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Why Bohm?

  1. May 3, 2007 #1
    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.)
     
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  3. May 3, 2007 #2

    Demystifier

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    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 Schrodinger 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.
     
  4. May 4, 2007 #3
    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.
     
  5. May 4, 2007 #4

    Demystifier

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    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.
     
  6. May 4, 2007 #5

    Demystifier

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    A possible answer to the question "Why Bohm?" is provided also by this essay:
    http://arxiv.org/abs/physics/0702069
     
  7. May 4, 2007 #6
    This seems quite good answer. I don't know how to strike it down :wink: 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.
     
  8. May 4, 2007 #7

    Fra

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    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
     
  9. May 4, 2007 #8

    Demystifier

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    So do you really believe that Moon is not out there if nobody looks at it?
     
  10. May 4, 2007 #9

    Demystifier

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    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%. :yuck: :rofl:
     
  11. May 4, 2007 #10

    Demystifier

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    You think like an experimentalist. :smile:
    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?
     
  12. May 4, 2007 #11
    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.)
     
    Last edited: May 4, 2007
  13. May 4, 2007 #12

    Fra

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    "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
     
  14. May 4, 2007 #13

    Fra

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

    I want to maximize logical and philosophical consistency from "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.

    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 :wink:

    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.

    Well, if you are talking about litteraly "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
     
  15. May 4, 2007 #14

    Fra

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    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
     
  16. May 4, 2007 #15

    Demystifier

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    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.
     
    Last edited: May 4, 2007
  17. May 4, 2007 #16

    Fra

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    > 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 :smile:

    /Fredrik
     
  18. May 4, 2007 #17

    Demystifier

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    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?
     
  19. May 4, 2007 #18

    Demystifier

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    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?
     
  20. May 4, 2007 #19
    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.
     
  21. May 4, 2007 #20

    Demystifier

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    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?
     
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