eli5: What evidence indicate towards the phenomenon of the Big Bang? How did they come to the conclusion of it happening?
In: Physics
There are two big pieces of evidence we have that the big bang occurred:
1. Astronomers noticed that everything in the universe is moving further apart from each other. This means if you were to “rewind” the universe, everything would be closer together, the further back you go. That leads to the conclusion that if you go far enough back, everything must be in one single location before it “exploded” outwards.
2. The big bang must have been extremely hot. As the universe expanded, it cooled down. Like all hot things, when the universe was very young and hot, it would have actually glowed with light. Since that light can’t escape out of the universe, it must still be around, but very dim. Scientists have been able to observe the very dim echos of that bright light in the form of “microwave background radiation”. This very faint radiation is the same no matter what direction you look, it is spread through the entire universe. This matches up exactly with the calculations that have been made of how the faint afterglow of the big bang should look.
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