i have searche alot ... but i couldn't fin an answer to this question concerning the universe(read details)

Question

The sun is considered as a black body .. it emit radiations to the outside .. these radiations reach the earth ...
how is the universe considered as a black body ... we are inside the universe ... however we get the CMBR red shifted 380000 years after the big bang ... Does the universe emit radiation to the inside ?

Answer 1

All the energy in the universe was once contained in a much, much smaller volume, so the temperature was far higher, but now that it has existed for almost 14 billion years, its energy density is consequently far less, resulting in the CBMR that we detect today. Don't get hung up on the theoretical concept of black body radiation: it's like uniform acceleration; there ain't no such animal.

Answer 2

Hi. A black body is only a theoretical entity, and the Sun is not. It is possible the what we see as the background radiation IS the event horizon for OUR universe, in my opinion.