Quantum mechanics is not weird, unless presented as such

[ProfChuck]

Does quantum mechanics have to be weird?

It sells much better to the general public if it is presented that way, and there is a long history of proceeding that way.

But in fact it is an obstacle for everyone who wants to truly understand quantum mechanics, and to physics students who have to unlearn what they were told as laypersons.

Quantum physics provides a more comprehensive view of reality than does classical physics. Classical physics, which includes both special and general relativity, are very accurate approximations of the behavior of "real" physical systems. However, the determinism of classical physics is an illusion that results from the aggregate behavior of vast numbers of individual quanta. It is all a matter of the statistical behavior of very large numbers of samples. It is recognized that classical physics is incomplete at the microscopic and probably also at the macroscopic scale. This suggests that unification of classical and quantum physics may require a rethinking of what we mean by "classical" phenomena.

 

[A. Neumaier]

unification of classical and quantum physics may require a rethinking of what we mean by "classical" phenomena.

Did you also read post #2 in this thread and look at my book? It achieves unification by instead rethinking of what we mean by "quantum" phenomena.

 

[crastinus]

I looked at your book. Fascinating stuff. It's actually kind of exciting, in my opinion.

Since you wanted this thread reserved for the informal discussion of quantum weirdness, is it possible for you to give a sketch of the unified vision of classical-quantum-statistical mechanics your are proposing? I've seen a few posts that do parts of it (Alice and Bob's ignored detailed have profound effects on measurement, etc.), but I don't have quite an adequate idea of how you actually carry the whole thing out. (Maybe I just missed a post, though.)

 

[ddd123]

From the other thread.

"still exhibiting a remarkable variation in foundational concepts among practicing physicists." That makes weirdness not a personal issue any more, but rather something that can be observed across a community of scientists, which is what I think is good about it.

Something like that. But also reconciling QM with physics' "tradition" of pursuing consistency and generality through falsifiable experiments. This seems to have run into a standstill. You can still do things and advance (a lot!) but there's an underlying feeling of incompleteness.

Maybe a way to put it is this: the very fact that nature's behavior was so peculiar as to break this game is weird.

Still, to play devil's advocate to that version of "weirdness", I would point out that classical mechanics supports many different interpretations as well-- is it forces, is it a principle of least action, or is it just the macroscopic correspondence of quantum mechanics?

There's also open problems like the Landau pole, the pre-acceleration and runaway solutions... But somehow these don't seem to bother people much. Newtonian vs. least action seem to be treated as mutually inclusive, not exclusive. You can derive one from the other. QM interpretations are strongly mutually exclusive. Either there's one world or many, either there's a principle of relativity or not, etc...

 

[rkastner]

Since the author of the thread has offered a reference to his interpretation in book form, I'll do the same and offer my interpretation in book form:

www.cambridge.org/9780521764155 (has some technical chapters)

http://www.worldscientific.com/worldscibooks/10.1142/p993 (for the general reader, extends some of the concepts presented in the first book)

It provides physical referents for the formal objects appearing in QM, including the Born Rule, which has been an ad hoc recipe for calculating empirical predictions from the theory. The interpretation also removes some of the 'weirdness' by resolving a major aspect of the measurement problem--specifying what constitutes the measurement transition from a pure to mixed state.

 

[mikeyork]

I'm late to this thread and don't have time to read it all. So, for what it is worth, QM is weird only to those who can't separate reality from observability.

 

[A. Neumaier]

offer my interpretation in book form:

It it available without a paywall?

 

[A. Neumaier]

is it possible for you to give a sketch of the unified vision of classical-quantum-statistical mechanics your are proposing?

You can find something in my Thermal interpretation FAQ and in Chapter 10 of my online book mentioned in post #2. I plan to write an Insight article here on PF covering the main aspects, but haven't found yet the time for it.

 

[crastinus]

Great. Close enough to what I was looking for. Thanks!

 

[Ken G]

Newtonian vs. least action seem to be treated as mutually inclusive, not exclusive. You can derive one from the other. QM interpretations are strongly mutually exclusive. Either there's one world or many, either there's a principle of relativity or not, etc...

Yet since we can regard all of classical mechanics as emergent from quantum mechanics in the macroscopic limit, classical mechanics automatically inherits all the same interpretations as quantum mechanics does. I agree with you that this doesn't seem to bother people much, but that may be only because it has been around for so long that everyone has kind of settled on a local realist view, which ironically, is not allowed in quantum mechanics. That is probably closest to taking the deBroglie-Bohm interpretation, in the limit where macroscopic decoherences in the pilot wave allow its locality violations to be eliminated or ignored. But we could equally well extrapolate into the classical realm the instrumentalism of the Copenhagen interpretation, we would just say that all that exists for us is the outcome of our experiments, and everything else is a kind of mental fabrication. Or, we could equally well extrapolate the many worlds view, and say that any time something occurs that is fundamentally unpredictable, all outcomes occur, but we are only privy to one of them. These interpretations work fine in classical physics, they are simply not the ones adopted by the majority. So I agree with you that what sets quantum interpretations apart is the absence of widespread agreement on the best one, but I wonder if classical physics did not go through a similar phase, long forgotten. Perhaps the physics itself does not get more or less weird as our discoveries advance, we just get used to it and settle on a majority opinion.

