originally appeared on Quora: the place to gain and share knowledge, empowering people to learn from others and better understand the world.
Let me explain, before going all reality based on me.
I know, I know... universe technically means "everything".
The fact that we are in this "Goldilocks" universe, not too hot or too cold, suggests there may be an infinite number out there.
In fact, if the strength of gravity was changed just a very minute amount (I'm talking by trillionths of a fraction), our universe would be very different than it is now, without stars, or crushed back to a singularity before it could inflate for more than a few years.
This is called the Many Worlds Interpretation, or MWI, originally formulated by Hugh Everett in 1957.