Why Explore the Bohmian Interpretation of Quantum Mechanics?

[jostpuur]

Why Bohmian interpretation? It's now one and half year after I took my first course on quantum mechanics, and I've already started liking it the way it is. I have trouble seeing any motivation for deterministic theory. Is there any reasons to study the Bohmian interpretation? (I haven't studied it myself at all yet, except I've checked the wikipedia's article briefly.)

(btw. I couldn't have missed Demystifier's eagerness of talking about Bohmian interpretation here.)

 

[Demystifier]

Actually, the main motivation for Bohmian interpretation is NOT the determinism. Instead, the main motivation is to have some sort of objective physical reality that exists even without measurements or observations. However, the structure of the Schrödinger equation for a wave function written in the polar form suggests the deterministic Bohmian interpretation as the most "natural" interpretation, given the similarity with an analogous mathematical structure in classical mechanics written in the Hamilton-Jacobi form. Thus, the determinism appears as a bonus, not necessarily as a part of the original desire.

 

[ueit]

Why Bohmian interpretation? It's now one and half year after I took my first course on quantum mechanics, and I've already started liking it the way it is. I have trouble seeing any motivation for deterministic theory. Is there any reasons to study the Bohmian interpretation? (I haven't studied it myself at all yet, except I've checked the wikipedia's article briefly.)

1. Science has the purpose of predicting experimental results.

2. In order to predict an experimental result you need the assumption of determinism, you have to assume there is a reason why you've got that experimental result.

3. There are experimental results that are not predicted by QM (the exact moment of decay of an unstable nucleus, the place on the screen where a particle will be detected in a double slit experiment, etc.).

From 1, 2, 3 -> we need a fundamental, deterministic theory underlying standard QM, which is a statistical theory.

Bohm's interpretation might be the first step towards the development of such a fundamental theory.

Assuming things happen without a cause is not science.

 

[Demystifier]

1. Science has the purpose of predicting experimental results.

Assuming things happen without a cause is not science.

Although I am an adherent of the Bohmian deterministic interpretation, I do not completely agree with these statements. First, the purpose of science is not only to predict, but also to make observations and to note down systematically the knowledge obtained by observations. Second, the stochastic theory and the theory of probability, which do not study possible causes of things happening, are also scientific theories. Finally, even if we accept that the ultimate purpose of science is to understand the ultimate causes, a possibility that such causes do not exist is not unscientific and cannot be excluded.

 

[Demystifier]

A possible answer to the question "Why Bohm?" is provided also by this essay:
http://arxiv.org/abs/physics/0702069

 

[jostpuur]

Actually, the main motivation for Bohmian interpretation is NOT the determinism. Instead, the main motivation is to have some sort of objective physical reality that exists even without measurements or observations. However, the structure of the Schrödinger equation for a wave function written in the polar form suggests the deterministic Bohmian interpretation as the most "natural" interpretation, given the similarity with an analogous mathematical structure in classical mechanics written in the Hamilton-Jacobi form. Thus, the determinism appears as a bonus, not necessarily as a part of the original desire.

This seems quite good answer. I don't know how to strike it down It seems reasonable to want to have "objective physical reality". Altough this didn't convince me of Bohmian interpretation. I think it is actually good thing that we have philosophical problems conserning quantum theory, because as long as a theory is not trying to tell too clearly what reality is, there is a good chance it is not completely wrong.

 

[Fra]

Instead, the main motivation is to have some sort of objective physical reality that exists even without measurements or observations.

This is what I personally don't like about the approach. In fact it doesn't make much sense to me.

To me "reality" is formed by interactions/measurements/observatons. And that is thus inherently relative, but that does not mean it doesn't exist connections between the views. And to a certain extent, these connections are at least less relative.

I don't even understand how you can define something that you've never interacted with. It sounds almost a bit religious to me.

