The theory that has the most evidence in support of it currently
is M-Theory. Under M-Theory there are a number of planes of
existence that shift and move and create what we perceive of as
dimensions. These dimensions are actually objects called
super-strings that vibrate and interact with each other in such a
way as to create the laws that govern how our universe reacts.
Under M-Theory these super-strings generate a near infinite
number of universes, and our own is just one of them. So our
universe is just the result of many interacting, vibrating
super-strings. These came together in such a way as to generate the
event we call "The Big Bang" that was the start of our
universe.
There are other theories that also attempt to explain the origin
of the universe but none are as widely accepted right now as
M-Theory in the scientific community. There are also religious
beliefs about the origin of the universe. For instance, according
to the Aboriginals of Australia the world was flat and barren until
Baiame, The Maker of Things, brought the ancestral aborigines forth
from The Dreaming and guided them across the land in an adventure
that caused the formation of all. None of the religious creation
stories have sufficent detail to be accurately tested for
veracity.
