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Is this not mathematical evidence that the universe is an open system?

  1. Dec 20, 2009 #1
    Well, if we consider the universe as a closed, isolated system, then the law of conservation of momentum should kick in.

    P = MV

    We know that Hubble's law states that the velocity of bodies on an astronomical scale is increasing and P is a constant, so that means M must be decreasing. However, the first law of thermodynamics states that the amount of matter/energy in the universe is also a constant.

    Therefore, if the universe is a closed system, P and M must be constant, ergo V must be constant too and thats absurd to say by the means of Hubble's law. Can I be refuted?
  2. jcsd
  3. Dec 20, 2009 #2
    If the universe is a closed isolated system, then p is the momentum of its centre of mass(no such thing actually) and v is the velocity of the CM which doesn't depend on the velocities of what constitute it.
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