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Strings and Non-Locality

  1. Jul 9, 2005 #1
    If particles are made out of strings then it seems to follow that strings are, or can be, both local and non-local. Is this correct? I haven't seen any discussion of the wave-particle nature of strings (or the property of strings that allows particles to be also waves) so I assume I'm wrong about this. Can somebody explain how the ambivalent nature of particle/waves arises from strings, or haven't we got that far yet?
     
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  3. Jul 9, 2005 #2
    If I'm not mistaken, the "wave-particle" (using that term as loosely as possible) arises simply from applying the quantization formalism to strings themselves.
     
  4. Jul 10, 2005 #3
    Sorry but I don't understand that answer. Can you clarify it a little.
     
  5. Jul 10, 2005 #4

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    He means that in quantization, the dynamic variables of a classical theory, such as position and momentum, are replaced by "operators" acting on "states" of the quantum system, and the states can be thought of as wavelike, while the operators can reduce the wave to an "eigenstate" - a sharp localized value. Since strings are quantized in string theory, they share this apercu.

    However it has to be stated that after all is said and done, string theory is relativistically covariant, and does not support dreams of a nonlocality at the root of being.
     
  6. Jul 11, 2005 #5
    Thanks. I'm out of my depths here so please bear with me, but this seems self-contradictory. You seem to be saying that non-locality is not a property of fundamental quanta after all, because string theory is relativistically covariant. I thought non-locality was an established fact, and that therefore strings must have this property. How can electrons, protons, atoms etc. have a non-local aspect but strings not have one?

    Also, what does "nonlocality at the root of being" mean? Do you mean that string theory does not support the dream that non-locality is a property of the fundamental constituents of matter? If you have the time and patience could you also unpack "relativistically covariant" a little for me, I have the glimmer of an idea of what it means, but that's all.

    Thanks
    Canute
     
  7. Jul 11, 2005 #6

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    I think you misunderstand entanglement. No cause can pass between spacelike separated entangled particles, according to quantum theory. After the fact, in the intersection of the future light cones of the particles, you can establish a correlation in their behaviors, but one does not affect the other in real time. This is quantum weirdness if you like but it is not what I think you mean by nonlocality.

    Relativistic covariance means that an equation that is true in one frame remains true in any boosted frame. The two sides of the equation may vary due to Lorentz transformations, but they remain equal. The equations of the Dirac electron, QED, the Standard Model, and string theory all meet this criterion. It is a consequence that they do not support nonlocality in the sense of causes acting over spacelike intervals, or to put it in other words, causes travelling faster than light.
     
  8. Jul 11, 2005 #7
    I'm not suggesting that something travels between entagled particles faster than light, and I don't believe anything does, and certainly not causes. I didn't think anybody thought this (although the absorber theory of time seems to me to allow faster than light communication in a sense). I'm just wondering how string theory deals with the issue of non-locality. After all, if particles are made out of strings then presumably the behaviour or particles can be, indeed must be, theoretically explained in terms of the behaviour of strings. I'm just wondering how theorists go about doing this, or whether it's a problem that's being left to one side for now. The books I've read on string theory, QLG etc. (Kaku, Greene, Smolin etc) mention non-locality but do not relate it string theory. I'm just wondering why not.

    As far as I know I do not misunderstand the concept of entanglement. I'm asking how string theory deals with the dual nature of particle/waves, and in particular the issue of non-locality, not specifically about entanglement.

    It's really a very naive question. If protons are made of strings and protons behave non-locally, to put it clumsily, then presumably strings also behave in this way. I just wondered why this has not been discussed in what I've read.
     
  9. Jul 11, 2005 #8

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    Could you enlarge on what you mean by non-local in your premise: "... and protons behave non-locally"? I am not aware of any behavior of protons that I would myself characterize as non-local.
     
  10. Jul 12, 2005 #9
    By non-locality I mean what Einstein called "spooky action-at-a-distance", or more generally the idea that all particles that have ever interacted are part of a single wave function. Particular effects would be entanglement, the interaction of spatially separated particles as if they were in the same place, and the spatial/temporal distribution of probable postions for unobserved particles, which seem to have a finite probability of being anywhere in the universe at any time.
     
  11. Jul 12, 2005 #10
    And here are five 'die' cast recently:http://physicsweb.org/articles/news/8/6/18

    Abstract Quote:By taking advantage of quantum phenomena such as entanglement, teleportation and superposition, a quantum computer could, in principle, outperform a classical computer in certain computational tasks. Entanglement allows particles to have a much closer relationship than is possible in classical physics. For example, two photons can be entangled such that if one is horizontally polarized, the other is always vertically polarized, and vice versa, no matter how far apart they are.

    This is going to get tougher as the cross-sections of the combined photons are extended, the first encounter with anything that is 'NOT' part of the entanglement, will according to QMI, collapse the wavefunction generated.

