A Criteria for a good quantum interpretation

[PeterDonis]

Special Relativity did not push any specific interpretation forward strongly. But Minkowski did

By "Special Relativity" you appear to mean "what Einstein originally published in 1905". But @bhobba used the phrase "Modern SR", which does not mean that; it means SR as it is taught and practiced today, which does include spacetime geometry as first formulated by Minkowski. Indeed, the particular flat spacetime geometry used in SR today is called "Minkowski spacetime".

Minkowski requires static spacetime

More precisely, it requires a specific static spacetime geometry, that of flat Minkowski spacetime. (There are other static spacetime geometries which are not flat, but curved. These are solutions of the Einstein Field Equation in GR, but are not part of SR.)

in which non-locality leads into inconsistency

No, it doesn't. It's perfectly possible to have a set of measurement results in Minkowski spacetime (or any static spacetime) that violate the Bell inequalities.

What you cannot have in classical relativity in general (not just Minkowski spacetime or even any static spacetime, but any classical spacetime whatever) is more than one measurement result occurring at a single event (point) in the spacetime.

The only difference for Lorentz version is that there is a specific state to reality

If by "state" you mean "preferred frame" or "preferred set of surfaces of simultaneity", this is correct.

Being able to measure superluminal signals

Is not the same thing as "non-locality". Allowing superluminal signaling is actually a stronger condition than just non-locality. Note that standard QFT allows non-locality (violation of the Bell inequalities) but not superluminal signaling.

a static universe interpretation

"Static universe" is not an interpretation. It's a property that a spacetime geometry can either have or not have.

 

[bhobba]

? What could be the problem with introducing a hidden preferred frame into standard QFT which could lead to some "not successful"?

We discuss standard physics here that, by our rules, you agreed to when you signed up, is peer-reviewed papers, textbooks, talks by respected scientists etc. If ever there is any worry about a relevant source, you can write to a mentor. Instead of simply posting such a source to discuss it, as I requested, it indicates these are just ideas you have. Personal theories (unless published in peer-reviewed journals or equivalent) are not allowed. As I said, this aether thing is not an interest of mine, but as you mentioned, Glet would do:
https://www.ilja-schmelzer.de/glet/

I asked for the link between the aether and QFT. Yes GLET is a legit theory about that the aether, now you need to link it to QFT. Dymysifyer, as mentioned by Peter, has papers on that, so they exist. Quantum fields, of which there are many, are not similar to the old idea of light as classical undulations of the aether. QFT obeys Lorentz symmetry, meaning it has the same properties regardless of the inertial reference frame. In contrast, the aether has Galilean symmetry which means if you move relative to the fixed frame of the ether, the fields will be different. LET explains this using the Lorentz hypothesis of length contraction. Internal length contractions of clock components changed time. In modern times we have atomic clocks, so such an explanation will not work. Electric fields are a dielectric shift in the aether - totally at odds with what they are in QFT. These issues and others all need to be explained by LET.

It is not well known that LET is only philosophically different to modern SR any more than my angel theory is only philosophically different to Newton's laws. It makes a specific claim, a claim that is not just philosophy. For it to be a legit physical theory, you need evidence for the existence of the angels. We have none, so it is rejected. The same with the aether.

All you have to do is post up a source so we can discuss your ideas. It is not hard. There are issues here, such as the quantum vacuum is the aether (it isn't), dark matter, or the CBMR etc., is the aether (again, they are not), but to discuss it, you need a source. Or you could ask why the CBMR is not considered the aether, but that would require a new thread - here you are assuming such exists.

The issue of non-locality in QM is different. I was even a bit confused by it until I came across a paper at CERN. The CERN server is not working for me right now, so I can't give a link, but here is the gist. Bell showed, assuming the Kolmogorov axioms, showed QM is incompatible with counterfactual definiteness. If we relax the Kolmogorov axioms requirement, i.e. assume from the start QM is a Generalised Probability Theory, then the whole 'issue' is bypassed. Technically outcome and parameter independence is assumed. See section 3.1.2 of the following:
https://plato.stanford.edu/entries/bell-theorem/

The generalised probability view of QM is fascinating in its own right:
https://en.wikipedia.org/wiki/Generalized_probabilistic_theory

It shows such theories, as a class, allow for many features of QM, with QM perhaps the simplest. This has been my view for a long time. We also have discussed many times on this forum its compatibility with the cluster decomposition property as expressed by Wienberg. But that requires its own thread.

