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I Does isolated = closed for relativistic thermodynamics?

  1. Mar 2, 2016 #1


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    If you put everything in a rest frame, it seems as if it's impossible to tell an isolated system from a closed system (globally in SR, locally in GR). Am I off my rocker to think so?

    There's at least one catch I've thought of so far: light. I can't say for sure that it satisfies either definition because it can't be dragged into a rest frame, but I also can't say it shouldn't be thought of as a closed or isolated system. It's counterintuitive in a 3space+1time worldview, because EM radiation behaves almost like a dissipative transport process as seen in Poynting's Theorem (flow of charges through an E field gives you a work that is distributed in an irreversible fashion as radiation). But could a 4-volume element full of EM radiation be called an isolated/closed system? If so, is the specific internal energy of that volume element defined? Or am I just completely off my rocker?
  2. jcsd
  3. Mar 3, 2016 #2


    Staff: Mentor

    What are your definitions of "isolated" and "closed"?
  4. Mar 5, 2016 #3


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    Sorry for the late reply.

    You hit the nail on the head, thanks. I was defining them both to be systems with no flow of invariant mass/energy in or out, so my question was a silly one. My bad.
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