New experiments supporting Bohmian mechanics?

[Denis]

Wilson only solved fake philosophical problems. QED was successful before Wilson.

No. Wilson has shown that QFT is not a basket of horrible manipulations with throwing away infinitely large things, but a meaningful theory, if understood correctly. It also allowed to make sense of quantum gravity as an effective field theory. I would say this is much more than solving "fake philosophical problems".

The EPR paper is very vague in stating what their criterion of reality is. ... [It] just says that a physical quantity only represents "an element of physical reality" if the system is prepared such that this quantity has a determined value. This is possible for any observable within quantum theory. The point, however, is that there's no state for which all observables have "an element of physical reality". So what?

What "so what"? The question is simple: Do you explicitly reject it? If "just" says, indeed. Are you ready to accept that, "just" in this particular case, there really exists this element of physical reality?

The point of a criterion which "just" says something about a very specific case is quite clear: In "just" this particular case the situation is so clear that if you refuse to accept, nonetheless, that there exists this "element of physical reality", then you clearly and obviously enough reject realism.

But if you accept this criterion - that means, nothing but that "just" in this case there exists that "element of physical reality" - then you can start to prove Bell's theorem. All you need there is to accept also Einstein causality. And in some realistic version of it, which is not "one cannot send signals FTL", but one which allows to claim that Bob's decision what to measure is not "in any way disturbing" the measurement made by Alice. Then you have Bell's theorem, which is falsified by observation and incompatible with QT, and after this you have the possibility to rethink what was wrong: The acceptance of the EPR criterion, or the thesis that Bob's decision what to measure does not disturb the measurement made by Alice.

Does that make QT "unrealistic"? Of course not, because

Indeed, because we know that there are realistic interpretations of QT. There is no problem with reality. There is only a problem with reality for those who are ready to reject realism - even in the extremely weak form of the EPR criterion of reality - to save Einstein causality.

 

[stevendaryl]

I'm not a positivist, but I'm a realist. It's almost a nuissance to discuss about "realism", because this is a notion that the philosophers have loaded with so much unsubstantiated meaning that nobody knows, what is discussed anymore. So what's "realistic" for a scientist? It's defined as reproducible objective and quantitative observations of phenomena in nature, no more no less.

I would not consider that "realism". I would consider it the opposite of realism, actually. Realism is the assumption that are observations are due to phenomena that exists independently of our observations.

 

[vanhees71]

Ok, again we are at the point, where I have to ask what you define as "realistic". For me QT is perfectly realistic, because it describes with high accuracy all and many even very precisely measured observational facts. That's enough for me to say that QT is a realistic (at the present time the most realistic) theory we have. Concerning EPR, my "so what?" was referring to the fact that according to EPR in all states a system can be in there are observables that don't take determined values and thus according to EPR do not reflect "an element of reality". This makes me ask "so what?", because it only shows that the definition of "reality" is an empty phrase, because we observe the very predictions of QT concerning the indeterminacy of observables for given state preparations and so it's realistic, contradicting the very assertion made that it is not realistic. The rest of the paper only shows that the collapse assumption leads at least to serious logical problems, but since the collapse assumption is not part of the standard QT formulation and it's never really needed to relate this formalism to real-world observations, you just drop it, and QT has no more problems (at least as far as the EPR paper is concerned).

 

[stevendaryl]

So what? Does that make QT "unrealistic"?

I would say yes.

 

[vanhees71]

I would not consider that "realism". I would consider it the opposite of realism, actually. Realism is the assumption that are observations are due to phenomena that exists independently of our observations.

I never denied that phenomena exist independently of our observations. How did you come to the assumption, I did imply this? Of course "the moon is there if nobody looks at it". Why shouldn't it? In QT there's nothing to imply that it might not be there, only because nobody looks at it.

 

[vanhees71]

I would say yes.

Why? The indeterminism of the spin-$x$ component of a particle prepared to have determined spin-$z$ component should be clearly observed (I guess with ultracold neutrons to a high accuracy; perhaps one can google it). Why does that (correct) prediction of QT make QT "unrealistic". To the contrary the observed facts agree with QT. So is reality itself unrealistic because of that?

 

[stevendaryl]

I never denied that phenomena exist independently of our observations.

Your definition of "realism" made no mention of it. You talked about reproducible observations.

 

[stevendaryl]

Why? The indeterminism of the spin-$x$ component of a particle prepared to have determined spin-$z$ component should be clearly observed (I guess with ultracold neutrons to a high accuracy; perhaps one can google it). Why does that (correct) prediction of QT make QT "unrealistic". To the contrary the observed facts agree with QT. So is reality itself unrealistic because of that?

