What if the Bohmian model turned out to be correct?

[Schrodinger's Dog]

I realize this is quite speculatory so feel free to move it somewhere more apt? But what implications would there be for science if the the Bohm interpretation proved to be the correct one (understand I am not favouring it I'm a Copenhagen man atm) But if it were proved that it was correct and that further the Universe only appeared probabilistic and was in fact deterministic what impact do you think this would have on the world of physics?

Just an Idle thought really. I want to understand the Bohm interpretation better so I Thought posing such a question would allow people to discuss it and it's positives and negatives.

Thanks. I suppose I could buy a book, but I'm a little short atm, so anyway, discus:

 

[jostpuur]

In order to answer the question what would happen, if the Bohmian model turned out to be correct, we should first know that how precisely would it have turned out to be correct? What enabled scientists to verify it?

 

[Schrodinger's Dog]

In order to answer the question what would happen, if the Bohmian model turned out to be correct, we should first know that how precisely would it have turned out to be correct? What enabled scientists to verify it?

Fuzziness is explained in classical terms, ie such niggles as the wave can be represented as deriving from a bohmian model, hidden variables becomes more valid for whatever reason.

And of course Quantum mechanics itself proved not to line up with an experiment, ie the theory itself was destroyed and Bohmian mechanics and thus it's interpretation became a fitter model.

I'm interested in any ideas of how these could be overcome, and any ideas why they would be unlikely to be overcome.

 

[peter0302]

The only thing that any of these alternative interpretations have to offer, in my view, is the speculative possibility that a deeper understanding of how quantum events work might lead to a better ability to predict or, the ultimate achievement, influence them. One can easily imagine the practical applications of this ability, if it were ever achieved. But we are way, way, way off from that point. To me, it at least provides enough of an incentive to keep asking questions, but that's about it.

 

[Demystifier]

But if it were proved that it was correct and that further the Universe only appeared probabilistic and was in fact deterministic what impact do you think this would have on the world of physics?

I think such a discovery would be very promissing for potential applications. Physicists would start to think how to control the "hidden" variables, i.e., the initial positions of particles when the wave is not an eigenstate of the position operator. If this could be done, then EPR correlations could be really used for sending information instantaneously.

In addition, in
http://xxx.lanl.gov/abs/0705.3542
I have argued that validity of Bohmian mechanics could be used as a new argument for adopting string theory.

 

[Demystifier]

In order to answer the question what would happen, if the Bohmian model turned out to be correct, we should first know that how precisely would it have turned out to be correct? What enabled scientists to verify it?

In
http://xxx.lanl.gov/abs/quant-ph/0406173 [Found.Phys.Lett. 18 (2005) 549]
I have explained how, in principle, a relativistic version of Bohmian mechanics could be experimentally verified.

 

[peter0302]

Thanks very much for that link! Very interesting article. I will cite it to anyone who insists that the Bohmian interpretation or idea of particle trajectories are useless! :)

 

[reilly]

Bohm's interpretation has been around since 1952; more than 50 years. This is less time than between Maxwell's Equations (1861) and Einstein's Special Relativity (1905). During the 50+ years between 1952 and now, the lack of impact upon the physics community is stunning; few accept Bohm's approach. And, as I've repeatedly noted; no new physics has emerged from Bohm's approach to interpretation.

There's a certain irony, in addition to Bohm-Arhronov, Bohm did pioneering work in many-body physics, often with David Pines, on the electron gas, which helped point the way to the BCS theory of superconductivity. This work was right in the mainstream with use of the practical Copenhagen interpretation.

As time goes by, the odds diminish that Bohm's approach will be found to be valid. If it is, then the impact could be huge in ways that we cannot know at this time. And remember that any new approach must reproduce all the quantum physics that his been done over nearly a century. I very much doubt this will happen.

Nonetheless, Bohm will be remembered as one of the outstanding physicists of his generation. His text on qunatum theory is superb.
Regards,
Reilly Atkinson

 

[reilly]

I challenge Dr. Nikolic or anyone else to do some real problems in the Bohmian way:

1.Calculate the the LS and other relativistic corrections for hydrogen.

2. Work out the temporal interference pattern of the neutral K meson system;

3. Work out the radiative corrections to coincidence detection high energy electron-proton scattering.

4. Calculate the electron's magnetic moment to 13 decimal places.

5.With all spin and isospin factors in a relativistic format, show that the so-called 3-3 resonance exists in pion-nucleon scattering, with the partial wave approach, and estimate the mass of the resonance.

6. (Too much scattering?) Do superconductivity.

With the exception of number 4 and 6 these are all relatively straightforward to formulate with conventional field theory. The magnetic moment problem is very difficult, but it can be and has been done. And 2-6 have been done during the last 50 years; number 1 was done in the 1930s.

These will provide a very minimal test of the Bohm approach to do real physics.

Regards,
Reilly Atkinson

 

[peter0302]

Well, it only took a couple hundred years for Newton's corpuscular theory of light to catch on. :) Give Bohm's interpretation some time.

 

[bg032]

I challenge Dr. Nikolic or anyone else to do some real problems in the Bohmian way: [...]

I challenge Reilly to derive classical mechanics, namely the equation F=ma, from standard quantum mechanics.

 

[jostpuur]

I challenge Reilly to derive classical mechanics, namely the equation F=ma, from standard quantum mechanics.

<br /> i\hbar\partial_t \Psi(t,x) = \Big(-\frac{\hbar^2}{2m}\nabla^2 + U(x)\Big)\Psi(t,x)<br />

<br /> \implies\quad \int d^3x\; \Psi^*(t,x)\Big(-\nabla U(x)\Big)\Psi(t,x) = \partial_t \int d^3x\; \Psi^*(t,x)\Big(-i\hbar\nabla\Big)\Psi(t,x)<br />

<br /> \implies\quad F = ma<br />

Details are left as an exercise.