Thanks
Bill

 

[bobob]

"Interpretation" invariably means some scheme to make quantum mechanics behave like classical mechanics even at the expense of introducing very weird potentials and equally weird fictitious entities along with some "explanation" of how these things "really" don't violate other well known physics, like relativity. How about something more simple for starters, like what quantum mechanics is telling you is that you only get to define so much about nature, but you have a choice between mutually exclusive "pieces of information" (to avoid the word "observable") and that even (or obviously, really) nature has nothing else to offer because that's all that actually exists. I think that idea has been around from the very beginning (starting with the earliest ideas of the copenhagen interpretation).

I think the choices come down to accepting that nature can't divulge what doesn't exist (as in simultaneous values for mutually exclusive observables) or believing nature is engaged in some conspiracy to hide that from us and make it only appear as it does for no particular physical reason.

 

[bhobba]

"Interpretation" invariably means some scheme to make quantum mechanics behave like classical mechanics

That is not quite what is going on as well. QM is a theory about observations that occur here in the classical macro world. What is going on between observations is not addressed. This is unsatisfactory to some. Specifically:

1. What is going on when not observed.
2. QM itself is supposed to explain the classical world yet assumes it from the beginning.

Interpretations, for some, are meant to explain those issues. Some use 'classical' ideas, some bizarre stuff like many worlds. Others are minimalist and seek to give meaning to their probabilistic nature, e.g. the Ensemble interpretation. John Baez thinks many of the issues are just a continuation of those in what probability means:
https://math.ucr.edu/home/baez/bayes.html

Thanks
Bill

 

[bobob]

That is not quite what is going on as well. QM is a theory about observations that occur here in the classical macro world. What is going on between observations is not addressed. This is unsatisfactory to some. Specifically:

1. What is going on when not observed.

This is a complete misrepresentation of quantum mechanics which has been made popular in magazines like New Scientist, etc. When you prepare a state, you have choices of the states you can prepare with some properties being mutually exclusive. That exclusivity applies to nature as well and it has nothing to do with an "observer" in the colloquial meaning of that word. If there is one notion that is constantly being repeated, despite being wrong, it's anthropomophizing the word "observer."

2. QM itself is supposed to explain the classical world yet assumes it from the beginning.

You have it backwards. Quantum mechanics from the beginning was modeled on classical mechanics. Why would you not expect quantum mechanics to reduce to classical mechanics as a limiting case? If anything, it's classical mechanics that would be very puzzling as any sort of fundamental explanation of anything. Try explaining the collision between two billiard balls classically at the level of the collision without any approximationslike are usually just assumed (like finite propagation speed through the billiard balls or parameratizations to avoid those infinities like an elastic modulus, which explains nothing). Why is everyone so gung ho to try to make quantum theory into some bastardized version of classical theory when classical theory cannot explain anything without approximating away or parameterizing things which are quantum in origin?

Interpretations, for some, are meant to explain those issues.

Except that none of those interpretations explain anything. They just reflect the interpreter's bias of where they can shift what they perceive as an issue to some place they are comfortable ignoring it. Whatever they perceived as an issue did not go away. They just found a way to make it more palatable while wiping away any physics that there is to be found in whatever they saw as an issue. Here's a simple question. Assume nature allows you to position something with infinite precision. (Nature obeys the same laws of physics as we do.) How much information could we store at a single (in fact mathematical) point?

 

[bobob]

It's well known that Lorentz ether theory is only philosophically different from Special Relativity - Special Relativity did not push any specific interpretation forward strongly. But Minkowski did, and it is harmful that there are so many people professionals alike, who are not clear on the difference between Minkowski and Special Relativity.

No, what might be "harful" is not really understanding what you are objecting to. If you assume some ether theory, you have implicitly chosen a spacetime geometry that gives you Newtonian physics, i.e., a central extention to the Galilean group, which actually is more complex than choosing the Poincare group for the spacetime of special relativity. So, not only did you choose a spacetime geometry without realizing it, you are trying to introduce a fictional ether that makes it even more complicated as well as makes unphysical predictions to turn it into the spacetime you did not choose for some weird reason known only to ether advocates. As for unphysical predictions, if there is an ether, there should be pressure waves associated with it, yet none have been observed. Choose the right spacetime from the beginning and avoid all of the problems associated with choosing the wrong one and trying to compensate for choosing incorrectly.

