Big bang

Source : nasa.gov

The Big Bang Theory is the leading theory explaining how the universe began.

Simply it says the universe as we know it started with a small singularity, then inflated over the next 13.8 billion years to the cosmos that we know today.

This hypothetical starting point of universe was an infinite concentration of energy referred to as a singularity. Physical laws don't deal well with infinite numbers, meaning concepts such as the universe, time, and a bunch of different forces. The first public use of the modern term for Lemaître's idea actually came from a critic — English astronomer Fred Hoyle. On March 28, 1949, Hoyle coined the phrase during a defense of his preferred theory of an eternal universe that created matter to cancel out the dilution of expansion. Hoyle said the notion that "all matter of the universe was created in one big bang at a particular time in the remote past," was irrational. In later interviews, Hoyle denied intentionally inventing a slanderous name, but the moniker stuck, much to the frustration of some

Because current instruments don't allow astronomers to peer back at the universe's birth, much of what we understand about the Big Bang Theory comes from mathematical formulas and models. Astronomers can, however, see the "echo" of the expansion through a phenomenon known as the cosmic microwave background.