 

[peter0302]

Since the Schrodinger equation already assumes the momentum-energy relations of classical mechanics, it would be pretty hard to derive classical mechanics from the Schrodinger Equation in a non-tautological way.

 

[bg032]

<br /> i\hbar\partial_t \Psi(t,x) = ...
Details are left as an exercise.

Jostpuur, I think you mean that the Ehrenfest theorem solves the problem to derive classical mechanics from standard quantum mechanics. Indeed from that theorem one obtains that

\frac{d}{dt}\langle p \rangle = - \langle \nabla V \rangle,

where \langle \cdot \rangle is the mean value of the quantum operator. Thus, at the macroscopic level a localized wave packet can be associated with a trajectory evolving approximately according to the Newton's law. However it is well-known that, under measurement-like interactions, the wave function spreads over regions which are no longer localized, neither from a macroscopic point of view. In this case it is no longer possible to associate a trajectory to the wave function, and the problen to recover classical mechanics from standard quantum mechanics remains, in my opinion, open.

 

[ZapperZ]

Jostpuur, I think you mean that the Ehrenfest theorem solves the problem to derive classical mechanics from standard quantum mechanics. Indeed from that theorem one obtains that

\frac{d}{dt}\langle p \rangle = - \langle \nabla V \rangle,

where \langle \cdot \rangle is the mean value of the quantum operator. Thus, at the macroscopic level a localized wave packet can be associated with a trajectory evolving approximately according to the Newton's law. However it is well-known that, under measurement-like interactions, the wave function spreads over regions which are no longer localized, neither from a macroscopic point of view. In this case it is no longer possible to associate a trajectory to the wave function, and the problen to recover classical mechanics from standard quantum mechanics remains, in my opinion, open.

But isn't that the whole point of QM, that classical mechanics is only a "special case"?

Furthermore, your challenge to Reilly isn't exactly the same as his challenge for Bohm model. His challenge does not ask one to go from quantum to classical. His challenge for those who claim that Bohm model is a "better" interpretation of quantum phenomena, then the proof is in the pudding, i.e. one should use Bohm's formulation and derive those phenomena.

I think that's a fair request. We often tout Lagrangian/Hamiltonian mechanics to be better than straightforward Newtonian mechanics when solving certain problems. We can't just say that and hope to get away with it. Rather, we show it in painstaking details. I don't see this as being any different.

Zz.

 

[bg032]

But isn't that the whole point of QM, that classical mechanics is only a "special case"?

Furthermore, your challenge to Reilly isn't exactly the same as his challenge for Bohm model. His challenge does not ask one to go from quantum to classical. His challenge for those who claim that Bohm model is a "better" interpretation of quantum phenomena, then the proof is in the pudding, i.e. one should use Bohm's formulation and derive those phenomena.

I think that's a fair request. We often tout Lagrangian/Hamiltonian mechanics to be better than straightforward Newtonian mechanics when solving certain problems. We can't just say that and hope to get away with it. Rather, we show it in painstaking details. I don't see this as being any different.

Zz.

I think physicists can aspire to find a theory which explains in a unified, reasonably simple and compehensible way both quantum and the classical phenomena. I think Bohmian mechanics does not provide a better interpretation of quantum phenomena, but at least provides (or tries to provide) this unified explanation. This is surely not the case, for instance, of the Copenhagen interpretation ...

 

[ZapperZ]

I think physicists can aspire to find a theory which explains in a unified, reasonably simple and compehensible way both quantum and the classical phenomena. I think Bohmian mechanics does not provide a better interpretation of quantum phenomena, but at least provides (or tries to provide) this unified explanation. This is surely not the case, for instance, of the Copenhagen interpretation ...

I'm not sure to what extent it can unify, when it hasn't managed to derive just those within the quantum phenomena. That's a tall order to aspire - unification - when it hasn't shown any success yet within the realm that it should work.

Zz.

 

[peter0302]

I think physicists can aspire to find a theory which explains in a unified, reasonably simple and compehensible way both quantum and the classical phenomena. I think Bohmian mechanics does not provide a better interpretation of quantum phenomena, but at least provides (or tries to provide) this unified explanation. This is surely not the case, for instance, of the Copenhagen interpretation ...

I agree with the sentiment, certainly. The Copenhagen "interpretation", of course, doesn't even try to do this. But Reilly does have a good point too that the fact that Bohmian mechanics hasn't been able to provide anything new in so long is decent evidence that it might not be such a good candidate for a unification theory. Something more radical is probably going to be necessary.

 

[Hans de Vries]

I challenge Reilly to derive classical mechanics, namely the equation F=ma, from standard quantum mechanics.

Presuming Special Relatively, the only assumption one has to make is E=hf to equate
the principle-of-least-action of Classical Mechanics to the principle-of-least-phase
of Quantum Mechanics to the principle-of-least-proper-time of Special Relativity.

This is the Heart and Soul of Physics.


Regards, Hans

 

[peter0302]

Presuming Special Relativity - but doesn't Special Relativity presume a great deal of classical mechanics itself, namely the conservation laws and energy-momentum relations?

 

[akhmeteli]

no new physics has emerged from Bohm's approach to interpretation.

No offence, but you seemed to agree that the Bell's inequalities, inspired by the Bohmian interpretation, qualify as new physics, so maybe your statement is too categorical?

 

[akhmeteli]

I challenge Dr. Nikolic or anyone else to do some real problems in the Bohmian way:

1.Calculate the the LS and other relativistic corrections for hydrogen.