I still respect Demystifiers philosophy, but to add the other side, my thinking is that if you never smoked before, don't start now. You don't need it and you will not miss it. I think it's only an addiction you'll have hard time to get rid of :)

/Fredrik

 

[Demystifier]

To me "reality" is formed by interactions/measurements/observatons.

So do you really believe that Moon is not out there if nobody looks at it?

 

[Demystifier]

I think it is actually good thing that we have philosophical problems conserning quantum theory, because as long as a theory is not trying to tell too clearly what reality is, there is a good chance it is not completely wrong.

So, the best theory is the theory in which it is completely unclear what reality is? Good, then I have a perfect theory. It says that things appear to us as they appear. Indeed, the chance that it is correct is 100%.

 

[Demystifier]

I don't even understand how you can define something that you've never interacted with. It sounds almost a bit religious to me.

You think like an experimentalist.
On the other hand, quantum physics is a THEORY. In theory, it is not problem to define something that never interacted with something else. For example, in standard QM, it is not a problem to define a free wave function.

By the way, would you call real two particles that interact between themselves, but never interacted, either directly or indirectly (via other particles), with YOURself? Would you call them real if they interacted with ME, but I never told you about that?

 

[jostpuur]

So, the best theory is the theory in which it is completely unclear what reality is? Good, then I have a perfect theory. It says that things appear to us as they appear. Indeed, the chance that it is correct is 100%.

A theory that explains what reality is, would certainly be even better, but I don't think we are going to get such a theory for some time. It's just too difficult problem.

My point was this: If a theory is not attempting to explain what Reality is, then the theory is not neccecarely wrong. If a theory instead is attempting to explain what Reality is, I can guarantee, it is wrong.

(Edited add:

I just realized this can be understood in many different ways. I truly did have something in mind, that had to do with the current topic. I'll see how this goes, and maybe explain better.)

 

[Fra]

So do you really believe that Moon is not out there if nobody looks at it?

"Look at" in the litteral sense is of course not a proper extension of the analogy.

I mean that if the moon did not affect us, it wouldn't have a real level of justification beyond anything else.

Of course, you may still choose to incorporate it in your theory if you like, but it would be somewhat arbitrary and not comply to the principle of insufficient reason that serves to minimize unjustified complexity.

We don't have the choice to "not look" at the moon in the proper meaning of the generalisation - we can not choose to ignore the gravity of the moon, and it's other effects. If we didn't actively look at it, it would impact us by deviations cause by our ignorance of it.

I think new structures should ideally be introduced upon justification. It is true that justification when it comes to human mind ma be quite relative, so I can of course not prove that this strategy isn't the best for you or anyone else.

I act based upon the information that reaches me, and when I am wrong I will adjust according to feedback.

/Fredrik

 

[Fra]

You think like an experimentalist.

Perhaps, but I am not one. I'm rather more of a philosopher to mind

I want to maximize logical and philosophical consistency from "theory".

On the other hand, quantum physics is a THEORY.

Yes but it's a theory of reality, including the problems and issues it implies. We better deal with it as they reveal themselves.

In theory, it is not problem to define something that never interacted with something else. For example, in standard QM, it is not a problem to define a free wave function.

Standard QM is not satisfactory. Within the classical domains, it's a great effective theory, but it has logical and philosophical problems. I'm sure you agree since you like Bohm, but I think we may disagree upon the way to go

By the way, would you call real two particles that interact between themselves, but never interacted, either directly or indirectly (via other particles), with YOURself?

If I understand you correctly, they never ineracted with me in any way, then they do not have a place in my current understanding.

However, if they ever appear to interfere wit me at some later point, they are invited. I believe in evolutionary approach. I think even event spaces may evolve. This is a flaw in the current theory.

Would you call them real if they interacted with ME, but I never told you about that?

Well, if you are talking about literally "talking" it's an analogy that's a bit out of context, but if they interact with you, and you interact with me, there is a good chance they have indirectly interacted with me. But wether I have the capacity to respond to everything depends on me. Am I a human or an atom?

/Fredirk

 

[Fra]

the chance that it is correct is 100%.

