How can you theoretically explain why cosmic microwave background seems to be coming from a perfect blackbody given that the universe is no longer at thermal equilibrium?

  • $\begingroup$ You do know that the CMB was emitted a long time ago, right? $\endgroup$ – PM 2Ring Apr 13 at 6:23
  • $\begingroup$ Yes, indeed. But my doubt is that, how can we explain the fact that CMB fits with a black body spectrum given that universe's expansion is affecting the wavelength of the CMB. $\endgroup$ – Debasish Dhal Apr 13 at 6:28
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    $\begingroup$ You redshift a black body, still a black body $\endgroup$ – Thomas Apr 13 at 6:31
  • $\begingroup$ You need to edit that info into your question, and explain why you believe that the expansion would lead to a distortion of the spectrum. $\endgroup$ – PM 2Ring Apr 13 at 6:34
  • $\begingroup$ @Thomas. Your point sounds interesting. Still, for applying the wein's displacement law, we need the temp of the system to be constant but the universe is not so. Any suggestions? $\endgroup$ – Debasish Dhal Apr 13 at 6:36

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