    The reason TWO-STATE entangled photons cannot be at either end of the Universe, is there has to be no intervening matter to 'intefere', regardless of what quantum state is produced or invisaged.

    If TWO-PHOTON's are deeemed to be entangled at either end of the Universe, then acccording to the photons, its a pretty SMALL Universe!
     
  12. Jul 12, 2005 #11

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    And in addition to what Spin_Network said, all that "spooky action at a distance" is precisely the action of causes over spacelike intervals, AKA FTL, that quantum mechanics DOES NOT assert. The Einstein-Podolski-Rosen (EPR) conjecture that you could measure both of two complementary observables momentum and position precisely for the same particle at the same time, by exploiting entanglement, was DISPROVED by the experimental confirmation of the Bell inequalities.
     
  13. Jul 12, 2005 #12
    OK I'll try another way of asking the question, since my mention of non-locality seems to have confused the issues. If particles have a wave aspect then what they are made out of must also have a wave aspect, it seems to me, with my simpleminded appreciation of the issues. Is this true or false? If it is false then as yet I don't understand why it is false; if it is true then how, roughly-speaking, does string theory incorporate this feature? Thanks for your patience.
     
  14. Jul 12, 2005 #13

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    The states of a quantum system are vectors (actually rays) in a complex vector space. The operators that act on them are unitary. These two facts mean the states can be given a wavelike interpretation. But these "waves" are in Hilbert or Fock space; that is they are a part of the mathematical formulism, not events in spacetime. Quantum mechanics does say that the waves are projected down into probabilities of actual phenomena by "observation", but the waves themselves are not part of spacetime reality. This is a subtle point because it is the probabilities that support wavelike phenomena in spacetime such as two slit interference. But note that "quantum eraser" and "delayed choice" experiments show that these probabilities are more complicated than simple probabilities of stochastic systems in spacetime. You can't get away from the linear algebra of the complex vector space.

    Entanglement is the sharing of a single compound state in Hilbert or Fock space between two or more localized quantum objects. An observation that projects the entangled state into probabilities destroys the entanglement. An observation of one of the localized particles produces probabilities for both of them, and the probabilities are algebraically related.

    When one probability is pinned down, so is the other, but this is not the action of one particle on the other. In one relativistic frame the two reductions are simultaneous, but you can easily find two other legitimate inertial frames in which one of the particles came first and the other followed (i.e. there a frame in which A seems to have caused B and another equally good frame in which B seems to have caused A, together with the one frame in which A and B were simultaneous).

    You have to juggle the quantum assertions and the relativity assertions at the same time, but it can be done and it does give the answer for standard relativistic quantum mechanics.
     
    Last edited: Jul 12, 2005
  15. Jul 13, 2005 #14
    Thanks. But what about my question? I'll try another version.

    In the formalism of the different string theories do strings have the same complementary/contradictory properties that particle/waves have in quantum theory, or do these properties emerge only at the level of electrons, protons etc.?
     
  16. Jul 13, 2005 #15
    Canute--you are right. String Theory is a complete waste of time, as it allows for no explanation of non-locality, a demonstrated FACT, as show below.

    [deleted - reference to non-mainstream and unverified work]

    http://en.wikipedia.org/wiki/B ell's_inequality

    [deleted - you have already made a reference to the Wikipedia site. There is no need to copy it to here]
     
    Last edited by a moderator: Jul 13, 2005
  17. Jul 13, 2005 #16
    String Theory is non-verified and non-mainstream work!

    String theory is non-verified and non-mainstream work!

    Only 1,000 physicists use it: a tiny, tiny percentage of the human population. They use it to raise government grants, enslave students to meaningless careers, and pick the pock of the tax-payer.

    Billions use QM and SR every day, to communicate on phones and over the internet.

    I propose that all posts pertaining to string theory be deleted.

    That way all the hundreds of millions of dollars they consume can go to support real physics, based in logic, reason, and reality.

    [deleted]
     
    Last edited by a moderator: Jul 13, 2005
  18. Jul 14, 2005 #17
    I wasn't arguing for or against string theory, just asking a question. But thanks. I didn't think it allowed such an explanation but wasn't sure. I'll just hang on to see if anyone disagrees with you.
     
  19. Jul 14, 2005 #18
    an observation: there is in general an inverse relationship between the depth of a person's emotional attachment to a problem and the likelihood of that person making any contributions toward a solution.

    nc
     
  20. Jul 14, 2005 #19

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    There's another current thread on the general value of string theory. Let's keep this one for the issue of non-locality, or if we have exhausted what we have to say on that subject, let's close it.
     
  21. Jul 15, 2005 #20
    I don't want to discuss the general value of string theory either. All I want is an answer to my question. But it seems I'm not going to get one here so I suppose I'll have to ask elsewhere.
     
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