Ontology is to quantum theory what hardware is to computation theory

[lightarrow]

The two types of physicists are somewhat like the two types of computer scientists; those who care about hardware and those who don't.

If, in QM, the "hardware" really existed, I would be realist

--
lightarrow

 

[Demystifier]

Its published in a peer reviewed book!

This link gives me a page in German with a password requirement, without any info about the book. Is there another link, like Amazon's?

 

[vanhees71]

I'd like to come back to this point:

I do not think you are in the position to determine what is and is not the meaning of the wave function. If it turns out from experiments that it also has another meaning, you'd have to accept it I suppose. And interference is due to the wavefunction, doesn't it have a meaning there as well?

In nearly 100 years no such other meaning ever materialized. That's the point of my argument. There were strong attempts to somehow circumvent the conclusion that Nature behaves irreducibly random from the very beginning of Born's probability interpretation, and all these attempts failed. The strongest argument against it was that what was vaguely defined in the infamous EPR paper and was much clarified by Einstein in his Dialectica article of 1948, but also this was refuted by the work of Bell and subsequently the experimental realization of the corresponding tests of Bell's inequality. Today it's very clear that Q(F)T is right and socalled local realistic theories are wrong. Together with the fact that relativistic local (=microcausal) QFT is, well, local "realism" must be refuted, i.e., these tests clearly show that the values of observables are not necessarily determined, if the system is not prepared in a state, where they are determined, and thus measurements on quantum systems have to be described by probabilities and statistics.

I follow the consistent history interpretation, that wavefunction collapse is just entanglement with the macroscopic measurement device. That means your measurements of observables are merely wavefunctions entangled with a macroscopic object. Due to that entanglement, as far as I understand the interpretation, the Schrodinger equation squashes the wavefunction to a small point-like classical value of the quantum property. But the essence of what it is is still a wavefunction. In my definition of what is real, the entanglement in fact means that "the value of the measured observable" is not independent of the state of the measuring device so it is only real if you word it as "the value of the observable as measured by the measuring device" which then should be interpreted as "the wavefunction is [some formula] in the device and [the value] of the measured object" but then described as density matrix.

This is all true (although I'd not talk about "the wave function" but about "the quantum state"). For all this I don't need any interpretation besides the minimal statistical one.

I thought that's also what quantum physics tells, that classical reality is dependent on the measurement setting, isn't that right?

"Classical reality" is an emergent phenomenon and originates from looking at coarse-grained collective observables, which tend to behave classical. If you look in more detail, you can also observe quantum phenomena on macroscopic objects. One of the most impressive observations is the observation of quantum fluctuations of the mirrors of the LIGO experiment, which are objects of mass in the 10kg range.

But as I see it: quantum reality, the wavefunction, is not measurable without affecting it but all the more real.

I don't know, what you mean by "quantum reality". The wave function itself is not measurable. You can only do statistics on ensembles and check the predictions for the probabilities of the outcome of these measurements.

 

[Lord Jestocost]

P. A. M. Dirac in “The Evolution of the Physicist’s Picture of Nature” (Scientific American Vol. 208, No. 5 (1963)):

“….. That is how quantum mechanics was discovered. It led to a drastic change in the physicist’s picture of the world, perhaps the biggest that has yet taken place. This change comes from our having to give up the deterministic picture we had always taken for granted. We are led to a theory that does not predict with certainty what is going to happen in the future but gives us information only about the probability of occurrence of various events. This giving up of determinacy has been a very controversial subject, and some people do not like it at all. Einstein in particular never liked it.”

 

[Demystifier]

In this debate, Tim Maudlin defends more or less Demystifier's position, while Lev Vaidman defends an idea that I personally first learned about from A. Neumaier's book.

In this video, it was not clear to me what position Lev defends, it looked like some vague heuristic standard textbook QM to me. It seems to me that he was trying to say: Tim, there is nothing wrong with your perspective, it makes perfect sense, but other people have different perspectives and their perspectives make perfect sense too.

In other discussions, Lev is quite eclectic about quantum interpretations: sometimes he defends standard QM, sometimes many worlds, sometimes Bohmian trajectories, and sometimes his weak values and the two-state interpretation.

