With all this writing about the 'quantum problem' and quantum mechanics not making sense, I don't understand why quantum theorists don't take pilot wave theory and the oil droplet experiments more seriously.
It's because the problems mentioned in the article are primarily philosophical in nature and not things most physicists, even quantum physicists, spend actual time researching. For example anything related to the many world interpretation or more generally the measurement problem, would make for a terrible thesis topic, it also probably wouldn't get any funding (Pilot wave theory in particular is explicitly excluded from receiving funding from the NSF, see http://www.mth.kcl.ac.uk/~streater/lostcauses.html). So the only people working on such things are professors well into their tenure and even they will more likely write about such topics during the family summer vacation.
My thesis advisor does get NSF funding and he does Bohmian mechanics. I have a very talented colleague doing this as well and he ended up with tenure recently. But it is a very hard road.
I did a thesis on it which I am quite proud of. But I also left academia proper though more due to my disgust with various aspects of the system unrelated to the discrimination associated with Bohmian mechanics.
To be fair to your point, the successful ones pursuing this either hide out in mathematics departments or keep their mouth shut until well-established.
I can't speak for other quantum theorists, but pilot wave theory does nothing to make multi-particle entanglement less mysterious. It provides a nice story for wave-particle duality, but for a long time it has been apparent that this is not the central mystery of quantum mechanics.
It does focus the discussion clearly on the wave function as defined on configuration space, bringing to the front the importance of position.
But mostly the reason is that if you are going to develop a better theory (namely how relativity and qm work together), then it may be helpful to start on a clear foundation where irrelevant confusions have been eliminated.
For example, the role of operators is derived in pilot wave theory, not assumed. This greatly simplifies the issues of putting quantum mechanics on curved space where the Fourier transform may not be so easily defined, if at all. You do have to worry about the Hamiltonian and its boundary conditions, which is part of the physics of the space, but the relevant measurement operators are derivable from the ported theory.
I believe the Aeon article is referring to pilot wave theory when it talks about Broglie-Bohm, although it does so with almost no explanation, even though it's one of the main threads of the article.
I think the idea of pilot wave theory is really interesting, and that a variant of it could turn out to be more fundamental than our current understanding of quantum physics.
I don't understand why quantum theorists don't take pilot wave theory and the oil droplet experiments more seriously.
This goes back to Einstein, whose main beef with QM actually wasn't indeterminism. Instead, determinism was supposed to be a means to restore locality. Bell's theorem tells us this is doomed to fail, and indeed Bohmian mechanics restores determinism only at the cost of locality.
Even though experiments with walking droplets are an impressive demonstration that wave-particle duality isn't necessarily something mysterious, they don't help to address the issues at the heart QM.
I find it fascinating that there seems to be this assumption that the universe has to be trivially comprehensible to us.
Our brains are an emergent properly of the large scale behaviour of the universe. There is no reason we should even assume we're capable of comprehending the small-scale universe's properties, let alone that they should "make sense" to us.
There's a very good reason we should assume that we're capable of comprehending the universe's properties: we might be right, and there's only one way to find out.
Right, but if we find substantial evidence that the universe is behaving in a way that we can describe mathematically, make accurate predictions based on, but seems intuitively "weird"... maybe that last isn't a reason to dismiss it?
I don't think anyone is dismissing quantum mechanics just because it's intuitively weird. They're continuing to work on it, which is an optimistic strategy.
I think people do dismiss the many-worlds interpretation because it's intuitively weirder than the Copenhagen one, even though it makes a lot more mathematical sense. (It still fails to explain the Born rule, but that's a much smaller lacuna than the collapse mechanism required by the Copenhagen interpretation).
'a lot more mathematical sense'?
No, it'll only make more sense if/when it is able to make testable predictions different from the usual QM predictions.
All interpretations yield the same testable predictions, so the only way to choose between them is to say one is more or less simple/elegant than the other. Just like it's possible to construct Newton's laws of motion in a rotating reference frame, with multiple corrective terms, and end up with exactly the same testable predictions - but that theory is nevertheless in some sense "less true" than Newton's original theory.
I don't think we can have an argument about whether we can generate a description of the universe that agrees with reality until we agree on what "making sense" means in the first place.
Not OP, but I would think it that things make sense when they can be intuited. It's amazing how much we can intuit–people figure out orbital mechanics with enough time playing KSP.
Then there are things which we cannot imagine intuitively, like 5-Dimensional hypercubes, but we can describe them in math quite easily.
What fundamental limitation of human information storage/processing technology would prevent us from "making sense" of the universe at a general level? By "making sense", I mean coming up with a complete and consistent physical model.
Based on previous experiences, I suspect that the universe is governed by relatively simple rules that lead to complex emergent behavior, which would certainly be conducive to our understanding it.
> What fundamental limitation of human information storage/processing technology would prevent us from "making sense" of the universe at a general level? By "making sense", I mean coming up with a complete and consistent physical model.
The nature of that fundamental limitation may escape our grasp by definition. The article at least presents the idea that the strange observations of the quantum mechanical universe may sit outside the range of science. I think there's some merit to the idea that humans, not as "willful" entities, but as groups of particles swept up in a cosmic chain reaction, may face fundamental limitations to the "scope" of what we can grasp about the nature of the universe.
The person you're replying to meant "is intuitive to us" when they said "making sense".
As for systems where it's hard to come up with a complete and consistent model...
- If coin flips were decided by a cryptographic random number generator, it would be intractable for us to extract the seed or even to distinguish the output from true randomness or go-both-ways indexical uncertainty.