A realistic model would say: The universe behaves in such-and-such a way. A theory that only describes our observations of the universe is not a realistic model.

 

[stevendaryl]

I never denied that phenomena exist independently of our observations. How did you come to the assumption, I did imply this? Of course "the moon is there if nobody looks at it". Why shouldn't it? In QT there's nothing to imply that it might not be there, only because nobody looks at it.

Does an electron have a spin component in the z-direction if nobody measures it (and nobody prepares it that way)?

 

[vanhees71]

Then physics as a whole is unrealistic, because it's about what we objectively observe, but what's realistic then? I think we become totally off-topic again. That's predetermined starting with "philosophy" and leaving the safe grounds of the "hard sciences"!

 

[stevendaryl]

Then physics as a whole is unrealistic,

No, it's not. Newtonian physics is realistic in my sense. So is Bohmian mechanics. So is General Relativity.

I think we become totally off-topic again.

We can drop it, but I wish you wouldn't use the word "realistic" to mean the opposite of what other people mean by it.

 

[vanhees71]

Does an electron have a spin component in the z-direction if nobody measures it (and nobody prepares it that way)?

One can't answer this. If I've not observed the electron's spin-z component, I can only make a guess. Making this guess as objective as possible, i.e., minimizing the prejudice we get, using the usual Shannon-Jaynes definition of entropy as a measure for the missing information, we should assume that the electron's spin state is given by $\hat{\rho}=1/2 \hat{1}$.

To verify this, you have to observe (measure) the spin-z component of equally prepared electrons (i.e., of randomly picked electrons from some source in this case) and make a statistical analysis. Then you can say with which signififance your "educated guess" is correct. If the source in fact sends polarized electrons to you, you were wrong and you'd change your description according to what you measured, but if you forbid me to observe it, it's just useless to make any attempt of a description to begin with.

I still don't get, what you are after!

 

[atyy]

I never denied that phenomena exist independently of our observations. How did you come to the assumption, I did imply this? Of course "the moon is there if nobody looks at it". Why shouldn't it? In QT there's nothing to imply that it might not be there, only because nobody looks at it.

By "there", you mean position. So quantum particles have positions when no one is looking. You are a secret Bohmian.

 

[vanhees71]

No, it's not. Newtonian physics is realistic in my sense. So is Bohmian mechanics. So is General Relativity.
We can drop it, but I wish you wouldn't use the word "realistic" to mean the opposite of what other people mean by it.

How can Bohmian mechanics be "realistic" if QT is not. Stripping off BM of unobservable metaphysical elements, you end at QT!

Newtonian physics is only realistic in a quite approximate sense. We know where it limitations are, i.e., where it doesn't describe reality accurately anymore. It's still not clear to me, what you define as "realistic".

 

[vanhees71]

By "there", you mean position. So quantum particles have positions when no one is looking. You are a secret Bohmian.

Of course have particles positions as long as you don't consider massless particles with spin $\geq 1$. According to standard QT the positions can be, however, objectively indetermined (e.g., if the particles are prepared to have pretty well determined momentum as in a particle accelerator). What this has to do with BM, I don't understand. I always thought that the Bohmian trajectories are considered as unobservable.

 

[atyy]

Any philosopher would say that you are not a realist but a positivist. However, since you are not a philosopher but a scientist, who uses a scientific and not a philosophic language, you have a right to say that you are a realist and not a positivist.

The only problem is that you like to discuss philosophic questions with using scientific and not philosophic way of thinking. This is like discussing art with using scientific and not artistic way of thinking. If you try to explain the value of Mona Lisa by using a scientific way of thinking, it does not make much sense neither to artists nor to scientists.

Reality is just a tool to predict measurement outcomes:)

 

[Denis]

How can Bohmian mechanics be "realistic" if QT is not. Stripping off BM of unobservable metaphysical elements, you end at QT!

What about a realistic theory having to contain a clear and certain description of what really exists? This is the standard definition - a realistic theory has an ontology, a description what really exists. Remove this description, and the resulting theory remains compatible with realism, but is not a realistic theory. For such theories there is a name, phenomenological theories.

Newtonian physics is only realistic in a quite approximate sense. We know where it limitations are, i.e., where it doesn't describe reality accurately anymore.

Sorry, but a realistic theory is a theory which makes claims about reality. These claims may be false - but this does not make the theory non-realistic. Newtonian physics is a realistic theory, completely realistic, because it has a well-defined ontology. Its predictions are only approximately true.

