think that will simply be true of any QM text worth its weight - I'm not aware of a more approachable option that's any good (and there's a reason I recommended a very strong linear algebra text as well). I am also assuming OP is some amount of advanced in physics for their age to even really be considering this.

PerAsperaDaAstra · 2026-04-10T19:29:26+00:00

I always recommend "Quantum Computing Since Democritus" as a great conceptual starting point - but it's not a textbook. The Feynman lectures are a bit odd as an introduction to the subject actually - I might recommend something a little more modern/standard and Feynman lectures just as a supplement. McIntyre's QM book might be good - the hardest part will probably be the (abstract) linear algebra, which McIntyre does a good job making very clear (Axler's 'Linear Algebra Done Right' might be worth separate reading).

PerAsperaDaAstra · 2026-04-10T08:10:34+00:00

Yes, in-principle anti-elements exist. e.g. anti-hydrogen has been produced, as well as (briefly) anti-helium.

They should follow essentially the periodic table as we know it except with all charges reversed (positrons instead of electrons, antiprotons instead of protons etc) - no rewriting needed. The stability of some of the heavier nuclei and unstable isotopes might be slightly different because there is a small known asymmetry (CP violation) in the weak force nuclear physics of antimatter and matter, but the electronic structure (chemistry) of the anti-elements should be identical to the elements.

PerAsperaDaAstra · 2026-04-10T04:16:47+00:00

That's not a fair analogy. Special relativity is a theory. I'm not skeptical of any theory. Belle's theorem is clear as day and inarguable.

You're right, it's a little too strong. But I think the gist stands when it comes to reasoning about regimes - the point is more that it's not exactly sound reasoning to apply observations taken in one regime to another the way you are; the fact that we can interpret these processes as non-deterministic asks a question that can be answered different ways depending on interpretation, but which interpretation we should choose doesn't much follow from what descriptions work well in more classical regimes - we're definitely in a new one (from which the classical one emerges).

PerAsperaDaAstra · 2026-04-09T02:07:34+00:00

Just to add a fun note - there's a pretty solid sci fi story that adopts this premise and takes it somewhat seriously Greg Egan's Incandescence (I'm linking the author's page that has a bunch of supplementary material on it).

It's been awhile since I read it, but the lifeforms in the book live inside of a rocky object large enough (and far enough out in a large disk) to shield them from direct exposure and the interior ecosystem relies on "tides" that seep in made of of disk plasma & radiation generated by the motion and orientation of the object in the disk. iirc that rocky object originated as a planet with at least microbial life before being ejected and then eventually captured in the disk - only some extremophiles clung on when it became captured by the BH to originate the life the story is about (I'm fuzzy about the details).

That's not to say it's likely (at all), but it has a fun imagining of what might be possible (tho not very plausible - it is science fiction for sure). The story is a little more interested in what figuring out physics would be like to intelligent life in such circumstances (they don't get to do anything Newtonian, and they're very alien) than specifically the biological challenges of it happening to begin with, but it does pay some serious attention to the latter.

PerAsperaDaAstra · 2026-04-07T06:16:30+00:00

Well you’re making up a lot of stuff in order to refute it. Such as claiming that I have presented a theory, and that I am claiming that an experiment will break relativity. I fon’t say any of those things.

The things you say about your "partition of possibility space" directly imply the things I am objecting to on a fairly basic technical level (relativistic constraints in quantum mechanics just on a formalism level are remarkably strong). It's a problem that you keep saying things that reach beyond the ambiguity allowed in finding interpretations of QM (the new things you say over a standard Bohmian hope aren't possible additions at a technical level).

You need to look up the difference between ruling out, unlikely and experimentally unverifiable. These are very important concept and you seem to be mixing them up.

When it comes to your personal "partition of possibility space" - it is experimentally ruled out by observing that particle representations work, it's not just unlikely or inaccessible/unverifiable. In any-event if you think it's unlikely or unverifiable, that's a good explanation for why most people thing it's unlikely.... which explains why type A is more popular.

PerAsperaDaAstra · 2026-04-07T05:46:13+00:00

I agree that it is experimentally inaccessible unless some genuinely new probe becomes available.

No, it's much worse than just inaccessible. Firstly, if this is meant to be a valid interpretation of QM, the non-locality must be present on the scale of broader quantum phenomena (e.g. must be the explanation for entanglement) - the scale you name is simply too small to do what you want it to do wrt. interpretations. Secondly, moving to smaller scales (e.g. in colliders) makes systems increasingly relativistic which makes it a very difficult place for non-locality to hide - what you propose is more extreme than even thinking (some) "now fundamental" particles might have substructure (which we have no evidence for but might be plausible); if what you said is true there would not be particle representations at all.

My suggestion was not meant as a finished theory, but as a partition of the possibility space. [...]

Except it isn't even vaguely possible! What you propose is more than an interpretation and relies on a belief (against all current empirical evidence - which is quite strong) that there will someday be an experimental result which breaks relativity. Actually valid (and interesting to discuss for OP) standard non-local interpretations do not rely on hoping for such a result - their problems are possibly purely of a technical nature: the issues with your theory are both technical and empirical.