 

[ddd123]

If QM is still the culprit, it's a circular argument. But maybe you mean something like: we could have chosen to believe in the Lorentz Ether instead. But since we have a consensus on which was better, SR or LET, we chose mostly unanimously because the latter feels ad-hoc. Here, we have no better alternative, everything feels ad-hoc and you're just shifting the problem.

 

[Ken G]

I'm saying that I suspect eventually a single interpretation of quantum mechanics will rise to the fore, and quantum mechanics will always be framed according to that interpretation, as happened eventually to classical mechanics. Once that happens, it won't seem weird any more, even if it's many worlds-- because that's what people will learn to be the case. Once we all accept something to be the case, it never continues to seem weird-- we now think the universe had an origin, and that's not supposed to be weird, we think time is local and able to be itself dynamical, and that's not supposed to be weird, we think that past determines future, and that's not supposed to be weird, but somehow we get all hung up on where the random elements of quantum mechanics come from-- and that is supposed to be weird. Once an interpretation is settled on, it will be like all the other weird things we've just come to terms with.

I'll give you a prime example of what I mean, and it also comes from quantum mechanics. We often conceptualize white dwarf stars as containing a sea of some 10⁵⁷ identical electrons, and if we like, we can imagine they each occupy a different momentum state (or a pair of electrons, to keep track of spin). Because of the Pauli exclusion principle, this means that an electron undergoing an interaction at one place in that giant star cannot be put into a momentum state that another electron is already in-- even though we don't know where the electron that is already in that state is, we only know it is within several thousand kilometers! There's the grandaddy of all entanglement phenomena right there, a phenomenon that totally shatters the concept of local realism, yet no one even talks about it as strange at all because we've come to terms with it-- we view a white dwarf like a huge molecule, and we know the electrons occupy orbitals, and we're all just fine with it. The weirdness just goes away when there is a common interpretation.

 

[ddd123]

But the winning interpretation emerges for a reason, not arbitrarily, and it's clearly not going to be MWI.

 

[A. Neumaier]

Once an interpretation is settled on, it will be like all the other weird things we've just come to terms with.

The problem with your view is that even after 90 years of quantum mechanics, none of the conventional interpretations looks convincing enough to ''be settled on'' by an overwhelming majority. Why should this ever change?

 

[Ken G]

The problem with your view is that even after 90 years of quantum mechanics, none of the conventional interpretations looks convincing enough to ''be settled on'' by an overwhelming majority. Why should this ever change?

I think you'll find that the proper interpretation of Newtonian mechanics was still very much a matter of discussion 90 years after Newton-- especially in regard to the determinism of that theory. Even today, people don't quite know what to make of chaotic orbits-- in formal mathematical terms, those are still deterministic, but no science experiment could ever establish that they are indeed determined by the initial conditions. Hence, even if quantum mechanics were never necessary, we would still need to debate whether or not classical physics is telling us that the universe is deterministic. Even today, had classical mechanics been the "last word", I wager that a significant fraction of physicists would still regard it as "weird" if the conditions ten seconds after the Big Bang determine, to the minutest detail including what you will have for breakfast tomorrow, everything that has happened since. Weirdness doesn't go away, we just stop thinking about it after awhile.

 

[ddd123]

But you wouldn't have a plethora of conflicting interpretations.

 

[Ken G]

I'm saying we would have a plethora of conflicting classical-mechanics interpretations (such as, whether or not the universe is deterministic), had classical mechanics not been superceded by quantum mechanics. It is always the most fundamental theory that we try to interpret, because we think that's where the "fundamental interpretation" lives. It's just the nature of the beast, it has always been that way in physics. Action at a distance, or not? Material particles, or fields? Aether, or no? GR or QM? At any point in the history of physics, if you want to find where the debate on interpretations was, just look at whatever was regarded as the most fundamental theory of that age.

 

[ddd123]

Fair enough. It's notable though that the pre-quantum mood was that of "we've mostly figured it out", then came the radical crisis of quantum discoveries. Although it was debatable even then, say, determinism wasn't really menaced because those you mention are only theoretical problems, whereas QM manifests in real experiments.

 

[Ken G]

I agree the loss of local realism seems to have had more in the way of aftershocks that the loss of the aether. People dropped Poincare's aether pretty much overnight, but dropping local realism seems weirder. I don't really know why though, both relativity and quantum mechanics have a very satisfactory elegant structure, and neither seems at all like what we experience day to day.

 

[ddd123]

I don't really know why though

Probably because realism was/is the main tenet of the scientific endeavor. You figure out the objective properties of things. So, relativistic space-times are removed from everyday experience but they consist in a very definite objectivity. In a sense they strengthen the realism of science because science convinces us of something that is so intangible: it means it's so powerful. The loss of realism does the opposite.

