Quantum Theory and Philosophy

Discussion in 'Physics & Math' started by Human001, Sep 24, 2010.

  1. RJBeery Natural Philosopher Valued Senior Member

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    Sure, but first I need to make sure I'm not just wasting my time. I want prometheus, and anyone else who believes so, to state explicitly that they believe the Bohm Interpretation is ruled out as a viable QM interpretation because of Bell's inequalities and that IF they are proven to be wrong they will admit so contritely without any snarky comments.

    You see NeverFly, in my experience when demands of production are put on me and I do what I can to deliver, the subject changes or the goal posts move or the other party goes "off the grid" and stops posting.

    This will be your moment in the sun, prometheus, after all of the harping on Green Destiny for not admitting when he's wrong, to show the rest of the forum how it's done. And if I'm the one that's mistaken I'll be happy to do the same.
     
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  3. BWE1 Rulers are for measuring. Registered Senior Member

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    thread just got interesting.
     
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  5. przyk squishy Valued Senior Member

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    Hi, it isn't. The Bohm interpretation is a nonlocal hidden variables theory. Bell inequalities don't cover it.
     
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  7. prometheus viva voce! Registered Senior Member

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    I'll take your word for it.
     
  8. prometheus viva voce! Registered Senior Member

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    Not that I really understand too much about the various interpretations of QM (and in fact, see them as rather pointless because almost all of these types of interpretations are based on the mechanics of particles. The notion of a particle is actually a very limiting viewpoint when one considers the fact the universe contains quantum fields, not particles, but I digress...) but having done a little more reading about it it seems a big problem with the Bohm interpretation is that it doesn't match too well with relativity. Any comments?
     
  9. prometheus viva voce! Registered Senior Member

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    PS, Beery, if you look through my posting history you will find plenty of occasions where I have been wrong and admitted it. Maybe it's time you started practising what you preach like on the subject of coordinates on a sphere for example?
     
  10. przyk squishy Valued Senior Member

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    Not all of them are. I've studied "textbook QM" and have started to develop a reasonable intuition for it, so attempts to dress QM up in a more intuitive fashion (intuitive to whom?) or restore feature X of classical mechanics won't resonate with me. The only motivation I've ever had for "interpreting" QM is its apparently dualistic treatment of nature (artificial separation between the "classical" and "quantum" world), and its special treatment of observers and measurements.
     
  11. RJBeery Natural Philosopher Valued Senior Member

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    Actually, prometheus, to this point I don't think I've ever "made demands" that anyone publicly admit they were wrong about anything (with the exception being a few posts up, giving you the chance to avoid the appearance of hypocrisy). From what I've seen, these are the types of demands you, BenTheMan, Guest, AN, etc. place on others*, yet do not apparently demand of yourselves. Frankly I don't care that much. I'm not here to score points, I'm here to learn. I understood pretty quickly that I would need to suffer certain personalities in order to continue posting here and I've accepted it. As far as the coordinates on a sphere goes, I'm going to start a new thread...

    *Others outside of your "clique". Despite NeverFly's attempts to suggest otherwise, there does exist a clique on this forum. However, the existence of such a clique does not invalidate NeverFly's other comments. The concepts are not mutually exclusive.
     
  12. prometheus viva voce! Registered Senior Member

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    That's kind of the point though right? All these interpretations are perpetuated by people that don't like the quantum features of QM. The physicist interpretation of QM is "shut up and calculate," which seems to do a pretty good job of getting the answers right. Doesn't that mean that X interpretation of QM is pointless?
     
  13. prometheus viva voce! Registered Senior Member

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    If by "clique" you mean "people that are qualified and smart enough to do real science," then I'm flattered that you put me in that group. Neverfly is a great example of an enthusiastic amateur that's willing to learn, as opposed to, say, a self delusional ego manic with a bag full of ignorant but hardy preconceptions they want to impose on the world*.


    *Author is not qualified to make mental health diagnoses. Similarity to Persons Living or Dead Is Purely Coincidental.
     
  14. Neverfly Banned Banned

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    Aside; I find this an excellent post. I wonder what ever happened to Human001? He should be sniffing this stuff up like 'twas a pixi stick.

    All forums have cliques. I was pointing out to Green Destiny that that was not exactly the problem he was having...
     
