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Popper/Lande interpretation of QM

  1. Aug 12, 2009 #1
    Karl Popper, the highly influential philosopher of science was unusual in that, as a philosopher, he had a large impact on science itself. He was actually listened to by physicists! He's best known, of course, for his falsifiability criterion for theories to be considered scientific, which has become de rigeur in most branches of science.

    He's less well known for his commentary on quantum physics and his interpretation of the mathematical formalisms of quantum physics. In his 1982 Postscript to the Logic of Scientific Discovery - Vol. 2 being Quantum Mechanics and the Schism in Physics - Popper presented the most fully developed discussion of his "propensity field interpretation" of quantum mechanics, in "thirteen theses." He poses a hard-hitting critique of the Copenhagen school of QM, arguing for a realist, particle-based, non-deterministic interpretation in which the most basic pieces of nature are indeed particles, with real positions and momenta, even if we can't know them precisely, there is no wave/particle duality, there is no "collapse of the wave function" caused by a conscious observer, and most importantly an interpretation of the Schrodinger wave equation as applying only to epistemology - what we can know abouat nature, what nature actually is - and not supporting the notion that particles are in fact waves in some instances and particles in others (or as Schrodinger believed simply waves that seem particle-like in some situations).

    His thirteen theses are based in large part on Alfred Lande's 1965 work, New Foundations of Quantum Mechanics. Lande was a strong proponent of the Copenhagen school until later in life becoming disillusioned with the Bohr/Heisenberg/Pauli dismissive approach to reality and causality.

    Here is my paraphrase of his thirteen theses:

    1. Quantum mechanics concerns statistical problems about matter and energy.
    2. Statistical questions demand statistical answers.
    3. Because quantum mechanics provides statistical answers to statistical problems, it is a mistake to insert an “observer” into quantum mechanics as a necessary component of “wave collapse.”
    4. The “great quantum muddle” results from mistaking the wave function – the statistical answers of quantum mechanics – for a physical property of the particles at issue. The wave function is a mathematical device, not a physical property.
    5. Heisenberg's uncertainty formulae are not actual limits on the precision of our knowledge, they are, rather, “statistical scatter relations.” “They thereby limit the precision of certain individual predictions.”
    6. The statistical answers of quantum mechanics refer to populations of particles, which do, contrary to the Copenhagen Interpretation, have a real and precise position and momentum. (We cannot know with absolute precision, however, these data for any particular particle, but this does not mean the particle itself does not actually have a defined position and momentum).
    7. Heisenberg effectively admitted the truth of the previous theses but the commonly accepted Copenhagen Interpretation has for some reason maintained the contrary views for the most part. Heisenberg was, however, on final reflection, agnostic about the reality of a given particle's past history, based on retrodictive measurements: “It is a matter of personal belief whether such a calculation concerning the past history of the electron can be ascribed any physical reality or not.”
    8. The mistaken Copenhagen Interpretation is closely related to the common interpretation of the calculus of probability, which mistakes certainty (or lack thereof) about our knowledge of events in the world with the certainty (or lack thereof) of certain events actually happening. The objective “propensity interpretation” of probability calculus is the best approach for quantum physics, which avoids the mistake of the common interpretation. The “propensity field” indicates the likelihood of a certain outcome of the experimental arrangement. A given experimental arrangement's propensity field is a real physical quality, though a “somewhat abstract kind of physical quality.”
    9. The collapse of the wave function is not an effect unique to quantum mechanics – it is an effect common to all probability theory. There is no more to the wave collapse in QM than the “trivial principle: if our information contains the result of an experiment, then the probability of this result, relative to this information (regarded as part of the experiment's specification), will always trivially be” 100 percent.
    10. The propensity interpretation of probability calculus solves the problem of the relationship between particles and their statistics, that is, between particles and the wave function, because in Popper's interpretation there is a real particle, with defined position and momentum, and the propensity field of the entire experimental arrangement (or situations outside of any actual human experiment, though human knowledge will require an experiment).
    11. It is misleading to speak of wave/particle duality or of a duality of particles and propensity fields. This is the case because propensity fields are properties of a given experimental arrangement, not of the particles that are the object of study. There is, therefore, no need for an “observer” to collapse the wave function because there is no “collapse” in a physical sense.
    12. The mistaken idea of wave/particle duality arose from de Broglie and Schrödinger's attempts in the 1920s to create a wave theory of the structure of particles. These attempts failed, but the wave/particle duality interpretation was mistakenly retained.
    13. Both quantum physics and classical physics are indeterministic. Popper doesn't clarify this point in his paper.