 

[Ken G]

So the weirdness simply stems from a certain brand of realism. But I don't agree this is the main tenet of science, the main tenet of science is to make sense of observations. So if a certain way of doing that makes us regard science as weird, then get rid of that way of doing it. That's what we did to the aether, and for the same reason.

 

[ddd123]

So the weirdness simply stems from a certain brand of realism. But I don't agree this is the main tenet of science, the main tenet of science is to make sense of observations. So if a certain way of doing that makes us regard science as weird, then get rid of that way of doing it. That's what we did to the aether, and for the same reason.

That's why I wrote "was/is. I can agree it is not the main tenet, but was? I think we can say objectivity isn't the main goal only because we've started doubting we can have it. So we reflected upon that and came out with the more lax requirement of "making sense of observations" (it's a little vague but I think it's not necessarily bad).

 

[Ken G]

Ah I see, I didn't notice the was/is! Yes, I think that's the main point here, what we regard as weird depends on our philosophy, but we should always expect our philosophy to need to change as science advances. So we should expect constant weirdness, and I think that is exactly what the history of science has always been. We tend to focus only on the current weirdnesses as if they were somehow special.

 

[ddd123]

So we should expect constant weirdness

You might see it differently: we should expect increasing weirdness. Since this is related with our intuition, the more we explore phenomena that are distant from us, the weirder it gets for our intuition, and with QM it even altered the very nature of our knowledge of things, something which we didn't think possible.

 

[adeborts]

When do you think your book will be published?
(You state that what is available on the net is just a draft.)

 

[adeborts]

No, the more I think about quantum mechanics, the less weird it is. I have written a whole book about it, without any weirdness; see post #2.

Quantum mechanics is weird only in the eyes of those who take the talk about it too serious and neglect the formal grounding which contains the real meaning.

You state that what is available on the net is only a draft.
When will the book reach the final format and be published?

 

[adeborts]

Sorry for the repetition!
My first inquiry was not immediately posted and I thought it got lost...

 

[A. Neumaier]

When do you think your book will be published?

A revised version is scheduled to be published in fall 2017. I'll probably add a much more polished and complete discussion of nonequilibrium thermodynamics (except for its field theoretic aspects) and take out the stuff on general manifolds. Field theory needs a second book, and I haven't yet a schedule for its publication.

 

[Feeble Wonk]

Yes. It is only surprising and looks probabilistic to us, because we do only know a very small part of its state.

Please forgive my ignorance on this matter, but is determinism a fundamental principle of QFT? I assume that there are a range of conceptual variations regarding quantum fields. While the version you subscribe to is deterministic, are there versions of QFT that are not?

 

[ddd123]

Please forgive my ignorance on this matter, but is determinism a fundamental principle of QFT?

Actually the opposite, non-determinism is fundamental to QFT. It's a theory, if a deterministic underpinning is found to QFT it will be something else. Actually, since QFT seems to prefer locality in some sense, its non-determinism is pretty essential for it not to violate Bell's inequalities: http://arxiv.org/abs/hep-th/0205105 .

 

[A. Neumaier]

While the version you subscribe to is deterministic, are there versions of QFT that are not?

Most of QFT is applied only to small systems, in which case it is probabilisitc like any (classical or quantum) model that excludes part of the full dynamics from its set of relevant observables.
Whether the full universe (the only system containing us not coupled to an environment) is or is not deterministic is unknown. I believe that it may be taken as deterministic, while those who subscribe to a statistical interpretation would say a quantum model of the universe is meaningless since one cannot replicate it often enough to make statistics about it.

 

[vanhees71]

Well, QFT is also applied to very large systems, and there it's very successful too in at least making it very plausible, why such macroscopic systems usually behave according to classical physics. Particularly QFT of the thermal-equilibrium state is very well developed and very successful in the wide area from condensed-matter physics to cosmology.

 

[rkastner]

It it available without a paywall?

Sorry, I just saw this. You can find a lot of free material on PTI on my blog:
transactionalinterpretation.org

 

[A. Neumaier]

Particularly QFT of the thermal-equilibrium state is very well developed

But it is determinsitic in the thermodynamic limit, and no trace of probabilities is left.

 

[stevendaryl]

But it is determinisitic in the thermodynamic limit, and no trace of probabilities is left.

I don't find that completely satisfying. If you treat Brownian motion using statistical mechanics, then it's deterministic. If you analyze a dust particle suspended in a liquid, your statistical mechanics will give a probability distribution for the location of the particle as a function of time, and that distribution evolves deterministically. But of course, if you're actually looking at a dust particle under a microscope, you'll see it jerk around nondeterministically.

In classical mechanics, we have a theory explaining the actual observation (the dust particle moves when a molecule of the liquid collides with it), as well as the statistical mechanics description. If you only had the statistical mechanics, I would consider the theory incomplete.