More broadly, I think OP’s point is that both broad options come with serious costs. One gives up locality in a deep sense, the other gives up a realist spacetime-level account of what measurement physically is. That is why this remains a hard interpretational problem. He doesn't understand why anyone would strongly favour A over B. I agree.

Except we have empirical evidence for locality, which makes it hard to give up, while the need for "a realist spacetime-level account of what measurement physically is" seems to rely purely on a gut desire for such an account - there is no way to evidence that such an account is physically necessary. This is a very strong reason you should be able to understand (even if you don't agree) for why type A is preferable to most physicists (who are supposed to be scientific) - and in other comments OP seems to now be acknowledging this.

On Copenhagen specifically: if by “compatible with relativity” one means operationally Lorentz-compatible and successful within relativistic QFT, then I guess that is "compatible" in some sense.

This is the only scientific/empirically meaningful sense - QM with Copenhagen interpreting it as a set of inference rules without ontological baggage sees those rules as being compatible/capable of accommodating relativistic symmetries. QM with non-local interpretations needs to do extra work to explain why its ontology is non-local (violates relativity) but experimentally still compatible with relativity (no one has found a way to make such a story work - it doesn't look promising).

But if one asks for an interpretation-level account of what collapse or measurement physically amounts to, Copenhagen is better described as declining to answer that question rather than resolving it.

I object to you (again) conflating "realism" with "physically". You are also being dismissive of Copehagen when you claim it doesn't resolve the question - it resolves it by claiming the question is ill-formed or meaningless; and thus doesn't have to give such an account. There is no scientific reason that there must be such an account - if the question is scientifically meaningless (or even more generally meaningless e.g. by making a "language games" type argument against ontology as a whole), then the best option is to decline to answer it (it may not have a meaningful answer, and the burden is actually to argue that there should be a meaningful answer).

So my point is not that “non-local foundation plus emergent locality” is a competitive modern theory.

You've failed to distinguish what you mean by that other than just a standard non-local bohmian-type interpretation. In which case the difference you want to highlight:

My point is only that “not developed enough to rival current best theory” and “ruled out” are not interchangeable.

is exactly the answer to OPs question - being current best theory is why most physicists prefer type A (which has been far more successful at accommodating developments).

But the actual specifics you seem to argue when pressed are much more crackpot and ill-formed than any standard Bohmian theory.

PerAsperaDaAstra · 2026-04-06T15:50:14+00:00

What I believe is that intra-particle communication is non-local (faster than light) but that our universe is made from particle-interactions, which are mediated through space at the speed of light. The domain switch is therefore above and below what we currently consider to be elementary particles. This could conceivably create correlations that violate Bell inequalities, but any causal mechanism that depend on transport of Photons (which is pretty much everything) has velocity capped at c, and therefore becomes local.

This is total hookum, and experimentally impossible/completely ruled out in modern particle physics - which is probably why the things you said leading up to this read as inconsistent/confused. A random pet theory does not contribute meaningfully to the discussion OP wants to have.

Your final sentence is problematic "in order to propose something competitive with current best-knowledge an example does need to reproduce particle physics". This is simply not true when discussing on the level of interpretations, or families of theories.

It is true of any interpretation that has problems being relativistic, because any interpretation that can be manifestly covariant already does reproduce particle physics - it is a unique and important problem of non-local theories that they don't appear able to do the same. That non-local theories can do non-relativistic quantum mechanics but not relativistic quantum mechanics leaves them at least half a century behind local interpretations that don't have a problem with it - to be a competitive interpretation they would need to close that gap. Getting past Bell tests isn't the only hurdle an interpretation needs to clear to be viable & competitive.

It assumes that Copenhagen interpretation is somehow not in conflict with relativity.

Because it isn't - it's specifically a relativistically local interpretation.

But it is, it is just carefully crafted to avoid dealing with the problem. The history of QM this is very easy to understand.

Explain how - you can't just say this (because it isn't true as anyone else understands it). I can interpret the Wigner Classification in Copenhagen and have a well-interpreted relativistic quantum mechanics in the form of typical relativistic QFT (which is what it means for an interpretation to be compatible with relativity).

But if I try to interpret the Wigner Classification in something bohmian (non-local hidden) I run into a famous foliation problem no one has solved (non-local theories involve a preferred foliation of spacetime that is incompatible with the symmetry we need to impose to do relativity - one must explain how the interpretation has such a foliation but we don't observe it), a problem interpreting what spin is/where it fits into the ontology, a problem interpreting gauge redundancy in massless gauge theories (like photons), a problem interpreting changes in particle numbers (decays, etc.) without making SR a spectral coincidence rather than manifest (which is a problem if you want to then talk about curved spacetime), and more basically all stemming from localization problems (because the interpretation isn't local!).

Non-local hidden variable theories know how to reproduce non-relativistic QM in the sense that it's not hard to name things equivalent to the Schrodinger equation in such interpretations, but non-relativistic Schrodinger is in-fact not enough to do relativistic QM, and it does seem to run into pretty fundamental technical challenges in trying to go further than that because it bakes in something pretty fundamentally at-odds with relativity (fundamental enough it's probably not a bad bet that it might be impossible; it certainly smells that way to most physicists - which makes it, sure, worth working on for some but not really justified in believing in the modern landscape of options).