 

[vanhees71]

In other words as many "interpreters" he confuses the subject rather than clarifying it. That's against the scientific goal of making "things as simple as possible, but not simpler".

 

[Fra]

P. A. M. Dirac in “The Evolution of the Physicist’s Picture of Nature” (Scientific American Vol. 208, No. 5 (1963)):

“….. That is how quantum mechanics was discovered. It led to a drastic change in the physicist’s picture of the world, perhaps the biggest that has yet taken place. This change comes from our having to give up the deterministic picture we had always taken for granted. We are led to a theory that does not predict with certainty what is going to happen in the future but gives us information only about the probability of occurrence of various events. This giving up of determinacy has been a very controversial subject, and some people do not like it at all. Einstein in particular never liked it.”

Unfortinately the revolution is not complete from the perspective of inference as we still have the exact same deterministic picture (newtonian paradigm); with

timeless statespace
timeless evolution rules (hamiltonian)

The difference is that we went from (q,p) to the quantum state.

But both "ontologies" are given, rather than explained/inferred.

So we still hang onto a deterministic picture of dynamical law. Here QM is not one bit more satisfactory than classical mechanics. Its just that its more annoying in QM, because I have much higher expectations on QM than I ever had on classical mechanics, so the fact that its half baked is annoying. The bigger part of the revolution is still ahead I am sure!

/Fredrik

 

[Demystifier]

In other words as many "interpreters" he confuses the subject rather than clarifying it. That's against the scientific goal of making "things as simple as possible, but not simpler".

In your opinion, did Einstein himself followed his rule of explaining "things as simple as possible, but not simpler"?

 

[vanhees71]

I think so. His papers are examples of clarity and masterful scientific prose.

 

[martinbn]

In this video, it was not clear to me what position Lev defends, it looked like some vague heuristic standard textbook QM to me. It seems to me that he was trying to say: Tim, there is nothing wrong with your perspective, it makes perfect sense, but other people have different perspectives and their perspectives make perfect sense too.

In other discussions, Lev is quite eclectic about quantum interpretations: sometimes he defends standard QM, sometimes many worlds, sometimes Bohmian trajectories, and sometimes his weak values and the two-state interpretation.

I haven't seen the whole debate, but my impression was that Lev didn't exactly know what Tim meant by a beable and was saying that you don't need it, all the information is already in the wave function.

 

[martinbn]

In your opinion, did Einstein himself followed his rule of explaining "things as simple as possible, but not simpler"?

Do you think otherwise? Any examples?

 

[Fra]

I sometimes wonder if Einsteins objections to QM is misinterpreted or have more components? The lack of determinism etc may be a bit simplistic, I guess where was more to it! Especially his quest for a unified field theory?

It's a pity we can't listen to Einstens view of the ideas of holography and dualities between theories of different topologies etc.

Even if SR and GR is not at all a theory of "measurements" - like QM, Einstens seems to make forceful use of thinking tools with gedanken observers, what was "inside the system". And then adding the idea of observer equivalence. And somehow, the construction of SR is the purest example of constructing a theory by enforcing observer equivalence (+ invariant sup speed limit)!! Then when he widened the class of "observer" there was quite a challenge to find the equivalence relations, but via some not as pretty turns he made something up.

But conicidently this is exactly the problem with QM, as alot centeres around the "problem of the observer", and this was as far as I understand, the key constructingprinciple of Relativity as well. But the gedanken observer in QFT, really isn't inside the system, they are at scattering distance. This is a headache, that I would presume Einstein - giving the central use of obserer equivalence and gedankend observers - that would bother him with QM. This way of seeing it, has little todo with "dice" issues, its something much harder to grasp.

/Fredrik

 

[Demystifier]

Do you think otherwise? Any examples?

Many of his papers are quite philosophical (EPR for instance), so I thought @vanhees71 might not think that these papers are very clear.

 

[Demystifier]

I haven't seen the whole debate, but my impression was that Lev didn't exactly know what Tim meant by a beable and was saying that you don't need it, all the information is already in the wave function.

Maybe Lev had a bad day. It looked as if he didn't even understood that a particle entangled with other particles does not have a wave function of the form $\psi(x,y,z)$.

