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Is dark energy observer dependent?

  1. May 30, 2014 #1


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    Science Advisor

    If yes, does dark energy define a frame of absolute rest?

    In the Einstein field equations, the cosmological constant is just a scalar, so it is independent of frame. But, sometimes, the cosmological constant is described as being a kind of vacuum energy density. Wouldn't a vacuum energy density be frame dependent? Or is it assumed that the vacuum energy density is always combined with a negative vacuum pressure density which cancels out the frame dependence?
  2. jcsd
  3. May 30, 2014 #2


    Staff: Mentor

    No. Dark energy is Lorentz invariant, whether you view it as a cosmological constant or as a vacuum energy density, since both appear the same way in the GR equations.

    It's not "assumed"; it's required by the equations. Dark energy (whether it's a cosmological constant or a vacuum energy density) appears in the equations as a constant that multiplies the metric; that means that in any local inertial frame, it looks like a positive energy density and an isotropic negative pressure that both have the same magnitude.
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