 

[bhobba]

This is a complete misrepresentation of quantum mechanics which has been made popular in magazines like New Scientist, etc.

While we have the standard axioms of QM detailed on this forum, my statement is easier to see using the two axioms from Ballentine - QM - A Modern Development.

They are:

1. To each observation, there is a Hermitian operator O, whose eigenvalues are the possible outcomes of the observation.

2. The average of the outcomes, A, is given by the Born rule, which says A = Tr (OS), where S is a positive operator called the system state.

Note - it is an interpretational matter if S is something real, or simply a mathematical aid in calculating that average, or with a bit of probability theory, the probability of a particular outcome. 2. actually follows from 1. via Gleasons Theroem, whose foundation is non-contextuality. That was the famous mistake Von Neumann made in his no hidden variable proof, but that is another story for a separate thread.

The point is all QM assumes observations - that's it - that's all. What observation is, is not made particularly precise. To remedy that, it is usually taken as when some change is left, here in the macro world. More technically, once the theory is developed further, decoherence has occurred, and the system is in a mixed state where each element of the mixed state is a possible outcome. With even greater sophistication, it can be developed into a quantum theory of measurement to include thing like probes:
http://www.quantum.umb.edu/Jacobs/QMT/QMT_Chapter1.pdf

The point is at rock bottom; QM is a theory about calculating the probability of observations. The state is simply a calculational aid in determining those probabilities.

Thanks
Bill

 

[PeterDonis]

This is a complete misrepresentation of quantum mechanics

This may be your opinion, but it's not fact. Please keep the difference in mind--particularly in this subforum, where most of what is discussed is people's opinions (since, as is noted in the guidelines for this subforum, all interpretations of QM make the same predictions for all experiments so there is no way of testing them against each other).

Quantum mechanics from the beginning was modeled on classical mechanics.

I'm not sure what you mean by this. QM was forced on physicists precisely because phenomena were discovered, like black-body radiation, the photoelectric effect, and the stability of atoms, that classical mechanics could not explain.

none of those interpretations explain anything. They just reflect the interpreter's bias of where they can shift what they perceive as an issue to some place they are comfortable ignoring it.

Again, this is your opinion, but it's not fact. Please keep in mind the difference.

 

[PeterDonis]

If you assume some ether theory, you have implicitly chosen a spacetime geometry that gives you Newtonian physics

Ether theory is off topic here, but incorrect factual claims about it are worth correcting. Your claim here is false: the specific ether theory @AnssiH was referring to, Lorentz Ether Theory, is mathematically equivalent to (and makes all the same experimental predictions as) standard Special Relativity, not Newtonian mechanics.

 

[bhobba]

You have it backwards. Quantum mechanics from the beginning was modeled on classical mechanics. Why would you not expect quantum mechanics to reduce to classical mechanics as a limiting case?

One possibility is except for stationary paths, in the classical domain, when considering the path integral, all others have a nearby path that cancels, leading to the Principle Of Least Action. From that, Galelain Relativity, and the POR, QM basically implies classical mechanics. The detail can be found in Landau - Mechanics.

Another aspect is chapter 3 of Ballentine, where he proves, using nothing but Galelaian Relativity, Schrodingers equation. However, if one applies Erenfest's Theorem, one gets the classical Hamiltonian. This suggests one of the key, but sometimes not emphasised, assumptions of QM. Namely, to quantise a classical system, you replace the Hamiltonian with the corresponding quantum operators. IMHO that is really the key assumption of QM - just a personal opinion.

Thanks
Bill

 

[bhobba]

Ether theory is off topic here, but incorrect factual claims about it are worth correcting. Your claim here is false: the specific ether theory @AnssiH was referring to, Lorentz Ether Theory, is mathematically equivalent to (and makes all the same experimental predictions as) standard Special Relativity, not Newtonian mechanics.

It is on-topic in a historical context. I always thought it assumed Galilean relativity and the Lorentz Transformations are a mere appearance due to the shortening of objects as they move through the aether. However, that will be way off-topic in this thread, and I think it would best be taken up on the Relativity subforum. All predictions are equivalent to SR - but the reason is completely different. This may be due to confusion between the existence of a preferred frame and LET, where the aether is assumed to have certain properties. From a historical perspective, that would be interesting to get to the bottom of.

