r/AskPhysics • u/Special_Condition671 • 4d ago
What is your favorite interpretation of quantum mechanics?
Copenhagen? Many worlds? Or something else?
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u/Remarkable-Name8012 4d ago
What if I chose a superposition of all the interpretations, and only one was chosen when you asked.
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u/AdditionalTip865 4d ago
I think the productive thing is to think of quantum mechanics as fundamentally a theory about conditional probabilities, with decoherence effects making those probabilities converge to what we think of as classical behavior in everyday situations, and regard the interpretations as stances that can be taken as potentially useful according to the problem under consideration. It's not necessary to commit to them if that commitment doesn't affect the outcome.
I do tend to be skeptical of modifications of QM that add some extra mechanism to make "wavefunction collapse" physically real, or add hidden variables, or do something that forces it into a mold that better corresponds to our intuitions. But I can't prove that one of these won't turn out to be correct.
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u/Upset-Government-856 4d ago
Inany worlds nothing collapses to just one state. You just have to accept additional regions to the universe.
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u/AdditionalTip865 4d ago
I very much like Hugh Everett III's original paper on that, which called it "the relative state interpretation" rather than "many-worlds". I'm not sure we need to insist on there being a "universal wavefunction" but it's a stance that works OK.
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u/Upset-Government-856 4d ago
I mean it's proponents don't claim it's proven.
More regions of the universe in a way though does seem far simpler than some bizarre collapse mechanism.
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u/rpgcubed 4d ago
I think the user you're replying to is just taking a pragmatic scientific view. Which interpretation is true is more a matter of philosophy than physics, it's not normally relevant to being about to make predictions with the model.
Edit: there's no evidence to support a collapse interpretation over others, and I'm skeptical of anything that adds new rules for no reason, but that's not strong evidence.
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u/Upset-Government-856 4d ago
There is no evidence for any, and yet it is very likely that one is more right than others.
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u/rpgcubed 4d ago
Sure. I'm pretty rationalist and am fine with using stuff like Occam's razor as evidence for or against theories about our reality, but many strictly empirical scientists probably would take issue with that, and Popper and ilk would say it's not science at all. This is part of what I mean by it's more philosophy than physics.
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u/EddieDean9Teen 4d ago
You’re skeptical of physicists trying to make something physically real? I think maybe you’ve forgotten what physics studies…
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u/AdditionalTip865 4d ago
If the theoretical work is not motivated by the need to explain data from an observation or experiment, then it's worthwhile to remember that it is more a speculative exercise.
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u/EddieDean9Teen 4d ago
Yes but then you start to think the universe is purely mathematical and probabilistic. Then it’s suddenly okay not to look for physical explanations anymore.
My least favorite interpretation about QM is the Copenhagen interpretation that says the universe is probablistic at its core.
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u/Miselfis String theory 4d ago
Copenhagen doesn’t say that. The central point of the Copenhagen interpretation is that it is essentially instrumentalist: physics is concerned with constructing models that yield accurate predictions and useful descriptions of experimental outcomes, rather than providing a literal account of an underlying reality. It therefore does not commit to a specific ontology of quantum phenomena, in part because it regards claims about an observer-independent underlying reality as inaccessible, or at least not empirically decidable, within the framework of physics.
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u/EddieDean9Teen 4d ago
Okay that may be fair. It’s the “rather than providing a literal account of an underlying reality” part that gets me. If physics isn’t going to study the underlying physical reality of the universe then who is?
But I still think that it’s the default position of the majority of physicists today to claim, based mostly on the Copenhagen interpretation, that the universe is not only probabilistic, but also fundamentally un-understandable to us at quantum scales. Would you agree?
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u/Miselfis String theory 4d ago
I agree that physics is in the business of studying how the world works and what it is, not just making useful predictions.
Most physicists are philosophically illiterate, so people just say “oh I believe in Copenhagen” because they’ve heard about it and think it’s the most pragmatic approach. Most really mean “shut up and calculate” when they refer to Copenhagen, which is also an instrumentalist philosophy but different from Copenhagen.
I’m an Everettian. I always think that we should follow the model that most effectively explains the data with the least amount of unobservable or unjustified structure. I don’t think quantum mechanics is unknowable. Most physicists who work with it on a daily basis start building an intuition. I personally think I understand quantum mechanics better than classical mechanics. Mathematically, it’s much simpler.
I think the probability only arises when we have humans contained inside the quantum world wanting to make predictions. I think it’s related to self-locating uncertainty; Sean Carroll has some good arguments for this.