 

[Structure seeker]

That's the point of my argument. There were strong attempts to somehow circumvent the conclusion that Nature behaves irreducibly random from the very beginning of Born's probability interpretation, and all these attempts failed.

Thanks for your reply. It seems to me you are from the perspective of classical reality wording what quantum physics tells, which is kind of logical from science history perspective. But I think with quantum physics we have a deeper level of understanding physics, so I try to look at classical "reality" (your definition of realism) to point out what about the underlying quantum physics (or reality, that is mostly the same to me) it hides. So the "reality" of measured observables are a foundation of classical physics, but in fact they don't give the entire truth (that is quantum physical).

That does not amount to hidden variables: those try to re-establish classical "reality" and determinism. It is instead about considering classical reality as just the only way quanta can be represented in the macro world, while in fact they are in the micro world wavefunctions or whatever QM tells, and governed by the (deterministic) Schrodinger equation. It's nice if for now all we know about it can be described in probabilistic terms.

 

[Demystifier]

I think so. His papers are examples of clarity and masterful scientific prose.

Would you say so also for the EPR paper?

 

[gentzen]

In other discussions, Lev is quite eclectic about quantum interpretations: sometimes he defends standard QM, sometimes many worlds, sometimes Bohmian trajectories, and sometimes his weak values and the two-state interpretation.

In other words as many "interpreters" he confuses the subject rather than clarifying it. That's against the scientific goal of making "things as simple as possible, but not simpler".

I have a very high opinion of Lev Vaidman, and I adore his courage to tell other MWI supporters when they are wrong or "cheat". I didn't hear of "his weak values and the two-state interpretation" before, and have not yet tried to look it up. From my point of view, Lev is certainly somebody who tries to clarify the subject. In the debate, Lev's behavior feels more appropriate than Tim's to me, but I don't know who is right.

I don't understand why vanhees71 is currently so eager to bash philosophers or Lev, or ... I thought of quoting one of the many nasty passages from René Thom/Paraboles et catastrophes (1980), in French ... ("Les remarques de René Thom ne sont pas de nature à lui faire beaucoup d'amis dans les milieux scientifiques.") But then I decided instead to quote from my reply to a very friendly email by S. Goldstein:

You might also be interested in "On the Role of Density Matrices in Bohmian Mechanics"

I will definitely read this one. Also because it is "just" 16 pages. I will be more careful with the two papers with >70 pages. I know from past experience with myself that I invariably fail to read such papers from start to finish, even if the topic really interests me. But hopefully I will already learn more by selective reading and merely browsing them.

The papers in question were

• Quantum Equilibrium and the Origin of Absolute Uncertainty, by D. Dürr, S. Goldstein and N. Zanghì, Journal of Statistical Physics 67, 843-907 (1992), quant-ph/0308039
• Quantum Equilibrium and the Role of Operators as Observables in Quantum Theory, by D. Dürr, S. Goldstein and N. Zanghì, Journal of Statistical Physics 116, 959-1055 (2004), quant-ph/0308038
• On the Role of Density Matrices in Bohmian Mechanics, by D. Dürr, S. Goldstein, R. Tumulka, and N. Zanghì, Foundations of Physics 35, 449-467 (2005), quant-ph/0311127

In the meantime, I did read those 16 pages, and also tried to read and browse the two papers with >70 pages. I enormously enjoyed the short paper (and learned a lot), but on reflection what I learned from the long papers, there was nothing. Really nothing! And that is why I could never have become a philosopher, because they need that ability to read overly wordy and long texts, and draw something substantial from them. And I guess vanhess71 has the same problem, but instead of admitting it, he prefers to bash philosophers.

 

[Demystifier]

I have a very high opinion of Lev Vaidman, and I adore his courage to tell other MWI supporters when they are wrong or "cheat".

Can you be more specific, what did he criticize about MWI?

 

[gentzen]

Can you be more specific, what did he criticize about MWI?