Thanks
Bill

 

[RUTA]

While we have the standard axioms of QM detailed on this forum, my statement is easier to see using the two axioms from Ballentine - QM - A Modern Development.

They are:

1. To each observation, there is a Hermitian operator O, whose eigenvalues are the possible outcomes of the observation.

2. The average of the outcomes, A, is given by the Born rule, which says A = Tr (OS), where S is a positive operator called the system state.

Note - it is an interpretational matter if S is something real, or simply a mathematical aid in calculating that average, or with a bit of probability theory, the probability of a particular outcome. 2. actually follows from 1. via Gleasons Theroem, whose foundation is non-contextuality. That was the famous mistake Von Neumann made in his no hidden variable proof, but that is another story for a separate thread.

The point is all QM assumes observations - that's it - that's all. What observation is, is not made particularly precise. To remedy that, it is usually taken as when some change is left, here in the macro world. More technically, once the theory is developed further, decoherence has occurred, and the system is in a mixed state where each element of the mixed state is a possible outcome. With even greater sophistication, it can be developed into a quantum theory of measurement to include thing like probes:
http://www.quantum.umb.edu/Jacobs/QMT/QMT_Chapter1.pdf

The point is at rock bottom; QM is a theory about calculating the probability of observations. The state is simply a calculational aid in determining those probabilities.

Thanks
Bill

Why do you think QM is a probability theory to begin with? As Mermin points out (p. 10*):

Quantum mechanics is, after all, the first physical theory in which probability is explicitly not a way of dealing with ignorance of the precise values of existing quantities.

*N.D. Mermin, ``Making better sense of quantum mechanics,'' Reports on Progress in Physics 82(1), 012002 (2019). https://arxiv.org/abs/1809.01639

 

[Sunil]

We discuss standard physics here that, by our rules, you agreed to when you signed up, is peer-reviewed papers, textbooks, talks by respected scientists etc. If ever there is any worry about a relevant source, you can write to a mentor. Instead of simply posting such a source to discuss it, as I requested, it indicates these are just ideas you have. Personal theories (unless published in peer-reviewed journals or equivalent) are not allowed. As I said, this aether thing is not an interest of mine, but as you mentioned, Glet would do:
https://www.ilja-schmelzer.de/glet/

Sorry, but I don't understand the point of this. Once GLET would do it, fine, you are satisfied, or not?

I asked for the link between the aether and QFT. Yes GLET is a legit theory about that the aether, now you need to link it to QFT.

GLET derives essential parts of the SM, in particular the SM gauge group and the three generations of SM fermions. This is done using a lattice. Lattice theories are a reasonable way to define a QFT as far as this is possible at all given the infinities. So what do you miss here?

Quantum fields, of which there are many, are not similar to the old idea of light as classical undulations of the aether. QFT obeys Lorentz symmetry, meaning it has the same properties regardless of the inertial reference frame.

I disagree. The math of QFT and quantum condensed matter theory is essentially the same. The Lorentz symmetry is the symmetry of the wave equation, thus, as long as the wave equation is fine as an approximation for condensed matter waves, there will be an effective Lorentz symmetry too. The Lorentz-transformed solutions are simply the Doppler-shifted solutions.

LET explains this using the Lorentz hypothesis of length contraction. Internal length contractions of clock components changed time. In modern times we have atomic clocks, so such an explanation will not work.

Once the equations of the matter fields are wave equations with the same c in it, the basic idea of LET works in the same way. Lorentz idea in modern language was that if matter is held together by the EM field, the symmetry of the EM field will extend to whatever describes the matter too. Ok, matter is held together also by the other forces of the SM, but they are all wave equations, they all share the symmetry with the same c, and so they will also have the same Lorentz symmetry. This works for atomic clocks too, as well as for everything constructed out of SM fermions and gauge fields.

This is not a complex own theory, but an elementary symmetry consideration, it would not be worth a separate publication because it is too simple and obvious, therefore I don't hope to find such things in a separate publication.

