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Action at a distance

  1. Aug 23, 2004 #1

    wolram

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    Just thought i would post what Wikipidia has to say on this topic.
    In physics, action at a distance is the instantaneous interaction of two objects which are separated in space; the term was coined as "spooky action at a distance" by Albert Einstein. Newton's theory of gravity was one of the first theories incorporating this notion. After the advent of special relativity, action-at-a-distance was seen to violate the principle of relativity - if one of the interacting objects were suddenly displaced from its position, the other object would feel its influence instantaneously, whereas the special theory of relativity sets the speed of light as the upper limit to the speed of propagation of an interaction. Attempts to sort out the conflict between Newton's theory with action-at-a-distance, and the principle of relativity in the theory of gravitation led to the theory of general relativity.



    Incidentally, there is no problem with Coulomb's law in electrostatics seeming to be a theory with action-at-a-distance - Coulomb's law deals with charges which have been static since eternity, and the completion of Coulomb's law to include moving charges lead to Maxwell's equations, which are fully compatible with special relativity.

    Current physical theories incorporate the principle of relativity as one of their basic building blocks, hence ruling out action-at-a-distance. At the same time however, action at a distance appears to be an essential feature of some very fundamental quantum mechanical effects like entanglement and quantum nonlocality. Further understanding of these effects, in order to reconcile them with the principle of relativity, might lead to some new physics.
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    It seems this is saying SR could be wrong but we need some new science
    before a new understanding of gravity can come about, But if action at a
    distance is possible in one science then why cant it apply to gravity?
     
  2. jcsd
  3. Aug 23, 2004 #2
    it does apply to gravitation. We just havent seen it do this yet because it is soo hard to do so. Most scientists there days believe that gravity propagates at c.
     
  4. Aug 23, 2004 #3

    wolram

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    Nenad
    it does apply to gravitation. We just havent seen it do this yet because it is soo hard to do so. Most scientists there days believe that gravity propagates at c.
    ----------------------------------------------------------------------------------------------------------------
    Is this the "metric distortion" or the graviton that travels at C ?
    I think when the above refers to," entanglement", it is an instantaneous
    action, and this is where QMs is seemingly at odds with SR.
     
    Last edited: Aug 23, 2004
  5. Aug 23, 2004 #4

    pervect

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    You'll find few people who find the "action at a distance" formulation of quantum mechanics attractive. This would basically be "Bohm" AFAIK, who formulated a *non-relativistic* form of QM that involved action at a distance.

    The ability to formulate a non-relativistic theory that involves action at a distance is nothing new as your discussion of Newtonian gravity indicates.

    Action-at-a-distance theories have not contributed anything to relativistic formulations of quantum mechanics as far as I know.

    The solution to quantum non-locality that seems to be in favor nowdays involves not non-local theories, but non-realistic theories. "Many Worlds" would be the typical pop-sci name for this, though at least some practicioners don't like the pop-sci versions and insist on more sedate names, like "The relative state hypothesis" and/or decoherence.
     
  6. Aug 23, 2004 #5
    I believe that SR is correct, and that gravity propagates at c.
     
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