  15. Neverfly Banned Banned

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    Trust, I have my moments when I can act like Green Destiny

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    But this is also why I've been trying to reach him. Be assured, I'll put my foot in my mouth and end up eating crow around here often enough...
    But it IS a learning thing, that I had to and still struggle to learn-- To Accept Correction With Grace.
     
  16. RJBeery Natural Philosopher Valued Senior Member

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    Who's scruffy-lookin??

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  17. przyk squishy Valued Senior Member

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    Depends on your goals. If you're just interested in making predictions, then yes it's probably pointless. Personally I think of the goal of physics as being to produce self-contained models of nature. And certainly a requirement that's always been placed on theories is that they should be internally consistent. When you look at how quantum mechanics is usually formulated, the theory makes two statements about how systems evolve: the Schroedinger equation, and the measurement/collapse postulate. In addition to attributing a privileged role to "observers" and "measurements", the domain of applicability of the measurement postulate arguably overlaps with that of the Schroedinger equation, since you could always imagine describing a system, observer, and measuring apparatus as one large quantum system, and the Schroedinger equation makes a deterministic prediction about how it will evolve. That suggests a redundant postulate, and variations of the Everett interpretation suggest that it isn't really needed after all. So if you like, a goal I sympathise with is removing redundancy and arriving at a minimal axiomatic formulation of QM. The Everett and similar interpretations are based on a subset of the axioms of quantum mechanics.
     
  18. RJBeery Natural Philosopher Valued Senior Member

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    Yet you say
    This strikes me as a contradiction. You say that there is merit in seeking a QM interpretation with minimal axiomatic formulation, as well as eliminating arbitrary or artificial separation between the classical and quantum world, YET attempts to restore feature X from classical mechanics does not resonate with you. To me, sacrificing "feature X" from classical mechanics due to our initial reactions to quantum phenomena is equivalent to making an arbitrary separation between the two worlds, particularly if we later realize that such a sacrifice was not necessary.

    I think I'd enjoy a QM interpretation discussion with you, przyk. We could start a new thread or, preferably, exchange points of view via PM or email...what say you?
     
  19. BWE1 Rulers are for measuring. Registered Senior Member

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    I'd just like to add that GR is not at all intuitive either. We use all kinds of examples, marbles on a sheet, shadows on a globe, etc etc but space and time are not experienced nor perceived that way and the visualizations actually are mostly not approximations of the equations in terms of predictive utility.

    GR and QM are equally unintuitive because in each case, we have to take quantities and translate them into discrete things with discrete boundaries.

    ETA: This is an interesting thread.
     
  20. przyk squishy Valued Senior Member

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    For starters, an easy justification is that preferring a minimal axiomatic formulation is just applying Occam's razor: don't postulate more rules or entities than you actually need. If quantum states + the Schrödinger equation are enough, why entertain a theory that postulates quantum states + observers + measurement + the Schrödinger equation + wavefunction collapse?

    As far as I'm concerned, I see the measurement problem as a consistency issue. There's nothing stopping me in principle from giving a full quantum description of an observer, a measuring instrument, and eg. an atom he's observing, then applying the Schrödinger equation to the whole system and extracting a prediction. But because this is an "observer" (left undefined in QM textbooks) performing a "measurement" (also left undefined), there's another rule that says "wavefunction collapse" occurs, which also produces a prediction. Then it's really simple: either both predictions are compatible and the collapse postulate is redundant, or they conflict and quantum theory is internally inconsistent.

    In general, you want to avoid mixing "macroscopic" postulates into a fundamental theory, since there's no guarantee the "macroscopic" postulate will actually be consistent with the rest of the theory. My motivation for this doesn't have anything specifically to do with classical mechanics. The root of it isn't even restricted to physics for that matter: it's actually a sort of formulation or design ideal that I'm sure you'll find in some form in any technical discipline. The closest analogue I can think of in software engineering for example is the preference for orthogonality and modular design and information hiding (ie. implementing an application as a set of components interacting through well defined interfaces). There are practical benefits to this kind of attitude (eg. modular software tends to be more robust and easier to test, modify, and debug; fewer well-chosen postulates that don't step on each other's domain of applicability are less likely to conflict with one another), but I'm the sort of person who has it hardwired instinctively.

    I'm not sure what you mean by this. By feature "X" of classical mechanics, I meant the sort of features I felt QM threatened back when I was in highschool, eg. classical particles, determinism, and realism.