How about asking another question to measure your theory:

What is the chance that your theory will recover from the event it makes one incorrect prediction? What about the physics of the corrective action required to get back on track with reality?

An example from biology. A good organism is one that is adaptive and outperforms it's competitors when it come to adaptions. The organism that happens to be in the lead because it was lucky aren'y likely to make the next turn.

Suppose we have an incident beam of electrons to a hard target. Those foolish electrons don't know how stupid they are to be heading that target. But as soon as they start sensing the target they will readily resolve the situation, one way or the other.

/Fredrik

 

[Demystifier]

If a theory instead is attempting to explain what Reality is, I can guarantee, it is wrong.

I disagree. For example, classical mechanics says what reality is. Still, it is not really wrong. Instead, it is only approximately correct. In a similar sense, a realistic modification of standard QM could provide a better approximation, even if this would not be the final theory either.

 

[Fra]

> Still, it is not really wrong. It is only imperfect.

If that's the way you see it, ok. But then it leads me to conclude that perfect or not, isn't so much the issue. As long as we know how to improve? Right?

Do we agree there?

Thus, what kind of theory are we looking for to have those properties we look for? My personal conclusion is that it's anything but bohmian mechanics

/Fredrik

 

[Demystifier]

Standard QM is not satisfactory. Within the classical domains, it's a great effective theory, but it has logical and philosophical problems. I'm sure you agree since you like Bohm, but I think we may disagree upon the way to go

So, in your opinion, what is the way to go?
You may also vote here:
https://www.physicsforums.com/showthread.php?t=146601

By the way, if I understood you correctly, you say that real is something that interacts with YOU. Isn't it a slightly egocentric definition of reality? Or are you just saying that reality is relative or (as C. Rovelli would say) relational?

 

[Demystifier]

1. If that's the way you see it, ok. But then it leads me to conclude that perfect or not, isn't so much the issue. As long as we know how to improve? Right? Do we agree there?

2. Thus, what kind of theory are we looking for to have those properties we look for?

3. My personal conclusion is that it's anything but bohmian mechanics

1. Yes, we agree.

2. Nobody knows yet. There are various approaches. Those who look for a realistic theories represent a minority, but it is perhaps interesting to say that one winner of the Nobel Prize also belongs to this minority.

3. Is that really a conclusion, or just an intuition? If it is a conclusion, what is the argument?

 

[Tomsk]

So do you really believe that Moon is not out there if nobody looks at it?

To add something to this, I think if every photon, graviton and any other particle coming from the moon and directed towards the Earth did not interact with the Earth in any way, and if that happened for some period of time, then I would have to say, yes, the moon is not there. But the chances of that happening are so minute you may as well say the moon is always there, and is objectively real. I think it's that sort of continuous flow of information between the moon and earth, for example, that tricks us into thinking that there is an objective reality out there.

 

[Demystifier]

To add something to this, I think if every photon, graviton and any other particle coming from the moon and directed towards the Earth did not interact with the Earth in any way, and if that happened for some period of time, then I would have to say, yes, the moon is not there. But the chances of that happening are so minute you may as well say the moon is always there, and is objectively real. I think it's that sort of continuous flow of information between the moon and earth, for example, that tricks us into thinking that there is an objective reality out there.

I still do not understand:
Are we just tricked into thinking that it is real, or is it real?
Is the flow of information more real than material objects?
And what about observers falling into a black hole? They cannot send us any information about themselves, so are they real?

 

[Demystifier]

Thus, what kind of theory are we looking for to have those properties we look for? My personal conclusion is that it's anything but bohmian mechanics

Without new experimental results that would suggest us new ways to go, the only criterion that remains is the internal consistency and simplicity of the theory. In my opinion, non-realistic theories suffer from a problem of being ambiguous (see e.g. the Conclusion in http://arxiv.org/abs/quant-ph/0609163 )
which ruins their internal consistency. Among realistic interpretations of QM, the Bohmian one is the simplest one.

