I Copenhagen Interpretation vs Pilot Waves

[lukephysics]

I was unsatisfied with the measurement problem so I was looking at pilot wave (PW)

Sabine says one downside of pilot wave is there is no QFT version for pilot wave yet. And a significant problem in replacing the QFT is that PW is non-local, and that copenhagen very much depends on being local. But i was confused by this. The copenhagen wavefunction collapses in two places instantaneously. doesnt this make it non-local as well?

so then why did Sabine say locality is important for Copenhagen and the standard QFT? (it was from this video )

has anyone done work on producing a new QFT based on pilot wave? I think it would be fruitful. Pilot wave seems more correct and its a physical deterministic solution rather than the philosophical copenhagen.

 

[Demystifier]

I had several discussions with Sabine on pilot waves, she doesn't really understand it. There is a plenty of work on the QFT version of pilot waves. See e.g. my recent https://arxiv.org/abs/2205.05986

 

[vanhees71]

But in this paper you rather confirm the skepticism, because you admit already in the abstract that your Bohmian verion of relativistic QFT theory is not relativistic, because it "lacks Lorentz covariance". So it's not relativistic.

 

[Lord Jestocost]

Pilot wave seems more correct and its a physical deterministic solution rather than the philosophical copenhagen.

Maybe, a pilot wave theory might be more illustrative for someone. However, how does a pilot wave theory get rid of the irreducible randomness related to Born’s rule?

 

[gentzen]

However, how does a pilot wave theory get rid of the irreducible randomness related to Born’s rule?

Basically just like in chaos theory. Do you know a bit of symbolic dynamics? Basically, all the randomness is encoded in the initial conditions, and it turns out to be an endless supply of randomness which never gets reduced, no matter how many measurments you do.
I have also read somewhere how this plays out more in detail for Bohmian mechanics, but my attempt to find it again just now "on the fly" failed. If it really interests you, I can take the time to find it again.

However, it should be clear that this will not resolve the disagreement between Demystifier and vanhees71.

 

[Lord Jestocost]

Basically, all the randomness is encoded in the initial conditions.....

So what?

Chaos Theory: Because we can never know all the initial conditions of a complex system!

The “in principle knowable unknowns” are grounded in epistemology alone.

 

[Demystifier]

Maybe, a pilot wave theory might be more illustrative for someone. However, how does a pilot wave theory get rid of the irreducible randomness related to Born’s rule?

The Born rule does not say that the randomness is irreducible. It just says that probability should be computed by this rule, but it says nothing about irreducibility. Copenhagen-like interpretations assume that it's irreducible, but there is no formal proof that it must be irreducible.

Anyway, according to the Bohmian interpretation, the randomness is reducible. For a thorough analysis see https://arxiv.org/abs/quant-ph/0308039

 

[Demystifier]

But in this paper you rather confirm the skepticism, because you admit already in the abstract that your Bohmian verion of relativistic QFT theory is not relativistic, because it "lacks Lorentz covariance". So it's not relativistic.

https://www.physicsforums.com/threa...sed-opportunities.1054134/page-2#post-6916115

 

[Demystifier]

However, it should be clear that this will not resolve the disagreement between Demystifier and vanhees71.

As I said elsewhere, our disagreements would be easily resolved if he could make some decisions and stick to them.
https://www.physicsforums.com/threa...sed-opportunities.1054134/page-2#post-6916115

 

[vanhees71]

Should I really address this gibberish? I don't see, what merit it has to introduce superfluous mathematical elements, which do not even help in calculation techniques to get to the observable predictions of the theory. For me Bohmian mechanics doesn't add anything to Q(F)T as a physical theory. Is that clear enough?

 

[Demystifier]

For me Bohmian mechanics doesn't add anything to Q(F)T as a physical theory. Is that clear enough?

It is not clear enough. Since you are very active on this subforum, it is clear enough that you actually care a lot about interpretations and philosophy, even when it is not relevant to physics.

 

[vanhees71]

I care about to give the scientific point of view in addition to all these confusing philosophical statements. That's all.

 

[lukephysics]

I care about to give the scientific point of view in addition to all these confusing philosophical statements. That's all.

Boemian is less philosophical and more ontic than Copenhagen so you should be in to that right? The whole thing is physical! Coming from the top of a different field and in to physics with fresh eyes, Copenhagen seems lost in metaphysics for no reason when here is a better alternative.

