i have searched alot ... but i couldn't find 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

In the earliest moments of the Big Bang, all matter in the universe was ionized and therefore opaque. When matter had cooled enough to form atoms, the universe became transparent -- all all those photons that had been trapped bouncing around between ions were suddenly free. Since all matter in the universe was very close together at that time, this illumination took place everywhere in all directions at once.

Those are the photons we see now as the CMBR.

Answer 2

The sun radiates heat but it is not a black body.
The universe emits nothing to the outside simply because nothing exists out side the universe.
Once the process of star building got under way the universe started emitting light to it's surroundings,within the confines of it's boundaries.

Answer 3

The Sun is an approximate black body - the universe is a perfect one.

When the big bang occurred, the universe was very small and hot. As it expanded, it cooled. So at early times, it was very hot, and at later times, it was cooler - down to about 3 degrees now. The cosmic microwave background is that leftover heat, and it's EVERYWHERE in the universe. It's filling the universe, so we see it in every direction. It's the big bang remnant. So yes, the universe is radiating all over, in the microwave part of the spectrum.

Answer 4

I would seriously consider asking for a real teacher if I were you.
The Sun isn't black and neither is the universe. The universe consists of NOTHING. Nothing cannot emit anything, is not radioactive, and was not created by a big bang or anything else. The universe just is.