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Pauli exclusion principle at distance

  1. Dec 14, 2013 #1
    Hi.

    New member to this Physics forum and not a physicist, although have an interest in physics from a layman's position.

    I saw a series of threads on a Twitter discussion posted about a year ago concerning Brian Cox and some other physicists concerning a statement made by Cox that the Pauli Exclusion principle work over macro distances, so that when an electron is excited in one part of the universe, all other electrons in the universe change their energy state, even if that change is at an imperceptible level. The argument was about whether there was a misunderstanding of the PEP, in that it should only work within a single atom or atoms in proximity so that there is an exchange of information between the two. One side states this is the case, the other side states that the PEP is valid even over vast distances.

    Does anyone know what the current understanding of this issue is?

    Many thanks

    airydisc
     
  2. jcsd
  3. Dec 14, 2013 #2

    atyy

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    The Pauli exclusion principle in a general form states that the wave function of identical fermions should be anti-symmetrized. In principle, the wave function of the electrons of a rock on earth does depend on the electrons on the moon. However, the error made by ignoring the electrons on the moon is negligible. There is a quantitative discussion of this in Shankar's "Principles of Quantum Mechanics", p283.
     
  4. Dec 14, 2013 #3
    Ah OK. So suggesting that exciting electrons in a diamond on Earth forces electrons the other side of the Universe to alter their state so that they remain anti-symmetrized is theoretically correct, but in reality the impact is so tiny, its immeasurable. It only becomes measurable (and therefore a big enough deal) when the fermions are within close proximity, i.e. in a single atom or close group of atoms?
     
  5. Dec 14, 2013 #4

    atyy

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    Yes, roughly. However, the number of atoms to which it applies with consequences we can measure can be quite large. For example, the symmetrization of the wave function applies for 2000 atoms in a Bose-Einstein condensate. http://en.wikipedia.org/wiki/Bose–Einstein_condensate . (The Pauli exclusion is a different effect in which the wave function is anti-symmetrized for identical fermions, while in the Bose-Einstein condensate the wave function is symmetrized for identical bosons. Nonetheless, the idea the idea is the same in that the effect in principle applies to identical particles throughout the universe.)
     
  6. Dec 17, 2013 #5

    zonde

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    If we have 2000 atoms moving in a common potential well it the same as electrons in a single atom. So it does not make the point that PEP works for two particles that are confined to two separate potential wells.
     
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