Quote:
Originally Posted by tommac
Other than because theory says so, how do we know that the CMBR is coming to us from 13.7 light years away?
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We don't. The cosmological interpretation of the CMB is entirely dependent on cosmological models. However, one should not take this too lightly, as in "it's just a model", or fall for the notion that because it is model dependent, then it is "just a guess".
Every observation that we make about anything is subject to interpretation in the context of one model, or a few, or even many, models. We always ask, what are the alternatives? The
observational fact that the CMB is strictly thermal is a strong constraint on physical causes for the CMB. I can't think of any local mechanism that can do it.