2. Work out the temporal interference pattern of the neutral K meson system;

3. Work out the radiative corrections to coincidence detection high energy electron-proton scattering.

4. Calculate the electron's magnetic moment to 13 decimal places.

5.With all spin and isospin factors in a relativistic format, show that the so-called 3-3 resonance exists in pion-nucleon scattering, with the partial wave approach, and estimate the mass of the resonance.

6. (Too much scattering?) Do superconductivity.

With the exception of number 4 and 6 these are all relatively straightforward to formulate with conventional field theory. The magnetic moment problem is very difficult, but it can be and has been done. And 2-6 have been done during the last 50 years; number 1 was done in the 1930s.

These will provide a very minimal test of the Bohm approach to do real physics.

Regards,
Reilly Atkinson

Non-relativistic Bohmian interpretation predicts the same probabilities as the standard quantum mechanics. So, whether one is a fan of this interpretation or not, there is no need to solve any non-relativistic problems "the Bohm's way". If something is easier to do in the Heisenberg's picture, that does not mean that the Schroedinger's picture is worse, or vice versa.
There is no generally recognized relativistic Bohmian quantum theory, as far as I know, so it's difficult to offer "Bohmian" solutions of relativistic problems. Certainly, this is a drawback of the interpretation. Its strong point is that it exists at all, proving that quantum mechanics is not necessarily indeterministic. That's what Bell highly appreciated.
You offered your "very minimal test", but somebody may disagree. Indeed, many problems, where quantum effects are not important, can be solved (exactly or approximately) in classical mechanics, but cannot, or are very difficult to solve in quantum mechanics. Does it mean that quantum mechanics is worse than classical mechanics?

 

[ZapperZ]

Non-relativistic Bohmian interpretation predicts the same probabilities as the standard quantum mechanics. So, whether one is a fan of this interpretation or not, there is no need to solve any non-relativistic problems "the Bohm's way". If something is easier to do in the Heisenberg's picture, that does not mean that the Schroedinger's picture is worse, or vice versa.
There is no generally recognized relativistic Bohmian quantum theory, as far as I know, so it's difficult to offer "Bohmian" solutions of relativistic problems. Certainly, this is a drawback of the interpretation. Its strong point is that it exists at all, proving that quantum mechanics is not necessarily indeterministic. That's what Bell highly appreciated.
You offered your "very minimal test", but somebody may disagree. Indeed, many problems, where quantum effects are not important, can be solved (exactly or approximately) in classical mechanics, but cannot, or are very difficult to solve in quantum mechanics. Does it mean that quantum mechanics is worse than classical mechanics?

But to carry your analogy further, there are problems that are easier to deal with in the Schrodinger picture, and then there are problems that are easier to handle in the Heisenberg picture. That's why we are taught both so that we can switch back and forth. Are there any such examples we can attribute to the Bohm picture? If there is, then it will illustrate very clearly the usefulness of Bohmian QM.

The same can be said of your analogy of classical and quantum mechanics. There are definitely situations when one is more appropriate to be used versus the other. In what type of problems would an analogous situation arises between CI and Bohm?

Zz.

 

[lightarrow]

Presuming Special Relatively, the only assumption one has to make is E=hf to equate
the principle-of-least-action of Classical Mechanics to the principle-of-least-phase
of Quantum Mechanics to the principle-of-least-proper-time of Special Relativity.

This is the Heart and Soul of Physics.Regards, Hans

I would add phase (Lorentz) invariance; what do you think?

 

[akhmeteli]

But to carry your analogy further, there are problems that are easier to deal with in the Schrodinger picture, and then there are problems that are easier to handle in the Heisenberg picture. That's why we are taught both so that we can switch back and forth. Are there any such examples we can attribute to the Bohm picture? If there is, then it will illustrate very clearly the usefulness of Bohmian QM.

The same can be said of your analogy of classical and quantum mechanics. There are definitely situations when one is more appropriate to be used versus the other. In what type of problems would an analogous situation arises between CI and Bohm?

Zz.

Somebody (I don't remember who it was) proposed to use the Bohm's approach as a purely calculational method for numerical solution of the Schroedinger equation. Whether this has any advantages for some problems, I don't know, but it seems possible. But , as I said, this may be much less important than the fact that the mere existence of the Bohmian interpretation proves that quantum mechanics is not necessarily indeterministic. Thus, this interpretation has great conceptual significance for any physicist, whether he/she loves or hates determinism. What may be even more important, it has great conceptual significance for any layman, as (in)determinism of the nature is an extremely important and intriguing philosophical issue, relevant for everyone. So, for example, however deeply we may hate determinism, we cannot just shut up a deterministically minded philosopher, telling him that his beliefs contradict firmly established results of quantum physics. If you wish, the Bohmian interpretation has also significance similar to that of a no-go theorem. A no-go theorem is, by definition, extremely non-constructive, but it saves us efforts, as we are not trying to do something that just cannot be done. For example, von Neumann's theorem proving impossibility of hidden variables is mathematically impeccable, but the existence of the Bohmian interpretation demonstrates that the assumptions of the theorem may be unreasonably strong.
Summarizing, I am not sure the fate of any interpretation hinges on the results of some "pissing contest" ("and how can you derive the Klein-Nishina formula in your interpretation?")
As for my opinion, the Bohmian interpretation is not very appealing, but, no offence, CI looks much worse:-)

 

[ZapperZ]