Let's also note that for the question discussed - if realist non-local interpretations are in conflict with relativity - only the preferred frame hypothesis matters. And introducing it into SR changes nothing, given that we are allowed to ignore all non-preferred systems of coordinates and do all the computations in the frame named "preferred" in SR too (also an elementary consideration where I do not expect separate papers because it would be too trivial to be publishable).

It is not well known that LET is only philosophically different to modern SR ...

It is. If you don't know such elementary things, this would be your problem. But I doubt - I think you know this very well. The preferred frame hypothesis is usually rejected out of philosophical arguments like your angles argument, not because of some problems with experimental predictions, and once you use such arguments (instead of, say, claims that LET is in conflict with MMX) you seem to know that there are no such experimental issues. If you like to reject some interpretations because of your personal philosophical preferences (like preferring a four-dimensional spacetime), your choice. This does not change the fact that I discuss here, namely that realist non-local interpretations of QT are compatible with relativity, and incompatible only with a particular interpretation of relativity which rejects the preferred frame hypothesis.

All you have to do is post up a source so we can discuss your ideas. It is not hard. There are issues here, such as the quantum vacuum is the aether (it isn't), dark matter, or the CBMR etc., is the aether (again, they are not), but to discuss it, you need a source. Or you could ask why the CBMR is not considered the aether, but that would require a new thread - here you are assuming such exists.

I have given a source. It does not have any of the issues you have mentioned here. The aim is not to discuss that particular theory here, as well as your angels theory, but simply a reference to the actual state of research about the Lorentz ether interpretation of relativity. So, if you think, for whatever reasons, that the Lorentz ether is outdated, wrong or whatever, I disagree and refer to this paper. If you have something to criticize in that theory, it would be better to start a new thread. If not, what's the problem?

The issue of non-locality in QM is different. I was even a bit confused by it until I came across a paper at CERN. The CERN server is not working for me right now, so I can't give a link, but here is the gist. Bell showed, assuming the Kolmogorov axioms, showed QM is incompatible with counterfactual definiteness. If we relax the Kolmogorov axioms requirement, i.e. assume from the start QM is a Generalised Probability Theory, then the whole 'issue' is bypassed.

That's the sort of "solutions" I don't consider worth to be studied. Giving up causality, realism, even probability theory or logic in a situation where we have simple causal realistic models working with classical logic and probability theory seem nonsensical to me.

 

[Demystifier]

May be a link.

One is in my signature.
The other is http://thphys.irb.hr/wiki/main/images/3/3d/QFound5.pdf

 

[bhobba]

Why do you think QM is a probability theory to begin with? As Mermin points out (p. 10*):

Because of Gleason's Theorem and the Born Rule. But thanks for the link. I will give it some study when I get a bit of time. I have found over the years, my view of QM has changed somewhat precisely because people like you have made me aware of things I had not considered, so I gave your reply my like. Thanks to Demysterfyer as well for the same reason.

Thanks
Bill

 

[bhobba]

GLET derives essential parts of the SM, in particular the SM gauge group and the three generations of SM fermions. This is done using a lattice. Lattice theories are a reasonable way to define a QFT

All I am asking for is a paper where QFT is developed, including the aether. I know GLET because I discussed it many years ago with Ilja. It originally was not published, and many people thought it a disgrace because it was of publishable quality. I am not interested in an aether or associated ideas, but I am very interested in science being done properly. If a paper is judged by experts like Steve Carlip and John Baez to be of publishable quality, as GLET was, it should be published IMHO. That has now been rectified. But it is not a quantum theory. It suggests some interesting things related to the SM but is not a theory that reduces the SM; a quantum theory. I am sure Demystifyer will be only too happy to post one of his papers up. He could even start a new thread, and we can get to the bottom of exactly why the aether is a problem for QFT.

I have given my reasons (e.g. in LET light is undulations of the aether) why it is not compatible with our current knowledge. But much has happened in physics since the days of LET, so that is no surprise. If you want to talk about an aether and QFT, much more detail as found in a paper is required. With my mentor's hat on, that is also one of our rules. You can't discuss the aether except in a historical context or a peer-reviewed paper.

Added later:
As Demystifyer knows, the DBB interpretation of QM, according to some, implies an aether. It is thought by some this makes it difficult, perhaps impossible, to extend to QFT. It is just something I have read, but since claims are brought about an aether, it needs clarifying. If it is impossible to incorporate into QFT, that is a big problem - likely fatal for the whole idea.

