The idea of alternate universes isn’t new. There was talk in the scientific community back when I was a kid. I don’t put a whole lot of stock in “man’s” understanding when it gets into the theoretical.
I think the main reason (and I might be wrong) for the theory on the alternate universes is that if the force of gravity was just a small fraction greater or less than what it is then the universe couldn’t exist. Therefore our alternate universe won the crapshoot of many universes. What is truly astounding is if we were the only universe and very conveniently had EXACTLY the correct gravitational force that ensures the existence of this universe.