 

[Demystifier]

I care about to give the scientific point of view in addition to all these confusing philosophical statements. That's all.

So tell us from the scientific point of view, does Bohmian QFT make the same measurable predictions as standard QFT? Yes or no? That's all what matters from the scientific point of view.

 

[vanhees71]

Bohmian trajectories are not physical since they are unobservable. Whether a theory is ontic or epistemic doesn't matter for a physical theory. All it should do is to describe observations in nature (within its realm of applicability, i.e., for QT as far as we know everything except the gravitational interaction).

 

[vanhees71]

So tell us from the scientific point of view, does Bohmian QFT make the same measurable predictions as standard QFT? Yes or no? That's all what matters from the scientific point of view.

I don't know. If it's not Poincare invariant, it seems to make different predictions than standard QFT.

 

[Demystifier]

I don't know. If it's not Poincare invariant, it seems to make different predictions than standard QFT.

If you don't know, then leave the talk about it to those who know.

 

[Demystifier]

Whether a theory is ontic or epistemic doesn't matter for a physical theory. All it should do is to describe observations in nature

To paraphrase Bohr: Stop telling the physical theory what it should do!

 

[vanhees71]

To paraphrase Bohr: Stop telling the physical theory what it should do!

If a theory doesn't describe anything observable, it's not a physical theory. Bohr did a lot to confuse QT with his philosophy. I never understood, why he had such a high reputation.

 

[Demystifier]

If a theory doesn't describe anything observable, it's not a physical theory.

It's one thing to say that a theory should describe something observable (nobody here denies it), but completely another to say that that's all it should do. Many physicists think that that's not all, that it should do this and something more.

This whole subforum is made for those who think that it should do something more. Those who disagree waste their time by even reading it, let alone writing in it.

 

[PeterDonis]

If a theory doesn't describe anything observable

Bohmian mechanics does describe observable things--the same ones that "basic" QM describes.

Bohmian mechanics also includes unobservable things--the particle trajectories and the pilot wave. But so does "basic" QM: the wave function is unobservable. In fact, every physical theory includes things that are unobservable. So I fail to see what distinction you are drawing here.

 

[vanhees71]

I fail to see the merit of the Bohmian trajectories. They are not needed at all to calculate the observable facts, QT predicts and which can be compared to experiments. So why should one calculate them? It's different with the wave function. E.g., solving the time-independent Schrödinger equation for, e.g., an electron interacting with a proton through the Coulomb interaction, it provides me with the energy levels of the hydrogen atom and scattering eigenmodes leading to the Rutherford cross section. So calculating the wave function, though not directly observable, is a way to get the predictions for observable (e.g., the spectrum of the H atom).

Of course, rigged Hilbert spaces + operator theory + observable-algebras/representation theory of symmetry groups, and all that, are not observable elements of the theory either, but they define the theory! Bohmian trajectories are not needed for the abstract formulation nor add them anything observable. So they are simply superfluous.

My argument against BM is just Occam's razor: Why should one introduce theoretical balast, which doesn't add anything to the physics content of the theory.

 

[PeterDonis]

I fail to see the merit of the Bohmian trajectories.

Yes, we know this because you have stated it repeatedly. That means that at this point you have nothing useful to add to a thread that is specifically about Bohmian trajectories. The best policy to follow for someone who does not see the merit of a particular intepretation is to refrain from posting in threads in this subforum that are about that specific interpretation.

My argument against BM is just Occam's razor: Why should one introduce theoretical balast, which doesn't add anything to the physics content of the theory.

You could make the same argument against any QM interpretation. And my statement about the best policy to follow for threads in this subforum would apply the same for all of them.

 

[vanhees71]

Yes, we know this because you have stated it repeatedly. That means that at this point you have nothing useful to add to a thread that is specifically about Bohmian trajectories. The best policy to follow for someone who does not see the merit of a particular intepretation is to refrain from posting in threads in this subforum that are about that specific interpretation.

So you define, what's useful? Why aren't objections against an interpretation useful? Is it not allowed to post scientific arguments against a specific interpretation anymore? What is then the interpretation subforum good for at all? Shouldn't one then strictly restrict the entire forum to the scientific content of QT (which is the minimal statistical interpretation) and forbid any discussions about interpretations?

You could make the same argument against any QM interpretation. And my statement about the best policy to follow for threads in this subforum would apply the same for all of them.

