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I Open or closed Casimir system?

  1. Jan 15, 2017 #1
    If you had the Casimir effect pushing two plates together, would that be an open or closed system? And why? I haven't been able to find a satisfying answer/explanation to that.
     
  2. jcsd
  3. Jan 15, 2017 #2

    PeterDonis

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    What is your definition of these terms?
     
  4. Jan 15, 2017 #3
    That's the thing: I'm not sure how they'd be defined here. It's obviously easy if you have a classical system, but things get fuzzy when you have virtual energy.
     
  5. Jan 15, 2017 #4

    PeterDonis

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    I'm not sure why you would think so. But let's start with the classical definition: what do you think that is?
     
  6. Jan 15, 2017 #5
    Isn't it closed if no energy/matter is entering or leaving the system, and open otherwise?
     
  7. Jan 15, 2017 #6

    PeterDonis

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    That'll work. Now, if we have two plates sitting in vacuum, nothing else present, what energy or matter could be entering or leaving the system?
     
  8. Jan 15, 2017 #7
    Possibly the virtual photons. But due to their nature, I'm not sure if that would constitute entering/leaving the system, or if they would be considered to be already part of the system. Hence my confusion.
     
  9. Jan 15, 2017 #8

    PeterDonis

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    The virtual photons are part of the system. They aren't coming in from outside.

    More precisely, "virtual photons" is only a heuristic way of describing what is causing the Casimir Effect. A better way is to say that the presence of the plates changes the vacuum state between the plates, in such a way as to create a force that attracts the plates to each other.

    But no matter how you describe it, it should be evident that there is nothing entering or leaving the system as a whole; you could draw a boundary around the whole apparatus and measure energy flow across the boundary and find that it is zero. That's part of the specification of the scenario.
     
  10. Jan 15, 2017 #9
    Fair enough. Would that also be related to it apparently being a conservative force?
     
  11. Jan 15, 2017 #10

    PeterDonis

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    Not really; conservative forces are not limited to closed systems, unless you want to consider the entire universe as part of the "system".
     
  12. Jan 15, 2017 #11
    Fair point. :P
     
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