Criteria for a good quantum interpretation

[Fra]

What else should I consider "real" as a physicist?

All we need is a stable illusion. Actualy reality is grossly overrated, and an illusion itself.

In the speculative economy, one can start what is the real value of things and what's inflated expectations? The truth is, no one cares and it makes no difference. As long as everyone has the same illusion, we have a working game, and we make money. You just have to stay on top of whatever the illusion is.

As long as all agents has the same illusion of the rules of the game, they will coexist in harmony. The question is more from point of view of physics, how does stable illusions of law emerge? And how does illusions of law explain actions? And how does all this explain the population of agents encoding these illusions? Answer that and I am happy, even without "reality".

/Fredrik

 

[atyy]

Matt Leifer gives criteria that any good quantum interpretation should satisfy.
http://mattleifer.info/2006/06/28/p...doA53UMty42JP5dADhA5SDxRjaTMNPkq1i9Ag3WPCwB5Q

So the only interpretation surviving (especially after "No facticious sample spaces") is Valentini's version of dBB?

 

[PeterDonis]

I find it interesting that Leifer mentions Bell's Theorem and the Kochen-Specker Theorem, but not the PBR Theorem (IIRC Leifer is one of the authors of a review paper on this theorem that was discussed here on PF some time ago). Shouldn't that be on the list of theorems that an interpretation has to deal with?

 

[Quantumental]

I find it interesting that Leifer mentions Bell's Theorem and the Kochen-Specker Theorem, but not the PBR Theorem (IIRC Leifer is one of the authors of a review paper on this theorem that was discussed here on PF some time ago). Shouldn't that be on the list of theorems that an interpretation has to deal with?

PBR was not even conceived at the time (2006) when Leifer wrote this piece up; ought to explain the gap. I know, based on following his papers since then, it would certainly look quite a bit different anno 2021

 

[PeterDonis]

PBR was not even conceived at the time (2006) when Leifer wrote this piece up

Ah, I didn't see the date on Leifer's article. Yes, I expect there would be plenty of changes if he did an update.

 

[atyy]

PBR was not even conceived at the time (2006) when Leifer wrote this piece up; ought to explain the gap. I know, based on following his papers since then, it would certainly look quite a bit different anno 2021

He knew about it, but left it out to rule out retrocausation, thereby proving it.

 

[bhobba]

But as he warns, are you prepared to face the later challenges? In particular, are you prepared then to say that the Moon is not there when nobody observes it? If you are not prepared for that, then actually Matt would not allow you to say what you said above.

I think that issue is at least very close to being solved, if it has not already, with detailed accounts of how the classical world emerges from coarse graining as detailed by Gell-Mann, Hartle and others. I have read just before he died Feynman was converted to the view as well eg:
http://spkurdyumov.ru/uploads/2013/08/gellman.pdf
'The place of classical physics in a quantum universe is correctly understood as a property of a particular class of sets of decoherent coarse-grained alternative histories, the quasiclassical realms. In particular, the limits of a quasiclassical description can be explored. Dechoherence may fail if the graining is too fine. Predictability is limited by quantum noise and by the major branchings that arise from the amplification of quantum phenomena as in a measurement situation. Finally, we cannot expect a quasiclassical description of the universe in its earliest moments where the very geometry of spacetime may be undergoing large quantum fluctuations'

In the classical world things do behave in a common-sense way - the moon is really there when you are not looking etc.

I, these days, think QM, like all physical theories, is a model - but a peculiar one in that we do not have direct experience with what it is modeling - we only have direct experience with the classical world. Certainly I believe, as most people do, that the classical world is objectively real and external from us. I have no reason to believe the quantum world is not the same - but since we have no direct experience of it such is not as certain. But we do have a mathematical model of it grounded in what we do have direct experience with - the classical world. For example experimental observations are very real and QM allows us to predict those - but the moon and other macro objects also are, using coarse raining. I do think while we have the broad outlines of such a view, more work needs to be done. Omnes in his book Understanding Quantum Mechanics mentions we are missing the proof of a few key theorems for example. What I do firmly believe is progress on the issue is being made and eventually will be fully resolved - but there may indeed be surprises along the way.

