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Particles not basic entities?

  1. Nov 19, 2009 #1
    According to http://arxiv.org/abs/quant-ph/0103041, particles cannot possibly be the fundamental elements of reality. Are you aware of any newer related papers? Does this conclusion seem to make sense?

    I can't find any reason not to buy it - it seems to follow pretty naturally from nonrelativistic QM already. What's your take? Are particles just useful macroscopic approximations?
     
  2. jcsd
  3. Nov 19, 2009 #2
    You may find references on more recent papers without any complicated math at my weblog.
     
  4. Nov 19, 2009 #3
    So to be clear, you agree that particles cannot be basic? Does anyone disagree with that claim?
     
  5. Nov 19, 2009 #4

    DrChinese

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    I would. A fundamental particle such as an electron cannot be subdivided into a constituent. I read the referenced article and I didn't draw the same conclusion as you. The article seemed to me to be an exposition on the nature of quantum non-locality. It includes no-go theorems which try to prove that localized particles are not compatible with relativistic quantum theory.

    Assuming that were so, I don't see how that changes my perspective on what a particle is. Its wave function is already spread out all over the place. And so what if there all there is are fields? Just change your definition of particle. To me, a fundamental particle is the lowest entity which can manifest observables.
     
  6. Nov 19, 2009 #5
    I wanted to say that what we call particles, for example, electrons and photons, are in fact some features of compound (non elementary) systems.
     
  7. Nov 19, 2009 #6
    Thanks Bob. I think that fits with how I'm thinking about it. From the conclusion of the article: "...relativistic quantum field theory also does not permit an ontology of localizable particles; and so, strictly speaking, our talk about localizable particles is a fiction."

    I believe this has a lot of philosophical weight, but I want to make sure I haven't misunderstood the physics first (not that I expect consensus on the issue right now).

    DrChinese, as for a wave function being spread all over the place, this is also covered by the paper. If I am reading correctly, particle properties cannot even be contained in discrete continuous regions of space - I may be confusing this paper with some others though, which I can look for. From the conclusion again: "...we provided two further results (Theorems 1 and 2) which show that the conclusion continues to hold for generic spacetimes, as well as for “unsharp” localization observables."

    Edit: Pretty sure I need to find those other papers now. I'll get back to you :smile:.
     
    Last edited: Nov 19, 2009
  8. Nov 19, 2009 #7

    RUTA

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    I agree. My reasons and ontology are posted at http://xxx.lanl.gov/abs/0908.4348.

    Here is a quote by Nobel Laureates, A. Bohr and B. Mottelson:

    “Indeed, atoms and particles as things are phantasms (things imagined).”

    A. Bohr, B. R. Mottelson & O. Ulfbeck, “The Principle Underlying Quantum Mechanics,”
    Found. Phys. 34, 405-417 (2004), p 411.
     
  9. Nov 19, 2009 #8
    Great; thanks for the link. I'm reading the paper now, but I'm still a relative beginner to technical QFT. I'm glad to see papers like this though. Frankly, many of the conclusions being drawn from QFT seem to follow from the physics of nonrelativistic QM, so I don't think I'm too lost so far :smile:.
     
  10. Nov 19, 2009 #9

    DrChinese

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    Perhaps I don't fully understand the context of the paper. From the abstract:

    Several recent arguments purport to show that there can be no relativistic,
    quantum-mechanical theory of localizable particles and, thus, that relativity
    and quantum mechanics can be reconciled only in the context of quantum
    field theory. We point out some loopholes in the existing arguments, and we
    provide two no-go theorems to close these loopholes. However, even with
    these loopholes closed, it does not yet follow that relativity plus quantummechanics
    exclusively requires a field ontology, since relativistic quantum field
    theory itself might permit an ontology of localizable particles supervenient
    on the fundamental fields. Thus, we provide another no-go theorem to rule
    out this possibility. Finally, we allay potential worries about this conclusion
    by arguing that relativistic quantum field theory can nevertheless explain the
    possibility of “particle detections”, as well as the pragmatic utility of “particle
    talk.”


    a) So what if particles are not localizable? Does that mean they don't exist?

