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Information travel faster than c ?

  1. Mar 2, 2010 #1
    Hi,all, my problem is:

    Consider a 2-D square well potential, say length 2L, and when I put one particle into this well,

    Does this particles IMMEDIATELY know what wavefunction it should have?

    I am trying to consider, once the particle enter the (middle of the)well, the information takes

    at least t=L/c to reach that particle, to let the particle knows where it is in the well, and hence

    what wavefunction should it have would be known by that particle.

    Am I right?

    Thanks in advance
     
  2. jcsd
  3. Mar 2, 2010 #2

    ZapperZ

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    This question is a bit puzzling, because the wavefunction IS the "particle", at least with the "standard" QM interpretation. That is why we say that the particle is spread out over all distance (non-local) before its position is being measured.

    Zz.
     
  4. Mar 2, 2010 #3
    Thanks for your answer, but what if say the length of the well is very very large, say the 10 light years? Theoretically, that particle would also spread out of this large potential well same as the small one? In these two cases, will it have no different in terms of thinking infomation travelling?
     
  5. Mar 3, 2010 #4

    ZapperZ

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    The length makes no difference. Before measurement, the particle IS spread out simultaneously over the region containing the wavefunction.

    I still don't see how this has anything to do with the speed of information. Once you've made your measurement, that particle is at a particular location already and nowhere else. So what is the "information traveling" here?

    Zz.
     
  6. Mar 3, 2010 #5
    Let me change to another example to expose the problem, say 2 stars has distance 1 light year, if I move one, how long does it take for another to move?

    If consider one starA have its own wavefunction(superposition of all the particles it contained), and another star offer its gravitation potentail for starA to ''sit'' in. If accroding to what you explained, because, starA's wavefunction is sperad all over the space, then if move starA, starB should be move instantly,i.e. infomation is instant updated.

    I asked this peoblem in Relativity part, the answer is, starB will move 1 year later rather than instantly.

    Am I right? Or wavefunction does not apply to big stuff? How about just two particles distanced 1 light year?

    Thanks a lot
     
  7. Mar 3, 2010 #6

    ZapperZ

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    Is this even an equivalent question? One is a quantum system. The other isn't!

    I'm getting even more confused here. Maybe someone else has a clearer idea on what you want, so I'll let him/her tackle this.

    Zz.
     
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