Re: It's just mathematical equivalency - @Mike Bell
IIRC it was Feynman's supervisor who came up with the idea that there's just a single electron. I'm not saying it's a valid description of reality, but is an indication that there are many seemingly odd theories bandied around.
There are different interpretations of Many Worlds. I'm giving you one now: Everything that could be, ever has been, and ever will be simply is. 'Splitting into different universes' is a succinct and decidedly human description of events that I've heard used many times. Given that neither you nor I really know what's going on, I wouldn't get too hung up on metaphysical descriptions of reality.
As to us being simulations in a computer, did I say it was a particular type of computer? With a creator? Or that it exists in any real sense that you would understand? No. I am suggesting that any physical rules - even the particular weird ones we see around us - could be invoked in a simulation. The 'design' of such a 'computer' could be far simpler than the reality - or multiple realities - that it generates Something that William of Ockham might have appreciated.