I did find an interesting overview article on the issues involved:
https://www.researchgate.net/publication/335869303_Understanding_quantum_mechanics_a_review_and_synthesis_in_precise_language

Thanks
Bill

 

[bhobba]

Within physics, there is no need for a quantum interpretation beyond the instrumentalist minimal interpretation (so to say “extreme operationalism”)

Of course there is no need - and indeed a hero of many here (including me), Dirac, would hold a similar view. But it leaves open an interesting question - how does the classical world that we experience everyday emerge from QM? Operationalism simply assumes it does, and we interpret QM by 'operationalism' in that world. Coarse graining research by Gell-Mann, Hartel and others has given us insights into that - and may have even resolved it. With that in hand we can analyse what is going on in 'extreme operationalism' to gain deeper insights into QM. Surely that is a worthwhile undertaking? As I mentioned in another post, QM, like all physical theories, is a mathematical model - but of a realm we do not have direct experience with. We do have direct experience with the world around us - and the operationalist view gives the link - but just assumes there is a link - no detail of it. If we can understand how that world emerges, and what is happening in that 'link' purely in terms of the mathematical model that is QM, then I contend progress has been made in making QM less mysterious. We do not need to do it to understand QM, but it will shed light on it.

I gave one link to the 'program' previously - here is another:
https://arxiv.org/pdf/1905.05859.pdf

Thanks
Bill

 

[Demystifier]

I find it interesting that Leifer mentions Bell's Theorem and the Kochen-Specker Theorem, but not the PBR Theorem (IIRC Leifer is one of the authors of a review paper on this theorem that was discussed here on PF some time ago). Shouldn't that be on the list of theorems that an interpretation has to deal with?

He wrote it before the PBR theorem existed. The P from PBR was a teenager at that time.

EDIT: Ah, now I've seen that @Quantumental already answered it.

 

[Demystifier]

Within physics, there is no need for a quantum interpretation beyond the instrumentalist minimal interpretation

Maybe physics doesn't need it, but physicists obviously do.

 

[martinbn]

Maybe physics doesn't need it, but physicists obviously do.

Physicists or philosophers?

 

[Lord Jestocost]

But it leaves open an interesting question - how does the classical world that we experience everyday emerge from QM?

Is there a “classical” world? Following the purely quantum mechanical von Neumann measurement chain, nothing emerges as long as we regard all chain links as pure physical systems.

 

[Cobul]

I don't agree with this. It's not meaningless for a macroscopic object. That is the fallacy. A statement about the macroscopic world is not meaningless because you can't pin it down precisely quantum-mechanically. QM does not have a monopoly on meaningful statements.

And what quantum interpretations deny the reality of unmeasured macroscopic objects? How do you make the wall unmeasured so it can be uncreated?

 

[WernerQH]

A good theory shouldn't need an interpretation. Do we have an interpretation of electrodynamics? Or, for those who have been told that every theory needs an interpretation: the interpretation should be obvious. Which means that there should be a direct correspondence between the basic concepts of the theory and the real world.

Most physicists today wouldn't hesitate to call electric fields real. But for Maxwell an electric field was a theoretical construct describing mechanical stresses in the ether. Since then the ether has vanished, but the electromagnetic field persists like the grin of the Cheshire cat.

Until 1905 electrodynamics was a rather peculiar, not to say weird, theory describing an hypothetical ether with contradictory properties: it was both solid, to allow transverse waves, and fluid, to allow vortex lines to form. Sticking to Maxwell's equations one could safely ignore the conceptual problems. Today, QT is routinely applied without giving a damn about backwaters like the "measurement problem".

In the case of Maxwell's theory it took more than four decades to jettison its superfluous metaphysical baggage. My feeling is that, after more than nine decades, QT still carries a similar unnecessary burden. We still talk of "quantum objects" with conflicting wave and particle properties. A good theory should clearly say what it is about. Saying "QM is about quantum particles and measurements on them" is like saying "Electrodynamics is the theory of the ether".

 

[PeroK]

We still talk of "quantum objects" with conflicting wave and particle properties.

Quantum objects are governed by their wavefunction leading to a resolution of what were previously (before QT) seen as conflicting wave and particle properties. QT resolved this pre-existing conflict.

 

[AlexCaledin]

Let's say, QM (Feynman variant) is simply the math underlying the least action principle, extending itself to the particles behavior.

 

[Demystifier]

Physicists or philosophers?

Yes.

 

[Demystifier]

In the case of Maxwell's theory it took more than four decades to jettison its superfluous metaphysical baggage. My feeling is that, after more than nine decades, QT still carries a similar unnecessary burden. We still talk of "quantum objects" with conflicting wave and particle properties. A good theory should clearly say what it is about. Saying "QM is about quantum particles and measurements on them" is like saying "Electrodynamics is the theory of the ether".

So what is quantum theory really about?

 

[bhobba]

Is there a “classical” world? Following the purely quantum mechanical von Neumann measurement chain, nothing emerges as long as we regard all chain links as pure physical systems.