 

[Fra]

Or are you just saying that reality is relative or (as C. Rovelli would say) relational?

Exactly.

Relational is a better word even, as relational can be applied to realism as well.

I am not specifically updated on Rovellis personal philosophy but I know what your asking and yes I'm definitely on the "relational side" of things. Relational concepts doesn't end with spacetime, there is also relational probability theory. And that's what I think is the proper interpretation of QM. Probabilities are always relational, there is IMO no such thing as an absolute probability. A relational probability is a conditional probability. Clearly the probability of any event, will be totally different depending on your prior information. And the whole point is that there isn't really anything like a universal prior. Only relational priors. It also leaves (IMO) the proper theory as intrisically evolutionary.

/Fredrik

 

[ueit]

Although I am an adherent of the Bohmian deterministic interpretation, I do not completely agree with these statements. First, the purpose of science is not only to predict, but also to make observations and to note down systematically the knowledge obtained by observations.

Sure, there are many activities involved, but the final purpose is to put that knowledge in a logical framework, a scientific theory. If that theory is not falsified, it allows us to understand how things work.

Second, the stochastic theory and the theory of probability, which do not study possible causes of things happening, are also scientific theories.

Sure, but the claim that such theories are fundamental, without a rigorous proof, is not scientific, I think it is even anti-scientific as it stops research in that area.

Finally, even if we accept that the ultimate purpose of science is to understand the ultimate causes, a possibility that such causes do not exist is not unscientific and cannot be excluded.

I disagree. With the exceptions of non-existence proofs (like the proof against squaring the circle) giving up in the face of an unexplained phenomenon is unscientific. In the case of QM, such a proof cannot exist because counterexamples, like BM, exist.

 

[Fra]

3. Is that really a conclusion, or just an intuition? If it is a conclusion, what is the argument?

To not get into too lengthy arguments here, I'll say it's intuition. But of course it's, I've got argumentations on my own, but that's a lot of philosophy and nothing that would quality as a proof. I just find what I perceived to be the bohmian desires, to be in conflict with the principles of relationism I look for.

I simply see Bohmian as more speculative, and the speculations are not justified from my point of view, and I also don't see what problem they solve. The problem of "objective realism" is IMO not a problem to start with.

My guidlines is that speculations that are inferred using sound reasoning is where I place my bets. This conclusion is maintained until I see reason to change it, at which point I will. Of course if you have a differing opinion, you should follow the path suggested from your perspective.

Long time ago I used to think in deterministic terms and require "realism" in the objective sense. But I have come to see what was wrong with this. It's hard if not impossible(probably so) to be both complete and consistent, and my preferred solution is to increase my completeness in a consistent manner, well aware of that total completenss will never most probably never be acheived.

/Fredrik

 

[Fra]

Is the flow of information more real than material objects?

IMO, it's manifestations of the same thing. I think the closest thing to reality we get is what patterns we can identify in the information flow we are fed.

Suppose I am informed that there is a wall ahead of me, I can't possibly tell the difference between the information and the supposed reality behind it. It's the same thing.

Or more commonly in everday life, reality is a severe idealisation and simplification of the "real reality" into something more comprehensible.

Clearly there is a possibility that I have been misinformed, and that the concept of this wall is in fact in logical conflict with other information I am also exposed to.

I personally consider information to be more fundamental, and physical interactions are really information exchange. And my opinion is that much more clarity will be found if we find the proper information theoretic abstraction of physics. If you ask me there isn't any doubt it will come, the question is just when.

/Fredrik

 

[Fra]

Without new experimental results that would suggest us new ways to go, the only criterion that remains is the internal consistency and simplicity of the theory. In my opinion, non-realistic theories suffer from a problem of being ambiguous (see e.g. the Conclusion in http://arxiv.org/abs/quant-ph/0609163 )
which ruins their internal consistency. Among realistic interpretations of QM, the Bohmian one is the simplest one.