Somebody (I don't remember who it was) proposed to use the Bohm's approach as a purely calculational method for numerical solution of the Schroedinger equation. Whether this has any advantages for some problems, I don't know, but it seems possible. But , as I said, this may be much less important than the fact that the mere existence of the Bohmian interpretation proves that quantum mechanics is not necessarily indeterministic. Thus, this interpretation has great conceptual significance for any physicist, whether he/she loves or hates determinism. What may be even more important, it has great conceptual significance for any layman, as (in)determinism of the nature is an extremely important and intriguing philosophical issue, relevant for everyone. So, for example, however deeply we may hate determinism, we cannot just shut up a deterministically minded philosopher, telling him that his beliefs contradict firmly established results of quantum physics. If you wish, the Bohmian interpretation has also significance similar to that of a no-go theorem. A no-go theorem is, by definition, extremely non-constructive, but it saves us efforts, as we are not trying to do something that just cannot be done. For example, von Neumann's theorem proving impossibility of hidden variables is mathematically impeccable, but the existence of the Bohmian interpretation demonstrates that the assumptions of the theorem may be unreasonably strong.
Summarizing, I am not sure the fate of any interpretation hinges on the results of some "pissing contest" ("and how can you derive the Klein-Nishina formula in your interpretation?")
As for my opinion, the Bohmian interpretation is not very appealing, but, no offence, CI looks much worse:-)

But see, what you describe is a preference based on a matter of tastes. This is very different than the analogy you have mentioned earlier. The choice of using classical mechanics over quantum mechanics to solve certain problems isn't a matter of tastes. It is a matter of whichever is more appropriate. The same can be said with Heisenberg versus Schrodinger picture. There's a distinct advantage of using one versus the other. It isn't a matter of personal preference.

If we are simply arguing one over the other simply based on personal preferences, then this issue cannot be solved rationally. It's like arguing over one's favorite color. However, if one technique can be shown to be more useful in certain situations, then this would be more meaningful in terms of making that technique to be considered to displace the other in those situations.

Zz.

 

[vanesch]

But , as I said, this may be much less important than the fact that the mere existence of the Bohmian interpretation proves that quantum mechanics is not necessarily indeterministic. Thus, this interpretation has great conceptual significance for any physicist, whether he/she loves or hates determinism. What may be even more important, it has great conceptual significance for any layman, as (in)determinism of the nature is an extremely important and intriguing philosophical issue, relevant for everyone. So, for example, however deeply we may hate determinism, we cannot just shut up a deterministically minded philosopher, telling him that his beliefs contradict firmly established results of quantum physics. If you wish, the Bohmian interpretation has also significance similar to that of a no-go theorem. A no-go theorem is, by definition, extremely non-constructive, but it saves us efforts, as we are not trying to do something that just cannot be done. For example, von Neumann's theorem proving impossibility of hidden variables is mathematically impeccable, but the existence of the Bohmian interpretation demonstrates that the assumptions of the theorem may be unreasonably strong.

I have to agree with you here that the Bohmian interpretation has conceptual advantages, and its biggest advantage is that it exists. As such, it can serve as a counter example to erroneous claims of what cannot be done.

However, the Bohmian interpretation has a serious drawback too: its conceptual incompatibility with relativity (even though it can mimick its results). So I'm not sure in how much adhering to the Bohmian interpretation helps you *understand* current-day physics, and in how much it is some excuse to stick with the old Newtonian paradigm. You will answer: that depends on what is "really" true! If the Newtonian paradigm is, after all, the ultimately correct world view, then Bohm will avoid us to "fall in the trap" of leaving it prematurely. However, if there is some "truth" in the principles of relativity and the superposition principle, then a Bohmian interpretation only allows us to live a bit longer in our erroneous illusion of Newtonian physics, by fiddling enough with it so that it can still fit with modern theories.

So let's say that in practice (as anybody else) I use Copenhagen ; in order to get a real feeling for what quantum theory and superposition is about, I prefer MWI ; but I'm also happy to know about Bohmian mechanics, just to know that it exists.

 

[DrChinese]

I have to agree with you here that the Bohmian interpretation has conceptual advantages, and its biggest advantage is that it exists. As such, it can serve as a counter example to erroneous claims of what cannot be done.

How can the Bohmian Interpretation address the GHZ theorem? I just don't see how a deterministic theory gets through that.

 

[vanesch]

How can the Bohmian Interpretation address the GHZ theorem? I just don't see how a deterministic theory gets through that.

Given that its predictions are identical with "normal" quantum theory, I don't see how that could be a problem ?

 

[Ken G]

So I'm not sure in how much adhering to the Bohmian interpretation helps you *understand* current-day physics, and in how much it is some excuse to stick with the old Newtonian paradigm.

I agree, taken as a map to new physics, the Bohmian approach is pure guess. As such, at present it is nothing more than a proof that there exists a deterministic interpretation of quantum mechanics.

What may be even more important, it has great conceptual significance for any layman, as (in)determinism of the nature is an extremely important and intriguing philosophical issue, relevant for everyone.

I realize this is a common view, and I can easily see why someone might cite this as a significance to Bohm's approach, but personally I see "determinism" as philosophy in physics. It's not that I "like" or "hate" it, I merely view at us nonscientific in its every guise, when taken as a philosophical principle. Determinism is a template that we lay over reality when it behooves us to do so, and irreversibility is a different template that is more helpful in other situations. So the question "is the universe fundamentally deterministic" is not a scientific question. The question for scientists is "what situations do we gain by the choice to treat deterministically?" Put in those terms, we come back to reilly's unmet challenge...

So let's say that in practice (as anybody else) I use Copenhagen ; in order to get a real feeling for what quantum theory and superposition is about, I prefer MWI ; but I'm also happy to know about Bohmian mechanics, just to know that it exists.

This is reminiscent of an important point Feynman once made about "interpretations" of physics-- he said in effect that a good physicist should have every tool in his/her chest, because you never know which one will make some new insight most transparent (I'm highly paraphrasing from memory). To me, the lesson here is "we should never take the philosophical scaffolding we build around our theories, simply to achieve cognitive resonance, too seriously".

 

[DrChinese]

Given that its predictions are identical with "normal" quantum theory, I don't see how that could be a problem ?

