ANSWER:
Cosmic background radiation is leftover thermal energy from the Big Bang best describes the origin and expansion of the universe.
Step-by-step explanation:
- 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.