 

[stevendaryl]

One can't answer this. If I've not observed the electron's spin-z component, I can only make a guess. Making this guess as objective as possible, i.e., minimizing the prejudice we get, using the usual Shannon-Jaynes definition of entropy as a measure for the missing information, we should assume that the electron's spin state is given by $\hat{\rho}=1/2 \hat{1}$.

To verify this, you have to observe (measure) the spin-z component of equally prepared electrons (i.e., of randomly picked electrons from some source in this case) and make a statistical analysis. Then you can say with which signififance your "educated guess" is correct. If the source in fact sends polarized electrons to you, you were wrong and you'd change your description according to what you measured, but if you forbid me to observe it, it's just useless to make any attempt of a description to begin with.

I still don't get, what you are after!

A realistic theory in my opinion would be a description of how the world works in the absence of observations, measurements, observers, etc. Newtonian physics is such a description. So is Bohmian mechanics. So is General Relativity. That doesn't mean that a realistic theory cannot account for observations. To account for observations, you need additional assumptions that our observations correspond to certain phenomena in the realistic theory. If it is an attempt to be complete, then in principle it should be possible to describe the observers themselves in terms of the realistic theory.

Quantum mechanics with a rule such as the Born rule is simply not a realistic theory. A realistic theory would have no need for a postulate saying "When we measure a physical variable, we get an eigenvalue of the corresponding operator". If an observer is a physical system, described by the same physical laws as the system being observed, then the act of observation should itself be describable in the same theory. There should be no need for an additional assumption about what happens when an observer performs a measurement. There isn't in Bohmian mechanics. There isn't in Newtonian mechanics. There isn't in General Relativity.

 

[atyy]

Of course have particles positions as long as you don't consider massless particles with spin $\geq 1$. According to standard QT the positions can be, however, objectively indetermined (e.g., if the particles are prepared to have pretty well determined momentum as in a particle accelerator). What this has to do with BM, I don't understand. I always thought that the Bohmian trajectories are considered as unobservable.

The there-ness of the moon is unobservable when you are not looking at it.

 

[stevendaryl]

How can Bohmian mechanics be "realistic" if QT is not.

Because Bohmian mechanics is (right or wrong) a description of how the universe works, while QT in the "minimal" interpretation is simply a description of how observations work.

Saying "If I do X, I'll see Y" is not a realistic theory. A realistic theory would allow you to derive that fact (if it's true).

 

[Denis]

I always thought that the Bohmian trajectories are considered as unobservable.

No, all what we observe are Bohmian trajectories. The Schrödinger equation gives us the superposition of the dead and the living cat. The Bohmian trajectory is either the dead cat, or the living cat - it has a well-defined position. What we observe is either the dead cat or the living cat - in any way it is not their superposition. So, what we really observe is the Bohmian trajectory of the large things.

 

[stevendaryl]

Newtonian physics is only realistic in a quite approximate sense. We know where it limitations are, i.e., where it doesn't describe reality accurately anymore. It's still not clear to me, what you define as "realistic".

I think you are confusing two completely separate issues: (1) What type of theory is it? (2) How accurate is it?

Newtonian physics is a realistic theory in that it attempts to describe the way the world works, independently of our observations and measurements. Whether it succeeds (whether it is accurate) is a separate issue.

 

[stevendaryl]

I'm guessing that this thread will be shut down soon. It's way too philosophical.

 

[Demystifier]

I always thought that the Bohmian trajectories are considered as unobservable.

Only in practice, not in principle. As I explain in
https://arxiv.org/abs/1703.08341
non-observability of Bohmian trajectories is analogous to non-observability of dark matter.

 

[Demystifier]

I'm guessing that this thread will be shut down soon. It's way too philosophical.

You just made a measurable prediction, so it's not philosophy.

 

[vanhees71]

No, all what we observe are Bohmian trajectories. The Schrödinger equation gives us the superposition of the dead and the living cat. The Bohmian trajectory is either the dead cat, or the living cat - it has a well-defined position. What we observe is either the dead cat or the living cat - in any way it is not their superposition. So, what we really observe is the Bohmian trajectory of the large things.

Well, that's a BM-biased point of view. Here is my minimal-QT biased view:

(a) states of a cat "dead" and "alive" are macroscopic quantities and from a quantum-mechanical point of view a very coarse-grained description, for which by application of the corresponding effective description from the underlying microscopic dynamics (which is impossible to do in full detail and also impossible to observe in that detail). Such quantities behave, according to this description, classical (at least FAPP).

