The proposed other universes are unreachable , and only conjectured. They are moving away from us at the speed of light or greater and no communication can happen. So they effectively don't exist. Unless we find new physics. So we are back to the case of countability and what are numbers. Numbers represent counting, when you talk about a number you need a way to define it and the Graham number gives a definition but can you really carry out this definition in real time in the universe. If you can't do that then you might as well talk about fairies. This is why there is no such thing as zero. You can never have zero of anything because quantum mechanics has the uncertainty principle. You can never pin down the location of anything with 100% precision. So you are counting apples that you pick from a tree and put in a basket. You put the first one in the basket but you don't know for sure that it is ever in the basket with 100 % confidence because there is a non zero probability that it is not in the basket. It is very low but not zero. So how do you get to zero ? It is simply not possible a 1/0 = infinity , so infinity is not possible either.