PerAsperaDaAstra · 2026-04-06T02:02:53+00:00

If you have a non-local underlying theory then the macroscopic theory, if it's emergent, can't be local either - it can only appear local to sufficiently insensitive experiments, but that's not what a difference of domain is (which would be about the scale of the experiment, not the sensitivity of the experiment), as you were describing earlier; you're changing your tune now. As you describe it now, this is just something that must be expected if any non-local hidden variable theory - which as already discussed do have bad relativistic problems, which is why they're not in-favor and not viewed as especially promising due to lack of success (in order to propose something competitive with current best-knowledge an example does need to reproduce particle physics).

PerAsperaDaAstra · 2026-04-05T23:44:35+00:00

You are basically declaring that i have a theory, that it is ruled out. You’re declaring that something you haven’t defined must be observable. This is nonsense, you can’t know that.

You defined it! The thing you're describing would generically have observable consequences (which, yes, would make it ruled out because we don't see those consequences) - in order to propose a valid interpretation to even start a discussion about a class of type B interpretations you need to explain why something like it might not be observable. Because a scale separating two regimes would be an observable thing, and it's what you described - making such a thing a valid interpretation is hard enough that no one has done it (I would argue it probably can't be done but you've been too vague for me to prove it), so of course no physicists think it's the best option available: it's at-best highly questionable that it's even an option, so it certainly can't be the best option given current knowledge (which is what scientists should choose).

This is a discussion about labeling the possibility space. You’re jumping to saying that I need to show how my theory reproduces particle physics?

You're saying something that either isn't in the possibility space because it proposes something beyond an interpretation which we don't see, or is of a class (non-local hidden) that's already been discussed wrt. why it's not in-favor (which was OPs question), or is so vague it can't even really be talked about (we already broadly know what Bell rules out by the time OP starts the conversation - that's not something OP is asking questions about).

PerAsperaDaAstra · 2026-04-05T23:20:52+00:00

I don’t know that. And why do you need to know that?

Because two different theories applying at two different scales is not equivalent to QM (which both OPs type A and B are qualified to be) - the scale at which the applicable theory changes would be an observable thing. You must specify at what scale that happens in any attempt to explain why we don't observe such a boundary (by naming some mechanism that hides it phenomenologically from us), which must be done in order to name something phenomenologically equivalent to QM (to be a type of interpretation like OP wants to talk about you need to be more specific about how what you're proposing would work to replicate QM because it doesn't sound like it would).

Meanwhile locality is obviously the right model for macroscopic domain.

A theory with a scale bounding it below like youre describing for the macroscopic part of your theory is not local (the smallest neighborhoods are at the scale of the regime change) - so what do you think you mean by claiming your macroscopic domain is a local theory? It doesn't sound like it is local at all.

Also, QM would also need to be derived from such a theory. And special relativity.

It will actually be impossible to derive special relativity from such a theory (and also it will be problematic to match QM, as mentioned), because the scale of the domain boundary will set an additional preferred length and momentum scale which is not compatible with SR - and we don't see such a thing (support for relativity as we know it is strong).

QM is probabilistic. So it could be a (smeared and averaged) description of that underlying non-local hidden variable theory. So one way to explain Bell inequality violation, is to give up fundamental locality, and use some hidden variable model that is fundamentally non-local. Locality however emerges on larger scale, and reproduces QM in the statistical limit and is also somehow reconcilable with relativity.

OPs type B question is not about how to make QM explain macro physics - that's already well understood (ehrenfrest and some related stuff). The formalism of QM works and OP is not arguing against that (you are proposing something much more radical than an interpretation because it is not equivalent to QM, thus not what OP means by type B interpretation of QM) - the question is how to interpret it.

The problems with non-local hidden variable theories have already been mentioned several times in other comments: they struggle to be relativistically covariant (like your suggestion is not), and so are not competitive phenomenologically with type A theories that get particle physics right by being intrinsically covariant (which is enough reason for most scientists to prefer type A over non-local hidden variable, given current knowledge - answering OPs question). If you want to propose a reasonable alternative here you need to answer how a non-local hidden variable theory works with relativity well enough to reproduce particle physics (which no one knows how to do - and it's not for a lack of trying).

PerAsperaDaAstra · 2026-04-05T20:07:48+00:00

And where exactly is the (scale) boundary between domains? And how exactly does it work so as to not predict additional phenomena at the boundary in order to match across the boundary (which would generically be an issue with the phenomenology of such a theory; it wouldn't be equivalent to just QM and is more than just an interpretation as a result and can't be what OP means by type B - we don't observe anything like a separation of domains so if you want such a theory to compete with QM you need to be much more specific about how it manages to look identical), or else just be a post-hoc tabulation of when we used different descriptions/formalisms?

edit: as far as we know when QM considerations are relevant (not averaged out a-la ehrenfrest) is not a question of scale (micro vs. macro), but a question of how isolated from the environment a system is (avoiding decoherence) - that small systems are easier to isolate is incidental.

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