The big bang theory was what a lot of people thought was how the universe began. According the to the big bang the universe was created about 10-20 billion years ago from a cosmic explosion the shbot out matter in all directings.

The big bang was suggested because it explains why far away galaxies are moving away from us so fast.

Although a lot of people believe in the big bang theory it probably will never be proven, which will leave a lot of un answered questions

The big Bang Theory was founded by Edwin Hubble. He found out that the universe was expanding out in every direction and that Galaxies that are twice as far from us are moving twice as fast .

The big bang theory is used to explain what happened a the beginning of the universe, lots of facts and studys have shown beyond reasonable dbout did have a beginning. 

After its initial appearance, it apparently inflated (the "Big Bang"), expanded and cooled, going from very, very small and very, very hot, to the size and temperature of our current universe. It continues to expand and cool to this day and we are inside of it: incredible creatures living on a unique planet, circling a beautiful star clustered together with several hundred billion other stars in a galaxy soaring through the cosmos, all of which is inside of an expanding universe that began as an infinitesimal singularity which appeared out of nowhere for reasons unknown. This is the Big Bang theory.