Conclusions


The Universe is filled with microwaves.
Spectrum exactly that of emission from hot material. Inescapable conclusion: remnant from a time when the Universe was hot plasma.

The brightness of the CMB is nearly the same in all directions:
The plasma was very smooth and featureless.

Very small degree of unevenness in the CMB brightness:
We are seeing a sample of the structure in the Universe at that time.