Roughly 13 Billion years ago, our knowledge of the cosmos was that of infinite singularity. The general consensus is that a massive cosmos event then happened know as the Big Bang. The Big Bang created the trigger that expanded our cosmos and gave us our three-dimensional space we know of now.
From that all the things we know of today such as galaxies, planets and even stars formed from this cooling along with light emerging.
One of the greatest mystery's is that of what is beyond our universe. Or for that matter, what is even the actual space time shape of our universe to begin with. By studying light scientists are able to take snapshots of the the early days of the universe.
Scientists have been able to successfully create snapshots of our universe when it was only 380,000 years old
(CMB as observed by Planck)
One claim is the evidence in the parallel universe theory is a mysterious glow that scientist Ranga-Ram discovered. By examining the CMB image and unusual light there is large regions of "cold spots" in the image.
The theory is the cold spots are from the parallel universe colliding with ours in this growth stage. And outside of our universe, into the endless parallel universes, lies yet the greater "multiverse" which is in theory an infinite number.
By stepping back the potential realities under this grand theory creates absolutely infinite possibilities of your existence.