Thanks
Bill

 

[Demystifier]

You can't discuss the aether except in a historical context or a peer-reviewed paper.

Good point!

 

[Sunil]

But it is not a quantum theory. It suggests some interesting things related to the SM but is not a theory that reduces the SM; a quantum theory.

What is "not quantum" in "The lattice fermion fields we propose to quantize as low energy states of a canonical quantum theory with $\mathbb{Z}_2$-degenerated vacuum state. We construct anticommuting fermion operators for the resulting $\mathbb{Z}_2$-valued (spin) field theory."? (from the abstract of arxiv:0908.0591)

I am sure Demystifyer will be only too happy to post one of his papers up. He could even start a new thread, and we can get to the bottom of exactly why the aether is a problem for QFT.

Feel free to start a thread why the aether is a problem for QFT while we use QFT in condensed matter theory without any problem. For the problem that in condensed matter theory we have only bosons while we need also fermions see Schmelzer's paper.

I have given my reasons (e.g. in LET light is undulations of the aether) why it is not compatible with our current knowledge.

Given that "our current knowledge" includes Schmelzer's papers I don't think you have given sufficient reasons for this claim.

But much has happened in physics since the days of LET, so that is no surprise. If you want to talk about an aether and QFT, much more detail as found in a paper is required. With my mentor's hat on, that is also one of our rules. You can't discuss the aether except in a historical context or a peer-reviewed paper.

The peer-reviewed paper has been given, so there is no need to go to the Lorentz ether in a version from 1905 given that we have a version from 2009, together with a large background of literature of how to do QFT for condensed matter theories which can be applied in a quite straightforward way to quite general ether theories.

And, again, my actual intention is just to correct the wrong claim that non-local interpretations of QT are in conflict with relativity - they are not, given that interpretations of relativity with a preferred frame are viable.

 

[gentzen]

Why is everyone so gung ho to try to make quantum theory into some bastardized version of classical theory when classical theory cannot explain anything without approximating away or parameterizing things which are quantum in origin?

One reason my be related to attitudes towards the usefulness of fictions:

I recently suggested as a possible explanation for the different prevalences of Mathematical fictionalism vs. physical fictionalism

Like many other mathematicians, I believe in a principle of 'conservation of difficulty'. This allows me to believe that mathematics stays useful, even if it would be fictional. I believe that often the main difficulties of a real world problem will still be present in a fictional mathematical model.
...
From my experience with physicists (...), their trust in 'conservation of difficulty' is often less pronounced. As a consequence, physical fictionalism has a hard time

But the specific example given to illustrate that explanation are themselves fictions: "So instead of accepting Bohmian mechanics as a useful fictional model with huge potential for analyzing various difficulties of quantum mechanics (and extracting insights about the real world from it), it was initially dismissed for being too obviously fictional."

It is a fiction, because we do know the historical reasons why Bohmian mechanics was dismissed:
1) Bohm himself had fallen out of favor of the physical community for political reasons.
2) A high dimensional configuration space cannot substitute for the expected 3+1 dimensional space, and arbitrarily breaking symmetries is ... well arbitrary, together with some more general objections summarized by Heisenberg.

In fact, a slightly different reason is that more low key figures like Arnold Sommerfeld and Max Born are ignored in favor of showmasters like Feynman or gurus like Bohr. And even Schrödinger and Heisenberg got mostly ignored when they tried later in their life to engage in more low key activities.

 

[RUTA]

Because of Gleason's Theorem and the Born Rule. But thanks for the link. I will give it some study when I get a bit of time. I have found over the years, my view of QM has changed somewhat precisely because people like you have made me aware of things I had not considered, so I gave your reply my like. Thanks to Demysterfyer as well for the same reason.

Thanks
Bill

Sorry, I meant, "What is the nature of reality such that when we discovered QM, this theory ONLY gives results in terms of probability?" Obviously, QM is a probability theory :-)

 

[stevendaryl]

"Interpretation" invariably means some scheme to make quantum mechanics behave like classical mechanics even at the expense of introducing very weird potentials and equally weird fictitious entities along with some "explanation" of how these things "really" don't violate other well known physics, like relativity.

I don’t think interpretation means making QM look like classical mechanics.

