Does the CMB allow special "almost" rest frames to be defined? In this sense, use a rocket to put yourself in a frame of reference such that in this frame observations of the CMB would average to zero (average over photon momentum) over your celestial sphere. In such a rest frame is the total momentum of the Universe is about zero? Such a rest frame could never be found precisely by experiment? How close could we get with present day observations of the microwave background radiation? Thank you for any thoughts.