I guess I would wonder how a theory can claim to be deterministic (and therefore qualifiy as non-local realism) if the assumptions of realism - either per Bell's Theorem or GHZ - are not adhered to.

 

[lightarrow]

But , as I said, this may be much less important than the fact that the mere existence of the Bohmian interpretation proves that quantum mechanics is not necessarily indeterministic. Thus, this interpretation has great conceptual significance for any physicist, whether he/she loves or hates determinism. What may be even more important, it has great conceptual significance for any layman, as (in)determinism of the nature is an extremely important and intriguing philosophical issue, relevant for everyone. So, for example, however deeply we may hate determinism, we cannot just shut up a deterministically minded philosopher, telling him that his beliefs contradict firmly established results of quantum physics.

I would agree, but I would like to invite you to this afterthought: there are properties of objects which are not "intrinsic" of that object in the sense that they also depend, for example, from the ref. frame in which you measure the object. No one worries of this fact; so, why physicists worry if a particle, in one experimental setting behaves A and in another behaves B? Why do they talk about "indeterminism" in that context?
http://plato.stanford.edu/entries/qm-relational/

 

[reilly]

I have yet to see any answers to my questions. If these challenges cannot be met, then, in my opinion, Bohm's approach is simply a curiosity, doomed to footnotes in the texts of tomorrow. For those of us that think physics is fundamentally an empirical science, then a theory that cannot provide numbers to confirm or suggest experiments is not worth much. Again the Bohm folks, perhaps somehow suffering from unrequited love, have developed nothing but controversy -- Bell uses ordinary QM to compute the appropriate probabilities, like he uses Clebsch-Gordan coefficients, and standard angular momentum theory.

Bell may well have been inspired by Bohm, but, unless someone can point to the use of Bohmian dynamics to explain his experiment, Bell and Born worked together, so to speak.
Bohmians ; give us some experiments to demonstrate your your claims; talk is cheap, experiments are dear.

Remember, one of the very early triumphs of modern QM is Schrodinger's theory of the hydrogen spectra; it worked, it took Bohr to a better place; all with the help of Laguerre. It was agreement with experiment that put Schrodinger on the map.If he had written hundreds of pages of how wonderful his theory was, and said nothing about experiments, he would have generated a 'ho hum"

After 80 years of spectacular success, what's wrong with QM? The Bohm team is like being behind in a basketball game, 100 to 1.

Where's the beef?
Regards,
Reilly Atkinson

 

[Ken G]

After 80 years of spectacular success, what's wrong with QM? The Bohm team is like being behind in a basketball game, 100 to 1.

I agree with your basic sentiment, which I might paraphrase as saying that Bohm is like adding a periscope to a car in hopes it will make it a submarine-- without justifying the extra air resistance when used like a car. But in fairness, the basketball game you refer to might be more like a quidditch game, which as I understand it, is basically a game where the score is strangely irrelevant if you "catch the Golden Snitch". So I think your objection at this point is aimed at when people go past a simple description of the Bohm model into allowing it to "mold a belief system" around quantum mechanics. You point out that we don't let science "mold our beliefs" until we think it let's us become better scientists to do so-- and I agree that otherwise we are using our science as a "philosophy engine" and we can do that with a whole lot less effort via things like religion. In fact, I would take it a step further and say that we are always "on our own" when we do that even if it does make us better scientists!

 

[peter0302]

I guess I would wonder how a theory can claim to be deterministic (and therefore qualifiy as non-local realism) if the assumptions of realism - either per Bell's Theorem or GHZ - are not adhered to.

Bell makes you throw out realism or locality, but not necessarily both. Bohm throws out locality.

agree with your basic sentiment, which I might paraphrase as saying that Bohm is like adding a periscope to a car in hopes it will make it a submarine-- without justifying the extra air resistance when used like a car. But in fairness, the basketball game you refer to might be more like a quidditch game, which as I understand it, is basically a game where the score is strangely irrelevant if you "catch the Golden Snitch".

Excellent analogy!

To further it, Newton had the Golden Snitch far longer than Bohr did. Bohm's just trying to give it back to its rightful owner. :)

 

[Ken G]

Bell makes you throw out realism or locality, but not necessarily both. Bohm throws out locality.

And science allows you to adopt them both at your whim, depending on the question being asked and the phenomenon being probed. What I'd like to know is, from whence comes one single shred of scientific evidence that the axiomatic substructure employed by science is now, or ever has been, any different than that? In other words, from whence comes this constant reemergence, like the phoenix, of the idea that our goal is to find "the real axioms", instead of "the axioms that help us predict an experiment, or organize existing experimental data, in regard to the phenomenon of interest"? The answer must account for why the vast majority of physics publications employ axioms that are "false" if taken as philosophical truths.

 

[Ken G]

To further it, Newton had the Golden Snitch far longer than Bohr did. Bohm's just trying to give it back to its rightful owner. :)

But I think reilly's question, if I'm not mistaken, is why is Bohm "trying" to do anything of the sort? Should our effort not be to understand existing experimental evidence and use it to plan and predict new experiments, rather than building a soothing mental picture including phenomena that have not been observed at the expense of economy of understanding of those that have? It seems we should "get out of the way" of our science, or we repeat the errors of ancient natural philosophy.

 

[peter0302]

And science allows you to adopt them both at your whim, depending on the question being asked and the phenomenon being probed. What I'd like to know is, from whence comes one single shred of scientific evidence that the axiomatic substructure employed by science is now, or ever has been, any different than that? In other words, from whence comes this constant reemergence, like the phoenix, of the idea that our goal is to find "the real axioms", instead of "the axioms that help us predict an experiment, or organize existing experimental data, in regard to the phenomenon of interest"? The answer must account for why the vast majority of physics publications employ axioms that are "false" if taken as philosophical truths.