In section "IX. What might be the reasons for the MWI not being in a consensus?" of "Why the Many-Worlds Interpretation?" (https://arxiv.org/abs/2208.04618) he writes:

Negative publicity for the MWI comes from the controversial claims about advantages of the MWI relative to other interpretations, e.g., that the Born Rule can be derived instead of postulated [30]. The claim is natural, because it is not simple to postulate the Born Rule in the MWI, but I believe it is false. In any case, the difficulties of this program reflect negatively on the MWI.
Another source of negative publicity is the controversy generated by presenting MWI as a theory of the universal wave function on configuration space [27], obscuring the connection between ontology and our experience. Avoiding non-separability by moving to configuration space [31], is hardly helpful.
In my view, similar damage comes from an attempt to present MWI in the Heisenberg picture with a controversial claim of bringing separability into quantum mechanics [32]. ...

 

[Fra]

See for example this discussion between Tim Maudlin (a philosopher) and Lev Vaidman (a physicist):

The debate starts at 36:20 and gets stopped at 44:33 (by a moderator). My link above starts at 39:00, where the debate gets hot. In this debate, Tim Maudlin defends more or less Demystifier's position, while Lev Vaidman defends an idea that I personally first learned about from A. Neumaier's book.

Haha... not knowing their faces, just jumping into the video I thought the physicists was the philosopher, but then i googled them and found out it was the other way around as the physicists seems to be the one confused at first :-)

I seems the physicists questions the purpose of a beable (or ontology to connect to the OT). Like what do we need it for?

It seems to me the physicists stances is mainly to stay descriptive, and to just describe the observables (given the states spaces and hamiltonian) indeed the beable seems to serve no purpose. This is I think close to the traditional conservative paradigm. It's certainly not wrong, but it seems like a narrow view.

I think that the motivation for the "local beable"(or some "local ontology" in general not not restrict to bohmain mechanics) is that it potentially adds explanatory value such as explaining WHY the hamiltonian of a composite system is what it is. If you always have the paradigm where the dynamical evolution operator, and the initial conditions are given (put in by hand or whatever). Such "hidden explanation" seems superflous, and seems esotheric or "philosophical" only. But I think when one starts to think about the unificaiton of forces; which is essentially in part to understand how as very small (or energetic) particles interact, the phenomenology changes as you go into lower energy. So from low energy perspective one could say, that quarks is just esotheric stuff that makes no difference - at least until we get up in energy and our theory breaks down.

Is it "philosophical" to expect a smooth coherent theory instead of a pathwork of effective ones with lots of experimentally fitted parameters, or is it part of foundational physics?

/Fredrik

 

[vanhees71]

I have a very high opinion of Lev Vaidman, and I adore his courage to tell other MWI supporters when they are wrong or "cheat". I didn't hear of "his weak values and the two-state interpretation" before, and have not yet tried to look it up. From my point of view, Lev is certainly somebody who tries to clarify the subject. In the debate, Lev's behavior feels more appropriate than Tim's to me, but I don't know who is right.

I don't understand why vanhees71 is currently so eager to bash philosophers or Lev, or ... I thought of quoting one of the many nasty passages from René Thom/Paraboles et catastrophes (1980), in French ... ("Les remarques de René Thom ne sont pas de nature à lui faire beaucoup d'amis dans les milieux scientifiques.") But then I decided instead to quote from my reply to a very friendly email by S. Goldstein:

The papers in question were

In the meantime, I did read those 16 pages, and also tried to read and browse the two papers with >70 pages. I enormously enjoyed the short paper (and learned a lot), but on reflection what I learned from the long papers, there was nothing. Really nothing! And that is why I could never have become a philosopher, because they need that ability to read overly wordy and long texts, and draw something substantial from them. And I guess vanhess71 has the same problem, but instead of admitting it, he prefers to bash philosophers.

The problem is that they make many words with unprecise meaning. You can read as careful philosophical papers as you wish, you never know, what there words really mean. They also use the same words as physicists with a different meaning (e.g., "local" becomes a totally confused notion, while for physicists it simply states that space-like separated events within relativistic theories cannot be causally connected).

 

[Fra]

The problem is that they make many words with unprecise meaning. You can read as careful philosophical papers as you wish, you never know, what there words really mean.

