Cosmic background radiation is leftover thermal energy from the Big Bang best describes the origin and expansion of the universe.
<u>EXPLANATION:</u>
The "Big Bang Theory" is used to describe how the universe has begun.
The theory basically states that the "universe" began as a "single point" and then "expanded and stretched" and is expanding even today.
When the universe began, it was "hot tiny particles" mixed with heat and light and as it "expanded" and took up "more space", it cooled down and formed atoms.
The "best evidence of the big bang" is the radiation of cosmic background that was leftover when the first big bang explosion took place and began the universe.