I think it goes back to the sort of Einsteinian goal of finding "the final answer" to everything. Einstein used to write of finding or understanding "the Old One" (or something to that effect). Clearly he wanted to do more than predict outcomes; he wanted to get into the mind of nature itself. I'm sure that's why QM was so distasteful to him, I think that's also what motivates those in the search for the "real axioms" s you put it.

But, there's also a practical motive, which is that if you can find different axioms that explain everything we've seen so far, but make new predictions that the old ones don't, and those predictions turn out to be correct, then you've done the world a great service. This is basically what Einstein did with relativity. Maybe Bohmian mechanics isn't the best example of this but there's no reason to believe continued searching for better axioms of QM won't be of value or will never result in anything new.

But I think reilly's question, if I'm not mistaken, is why is Bohm "trying" to do anything of the sort? Should our effort not be to understand existing experimental evidence and use it to plan and predict new experiments, rather than building a soothing mental picture including phenomena that have not been observed at the expense of economy of understanding of those that have? It seems we should "get out of the way" of our science, or we repeat the errors of ancient natural philosophy.

You're definitely right that nothing should be clung to just for comfort's sake. On the flip side, something that has been so successful for hundreds of years should not be thrown out on a whim if it need not be. If you have two possible interpretations of QM, one which is not consistent with prior theory, and one which is, and there is no particular reason to favor one over the other, why would you not choose the one that was consistent with what came before?

And, along those lines, suggesting that Bohmian mechanics is flawed because it is not the most convenient method with which to perform calculations misses the mark I think. Mathematical formalisms can always be adapted to make calculations easier. QM had to develop a whole new notation and concept of "state vector" just to be manageable.

What we're talking about here are the benefits to the fundamental ideas underlying Bohm's theory, and everyone here seems to agree that those ideas, if correct, could lead to some pretty radical breakthroughs, therefore I don't see why some are so eager to dismiss them.

I think it bears repeating that it took a long time for Newton's theory of light to result in new physics, let alone be widely accepted. We expect fast results in the 21st century but I think we're just spoiled like that. And QED and QFT have been so successful that I think a lot of people simply don't see the need or desire to pursue a radically different approach. These are all perfectly understandable circumstances, but they don't require the conclusion that interpretations or metaphysics or whatever you want to call it are not important.

That's why the quiddich analogy is so good. QFT can be the most successful theory in history (as Newton's was until 100 years ago) - but let's not forget that it hasn't explained everything. There's several candidates for "the snitch" (quantum gravity, dark matter, etc.) that, if a new theory explaining them came along tomorrow, would make QFT fare no better than Newton did.

 

[Ken G]

I think it goes back to the sort of Einsteinian goal of finding "the final answer" to everything.

I'd say it goes back to the ancients Greeks, but I think you're pointing out that after Galileo pretty much knocked that approach on its keester, it has made fitful comebacks, first with Newton and most recently Einstein. Whatever vestiges of Einstein's approach survived quantum mechanics are still in play today, it's true.

Einstein used to write of finding or understanding "the Old One" (or something to that effect). Clearly he wanted to do more than predict outcomes; he wanted to get into the mind of nature itself. I'm sure that's why QM was so distasteful to him, I think that's also what motivates those in the search for the "real axioms" s you put it.

Yes, I think that is completely correct. No one wants to be content with science, they all want to do natural philosophy. Feh.

But, there's also a practical motive, which is that if you can find different axioms that explain everything we've seen so far, but make new predictions that the old ones don't, and those predictions turn out to be correct, then you've done the world a great service. This is basically what Einstein did with relativity.

Absolutely true, but note that Einstein was working in an environment of considerable unexplained data. That is generally the case in science, as opposed to natural philosophy, and I would say accounts for their spectacularly different "shooting percentages".

Maybe Bohmian mechanics isn't the best example of this but there's no reason to believe continued searching for better axioms of QM won't be of value or will never result in anything new.

But is Bohm doing science, or natural philosophy? We've already heard of his great science works, so perhaps he felt justified in delving a little into the realm of the philosophical. I have no problem with that-- as long as we can clearly make the distinction and not mix it with science.

You're definitely right that nothing should be clung to just for comfort's sake. On the flip side, something that has been so successful for hundreds of years should not be thrown out on a whim if it need not be. If you have two possible interpretations of QM, one which is not consistent with prior theory, and one which is, and there is no particular reason to favor one over the other, why would you not choose the one that was consistent with what came before?

Because that is not the only difference that separates them, as per "reilly's challenge".

And, along those lines, suggesting that Bohmian mechanics is flawed because it is not the most convenient method with which to perform calculations misses the mark I think. Mathematical formalisms can always be adapted to make calculations easier. QM had to develop a whole new notation and concept of "state vector" just to be manageable.

But such a new notation was indeed developed, and widely used. There must be a reason for that.

What we're talking about here are the benefits to the fundamental ideas underlying Bohm's theory, and everyone here seems to agree that those ideas, if correct, could lead to some pretty radical breakthroughs, therefore I don't see why some are so eager to dismiss them.

The one way that I could see it being useful is if it motivates a new experiment we might not have thought of otherwise. That has been true for a long time now. So far I have only seen experiments that agreed with standard quantum mechanics, including Bell's work and EPR type work. So to say "imagine a new experiment gave results consistent with Bohm and nothing else" is pretty much to assume what is to be shown. I don't deny its possibility, I just don't see any reason to see it as more than a guess. The only reason I can see that it draws more attention than any other guess is that it restores an unsupported reliance on determinism, but that concept was already scientifically limited even in Newton's day, as thermodynamics indicates.

I think it bears repeating that it took a long time for Newton's theory of light to result in new physics, let alone be widely accepted.