I agree that QM has logical and philosophical issues. And I think some of these issues are also the causes why there is no consistent theory of quantum gravity. These needs to be solved indeed. And I belong to those who consider them to be fundamental issues, rather than just mathematical issues.

In fact I think it's not really much point in discussing copenhagen interpretation vs bohm. Neither is perfect, and I think it's not just the interpretation that has a problem, it's more fundamental.

I don't have the solution, but I know exactly where I am looking for it.

/Fredrik

 

[Fra]

Sure, but the claim that such theories are fundamental, without a rigorous proof, is not scientific, I think it is even anti-scientific as it stops research in that area.

Of course I couldn't care less than to discuss the meaning of the word "scientific" but I take it you mean that there is no benefit in researching stochastic approaches?

I would not draw this conclusion. Thermodynamics is basically a theory partly based on stochastic processes. Is that not scientific?

Quantum mechanics can also be given such interpretations : given constraints and a prior probabiltiy distributions, our optimal guess is a stochastic evolution under certain constraints. And this can in fact give rise to nontrivial dynamics.

Stochastic modelling and probabiltiy theory is also used in artifical intelligence modelling, and game theory, learning rules that has been terribly successful.

/Fredrik

 

[reilly]

There's physics and there's physics. Apparently there are many folks, primarily but not entirely non-physicists, who do not understand the basic purpose of physics. That purpose is to develop as good a description of Nature as possible. As we have found over the centuries, a good description allows us to build bridges and airplanes, computers, refrigerators; allows us to know where to point the rocket to get to the moon.

Why things are as they are is generally beyond our comprehension, but gives the philosophically oriented plenty of room for endless speculation.(See post #21 in the thread about photons,. How is light experimentally proven to be a particle? )

I first became acquainted with Bohm's work back in the late 1950s, when I was an undergraduate. When asked, my professors told me that studying Bohm's approach to QM was a waste of time. I completely concur.

In the past 50 years, Bohm's approach has led to no progress in physics, while the conventional QM approach has led to extraordinary progress in atomic, nuclear, solid state, and particle physics. (Most if not all of this progress involves what might be called a modified Copenhagen interpretation, which boils down to Born's idea that the square of the wave function is a probability density. None involves Bohm's interpretation.)

After 50 years of no significant contribution to physics, seems to me that Bohm simply did not get it.

(Fra -- Note that many AI firms, in the heyday of LISP, went belly-up; they ultimately had little to offer. The rise of artificial neural networks(ANN) provided a new and flexible approach to machine learning. ANN firms have had much more success than the "traditional" AI firms. I worked in the ANN field for about 10 years; stochastic modeling was little used -- except, perhaps, in the training of a feed forward network, to insure that the input signals are randomly fed to the network, not exactly a huge problem)

Those who yearn for the certainty of the 19th century will find no satisfaction now, nor in the future.
Regards,
Reilly Atkinson

 

[DrChinese]

In the past 50 years, Bohm's approach has led to no progress in physics, while the conventional QM approach has led to extraordinary progress in atomic, nuclear, solid state, and particle physics. (Most if not all of this progress involves what might be called a modified Copenhagen interpretation, which boils down to Born's idea that the square of the wave function is a probability density. None involves Bohm's interpretation.)

A good point, and probably the main reason why folks like Steven Weinberg (probably our greatest living theorist) pay it little or no attention.

And in all fairness to QM, I think that Bohmians should own up to a simple admission of their own: if there are non-local interactions, why is it that c is so fundamental in the propagation of information and all other cause/effect relationships? This has not been "unambiguously" answered (except maybe in their own minds) ...

P.S. I personally am interested in learning more, however.

 

[Anonym]

And in all fairness to QM, I think that Bohmians should own up to a simple admission of their own: if there are non-local interactions, why is it that c is so fundamental in the propagation of information and all other cause/effect relationships? This has not been "unambiguously" answered (except maybe in their own minds) ...

The existence of the maximum velocity propagation of interactions is the Principal Physical Postulate.