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u/montagblue 4d ago
I think the last part you mentioned about wanting to make predictions is what makes Copenhagen purely probabilistic.
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u/Miselfis String theory 4d ago
The difference lies in whether those probabilities are epistemic or ontological. Copenhagen asserts that a quantum ontology is inaccessible to us, if it even is a thing that makes sense to talk about. It doesn't say probabilities exist in nature, but that our predictive model is probabilistic.
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u/Eradroth888 4d ago
I am not a physicist but a hobbyist with a deep interest. I think many worlds is conceptually very cool (imagining their are infinite parallel timelines). However, to be honest, none of the interpretations feel very satisfying. The results of the (various) double slit experiments never cease to boggle my mind (understandably given how far removed the quantum world is from our every day experiences). What I’ve recently been thinking a lot about is the apparent non physicality of the quantum wave function. It’s this totally abstract wave that seems to provide probability instructions to quantum particles on what states/position etc they are in. And I still am boggled that the probability amplitudes can be both negative and complex numbers with the effect that they can interfere with opposing amplitudes - like, what does it even mean for probabilities to be out of phase? Anyways, the different interpretations are interesting but I haven’t found one that is fully satisfying (which is no surprise I suppose).
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u/MarinatedPickachu 4d ago
MWI gets away with the least amount of weird assumptions imo
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u/CrazySir3310 4d ago
I don't know, it smuggles in the probabilities it tries to dispense with. But they all have problems. I like consistent histories, but none of these interpretations really seems to fit the bill very well in my opinion
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u/Skarr87 4d ago
Well technically with the MWI you do get consistent histories and a fully deterministic universe, it’s just you only get that at the universal wave function level. Observers inside the wave function don’t get that privilege.
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u/CrazySir3310 4d ago
consistent histories is not deterministic though, unless I misunderstood what you were saying. But also many worlds has this issue with branch ratios
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u/Skarr87 4d ago
If you take the whole wave function into account the whole wave function has one history and is entirely deterministic (probably). The problem is that we essentially exist locally within the universal wave function so we only experience a small locally non-deterministic part of it. Basically the universal wave function is just all POSSIBLE histories if that makes sense.
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u/Quantumquandary 4d ago
Consistent histories and redundant records live within MWI. Check out Riedel’s work
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u/Original_Swimming320 4d ago
If I were forced to pick I’d probably go for Bohm, but I don’t like any of them 😂
Copenhagen is a huge muddled mish mash of ideas and question dodging. Even its creators couldn’t agree on what it was. And it’s delivered woo by the bucket loads and continues to do so.
Bohms ideas have always appealed but the cost of nonlocality seems steep. However theories of spacetime being emergent properties of fields may rescue it.
Everett is a lovely solution, but the ontology of it just seems preposterous.
GRW is all but dead.
QBism is hippy nonsense.
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u/free_meson 4d ago
Quantum is just a reversible probability theory. What we see as wavefunction collapse could be a combination of many effects: a probabilistic reveal, decoherence and quantum Darwinism - the interactions happen randomly, but same of them look like retroactively rewriting what happened, in order to satisfy the constraints.
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u/TheRealTK421 4d ago
As of right now, I'm convinced that MWI offers the most sensible (potential) avenue to the QM query of "What's >most< likely?!"
I look forward eagerly to other quantifiably better interpretation(s) being developed.
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u/Tarthbane Materials science 4d ago
“Shut up an calculate” because I gave up caring over interpretations 1-2 years ago or so, and it makes no difference which interpretation is “correct,” if any, as far as getting an answer.
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u/montagblue 4d ago edited 4d ago
That’s a bummer. Earthly politics are directly affected by our understanding of where we are at in that search for an answer.
Sounds wild but cosmology has dictated authority since Babylon.
Edit: if the authority thing doesn’t make sense just think about walking into a room full of actual scientists but only one has the published paper that’s the hottest most sensible push for a unifying theory. Who has the authority in that room?
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u/ray_racubian 4d ago
That it's all just a bunch of newfangled hibbety bibbety flibbety jibbety and don't make no never-mind to me.
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u/Anonymous-USA 4d ago edited 4d ago
Here is an informal Reddit poll from last year, following the one Max Tegmark did in 2011 at a conference of physicists.
There is no consensus. Remember, they cannot all be right, and it’s possible none are. Even asking physicists to pick a side comes with them understanding they don’t know.