(b) we observe superpositions always "only" in the sense of Born's rule, i.e., we always measure accurate values on a single system of an ensemble corresponding to the used basis to define the superposition of the state (you must always give a basis to which the superposition refers; otherwise it doesn't make sense to say a vector representing a pure state is described by a superposition). That it is in a proper superposition wrt. to this basis implies that this value is indetermined and you'll measure with the corresponding probability, i.e., a relative frequency of the outcome of the measurement on an ensemble, the corresponding values. QT says not more about this observable and according to the minimal interpretation there's not more possible to be known.

Of course, to determine whether a system is really in a pure state described by this superposition, or in another mixed state with the same probabilities this simple measurement is insufficient. A complete state determination is pretty complicated. The most simple way to achieve it theoretically is to measure a complete set of compatible observables. This implies that "measuring" here must necessarily refer to measuring each single observable of this complete set separately at sufficiently large equally prepared ensembles.

 

[Denis]

Well, that's a BM-biased point of view.

What else do you expect if the question was if the Bohmian trajectories are observable or not? This is a question about Bohmian mechanics. A "minimal interpretation" view of the question if Bohmian trajectories are observable is clearly meaningless, because they don't even exist in the minimal interpretation.

 

[vanhees71]

Only in practice, not in principle. As I explain in
https://arxiv.org/abs/1703.08341
non-observability of Bohmian trajectories is analogous to non-observability of dark matter.

Hm, I'll read this in detail later this evening. I'd put me in the Copenhagen camp in a "superposition or mixture" between 1. and 3. in the list in Sect. 2.1 of your paper. Concerning Qbism, I've only the quibble that at least some "Qbists" want to reinterpret probability (independent of its reference to QT or not) as if it could be applied to single events rather than an ensemble. This doesn't make any sense to me, and I think it's an abuse of Bayes's ideas to do so. Of course, we adapt our probability description when getting more detailed information about it, but it's still probabilities we use then, and this only means that it describes the expected relative frequency when measuring an ensemble. The only reference ot Bayes is that of course conditional probabilities change when the condition changes. That's almost trivial, isn't it, i.e., it's just saying that in general $P(A|B) \neq P(A|C)$, which is obvious already by notation.

On the other hand I like information-theoretical foundations of statistical physics, particularly the information-theoretical foundation of the notion of entropy. I believe it's (quite directly) empirically confirmed to be the correct picture by the experiments with "quantum Maxwell demons" (PRL 115, 260602 (2015)), but that's again another topic.

 

[atyy]

A complete state determination is pretty complicated. The most simple way to achieve it theoretically is to measure a complete set of compatible observables.

I don't think the observables can be compatible. For example, https://arxiv.org/abs/quant-ph/0006006v1 gives the Pauli matrices for state determination on a spin 1/2 system.

 

[Blue Scallop]

↑ What do you mean by "Demystifier BM"? Do you mean the idea outlined in https://arxiv.org/abs/1703.08341 Sec. 4.3? If you do, then fundamental ontology are non-relativistic particles, from which relativistic fields emerge as effective description, from which relativistic particles (which are really quasiparticles) emerge as excitations of those fields.

In Sec 4.3, you wrote: "Such a condensed-matter style of thinking suggests an approach to a Bohmian theory of everything (ToE). Suppose that all relativistic particles of the Standard Model (photons, electrons, quarks, gluons, Higgs, etc.) are really quasi-particles. If so, perhaps the truly fundamental (as yet unknown) particles are described by non-relativistic QM. If so, then non-relativistic Bohmian mechanics is a natural ToE. In such a theory, Bohmian trajectories exist only for those truly fundamental particles."

Demystifier. Do you have other papers that expound on these truly fundamental particles that are described by non-relativistic QM? Who are the other authors who expound on this? If you don't.. what do you think are these non relativistic truly fundamental particles? What shall be their characteristics and are they described by any gauge symmetry such as U(1)xSU(2)xSU(3)?.

Also Relativistic particles = did you mean near light speed so sensitive to SR or particles that can create/annihilate as per our QFT or what?
Non relativistic particles = did you mean low speed particles or particles that can't create/annihilate as per our QFT or what?

Thank you !

 

[Demystifier]

Demystifier. Do you have other papers that expound on these truly fundamental particles that are described by non-relativistic QM? Who are the other authors who expound on this?

See Refs. [31], [32] and references therein.

If you don't.. what do you think are these non relativistic truly fundamental particles?

I don't know (yet).