Yes, this statement is valid against any interpretation that goes beyond the minimal statistical interpretation. So?

 

[Demystifier]

Why aren't objections against an interpretation useful?

Your objections in particular are not useful because they do not help to understand any particular interpretation. We all know that all interpretations, except the minimal one, add something additional that is not directly observable, so it doesn't help us when you remind us that it is so. We want to understand this additional thing, you don't want to understand it (but only want to know whether it makes new predictions, which it usually doesn't), so your contribution is not useful.

 

[PeterDonis]

So you define, what's useful?

No, I am just reminding you what the interpretations subforum is for and what it is not for. It is not for claiming that any interpretation is either right or wrong. You are basically claming that a particular interpretation is wrong. That is off limits in this subforum by the PF rules.

Why aren't objections against an interpretation useful? Is it not allowed to post scientific arguments against a specific interpretation anymore?

Stating that certain objections are made in the literature to a certain interpretation is fine. But, as the guidelines to this forum note, arguments of this kind cannot be resolved here because there is no experimental way to distinguish between QM interpretations. So continuing to state the same objections in thread after thread is not fine; it's just hijacking the threads with your personal opinions for no useful purpose.

What is then the interpretation subforum good for at all? Shouldn't one then strictly restrict the entire forum to the scientific content of QT (which is the minimal statistical interpretation) and forbid any discussions about interpretations?

This discussion was had some time ago in the SA forum, before the intepretations subforum was spun off. It is off topic here. If you really want to make a case for the interpretations subforum being shut down, please do so in a thread in the SA forum.

 

[apostolosdt]

I had several discussions with Sabine on pilot waves, she doesn't really understand it. There is a plenty of work on the QFT version of pilot waves. See e.g. my recent https://arxiv.org/abs/2205.05986

I went through that paper of yours; I found Section 4.3 a bit daring. In just thirty lines, you manage to reject relativity as one fundamental pillar of contemporary physics and suggest that some nonrelativistist QM theory underlying QFT predicts BSM-like particles to be discovered in the future at CERN. Really?

 

[vanhees71]

No, I am just reminding you what the interpretations subforum is for and what it is not for. It is not for claiming that any interpretation is either right or wrong. You are basically claming that a particular interpretation is wrong. That is off limits in this subforum by the PF rules.Stating that certain objections are made in the literature to a certain interpretation is fine. But, as the guidelines to this forum note, arguments of this kind cannot be resolved here because there is no experimental way to distinguish between QM interpretations. So continuing to state the same objections in thread after thread is not fine; it's just hijacking the threads with your personal opinions for no useful purpose.This discussion was had some time ago in the SA forum, before the intepretations subforum was spun off. It is off topic here. If you really want to make a case for the interpretations subforum being shut down, please do so in a thread in the SA forum.

No, I don't want to propose that at all. To the contrary, it was split off as a subforum to be able to discuss freely about metaphysical implications and keeping the scientific QT forum free from it. I only wondreed that you now wanted to imply the stricter rules of the latter also in here.

 

[PeterDonis]

I don't understand the purpose of this subforum at all.

We had a detailed discussion on this before the subforum was added. Please go look it up. Also look at the sticky threads at the top of the subforum, which will give you the forum guidelines.

If you really can't grok the purpose of this subforum after reading all that, then the very least you can do is to stop posting in it, in order to not ruin the discussion for others who do see reasons for it and who post here in order to have substantive discussions.

 

[PeterDonis]

I only wondreed that you now wanted to imply the stricter rules of the latter also in here.

I have no idea what you're talking about. The only guidelines I have discussed at all in this thread are the guidelines for this forum.

 

[PeterDonis]

it was split off as a subforum to be able to discuss freely about metaphysical implications

No, it was split off as a subforum to discuss QM interpretations. As you will see from the forum guidelines, that still requires some basis in the literature; it is not open season to discuss whatever metaphysical speculations people can dream up.

and keeping the scientific QT forum free from it

Keeping that forum free from QM interpretation discussions, yes.

 

[PeterDonis]

What other purpose can a discussion about interpretations have than to figure out which one is the most useful one?

Such a discussion is pointless because it is a matter of personal opinion and cannot be resolved. That's why the forum guidelines for this subforum specifically prohibit claims of this sort.

The purpose of this forum is to help people improve their understanding of what the various QM interpretations actually say. Just as the purpose of PF in general is to help people improve their understanding of what mainstream science actually says.

