[GregBuchholz]

I've liked:

Clearing up Mysteries - The Original Goal http://bayes.wustl.edu/etj/articles/cmystery.pdf

" ...we must keep in mind that Einstein's thinking is always on the ontological level; the purpose of the EPR argument was to show that the QM state vector cannot be a representation of the "real physical situation" of a system. Bohr had never claimed that it was, although his strange way of expressing himself often led others to think that he was claiming this.

From his reply to EPR, we find that Bohr's position was like this:

"You may decide, of your own free will, which experiment to do. If you do experiment E1 you will get result R1. If you do E2 you will get R2. Since it is fundamentally impossible to do both on the same system, and the present theory correctly predicts the results of either, how can you say that the theory is incomplete? What more can one ask of a theory?"

While it is easy to understand and agree with this on the epistemological level, the answer that I and many others would give is that we expect a physical theory to do more than merely predict experimental results in the manner of an empirical equation; we want to come down to Einstein's ontological level and understand what is happening when an atom emits light, when a spin enters a Stern-Gerlach magnet, etc. The Copenhagen theory, having no answer to any question of the form: "What is really happening when - - - ?", forbids us to ask such questions and tries to persuade us that it is philosophically naive to want to know what is happening. But I do want to know, and I do not think this is naive; and so for me QM is not a physical theory at all, only an empty mathematical shell in which a future theory may, perhaps, be built."

[sedachv]

My favorite quote on the topic is from chapter 10 of Jaynes' Probability Theory: (http://omega.albany.edu:8008/ETJ-PS/cc10i.ps)

"Biologists have a mechanistic picture of the world because, being trained to believe in causes, they continue to search for them and find them. Quantum physicists have only probability laws because for two generations we have been indoctrinated not to believe in causes - and so we have stopped looking for them. Indeed, any attempt to search for the causes of microphenomena is met with scorn and a charge of professional incompetence and "obsolete mechanistic materialism." Therefore, to explain the indeterminacy in current quantum theory we need not suppose there is any indeterminacy in Nature; the mental attitude of quantum physicists is already sufficient to guarantee it."

[abdullahkhalids]

You are misrepresenting physicists. There have been many many different attempts to talk about quantum theory on an ontological level. Case in point, the widely debated interpretations: copenhagen, many worlds, bohemian etc.

However, one reason that physicists don't spend too much time thinking about what quantum theory really means (besides laziness and bad science) is because we know that quantum theory is not the ultimate theory of reality. Why try to force ontology on a theory that can not even answer all empirical questions without ad hoc additions (standard model of particle physics) or force mating with another theory (general relativity)? We are all waiting for a better theory of physics. Of course rewriting the quantum theory in different forms, like this attempt, might help in getting there.

[cabinpark]

I agree and disagree with what you're saying. I agree it is laziness and bad science that physicists stopped caring about the philosophical underpinnings of quantum mechanics but I disagree that it was because quantum mechanics not being the ultimate theory.

The reason most physicists don't think about the philosophical underpinnings has more to do with the way quantum mechanics is taught. Many of the founders were interested in the philosophical questions but after WWII you can see a sharp decrease in that aspect and more of the hardcore calculation and the philosophy kind of disappeared. Here [1] is a great talk that discusses this very point. Unfortunate for quantum mechanics because understanding the philosophical underpinnings is critical to understanding what quantum mechanics says and doesn't say. But, thanks to things like quantum computing and better experiments, interpretations is becoming more mainstream since there are experiments being planned (at least when I was heavily involved in the area in 2010) that would be able to test some of the claims made by different interpretations.

>We are all waiting for a better theory of physics. Of course rewriting the quantum theory in different forms, like this attempt, might help in getting there.

To me this is a contradiction. If we are all waiting for a better theory, then why are we re-writing the theory? A critical part of all the interpretations I've encountered [2] is making different ontological claims about quantum mechanics. Take Bohmian, which posits a guiding wave. Sure we can make some of the mathematics nicer, but we can't go very far without explaining what this 'guiding wave' is, which itself is rather ad hoc. Plus, how do we rectify it with Bell's theorem on hidden variables? To me, we can't really begin re-writing quantum mechanics without inevitably running into ontological statements.

But I still agree with your premise. I believe that by pushing the limits of quantum mechanics both scientifically and philosophically we will get a better grasp of what things to look for / where to look, for a deeper theory. Case in point, wavefunction collapse. Some might consider it a huge problem of quantum mechanics, but if you take a different ontological view, wavefunction collapse isn't that interesting or important. So maybe wavefunction collapse isn't as important and trying to develop a theory that doesn't have it is the wrong idea.

[1] http://pirsa.org/08090000/ [2] http://pirsa.org/C10002

[abdullahkhalids]

I agree that progress in experimental abilities and QC is really forcing physicists to think carefully about what QM means. In fact the month of May saw three papers by major physicists about these deeper issues in QM [1,2,3] In my own humble capacity as a graduate student in physics, my research is about clearly understanding the divide between classical and quantum physics.