    This thread already seems to be a QM interpretation discussion, so it's really up to you. You can also PM me if you want. It's not like I'm an expert on QM interpretations though.
     
    Last edited: Sep 30, 2010
  21. RJBeery Natural Philosopher Valued Senior Member

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    Agreed 100% but I suspect there are mechanisms that the Everett interpretation requires that you may not be considering (presuming you subscribe to the Everett Interpretation).
    Agreed!
    Here, I disagree and it's related to elegance (or Occam's Razor if you wish). Shouldn't we strive for an interpretation of physics that's impervious to scale?
    Just curious, but would have an affinity for a valid interpretation that was real and deterministic?

    I guess I asked if you wanted to discuss this topic because in my experience QM interpretations are kind of a "private subject" for Physicists (meaning, either they don't have an opinion on them or they don't want to make any bold statements publicly about them), and it just seemed to me that you had both an opinion and a willingness to discuss it...I was just giving you the chance to discuss it with me privately. Maybe I'll start a new thread for this but this forum has been eating up a lot of my time lately. Let me think about it...
     
  22. quadraphonics Bloodthirsty Barbarian Valued Senior Member

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    Well, all interpretations of QM have that problem one way or another, because QM itself doesn't match up too well with relativity, exactly because of the "spooky action at a distance" that Bell's Inequalities deal with. In the Bohm case, you've got a nonlocal theory, and that's a mismatch with relativity. But other interpretations have other problems - at bottom, QM and relativity, as they exist today, are not compatible, and no amount of interpretation will address that. The crux of the matter is that QM requires us to drop either locality or counterfactual definiteness, while relativity requires us to keep both of those.

    That said, my understanding is that this issue, as it relates to Bohm interpretation, has been addressed already:

    http://arxiv.org/abs/1002.3226
     
  23. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes and and the point of that paper is to show that your now bold text is wrong. To quote from the introduction of http://arxiv.org/PS_cache/arxiv/pdf/1002/1002.3226v2.pdf:

    “{common belief is} that nonlocality and relativity cannot live together. Thus, many believe that the whole idea of making nonlocal reality compatible with relativity is an impossible task. Recently, however, an explicit relativistic-covariant version of the Bohmian interpretation of QM has been introduced in [4], with some further developments presented in [5] and [6]. This provides an explicit counterexample to various arguments that such a theory should be impossible. But how that can be? Where do exactly the standard impossibility arguments fail? The purpose and intention of the present paper is to answer these questions and to make this relativistic-covariant model of nonlocal reality understandable to a general physics audience.”

    Some years ago I was very attracted to Bohm’s QM, even bought one of his books and read another. It is my understanding that experimentally one cannot distinguish between Bohm’s QM and the standard Copenhagen POV. I.e. all calculations of observables give the same results. And in many ways Bohm’s POV make easier to understand what is happening with entangled state experiments.

    However, I eventually ceased to accept Bohm’s QM because I continued to accept that all electrons are identical. Bohm has them passing thru only one slit of a two slit interferometer or only one path of a two path interferometer (and that is very appealing to humans) but each electron has an unobservable “guiding wave” that does go thru both slits or both paths and guides the electrons to strike the phosphor screen to make the interference pattern. This pattern can be produced with long duration experiments and such low intensity that only one electron exists at any time. The same is true if you arrange it so that two electrons leave the two path interferometer at the same time to start their journey to the screen. If one of the two paths called “L” is Longer than the other called “S” then the electron going by path L must be launched before the one going by path S. Their guiding waves go by both paths and if the electron emerge from the interferometer at the same time, so must the guiding waves.

    Somehow the guiding wave of the later launched must travel faster thru the path L than the guiding wave of the electron launched first does. That alone is a problem for me to believe, but more seriously each electron is guide by only its own guiding wave yet both waves are present in the space from the interferometer to the screen. How, in principle, can a guiding wave know which electron to guide? – if all electrons are identical?

    Thus while Bohm’s QM gives the same quantative predictions as Copenhagen and can be made compatible with relativity it seems, to me that each electron must in some way be recognizable different from all others. That is why I stopped being a convert to Bohm’s QM even though it has great appeal (as non-local for the entangled states, being a deterministic POV, but with past and future are controlling the present) to many humans with particles going only thru one slit etc.
     
    Last edited by a moderator: Oct 1, 2010

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