 

[Demystifier]

I went through that paper of yours; I found Section 4.3 a bit daring. In just thirty lines, you manage to reject relativity as one fundamental pillar of contemporary physics and suggest that some nonrelativistist QM theory underlying QFT predicts BSM-like particles to be discovered in the future at CERN. Really?

Well, it's quite generally accepted in the community that all contemporary theories are just effective theories that one day will be replaced by better theories. All BSM theories dare to say something about possible features of these future theories. In comparison with some other BSM theories, I would say that condensed-matter style theories in which relativity is emergent are rather conservative. If you just want more than thirty lines about such theories, I have cited two related books. If you are against all this business of BSM theories in general, I can understand that as well, but in that case it would be fair from your side to say so.

 

[Demystifier]

Then I don't understand the purpose of this subforum at all.

Exactly, you don't understand it. Please leave it to us who do understand it.

 

[lukephysics]

My argument against BM is just Occam's razor: Why should one introduce theoretical balast, which doesn't add anything to the physics content of the theory.

its not what it adds, it what it doesnt add - problems. Copenhagen has the measurement problem. Why live with that when you can have a problem free interpretation? Your model should be as simple as possible and no simpler.

Further it explains the uncertainty. Copenhagen and MWI introduce a 'god' of randomness. its not easy to create an RNG. it requires energy and structure. its like when creationists say god created the universe - its a form of hidden complexity. so arguing CI and MWI are simpler is not a given.

the only problem ive found with PW, so far is that its not well researched, which is a human problem not a theory problem. oh plus the non-local thing, but all interpretations should be non-local because we all know about entanglement. maybe i havent understood why CI and MWI are 'local' as that would violate bell.

 

[vanhees71]

its not what it adds, it what it doesnt add - problems. Copenhagen has the measurement problem. Why live with that when you can have a problem free interpretation? Your model should be as simple as possible and no simpler.

But also BM and any other interpretation of QT has a measurement problem, if you think there is one. If I understand the philosophers right, their problem is that they think it's not understood, which outcome a measurement on a single quantum system will have, knowing the state (even if it's complete knowledge, i.e., if the system is prepared in a known pure state).

They exspect that the dynamics of the theory explains, why this state through interaction with a measurement apparatus "collapses" to the eigenstate of the operator that represents the measured observable. That's however in contradiction to the standard version of QT, because unitary time evolution does not lead to such a dynamics. Rather you still have a superposition of entangled states of the measured system and the pointer states of the measurement device. There are two ways out:

(a) One accepts that Nature is inherently random and that the outcome of measurements are thus irreducibly probabilistic. All QT delivers are the probabilities for the outcomes of measurements, and there is nothing more in Nature. That's the minimal statistical interpretation. There's no collapse, the quantum state is purely epistemic. For me that's the most plausible solution of the measurement problem, which is only apparent. It's just a problem for our worldview, which is due to everyday experience with macroscopic systems, whose relevant macroscopic observables behave according to classical physics with determinism as an emergent, approximate phenomenon. All observations and high-precision tests of QT in very many manifestations are consistent with this assumption.

(b) Nevertheless, that's indeed only an educated belief, founded on the overwhelming success and lack of failure of (minimally interpreted) QT. It cannot be ruled out, of course, that maybe QT is nevertheless incomplete, and then QT has to be modified, maybe in such a way that there's an inherent collapse mechanism in the dynamics. What's for sure ruled out is naive EPR "Local Realism". This is the great achievement of Bell's theoretical and Clauser's, Aspect's, et al's experimental work.

Further it explains the uncertainty. Copenhagen and MWI introduce a 'god' of randomness. its not easy to create an RNG. it requires energy and structure. its like when creationists say god created the universe - its a form of hidden complexity. so arguing CI and MWI are simpler is not a given.

What's an RNG? Also one has to accept how Nature is found to behave. Whether there's a god who created the universe the way it looks, is not a question that can decided by the pure sciences. That's a matter of private belief for any individual.

For me CI is inconsistent. Even the versions, which do not assume a collapse (e.g., Bohr's as well as Heisenberg's version, as far as I can guess from their enigmatic philosophical writings), there's still the "quantum-classical cut", which in no way could be hitherto observed. To the contrary with more and more refined metrology bigger and bigger systems can be shown to behave according to QT (e.g., the motions of the LIGO mirrors, sevel 10kg objects, behave quantum theoretical and show "zero-point motion" of quantum oscillators).