 

[Fra]

Why do you think QM is a probability theory to begin with? As Mermin points out (p. 10*):

Quantum mechanics is, after all, the first physical theory in which probability is explicitly not a way of dealing with ignorance of the precise values of existing quantities.

*N.D. Mermin, ``Making better sense of quantum mechanics,'' Reports on Progress in Physics 82(1), 012002 (2019). https://arxiv.org/abs/1809.01639

I could be mistaken, but from I remember bhobbas older posts he views QM as a generalized probability theory, and this makes sense to me. (Unless I mixed up the users here, i now see there is bobo, if so i apologize for mixing it up)

But what I THINK mermin means with the above, is probably not to say that QM is not a generalized probability theory, but that probability itself can not be interpreted as ignorance measure? By ignorance I think "hidden variables" is implicit. Ie. it has more to do with the interpretation of "probability". This seems to be also more consistent with Mermins qbist view?

A few more lines below that quoted test Mermins writes also

"If one does take a subjective view of probability, then a QBist understanding of quantum mechanics is unavoidable. But I prefer to put it the other way around: the success of QBism in clarifying the murk at the foundations of quantum mechanics is a compelling reason for physicists too to embrace the widespread view of probabilities as subjective personal judgments"
-- p22, https://arxiv.org/abs/1809.01639

Edit: I just noticed post #260!

/Fredrik

 

[Lord Jestocost]

What observation is, is not made particularly precise. To remedy that, it is usually taken as when some change is left, here in the macro world.

To be precise regarding the phrase "when some change is left":
One shoiuld keep in mind the so-called "negative-result measurements" or "Renninger-type experiments". The sheer possibility for a quantum system to interact with an detector with an assumed perfect efficiency is, although it does not click, sucient for the - so to speak - collapse of the wavefunction.

 

[bhobba]

Feel free to start a thread why the aether is a problem for QFT while we use QFT in condensed matter theory without any problem. For the problem that in condensed matter theory we have only bosons while we need also fermions see Schmelzer's paper.

QFT has methods used in particle physics and condensed matter physics. True. Indeed Wilson used such an analogy in his investigations on renormalisation. But that does not mean particle physics is a condensed matter theory. Such should be pretty obvious anyway - how can you use condensed matter (which is made of particles) to explain those particles? It makes no sense. Or rather you would need more details on exactly what the condensed matter in such a theory is or all you have is analogies.

We may be getting somewhere however in that we have a peer-reviewed paper using that idea:
https://arxiv.org/abs/0908.0591

I do not buy it for the reason I mentioned above - but others may be able to comment.

Thanks
Bill

 

[RUTA]

I could be mistaken, but from I remember bhobbas older posts he views QM as a generalized probability theory, and this makes sense to me. (Unless I mixed up the users here, i now see there is bobo, if so i apologize for mixing it up)

But what I THINK mermin means with the above, is probably not to say that QM is not a generalized probability theory, but that probability itself can not be interpreted as ignorance measure? By ignorance I think "hidden variables" is implicit. Ie. it has more to do with the interpretation of "probability". This seems to be also more consistent with Mermins qbist view?

A few more lines below that quoted test Mermins writes also

"If one does take a subjective view of probability, then a QBist understanding of quantum mechanics is unavoidable. But I prefer to put it the other way around: the success of QBism in clarifying the murk at the foundations of quantum mechanics is a compelling reason for physicists too to embrace the widespread view of probabilities as subjective personal judgments"
-- p22, https://arxiv.org/abs/1809.01639

Edit: I just noticed post #260!

/Fredrik

I agree, Mermin and QBists are saying that ALL physics is truly about assigning probabilities to subjective belief states and therefore, even if the physics theory provides probability = 1 as in classical mechanics, it is a probability theory nonetheless. In our papers cited earlier, QM is necessarily a probability theory due to the relativity principle applied to the measurement of Planck's constant h. So, I was just wondering why bhobba thought QM is necessarily about probabilities. There is no doubt that QM can be viewed as a GPT. My question is, again, why is it that our fundamental theory of physics is a GPT? Is QM simply an incomplete version of something more fundamental that is non-probabilistic (as one views the kinetic theory of gases)? Or is the probabilistic nature of our fundamental theory unavoidable (as in QBism and our principle explanation)?