    So my question is: who has actually heard of the Popper/Lande "propensity field" interpretation of QM and what do people think of these ideas as a more common-sense interpretation of the queer QM maths?
     
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  3. Aug 12, 2009 #2

    DrChinese

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    The critique of CI falls flat given Bell's Theorem and the rise of entanglement experiments. So if his critique is to make sense, you must join the Bohmian school... a result which I doubt is intended. Probably why you don't really hear that much about Popper.

    I usually hear his name associated with "theory falsification" concepts, an important philosophical idea. Hadn't heard of the "propensity field" as such.
     
  4. Aug 12, 2009 #3

    Demystifier

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    The theses above correspond very well to what we call today (Ballentine) statistical ensemble interpretation. Concerning the last thesis that both quantum and classical mechanics are indeterministic, see also
    http://xxx.lanl.gov/abs/quant-ph/0505143 [Found.Phys.Lett. 19 (2006) 553-566]
    http://xxx.lanl.gov/abs/0707.2319 [AIPConf.Proc.962:162-167,2007]
     
  5. Aug 12, 2009 #4
    Dr. Chinese, I am personally also more drawn to the Bohmian interpretation but I'm not sure that Bohm and Popper/Lande are entirely incompatible. Bohm's "implicate order" may be likened to Popper's "propensity fields," which he described as real but not physical - just as Bohm did the implicate order. Popper did in fact make much of entanglement, calling in the early 1980s after the Aspect experiments for a broad-scale revision of relativity and quantum theory - on the former claiming that the Aspect experiments undermined the idea of relative simultaneity, which is the basis for the entire edifice of relativity theory. Could you flesh out why you think Popper's theory can't deal with entanglement?
     
  6. Aug 12, 2009 #5
    Thanks Demystifier, I'll check these out.
     
  7. Aug 12, 2009 #6

    DrChinese

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    If it is non-local, then it can. That is the only way to make it compatible with Bell's Theorem, since he is requiring realism. Obviously, entanglement experiments support the idea that distant particles share a common wave function, and therefore they cannot have both predetermined properties and independence. At the time Popper's ideas were being written, this area was being revolutionized and there is no shortage of confirmation at this point.
     
  8. Aug 12, 2009 #7
    Tam, have you read Bohm's concept of active information? It sheds some light on what the eventual implications of the "Bohmian Interpretation" are.

    Bohm suggests that there is an infinite recursion of physical properties reducing to mental properties reducing to physical properties etc. This seems to be the only way for him to explain nonlocal information transfer in a realist framework.

    After all of his efforts to create a deterministic realist theory, Bohm writes that there is a “deeper reality … beyond either mind or matter, both of which are only aspects that serve as terms for analysis.”

    I point this out because popular literature seems to have ignored Bohm for the past 30 years, and generally presents only his incomplete 1950s view. I was certainly surprised to read his more recent thoughts.

    Bohm, D. (1990) `A New Theory of the Relationship of Mind and Matter', Philosophical Psychology 3: 271--86.

    http://evans-experientialism.freewebspace.com/bohmphysics.htm

    ^ Try finding that or similar papers referenced anywhere on anything related to Bohm's interpretation.
     
    Last edited: Aug 12, 2009
  9. Aug 12, 2009 #8
    Thanks Kote, I have read that article by Bohm and I also recently finished his Wholeness and the Implicate Order. I am drawn to Bohm's interpretation and am glad to see that physicists in this forum at least are again discussing his ideas.
     
  10. Aug 12, 2009 #9
    Dr. Chinese, have you read about the Salart experiment from last year, finding that the non-local signal traveled at least 10,000 times the speed of light? What do most working physicists think of this experiment? I've found, surprisingly, almost no discussion of this experiment online (I don't have access to physics journals as I am not a working physicist).
     