That is true, but the issue with Bohm is not the amount of time, it is the lack of empirical support. Newton could point to simple experiments, it just wasn't being looked at by others. Quantum mechanics has been addressed from every conceivable angle with some of the most elaborate and expensive machines humanity can create.

We expect fast results in the 21st century but I think we're just spoiled like that. And QED and QFT have been so successful that I think a lot of people simply don't see the need or desire to pursue a radically different approach.

I can't deny that there's no telling how this overall landscape may have changed looking back in a thousand years. I wish I was going to be there, but I won't, unless the many-worlds people who accept "quantum immortality" turn out to be right.

There's several candidates for "the snitch" (quantum gravity, dark matter, etc.) that, if a new theory explaining them came along tomorrow, would make QFT fare no better than Newton did.

True enough. My personal prediction is that data will precede such a theory, not the other way around, but I suppose it can't hurt to try.

 

[peter0302]

So much agreement! Are we in the right forum?

By the way, was a single Quiddich game ever won _without_ someone getting the snitch?

 

[DrChinese]

Bell makes you throw out realism or locality, but not necessarily both. Bohm throws out locality.

Sure. But there is no "predetermined values" for all possible measurement settings in a Bell test. So what is the point? And GHZ doesn't require the assumption of locality anyway. It is merely based on the assumption of realism. So my point is that how does BM really qualify as realistic? I understand that it is non-local.

 

[akhmeteli]

In order to answer the question what would happen, if the Bohmian model turned out to be correct, we should first know that how precisely would it have turned out to be correct? What enabled scientists to verify it?

I think that hypothetically the Bohmian interpretation (BI) can prevail in one of two quite different ways. The first one is if BI makes predictions that differ from those of the Copenhagen interpretation (CI), and experiments confirm BI's predictions. So far predictions of BI do not differ from those of CI for the nonrelativistic case. It is difficult to say if the same is true for the relativistic case, as there is no generally recognized BI for that case AFAIK. Demystifier believes that BI and CI may have different predictions for the relativistic case, and he may be right, but his specific arguments, with all due respect to his research, cannot convince me.

The other way is if BI offers a description that is more appealing to physicists than that of CI. One of the problems with BI is that people just don't like it. There is a famous Bopp's phrase: "We say that Bohm's theory cannot be refuted, adding however, that we don't believe it." Einstein, who was no fan of CI, nevertheless said that Bohm's way is "too cheap". Smolin wrote: "In Bohm’s theory the ontology includes both the particle positions and the wavefunction, both of which live in the classical configuration space. If one believes that the particles are real one must also believe the wavefunction is real because it determines the actual trajectories of the particles. This allows us to have a realist interpretation which solves the measurement problem, but the cost is to believe in a double ontology."

Let me give an example of how an interpretation can prevail just because it's more beautiful and simple, without any experimental results that favor it. Copernicus' description of the world prevailed over the Ptolemeus' description not because experiments favored the former. One can correctly describe motion of planets using the Earth as the system of reference. True, such description would be complex and ugly. So Copernicus eventually prevailed. The question is then: can BI offer a nicer description than now? I think this is possible. For example, for a Klein-Gordon field interacting with electromagnetic field, the wavefunction can be eliminated in a natural way, and the electromagnetic 4-potential replaces the quantum potential as the guiding field (http://arxiv.org/abs/quant-ph/0509044 ).

 

[Ken G]

Let me give an example of how an interpretation can prevail just because it's more beautiful and simple, without any experimental results that favor it. Copernicus' description of the world prevailed over the Ptolemeus' description not because experiments favored the former.

Actually, that isn't true. Ptolemy's model had several elements that were fully refuted by Galileo's observations, and Tycho's observations as well. They included the motion of Venus, and moons clearly orbiting Jupiter not Earth. If not for these empirical facts, and others, I doubt Copernicus would have prevailed, given the flaws in that theory as well. I don't know of any modern-science theory that replaced a widely accepted one without new and unexplained observations, and I think it's kind of a myth that science is theory or philosophy driven.

True, such description would be complex and ugly. So Copernicus eventually prevailed.

I don't think you are talking about the Greek models, you are talking about geocentric models like Tycho's. But his was never a prevailing theory, because the real lesson of Galileo's observations was that the Earth is not special, not that the Earth is not at the center. That was the primary impetus behind much of the geocentric philosophy. So to me, the real lesson in the Copernicus vs. Ptolemy issue is, don't use philosophy to do science. That would make it a poor example to bolster the Bohmian approach, but of course I cannot say that approach is wrong.

 

[Demystifier]

I challenge Dr. Nikolic or anyone else to do some real problems in the Bohmian way:

1.Calculate the the LS and other relativistic corrections for hydrogen.

2. Work out the temporal interference pattern of the neutral K meson system;

3. Work out the radiative corrections to coincidence detection high energy electron-proton scattering.

4. Calculate the electron's magnetic moment to 13 decimal places.

5.With all spin and isospin factors in a relativistic format, show that the so-called 3-3 resonance exists in pion-nucleon scattering, with the partial wave approach, and estimate the mass of the resonance.

6. (Too much scattering?) Do superconductivity.

With the exception of number 4 and 6 these are all relatively straightforward to formulate with conventional field theory. The magnetic moment problem is very difficult, but it can be and has been done. And 2-6 have been done during the last 50 years; number 1 was done in the 1930s.

These will provide a very minimal test of the Bohm approach to do real physics.

It is trivial to do this minimal test of the Bohm approach. Just as it is trivial to show that standard quantum mechanics (QM) is consistent with observed motions of planets.