 

[Sunil]

QFT has methods used in particle physics and condensed matter physics. True. Indeed Wilson used such an analogy in his investigations on renormalisation. But that does not mean particle physics is a condensed matter theory. Such should be pretty obvious anyway - how can you use condensed matter (which is made of particles) to explain those particles? It makes no sense.

It makes sense. One uses condensed matter (which is made of atoms) to explain phonons - pseudo-particles with have the same mathematical properties as particles, but are not really particles. It is much more than a mere analogy - the math, as far as it matters, is the same. We have a microscopic theory (the atomic lattice) which gives a large distance limit - a field theory. And if that field theory gives a wave equation, we can use standard QFT techniques to obtain the corresponding pseudo-particles.

The ether theory would have to explain the particles we observe as phonons of the hypothetical fundamental structure. The fundamental structure is something different from those pseudo-particles. In condensed matter theory, these are atoms which have approximately fixed positions and oscillate around them. Those atoms have nothing to do with the phonons, which are (in the simplest case) free particles. Similarly, the fundamental structure of the ether has at a first look nothing to do with the particles we observe - they are the pseudo-particles of the resulting lattice theory, resp. the field theory obtained in the large distance limit. If that field theory is the SM, then QFT gives the particles we observe.

Or rather you would need more details on exactly what the condensed matter in such a theory is r all you have is analogies.
We may be getting somewhere however in that we have a peer-reviewed paper using that idea:
https://arxiv.org/abs/0908.0591
I do not buy it for the reason I mentioned above - but others may be able to comment.

Ok, fine. For the most obvious objection - condensed matter theory gives only bosons as phonons, but we also need fermions - Schmelzer gives an explicit construction which gives fermions too.

 

[RUTA]

I don’t think interpretation means making QM look like classical mechanics.

I agree. QBism is an interpretation of QM and it specifically highlights that as a GPT, QM is NOT like classical probability theory. So, that interpretation of QM is based on the DIFFERENCE between classical mechanics (CM) and QM. It does place CM and QM under the same umbrella (probability theories), but as distinctly different types of probability theory.

 

[bhobba]

*N.D. Mermin, ``Making better sense of quantum mechanics,'' Reports on Progress in Physics 82(1), 012002 (2019). https://arxiv.org/abs/1809.01639

I read it. A bit too 'philosophical' about what science is for my taste. I think I have posted it before, but my view is more like Dirac's as in the following:
https://core.ac.uk/download/pdf/295725056.pdf

Thanks
Bill

 

[Fra]

So, I was just wondering why bhobba thought QM is necessarily about probabilities. There is no doubt that QM can be viewed as a GPT. My question is, again, why is it that our fundamental theory of physics is a GPT? Is QM simply an incomplete version of something more fundamental that is non-probabilistic (as one views the kinetic theory of gases)? Or is the probabilistic nature of our fundamental theory unavoidable (as in QBism and our principle explanation)?

Now I got the point of your why question.

Reading the posts I can not read out bhobbas answer, unless his position is supposed to be more agnostic about the why question, as in thinking it's too philosophical? I tried to skim the Dirac paper but couldnt' find an answer to the question.

Bhobba, is this a fair summary of your position or did I miss something?

(My view is the latter option, but i seek a constructive motivation also to the principal explanation, I see them as supporting each other in the following way: An explicit constructive theory requires a lot of assumptions, that are not possible to defend fully. But an evolutionary theory may tune itself, to the point that the ambigous starting points are less important asymptotically, and one could qualitatively spot asymptotic behaviour from the constructions, and take the principles of asymptotics. So to me the probably answer is that: the GPT structure should be a result of self-organisation of relations between the parts. But the argument would require a tentative construction, similar to the Muller paper, except as Muller himself points out there are major pieces missing that may be critical. I trace this poblem into a reconstruction of probability theory as measures of degree of belief itself and also why computational complexlity matters, as each agent could has certain computational capacity only, and when tossing information the loss is minimal when the code is optimal.)

"the approach of this paper does not yet give a full-fledged theory that has all the properties that one would like it to have; in particular, it is not yet able to treat processes of “forgetting” or “memory erasure”, and Section 7 suggests that such processes might be of fundamental importance."
-- Müller, https://arxiv.org/abs/1712.01826

/Fredrik

 

[RUTA]

I’ll side more with Heisenberg :-)