  11. Aug 12, 2009 #10

    DrChinese

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    Yes I am familiar with this experiment. It conclusion essentially states that IF there is a superluminal influence, THEN it must occur at >10,000c. It does not, however, require a superluminal influence.

    In fact, there are some superluminal theories that are excluded by this result (as it tends to refute the notion of an absolute reference frame, which is a part of some variants). However, it is generally considered as to NOT refute standard Bohmian concepts (per Demystifier who generally does support an absolute reference frame, IIRC).
     
  12. Aug 12, 2009 #11
    Dr. Chinese, can you point me to additional info/articles on the Salart experiment and others like it? I'd like to follow up on your points but don't have access to the actual paper by Salart.
     
  13. Aug 12, 2009 #12

    f95toli

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    The reason why it is not being discussed is that the result was exactly what one would expect from conventional QM. The experiment was a test of QM; it did not give us any new information as such.
    There are lots of experiments being conducted to test various fundamental theories, either aspects of QM or GR.
    Now, this is important work but unless someone gets a result that is NOT what one would expect (as in the fine-structure experiments a couple of years ago) these experiment don't
    get much attention.
     
  14. Aug 12, 2009 #13

    Dale

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    I find these comments pretty amusing and hypocritical coming from the prince of "falsifiability". How could any of these statements be experimentally falsified?
     
  15. Aug 12, 2009 #14

    DrChinese

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    Sure, here it is: http://arxiv.org/abs/0808.3316
     
  16. Aug 12, 2009 #15

    DrChinese

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    And yet I actually think they have been. At least in local theories. I think the whole thrust of Bell and after is that you must give up one or the other cherished notions: realism or locality. Popper's referenced work doesn't seem to do either, so it won't go too far in this area.
     
  17. Aug 12, 2009 #16
    I won't go into it here, but that supposed choice between realism and locality always gets me :). Presented as such, "realism" seems like the obvious choice while locality is just an abstract concept. What is realism without locality though? A nonlocal realism won't adhere to classical notions of causality, it won't have classical spatiotemporal or wave properties as its basic features, and it won't adhere to relativity.

    I agree that giving up either is huge, and QM totally falsifies all notions of reality that are anything like the classical mechanized paradigm.
     
  18. Aug 13, 2009 #17

    Demystifier

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    Well, yes and know. I prefer theories without an absolute reference frame, if possible. A large part of my research in Bohmian mechanics consists in attempts to formulate Bohmian mechanics without an absolute reference frame. Still, a possibility that an absolute reference frame exists also makes a lot of sense to me.
     
  19. Aug 13, 2009 #18

    Demystifier

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    Bohmian mechanics suggests that realism is still local in the sense that the world consists of local particles, but nonlocal in the sense that forces between them "propagate" instantaneously.

    And yet, all these classical features emerge as approximations in a suitable limit. By the way, nonlocality IS compatible with relativity:
    http://xxx.lanl.gov/abs/0811.1905 [Int. J. Quantum Inf. 7 (2009) 595-602]
     
  20. Aug 13, 2009 #19
    f95: isn't the Salart experiment strong data in favor of non-locality, contradicting the no supraluminal signaling limitation of special relativity? Of course, the Aspect experiments established this more than two decades ago, but this truth seems to not have percolated into the prevailing physical paradigm of our era.
     
  21. Aug 14, 2009 #20

    DrChinese

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    That is not what the experiment is about, as the issue was whether there is a preferred reference frame and finite FTL propagation. Traditional Bell tests cannot set very high lower limits on the speed of FTL influences (if they exist). You might expect about 2c or so as the top you could achieve in this fashion. So clearly, setting the lower limit at 10,000c is a signficant improvement.

    You can easily convince yourself that either realism or locality must be false due to Bell; but it is easier to reject locality if you are trying to picture a physical mechanism. Not that a physical picture is necessary. On the other hand: Personally, I think it comes back to the HUP. If we could visualize the physical mechanism that it operates by, then it would be a lot easier to visualize rejecting realism (with the objective that locality can remain inteact). So in my book, both locality and the HUP should be equally fundamental; although I recognize that this view is not strictly demanded by the facts. Demystifier makes a lot of good points about the other side.
     
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