What shall be their characteristics and are they described by any gauge symmetry such as U(1)xSU(2)xSU(3)?.

I expect that gauge symmetry such as U(1)xSU(2)xSU(3) is not fundamental, i.e. not a property of these fundamental particles.

Also Relativistic particles = did you mean near light speed so sensitive to SR or particles that can create/annihilate as per our QFT ...?

I mean the latter.

Non relativistic particles = did you mean low speed particles or particles that can't create/annihilate as per our QFT ...?

The latter. They don't need to be slow at all, just as non-relativistic particles in condensed matter do not need to be slow compared to the velocity of sound.

 

[Blue Scallop]

See Refs. [31], [32] and references therein.I don't know (yet).I expect that gauge symmetry such as U(1)xSU(2)xSU(3) is not fundamental, i.e. not a property of these fundamental particles.I mean the latter.The latter. They don't need to be slow at all, just as non-relativistic particles in condensed matter do not need to be slow compared to the velocity of sound.

What do you call particles that is 99.9999% the speed of light yet can't create/annihilate? are these called relativistic particles?

If normal particles like electrons are quasi-particles that don't have trajectories yet can create/annihilate.. and there are more fundamental particles that have trajectories.. where does the quantum potential act on.. the fundamental particles or the quasi-particles?

And why propose there are more fundamental particles than than the quasi-particles. I mean.. why not just stop at the quasi-particles.. why does there need to be more fundamental particles with trajectories? Maybe to find determinism within the indeterminism?

 

[Denis]

Also Relativistic particles = did you mean near light speed so sensitive to SR or particles that can create/annihilate as per our QFT or what?
Non relativistic particles = did you mean low speed particles or particles that can't create/annihilate as per our QFT or what?

I would say that in this context "relativistic" means a field following a wave equation, and "non-relativistic" means objects of a more fundamental theory, similar to lattice nodes in a lattice regularization of such a field theory.

Do you have other papers that expound on these truly fundamental particles that are described by non-relativistic QM? Who are the other authors who expound on this? If you don't.. what do you think are these non relativistic truly fundamental particles? What shall be their characteristics and are they described by any gauge symmetry such as U(1)xSU(2)xSU(3)?

Gauge fields - the EM field - has been described in BM already in Bohm's original paper. For a condensed-matter-like approach which would give U(1)xSU(2)xSU(3) see arxiv:0908.0591.

 

[Demystifier]

What do you call particles that is 99.9999% the speed of light yet can't create/annihilate? are these called relativistic particles?

I don't have a special name for them, but I don't call them relativistic.

If normal particles like electrons are quasi-particles that don't have trajectories yet can create/annihilate.. and there are more fundamental particles that have trajectories.. where does the quantum potential act on.. the fundamental particles or the quasi-particles?

The quantum potential acts only on fundamental particles.

And why propose there are more fundamental particles than than the quasi-particles. I mean.. why not just stop at the quasi-particles.. why does there need to be more fundamental particles with trajectories? Maybe to find determinism within the indeterminism?

There are several reasons:
1) Analogy with condensed matter physics. If this is how things work effectively in condensed matter, perhaps this is how things work fundamentally everywhere.
2) To find ontology within a theory which does not explicitly talk about ontology.
3) To find fundamental determinism within an effective non-deterministic theory.

Note also that such a version of Bohmian mechanics makes a qualitative measurable prediction. It predicts that at very small distances (smaller than we can currently see with present technology) the nature should violate Lorentz symmetry in an observable way. This, for instance, makes it different from the mainstream string theory which predicts that at such smaller distances the nature should still be Lorentz invariant.

 

[Blue Scallop]

I don't have a special name for them, but I don't call them relativistic.The quantum potential acts only on fundamental particles.There are several reasons:
1) Analogy with condensed matter physics. If this is how things work effectively in condensed matter, perhaps this is how things work fundamentally everywhere.
2) To find ontology within a theory which does not explicitly talk about ontology.
3) To find fundamental determinism within an effective non-deterministic theory.

Note also that such a version of Bohmian mechanics makes a qualitative measurable prediction. It predicts that at very small distances (smaller than we can currently see with present technology) the nature should violate Lorentz symmetry in an observable way. This, for instance, makes it different from the mainstream string theory which predicts that at such smaller distances the nature should still be Lorentz invariant.

Do all Bohmian physicists working on relativistic BM use this concept of fundamental particles vs quasi-particles in the condense matter phonons analogy.. or does any still try to make the main bohmian non relativistic particles become suddenly able to create and annhiliate? what programme explore this? How successful.. and what are the main problems?