What is the Big Bang Theory? What other theories are there about the formation of the universe?

There are currently no alternative scientific theories. The universe is filled with singularities, which are also known as black holes, the bottom of which is a singularity. To put it simply, a singularity is the point at which the space/time continuum ends.

The most widely accepted cosmological model for explaining the universe's early development and expansion is the Big Bang Theory, which postulates that the universe began as a singular point some 13.8 billion years ago and has been expanding ever since. Other theories concerning the universe's formation include the Multiverse Theory and the Steady State Theory, which postulate the existence of multiple universes with different physical constants and properties and the idea that the universe has always existed and is constantly creating new matter to maintain a constant density.