As our understanding of cosmology grows, it becomes more and more difficult to avoid accepting that the universe is infinite.

In an infinite universe every possible event occurs an infinite number of times- it is argued that this means infinite regions of space- FAR beyond our observable universe- harboring worlds and occupants indistinguishable from us- and infinitely more with world's just slightly different... This is discussed in detail in Brian Greene's 'The Hidden Reality' and Max Tegmark's 'Our Mathematical Universe'.

Furthermore, theory strongly suggests that there are infinite universes where the fundamental constants are different- this allows us to avoid the assertion that our universe is 'Fine tuned' for our type of life- All possible combinations of values for fundamental constants exist, including some that are precisely right for our existence, naturally we exist in one of these universes.

On top of this incomprehensible infinity of infinities is another infinity multiplying them all- this time arising not from the Mega-macroscopic theories of cosmology, but from the the microscopic world of quantum mechanics.

The 'many world's' interpretation of quantum mechanics is a less artificial interpretation than the copenhagen interpretation that invokes- without any mathematical rigor- a collapse of the wavefunction. The many worlds interpretation suggests that all possible outcomes of any quantum event actually happen and are all equally 'real'...

There are more possible infinities on top of these... but at this point it starts to get REALLY weird....

Long story short- as we learn more, the more it seems that our universe is infinite, and that everything that CAN happen in our universe WILL happen an infinite number of times. Furthermore there are infinite other infinite universes with different fundamental constants where anything that can happen will happen infinite times. On top of all this, every possible quantum event in these infinite universes does happen creating another equally real universe....

And I haven't even mentioned 'simulated universes' within these universes, or Boltzman Brains or quantum suicide- feel free to google those... and never sleep peacefully again...