Well we certainly experience one day to day. The idea is not to challenge that chain, but to show using coarse graining a 'quasi classical' world can be defined that acts like that classical world. I have not kept up with the technical details of that program in recent years, but when I investigated it last there were still issues in showing that world is the classical world we experience. Certainly I think it has illuminated the so called quantum classical cut. In the 'extreme instrumentalist' view it must be accepted the instruments are themselves quantum. What exactly makes a quantum object an instrument? Of course that view simply accepts they exist and we can in practice tell what they are. That is simple and easy to conceptually grasp. But it is reasonable to want to be more precise. You are correct in that in order to have a viable interpretation you do not need to - but there is nothing wrong with seeing where such investigations lead.

Thanks
Bill

 

[bhobba]

So what is quantum theory really about?

We have no direct experience with the quantum world. So I would say it is a mathematical model about that world that has connections to the world we day to day experience. We can experimentally check the validity of the theory by checking it is accord with what happens in our everyday world.

Thanks
Bill

 

[PeroK]

We have no direct experience with the quantum world. So I would say it is a mathematical model about that world that has connections to the world we day to day experience. We can experimentally check the validity of the theory by checking it is accord with what happens in our everyday world.

Thanks
Bill

I think the question was in response to the lamentations of post #44.

 

[WernerQH]

Quantum objects are governed by their wavefunction leading to a resolution of what were previously (before QT) seen as conflicting wave and particle properties. QT resolved this pre-existing conflict.

I don't see how it resolves it. Is the photon a wave when it travels through the slits that instantly collapses to a point on the detector screen?

 

[PeroK]

I don't see how it resolves it.

Then you need to learn some QM. Or, in the case of light, QED. E.g.

https://en.wikipedia.org/wiki/QED:_The_Strange_Theory_of_Light_and_Matter

 

[WernerQH]

Then you need to learn some QM. Or, in the case of light, QED.

If you think that the term "wave function" solves the problem, rather than giving it just a different name, then you've had too big a dose of "tranquilizing philosophy".

 

[PeroK]

If you think that the term "wave function" solves the problem, rather than giving it just a different name, then you've had too big a dose of "tranquilizing philosophy".

If by "tranquilizing philosophy" you mean studying QM as a university-level academic subject, then yes, I'm guilty of that!

 

[WernerQH]

So what is quantum theory really about?

Good question! I think that the Aspect et al. experiments offer an important clue. And we should think about how calculations in QED are actually done, and not how the equations are supposedly derived.

 

[bhobba]

I think the question was in response to the lamentations of post #44.

That being the case I think you have set yourself up for a whole world of hurt. The minimalist statistical interpretation, or extreme instrumentalist view, are quite adequate to do QM. If you want to investigate issues like how a classical world emerges and get a better understanding of that minimalist interpretation then that is fine. But if you want something beyond that then the question that was posed - is it physics or philosophy starts to become apparent. That is when you enter the world of 'hurt'. From a personal viewpoint, it is amazing the views those of a more philosophical bent have - many really like trying to bring consciousness into it. I pointed one to a lecture Jack Sarfatti gave:


Philosophers were in raptures - Jack thought my views a waste of time.

Thanks
Bill

 

[Lord Jestocost]

So what is quantum theory really about?

To my mind, quantum theory is pointing to the metaphysics of neutral monism.

 

[Fra]

I'm not used to the philosophical terms in this context, googling this gets me stuff about human mind...

To my mind, quantum theory is pointing to the metaphysics of neutral monism.

...but I assume physicists would interpret the abstraction of "neural monism" as something alone the line "what the "material" observer "knows", is indistinguishable from what the observer is". Ie. the state of matter, encodes the observers state. Ie. they are two sides of the same coin, and you do not "construct one from the other", they emerge together.

Is this what you effectively mean with neutral monism in the context of QM?

/Fredrik

 

[RUTA]

In the case of Maxwell's theory it took more than four decades to jettison its superfluous metaphysical baggage. My feeling is that, after more than nine decades, QT still carries a similar unnecessary burden. We still talk of "quantum objects" with conflicting wave and particle properties. A good theory should clearly say what it is about. Saying "QM is about quantum particles and measurements on them" is like saying "Electrodynamics is the theory of the ether".

Here is a quote from Bell:

I think the problems and puzzles we are dealing with here will be cleared up, and ... our descendants will look back on us with the same kind of superiority as we now are tempted to feel when we look at people in the late nineteenth century who worried about the ether. And Michelson-Morley .., the puzzles seemed insoluble to them. And came Einstein in nineteen five, and now every schoolboy learns it and feels .. superior to those old guys. Now, it's my feeling that all this action at a distance and no action at a distance business will go the same way. But someone will come up with the answer, with a reasonable way of looking at these things. If we are lucky it will be to some big new development like the theory of relativity.

Now read Section 4 of this paper: https://www.mdpi.com/1099-4300/23/1/114/htm