I'm not sure about MWI. On the one hand they claim that there's nothing than unitary time evolution and the "wave function of the universe" is all there is. On the other hand, for the application of QT, again I have to assume Born's rule for subsystems as in standard QT. I don't know, what's gained with MWI compared to the minimal interpretation.

the only problem ive found with PW, so far is that its not well researched, which is a human problem not a theory problem. oh plus the non-local thing, but all interpretations should be non-local because we all know about entanglement. maybe i havent understood why CI and MWI are 'local' as that would violate bell.

I guess with PW you mean "pilot wave", i.e., de Broglie-Bohm. Within non-relativistic theory it's a consistent mathematical addition to standard QT, but it's not solving any "measurement problems" either. Particles do not follow Bohmian trajectories but behave probabilistically as predicted by standard QT. All attempts to extend the Bohmian program to relativstic QT I'm aware of are even less convincing, violating in the one or the other way Poincare covariance, i.e., they are not relativstic at the end.

 

[vanhees71]

Exactly, you don't understand it. Please leave it to us who do understand it.

Why? Because it's more convenient to have a skeptic less? ;-)).

 

[Demystifier]

Why? Because it's more convenient to have a skeptic less? ;-)).

No, to attract ten skeptics more who would like to take part in a constructive criticism.

 

[apostolosdt]

No, I am just reminding you what the interpretations subforum is for and what it is not for. It is not for claiming that any interpretation is either right or wrong. You are basically claming that a particular interpretation is wrong. That is off limits in this subforum by the PF rules. […] This discussion was had some time ago in the SA forum, before the intepretations subforum was spun off. It is off topic here. If you really want to make a case for the interpretations subforum being shut down, please do so in a thread in the SA forum.

My bad; I’m going to remind myself to avoid this particular sub-forum, for I don’t care about philosophical arguments about physics. I think it’s fair for both vivid practitioners of QM interpretations and plain physicists like me.

It’s only ironic that Feynman’s name is being cited in a philoZophical sub-forum.

 

[Demystifier]

maybe i havent understood why CI and MWI are 'local' as that would violate bell.

See my https://arxiv.org/abs/1703.08341 Sec. 5.3.

 

[vanhees71]

This once more ignores the fact that standard relativistic QFT is local.

 

[Lord Jestocost]

.... One accepts that Nature is inherently random and that the outcome of measurements are thus irreducibly probabilistic. All QT delivers are the probabilities for the outcomes of measurements, and there is nothing more in Nature....

To my mind, Max Born/1/ hit the nail on the head when he wrote:

“A more concrete contribution to this question has been made by J. v. Neumann in his brilliant book, Mathematische Grundlagen der Quantenmechanik. He puts the theory on an axiomatic basis by deriving it from a few postulates of a very plausible and general character, about the properties of 'expectation values' (averages) and their representation by mathematical symbols. The result is that the formalism of quantum mechanics is uniquely determined by these axioms; in particular, no concealed parameters can be introduced with the help of which the indeterministic description could be transformed into a deterministic one. Hence if a future theory should be deterministic, it cannot be a modification of the present one but must be essentially different. How this should be possible without sacrificing a whole treasure of well-established results I leave to the determinists to worry about.

I for my part do not believe in the possibility of such a turn of things. Though I am very much aware of the shortcomings of quantum mechanics, I think that its indeterministic foundations will be permanent, and this is what interests us from the standpoint of these lectures on cause and chance. There remains now only to show how the ordinary, apparently deterministic laws of physics can be obtained from these foundations.”

/1/ Max Born, Natural Philosophy of Cause and Chance (Clarendon, Oxford, 1949)

 

[gentzen]

Basically, all the randomness is encoded in the initial conditions.....

So what?

Chaos Theory: Because we can never know all the initial conditions of a complex system!

The “in principle knowable unknowns” are grounded in epistemology alone.

Oh sorry, I thought you had a technical question about BM. Good to know that at least I don't have to spend the time to find the technical details again.

The answer was more ment to explain that even in BM, the randomness is still irreducable (or at least could still be irreducable, dependent on the technical details). Not because we cannot know the initial conditions of a complex system, but because we cannot know a real number exactly, and hence not know exactly a set of real numbers describing the initial conditions either.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

After moderator review, the thread will remain closed. Thanks to all who participated.