An artist's conception of the Big Bang.
The Big Bang theory is a theoretical explanation on how the universe formed.
Expansion of the universe[]
Scientists are researching on why the universe formed. The universe is infinitely expanding, and so that's why the big bang theory formed. The theory is that the universe formed out of something that is smaller than an atom.
Research[]
Scientists have made a machine that makes particles collide to attempt to find out how the universe formed.