- Probably-approximate-correct learning is not possible for all models [1].
- If we're unable to eliminate Boltzmann brains [2] from cosmological predictions, that would seem to imply agents should constantly assign near-certainty to being surrounded by heat death and ignoring that is more of an optimization-for-the-cases-where-you're-not-and-things-matter.
- If the number of rules is larger than the number of atoms in the universe, we're never going to be able to remember them all or write them all down.
I really liked this article, which surprised me. Usually philosophical-ish quantum writings are much worse than this.
The post does a good job of roughly outlining several interpretations, and explaining why they're each a little weird or at least what the common objections are.
Personally, I'm hopeful that quantum computers will shed light on the issue. They make a lot of large-scale experiments possible, or at least significantly easier.
There is a large elephant in the room that was barely touched on in the article: gravity. How does QM relate to gravity? Wikipedia puts it thusly[1]:
Gravity has yet to be successfully included
in a theory of everything. ... Theoretical
physicists have not yet formulated a widely
accepted, consistent theory that combines
general relativity and quantum mechanics.
The incompatibility of the two theories
remains an outstanding problem in the field
of physics.
The best attempt that I've seen so far is from a slashdot[2] discussion:
Your momma so fat even if I'd entangle
with her no information would be able
to leave her event horizon.
Nobody has managed to put gravitation
and QM together yet, and you want to
do it in a your-momma-so-fat-joke? Wow.
I'm not sure it adequately supports its claim that "the debate should already be over", but it's worth reading. It's not science, but when all the interpretations other than collapse models predict the exact same observations, there's only so far the math can take you...
I agree. There is no debate or "problem" as far as quantum physicists are concerned. I'm not sure most of us would call our belief "many worlds", but you'll find very few who think that collapse is a real phenomena or that you cannot describe the world in terms of wave functions.
The author of this article is in a very small minority. Of course, the silent majority is silent because we generally have better things to do than philosophize.
There is a lot of wiggle room in quantum mechanics when it comes to how we perceive things compared to how they are. Minor changes in perception, or looking at a problem even slightly differently could make everything click. A big part of the problem with physics is that our observable universe isn't very observable.
There are a lot of questions we just can't answer until we have the instruments to take measurements at Planck scales, and it's likely that, at those scales, everything that doesn't fit quite right will seem obvious, and everything that niggles at the back of a physicist's brain will be put to rest.
I don't see what the big deal is. Measurement is handled perfectly well by the stochastic master equation, which can be obtained through bayesian inference. Quantum mechanics is still thermodynamicish because we don't really know what a wavefunction IS... I think that's still kind of an issue, but measurement is something we understand just fine.
Louis de Broglie thesis story is pretty fascinating. He wrote a short thesis basically stating that particles can be considered as waves. The examiners thought it was nuts but passed it to Einstein, who basically told them that not only should they reward him his doctorate, but likely a Nobel as well (supposedly).
Then why do you think you have the wherewithal to pronounce that quantum mechanics is fundamentally incorrect?
Seriously. The Standard Model has held up in spite of numerous attempts to break it. Physicists would love to break the Standard Model as it would lead to new, cool stuff.
Even things like hidden variables have been tested for. There aren't missing variables.
Just because something doesn't match your personal experience does not mean it isn't true.
To be fair, it's extremely likely that our conception of quantum mechanics is incomplete. Same with general relativity. One big clue is that we cannot reconcile them with each other; another is that there seem to be vast quantities in the universe--dark energy, dark matter--for which we do not have a solid theory.
That said, these problems are probably not going to be resolved by HN posters thinking about things abstractly. They're going to be solved (if they are ever solved) by subject-matter experts working very hard.
> Then why do you think you have the wherewithal to pronounce that quantum mechanics is fundamentally incorrect?
I didn't; I wrote that I suspect that it is.
As another notes, the inability to merge quantum theory and relativity indicates that there's something we're not accounting for. Given how comprehensive both of those theories are, I suspect that the fix which accounts for all the observed evidence will be something else entirely.
Ptolemaic epicycles looked iron-clad for centuries; the successfully predicted observed reality for quite a long time, and (IIRC) even when folks started supposing that they might need tweaking, it looked like still more epicycles might save the day.
On the other hand, there can be another explanation for the interference pattern that appears in the double slit experiment.
One such explanation might be the wavy nature of spacetime itself: any excitation of the medium called 'spacetime' maybe introduces ripples in that medium, causing the behavior of particles to seem as probabilistic, whereas in reality it is not, it is simply chaotic in nature.
This makes much more sense than the concept of a particle being a wave until the wave collapses.
And this theory ties in perfectly with relativity and gravity: particles create spacetime ripples just like any other body does. With this explanation, there is no need for multiple universes and other strange things. The hidden variables might be the universe itself after all.
Michelson and Morley called, they want their interferometer back. (In case this is too much of an in-joke: your theory was experimentally proven to be false more than a century ago.)
The thing that people forget is that epicycles were right, at the time. Working physicists used them, because they gave accurate predictions, and (unless they were specificly looking at that particular problem) got on with their lives. It was only when new experimental evidence came in (Kepler's observations) that progress was made. People who pontificated about the problem of the epicycles were wasting their time.
Also QM (in many-worlds form) is literally the most elegant scientific theory ever. It is a thing of staggering beauty, and to my eyes far more obviously true, far less epicycle-ey, than e.g. relativity.
http://www.wired.com/2014/06/the-new-quantum-reality/
Also, having people with expertise in other fields (fluid dynamics in this case) look at the problem is exactly what can create progress.