BM is NOT an alternative to standard QM. Instead, it is supposed to be an improvement of standard QM. But does standard QM really needs an improvement? Adherents of standard QM think that it doesn't. Nevertheless, in the relativistic case it does need an improvement and BM offers a possible solution:
http://xxx.lanl.gov/abs/quant-ph/0406173 [Found.Phys.Lett. 18 (2005) 549]
http://xxx.lanl.gov/abs/0705.3542

It is true that, at the moment, there is no experimental proof that the Bohmian interpretation is correct.
But there is also no experimental proof that the Copanhagen interpretation is correct either.
(Note that I distinguish the Copanhagen interpretation from the standard "shut-up-and-calculate" interpretation.)

 

[Demystifier]

Demystifier believes that BI and CI may have different predictions for the relativistic case, and he may be right, but his specific arguments, with all due respect to his research, cannot convince me.

Can you explain why?

 

[ZapperZ]

Let me give an example of how an interpretation can prevail just because it's more beautiful and simple, without any experimental results that favor it. Copernicus' description of the world prevailed over the Ptolemeus' description not because experiments favored the former. One can correctly describe motion of planets using the Earth as the system of reference. True, such description would be complex and ugly. So Copernicus eventually prevailed. The question is then: can BI offer a nicer description than now? I think this is possible. For example, for a Klein-Gordon field interacting with electromagnetic field, the wavefunction can be eliminated in a natural way, and the electromagnetic 4-potential replaces the quantum potential as the guiding field (http://arxiv.org/abs/quant-ph/0509044 ).

It is trivial to do this minimal test of the Bohm approach. Just as it is trivial to show that standard quantum mechanics (QM) is consistent with observed motions of planets.

BM is NOT an alternative to standard QM. Instead, it is supposed to be an improvement of standard QM. But does standard QM really needs an improvement? Adherents of standard QM think that it doesn't. Nevertheless, in the relativistic case it does need an improvement and BM offers a possible solution:
http://xxx.lanl.gov/abs/quant-ph/0406173 [Found.Phys.Lett. 18 (2005) 549]
http://xxx.lanl.gov/abs/0705.3542

It is true that, at the moment, there is no experimental proof that the Bohmian interpretation is correct.
But there is also no experimental proof that the Copanhagen interpretation is correct either.
(Note that I distinguish the Copanhagen interpretation from the standard "shut-up-and-calculate" interpretation.)

This is a heads up. Please use published references only. Unlike BTSM and High Energy Physics forums where arXiv preprints are commonly used, the rest of the physics forums (based on the practice of the respective fields) still favor heavily on only published papers.

I know some of the arXiv preprints have been published. So please include the exact reference. If not, they should not be used in here.

Zz.

 

[Ken G]

It is trivial to do this minimal test of the Bohm approach.

Do you mean by this that it is trivial to show that the Bohm approach is equivalent to QM, and then carry out the challenge using regular QM? If so, is that the same thing as meeting the challenge with the Bohm approach itself? Unless I'm mistaken, which I well may be, this argument sounds a little like proving that Shakespeare can be written in piglatin by showing there is a simple one-to-one transformation between that and English. But is such a transformation really the same as writing that great prose in piglatin from the outset? "Otay ebay or otnay otay ebay..."

Just as it is trivial to show that standard quantum mechanics (QM) is consistent with observed motions of planets.

To do that, wouldn't you have to treat a planet as a "quantum"? Can we claim that doing so is really within the axioms that make QM a "correct" theory? My point is that we pretend we are using an axiomatic system, but then in real applications we replace some of the axioms with any old thing we like in order to get an answer. Well, if we are going to do that, why pretend we have a self-consistent theory in the first place?

BM is NOT an alternative to standard QM. Instead, it is supposed to be an improvement of standard QM.

That is in interesting point, and I am inclined to take your word for that, but you may color me terribly unimpressed by a scientific theory that is "supposed" to be an improvement on purely philosophical grounds, yet has no experimental justification that is not pure guesswork. Why should we pay any attention to what a theory is "supposed" to be? That merely confirms what I said earlier that if I tack a periscope onto my car, and I can say that it is now supposed to be a submarine.

But there is also no experimental proof that the Copanhagen interpretation is correct either.
(Note that I distinguish the Copanhagen interpretation from the standard "shut-up-and-calculate" interpretation.)

Yes, the aspects of the Copenhagen interpretation that go beyond the "shut up and calculate" level are equally superfluous and we have no reason to pay any attention to them either. Are we empowering ourselves to do science, or philosophy here? I'll admit that the exercise can guide is to finding experiments that can test where the philosophies take us, but I'm not actually seeing any of those tests being done, so I tend to feel that all we are doing is trying to pretend we know more than we do-- a hallmark of unscientific paths to truth.

 

[Demystifier]

I'll admit that the exercise can guide is to finding experiments that can test where the philosophies take us, but I'm not actually seeing any of those tests being done, so I tend to feel that all we are doing is trying to pretend we know more than we do-- a hallmark of unscientific paths to truth.

I agree with most of your remarks, especially with the one I cite above.

 

[peter0302]

Sure. But there is no "predetermined values" for all possible measurement settings in a Bell test. So what is the point? And GHZ doesn't require the assumption of locality anyway. It is merely based on the assumption of realism. So my point is that how does BM really qualify as realistic? I understand that it is non-local.

I'm not sure what mechanism the BI provides to explain Bell experiments. I believe it's some kind of non-local influence but I could be wrong. You're certainly right that there's no possible configuration of "predetermined values" that could explain the Bell correlations.

I was just pointing out that even accepting Bell's Theorem it's possible to have realism without locality.

To respond to some other comments, I have previously suggested performing Bell experiments with measurements made at relativistic speeds. Obviously the measurements would have to be somewhat indirect since it'd be hard to accelerate a photon detector to .9c. :) But if such an experiment could be devised it would at least eliminate the possibility that measurement outcomes are frame dependent.

 

[Demystifier]

I'm not sure what mechanism the BI provides to explain Bell experiments. I believe it's some kind of non-local influence but I could be wrong.

You are right.