I agree this is bad. But it is also bad when there is precise meaning, but which are rooted in axioms, that you never know how they are precisely related to reality. A balances seem required, and one shoule be aware of the balance.

Mathematicians can define things, physicists postultes often comes with a idealized correspondence to reality. But even pure mathematics often have a purpose beyond physics, it describes all things in nature, I find in particular the history of probability theory in reasoning interesting. Such writings almost "motivates" mathematical axioms of probability theory, which are ultimately a "arbitrary choice", but if you plan to use this to quantify rational reasoning for example, the postualtes need motivation just like postulates in physics, so one can't get away from the philosophy connection I think?

In our ambition to be very precise we assume the cow is spherical: Everyone is happy, even if we know its wrong. But at least we are precise! You can't have both.

/Fredrik

 

[Demystifier]

(e.g., "local" becomes a totally confused notion, while for physicists it simply states that space-like separated events within relativistic theories cannot be causally connected).

So Bell, who introduced a different notion of locality, is not a physicist?
And Anderson, who discovered Anderson localization in condensed matter, is not a physicist?

 

[vanhees71]

Bell didn't introduce a different notion of locality, as you can read in his famous paper where he introduced the Bell inequality for local realistic theories.

I don't know, what Anderson thought with regard to interpretational issues and whether he ever considered relativistic quantum field theory. As a condensed-matter physicist, I guess he usually dealt with non-relativistic QM and non-relativistic QFT, which a priori is a non-local theory.

 

[Demystifier]

I don't know, what Anderson thought with regard to interpretational issues and whether he ever considered relativistic quantum field theory. As a condensed-matter physicist, I guess he usually dealt with non-relativistic QM and non-relativistic QFT, which a priori is a non-local theory.

The point is that the effect bearing his name is called Anderson localization, which is a non-relativistic effect, showing that your statement about what "local" means for physicists is not universally valid. The l-word has different meanings in different physical contexts, whether you like it or not.

 

[vanhees71]

That the physical terminology is also not always consistent is unfortunately true. Of course has "localization" also a meaning in non-relativistic QT. It simply makes that you can prepare states, where the probability to find a particle is sharply peaked around some mean position. This doesn't imply that the theory is local in the usual sense of relativistic QFT. In fact you can localize particles much more within non-relativistic QM than it is possible within relativistic QFT, which is due to pair creation in the latter case: If you try to localize, e.g., an electron at a certain accuarcy of localization you rather create new electron-positron pairs than to better localize the one electron you tried to localize. The typical length scale involved here is the Compton wavelength of the electron, $\lambda_{\text{C}}=h/m_{\text{e}}c$.

 

[A. Neumaier]

This link gives me a page in German with a password requirement, without any info about the book. Is there another link, like Amazon's?

https://www.amazon.com/dp/B0818SNQFY/?tag=pfamazon01-20

 

[Demystifier]

(https://arxiv.org/abs/2208.04618)

I have read the paper and now I better understand how Lev thinks about MWI. In particular, now I better understand the origin of misunderstanding between Lev and Tim in the video.

The crucial part of the paper is section "VII. CONNECTION BETWEEN OUR EXPERIENCE AND THE UNIVERSAL WAVE FUNCTION". In this section Lev does not provide any explanation why we see the world as 3-dimensional. Instead, he just accepts the phenomenological fact that we do, and discusses how to describe this fact with the wave function. Explicitly, he says

"the macroscopic objects are well localised and are not entangled within the world wave function, so every macroscopic object is represented by a product of the wave function of some collective variables defined in three dimensions, times the entangled state in the configuration space of degrees of freedom of the microscopic parts of the object."

While every practical physicist may accept that it is true in a FAPP sense, Lev does not attempt to explain why this is true, and this is what pisses Tim out. Other MWI-ers try to explain it in terms of emergence, but Lev dismisses the emergence program as useless:

"The “emergence” program [25] is not simple, and it is also not needed. In any case, we have very little information about the universal wave function, so the emergence program, even if successful, is of little practical value."

Lev thinks of MWI as a practical tool, not as a deep ontological theory of "everything", which is the exact opposite of what Tim thinks that MWI (or any other interpretation of QM) is supposed to be.