    b) On the other hand, they say that there is pragmatic utility for the term "particle" which I think is good, considering particles can be experimentally observed in finite regions. And do not yield any experimental substructure.

    c) Or alternately: if you have a field theory, how are there no particles? Seems to me the definition might be changed (field excitations?), but we weren't talking about classical particles anyway. I don't see the paper as being about semantics so I guess I read it as a way to constrain theory development.

    d) And finally: they specifically exclude the case of the preferred frame, saying: "Despite the fact that “no absolute velocity” is a feature of all post-Galilean spacetimes, there are some who claim that the existence of a (undetectable) preferred reference frame is perfectly consistent with the empirical evidence on which relativistic theories are based (cf. Bell 1987, Chap. 9). What is more, the existence of a preferred frame is an absolutely essential feature of a number of “realistic” interpretations of quantum theory (cf. Maudlin 1994, Chap. 7). Thus, this tacit assumption of Malament’s theorem has the potential to be a major source of contention for those wishing to maintain that there can be a relativistic quantum mechanics of localizable particles." As I understand it, the concept of a unknown preferred frame is currently viable.

    So while the paper seems to make some important points, I still don't get how there are no particles.
     
  11. Nov 19, 2009 #10
    Yes! :smile: I would say that our concept of a particle is that of a localized collection of properties. A particle is an object - a continuous region of extension - with certain properties. If those properties can't be contained in a continuous (perhaps fuzzy) region of space, then they aren't the properties of an object.

    The paper itself concludes that particles are fictions and cannot even be completely accurate macro pictures of underlying structures. The concept of a particle is incompatible with the results of experiments, given their other assumptions, which I may have to dig into more (like the 'no preferred reference frame' you mentioned).

    Please let me know if there is some other version of "particle" that I am missing though.

    You bring up some good points that I will have to leave for now.
     
  12. Nov 19, 2009 #11
    I think that if "real particles" exsist, many mathematical wavefunctions would not have been used.
    Instead the illustrations of the particles would have been often used in the textbook like in the classical mechanical books.
    (Though I personally think "real particles" exist. But in QM and QFT they don't.)

    First, as far as "the spin" exists, the spinor matrices must be used even in QFT (except in the photon spin).
    Because the real particles can not express the "two-valued" spinor rotation.

    Relativistic QFT has more mathematical property than QM.
    The relativistic electrons appear only when the wavefunctions of the Dirac equation are integrated in all space.
    This relativistic wavefunction is not real things. And the wavefunction doesn't mean the probability density of the electrons.
    This relativistic wavefunction was made to incorporate the relatividstic theory into QM, I think.

    QED was made to express "photon particles". (by the quantization of EM field)
    So photon particles have strong "mathematical properties".
    But in the case of the photon, the wavefunction is a real thing, which is different from the upper case of electrons.

    Personally, I think the idea of the quantization of the field is "a mathematical trick".
    But the phenomina of the relatividstic effect of the electrons were experimentally observed.
    It's very confusing.
     
    Last edited: Nov 19, 2009
  13. Nov 20, 2009 #12

    Demystifier

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    I think that the possibility that particles are fundamental objects is compatible with relativistic QFT. See
    http://xxx.lanl.gov/abs/0904.2287 [to appear in Int. J. Mod. Phys. A]
     
  14. Nov 22, 2009 #13
    There is a fundamental underlying assumption to any of these proofs.

    1) QM is a model of the particle rather than a model of the particle interaction (behavior)
    2) QFT is a model of the particle rather than a model of the particle interaction (behavior)

    But given that the massification of QFT is not gauge invariant while the "particle" is, that QFT requires renormalization (a mathematical process - is the particle smart enough to do the math) while it is likely the particle does not, and that the first law of logic (either A or not A) requires a wave particle unity model while all present theories are duality models

    Just might suggest (screams out) that the present theories do not represent the particle (P) but only the behavior of the particle (Q).

    Logic also states that if P the particle implies the behavior Q, it does not mean that Q must imply P.

    Therefore, this article concludes that the present Q model is inconsistent with relativistic theory.

    Thus this article is just further evidence that the present theory is not a P model of the particle but a Q model of its behavior.
     
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