|"You don't see THAT everyday..."|
Okay, so maybe there were a lot of comments with counter-arguments. I have a counterpoint that touches on the basis for several arguments for the very existence of other universes and what would cause them to exist at all, however, and I'm curious how it will be countered, so here we go:
Nothing is random.
Before I clarify that statement, here's why I bring it up: there is a hypothesis that every possible outcome of any given moment results in parallel universes. On the surface, this suggests an infinity of universes beyond even the most smarty-pants nerd's comprehension, with universes splitting for no more reason than a person having two different cereal options for their morning breakfast.
The problem with this is that nothing is truly random. There are tons of things that, for all human intents and purposes, are random, but that doesn't actually mean they're truly random. It just means they are beyond our ability to predict.
Three examples: the shuffling of a deck, the rolling of a die, and randomized damage dealt in an RPG video game.
Shuffling: The order of the cards is determined by what order they started in, how they were shuffled, whether they were cut, etc. While we cannot predict the final order they will wind up in, making it random for all human intents and purposes, it's not truly random at all as far as the universe is concerned. There is a clear sequence of events with every effect having a cause. A being of high enough intelligence, observational senses, and knowledge of the starting order could know the order of the cards after being shuffled without looking.
Die roll: Same as the shuffling. How the die is thrown, where it lands, etc, gives us a result that is, for all intents and purposes, random, but it landed on the number it did due to various measurable factors. There are too many factors for us to reasonably keep track of and know the ultimate outcome, but the universe is smarter than us. If it were a being capable of following all the variables, it would know the result of every die throw in advance.
Randomized computer number: One of the major issues in computer programming is generating a truly random number, and the reason for this is that it has to be based on something. In short, it's not truly random at all. Any randomization of the damage being dealt in the RPG is most likely the result of an algorithm that "randomizes" the number based on the internal system clock. If one were an android with lightning fast reflexes and could precisely follow that clock, one could time their menu selections in order to get the best possible results every time.
The end point is that the idea of multiple universes resulting from something like a coin flip doesn't make sense to me. When the coin is flipped, the outcome isn't actually random, meaning that there is only actually one possible outcome in spite of there being two sides. We don't know what this outcome is, but humanity's inability to predict something is not the same as it being random from the perspective of the universe as a whole.
This extends to human psychology and decision making. Going back to the two cereals to choose from example, there are various factors impacting the decision, more than we can even begin to comprehend if we really start to think about it, but none of those factors are themselves random. The decision will ultimately be the result of countless non-random factors that won't arbitrarily change. Regardless of how many types of cereal there are in the cabinet, as far as the universe is concerned, there is only one possible outcome.
...Wait, did I just prove the existence of fate? o_O
Okay, that was an exaggeration for my own amusement, but it's an interesting thing to consider. It's also worth noting that based on this argument, even if there is such a thing as fate, there may as well not be from our perspective. Our tiny human brains are incapable of accounting for the effectively infinite amount of x-factors, so there's no point in assuming we know what our fates are. I think we should be humble, accept the limitations of our own minds, and do our best to make our own destinies without arrogantly assuming we know what our fates are. We don't. That's what makes life both fun and tolerable.
This is the part where someone will comment about random quantum components or electrons out of sync or something like that. If one can genuinely prove quantum randomization resulting in other universes, I'm willing to consider it, but I would need some sort of real, solid proof to revise my opinion of randomness. At the moment, it sounds more to me like humans concluding that things they are incapable of measuring or predicting are truly random as opposed to just being beyond our ability to predict.