I remember at one conference where I was talking about my relativistic version of Bohmian mechanics, Lev objected that my interpretation does not offer a simple intuitive story of what happens in spacetime. For Lev, the purpose of interpretation is to offer a simple intuitive story, not to propose an ambitious, general, deep and fundamental vision of "truth". For Lev, any interpretation is good, as long as it offers a simple intuitive way of thinking about at least some phenomena.

 

[junjunjun233]

I sometimes wonder if Einsteins objections to QM is misinterpreted or have more components? The lack of determinism etc may be a bit simplistic, I guess where was more to it! Especially his quest for a unified field theory?

It's a pity we can't listen to Einstens view of the ideas of holography and dualities between theories of different topologies etc.

Even if SR and GR is not at all a theory of "measurements" - like QM, Einstens seems to make forceful use of thinking tools with gedanken observers, what was "inside the system". And then adding the idea of observer equivalence. And somehow, the construction of SR is the purest example of constructing a theory by enforcing observer equivalence (+ invariant sup speed limit)!! Then when he widened the class of "observer" there was quite a challenge to find the equivalence relations, but via some not as pretty turns he made something up.

But conicidently this is exactly the problem with QM, as alot centeres around the "problem of the observer", and this was as far as I understand, the key constructingprinciple of Relativity as well. But the gedanken observer in QFT, really isn't inside the system, they are at scattering distance. This is a headache, that I would presume Einstein - giving the central use of obserer equivalence and gedankend observers - that would bother him with QM. This way of seeing it, has little todo with "dice" issues, its something much harder to grasp.

/Fredrik

Einstien is more of geometry, some 'things' and forces - Reimannian. In my field, approximation is what makes reality.. Or should i say enough to fool you down to the pixels for a projected images or vids. We used quasi/ monte carlo to simulate lighting. We cant avoid dispersion and noises even in projection. Our reality is geometry -triangles. Its the only form and shape that behaves well. What im saying is even, in a projected image we cant avoid approximations.. For us, we.. locality is a myth that we put value and holds for it purposes. Like when we stop the machine to render and stick to that quality.

 

[gentzen]

I remember at one conference where I was talking about my relativistic version of Bohmian mechanics, Lev objected that my interpretation does not offer a simple intuitive story of what happens in spacetime. For Lev, the purpose of interpretation is to offer a simple intuitive story, not to propose an ambitious, general, deep and fundamental vision of "truth". For Lev, any interpretation is good, as long as it offers a simple intuitive way of thinking about at least some phenomena.

But the MWI story is that there are many worlds, so if Lev manages to defend this story, he should be fine, no? Of course, you may claim that deep in his heart, Lev does not believe this story himself. But I don't find your evidence for that claim convincing.

Moreover, I find it totally natural that Lev wanted to know which underlying story you are trying to defend.

Lev thinks of MWI as a practical tool, not as a deep ontological theory of "everything", which is the exact opposite of what Tim thinks that MWI (or any other interpretation of QM) is supposed to be.

My personal opinion is that defending the MWI story at some point also includes addressing the problematic behavior of the "Simon Saunders' decoherence/emergence" school. Otherwise, you risk to run into embarrassing situations sooner or later, like for example happened to me in
https://blog.computationalcomplexit...howComment=1667820461887#c8320038219898848189
Don't get me wrong, both David Deutsch and David Wallace made important contributions to current "ambitious, general, deep and fundamental programs," but ...

OK, maybe at this point, I should really find some MWI proponent that explicitly used the word "cheat". My link below starts at 1:05:42, and at 1:06:38 Sean says "... and I do think that even most Everettians kind of cheat when they write down a set of classical variables and then construct a wavefunction using them":


Before, Sean talked about "Quantum Mereology: Factorizing Hilbert Space into Subsystems with Quasi-Classical Dynamics," by Sean M. Carroll, Ashmeet Singh (https://arxiv.org/abs/2005.12938)
He described the crucial point where things go wrong at 21:55 "... interestingly, once you set things up this way and say I am going to start with a generic Hamiltonian, and try to factorize it into system tensor environment so that it has these nice features, a generic Hamiltonian never does have these nice features."