In the 1960's Arno Penzias and Robert Wilson worked for Bell Labs trying to minimize background noise for microwave transmissions. They found out there was some background noise that seemed to be coming from EVERY direction.
On a plane trip, one of them started up a conversation and the other person suggested calling Princeton University astronomer Dave Wilkinson. When they discussed it Wilkinson told him--"You have discovered the Cosmic Microwave Background that has been theorized."
That proved the Big Bang Theory is correct.
By the way--the "STANDARD Big Bang Model"--the idea that cosmic expansion is the result of some kind of EXPLOSION has been conclusively DISPROVED. If that were the case the expansion would SLOW DOWN, like a grenade exploding.
The "INFLATIONARY Big Bang Model" agrees with the evidence--the expansion is INCREASING in speed. "Inflation" says there is something currently called "Dark Energy" (because they don't know what it is) that is a BASIC ATTRIBUTE of EMPTY space and that causes the expansion.
