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Cosmic microwave background and a reference frame

  1. Feb 14, 2009 #1
    Dear Friends

    A fleet of spaceships is given, each equipped with a differential microwave radiometer,
    just like COBE was, whose detectors are antipodeanly pointing (this way one should catch
    blue shifted radiation and the other one red shifted). Could their acquisitions be used to
    establish a reference frame locally (!) motionless respect the cosmic microwave background ?
    Supposing a such reference frame does exist, is there any reason to think it's an inertial one ?

    Best wishes.

    Barbara Da Vinci
  2. jcsd
  3. Feb 14, 2009 #2


    Staff: Mentor

    Well, in GR the idea of inertial and non-inertial reference frames doesn't really exist any more.
  4. Feb 14, 2009 #3


    User Avatar
    Gold Member

    Interesting. The nearest thing to an inertial frame in GR is a freely-falling frame. If one of your ships should adjust itself to be stationary in the CBR frame, and can maintain that without using its engines then for that ship the CBR frame may be inertial.

    In other words, if the CBR frame coincides with the local FF frame, then it is inertial. Because of the irregular distribution of matter in the local universe, it's not likely to happen. Perhaps in one of the great voids where all matter is very, very far away, this coincidence would be more likely.
  5. Feb 15, 2009 #4
    Please, what's "FF frame" ?
  6. Feb 15, 2009 #5


    Staff: Mentor

    local FF = "local free falling" (i.e. a local frame centered on an inertial observer)
  7. Feb 16, 2009 #6
    I see. Thanks !!
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