On the rewriting of theory, I should have been clearer. I meant that when you rewrite the theory you should think about ontology. Differences in ontology between different rewrites, as well as interpretations of those rewrites, will point to how quantum theory can be generalized.

I agree completely that quantum mechanics is taught horribly. Strangest of all are introductory quantum/modern physics courses that are meant to give students an intuition of quantum theory use the Copanhagen interpretation -the one that says the least about ontology and emphasizes calculations and empiricism.

I still stand behind my central claim. Let me be clearer. The mathematical model of classical physics says something about physical reality. The mathematical model of quantum mechanics says something very different about reality. Even if there are disagreements, we all agree that the ontology of classical physics is very much incorrect. Extrapolating from this I claim that the next theory of physics will have an ontology that will look nothing like that of quantum theory. As I have said previously, the ontology of quantum theory can be a means to an end (the next theory), but not the end itself.

[1] http://arxiv.org/abs/1405.1548 [2] http://arxiv.org/abs/1405.3483 [3] http://arxiv.org/abs/1405.7577

[thedufer]

My understanding is that the pilot wave theory is a non-local hidden variable theory, which doesn't contradict Bell's theorem at all. Of course, this presents ftl information transfer, presumed to be impossible, which is part of the reason such theories have been unpopular for so long.

[danbruc]

Non-locality does not imply the possibility of FTL information transfer - a theory can be non-local but make exploiting the non-locality impossible.

[adamgravitis]

This is a vitally important point. Many people still naively believe entanglement allows communication. Simultaneous randomness doesn't permit a signal.

[GregBuchholz]

>Plus, how do we rectify it with Bell's theorem on hidden variables?

I'm not a physicist, but I've always wondered about Caroline Thompson's work, like:

"Chaotic Ball" model, local realism and the Bell test loopholes

http://arxiv.org/abs/quant-ph/0210150

[spacehome]

I disagree completely. Putting quantum mechanics on firm ontological footing will probably aid developing intuition for whatever the real truth of the matter is.

Note Einstein developed his theories of relativity based on very scant evidence just by contemplating the aesthetics of what physics should be. I think there's a big lesson to be learned here - that some heuristics are generalizable.

[abdullahkhalids]

I agree with you. Read my reply to the other comment. I should have been clearer in my first comment.

[GregBuchholz]

>You are misrepresenting physicists.

Small correction. Except for the first two lines of the parent post, the rest is a quote from Jaynes' paper linked above. It may be hard to tell because of the limited formatting options on HN.

[wuliwong]

If that was the case, they will be waiting for eternity. There will never be a complete theory of everything, just ask Godel. :)

[alphydan]

Could it be that you're not prepared for "What is really happening"? It seems like you'r expecting that QM's unintuitive properties will go away with a better theory.

They may, but it doesn't have to be that way. It may just be that reality at that scale is not made of trajectories, balls, and simple causality. As evolved monkeys with 5 senses we are used to intuitive concepts like continuity, predictions, trajectories, objects.

Now imagine a world 1,000,000 times smaller. Will it behave, look and feel the same way? Maybe. Let's shrink it 10,000 times again. Now we are at the size of an atom. Does the landscape look familiar? It may be so unfamiliar that trying to shoehorn our monkey intuitive world-view is helpless.

No objects, no concept of position, no matter as "substance occupying a space", no limitations regarding being in different places at the same time. It may well be that things are so different that it's best described as a mathematical abstract world ... because no intuitive structures and behaviours exist there. (Heisenberg has some interesting correspondence with Bohr on the matter)

It would be like trying to search for Mario inside your nintendo. Mario and his physics only live as abstract equations. Taking apart the computer will not show us what Mario's flesh is made of. The analogy can't be taken too far of course, because there is no known "chip" besides the mathematical structure of the universe.

There is plenty of research on quantum reality (from one of my colleagues, for eg. http://arxiv.org/abs/0709.1149), but it may turn out that there isn't an easy "particle does X when it enters Stern-Gerlach". The concept of particle is probably completely inadequate.

[kybernetikos]

I'm not sure how science can expect to answer questions of the form "What is really happening when... ?", since that is entirely unknowable.

Science looks at results and provides useful models. Whether those models are representations of the 'real', or whether the entire universe is actually a bunch of magic pixies who just happen to arrange the universe to look as if it follows a particular theory, or whether the whole thing is a simulation embedded in the real universe which is entirely different are questions not actually accessible to science.

[DanielBMarkham]

This goes back a long ways before QM. Even Newton, observing gravity, concluded that he had no idea why it worked, he could only describe how to numerically model the results of it working.

We've been modeling ever since, hoping that enough pieces of the puzzle come together for a cogent picture to emerge.