I New experiments supporting Bohmian mechanics?

[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?

 

[Demystifier]

Do all Bohmian physicists working on relativistic BM use this concept of fundamental particles vs quasi-particles in the condense matter phonons analogy..

No. I guess I am the only one who, so far, proposed it explicitly. Implicitly, if you can read between the lines, it can also be seen in the work of Ilja Schmelzer and Forum posts by @atyy .

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?

A not-so-long time ago, I was trying to make Bohmian mechanics inherently relativistic. How successful, judge by yourself:
https://arxiv.org/abs/1205.1992