Can the CMB be used as an absolute reference frame?

22 April 2011



Hi Chris, great show , Im hooked. I have a question:

The cosmic microwave background (CMB) shows a dipole distribution which is normally subtracted from the data to reveal the underlying "wrinkles" that appear in the public relations images (George Smoot´s "face of god"). This dipole distribution means that one side of the sky is slightly hotter than the other and this is usually described as being due to the doppler shifts in the CMB due to the solar systems motion through space. Surely this implies that the CMB provides an absolute frame of reference in space against which velocities can be measured? Einstein showed us that all velocities are relative. How can this apparent paradox be explained?


Simon Tulloch


The photons that forms the cmb come from what is called the last scattering surface. This surface is a different one depending on the position in spacetime of the observer. So each observer will have a different reference frame in which the cmb has no dipol term.

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