As a result of commenting on someone else's blog, I feel compelled to offer you this post.
When I was writing EDWARD - http://edwardstafford.co.uk - I was forced to look at reincarnation and the possibility of changing the past. These can be very arcane subjects and I needed them rendered simply.
Simply, if you do change the past that must result in two universes (a contradiction in terms) the one you came from, and the one you create by changing the past.
You will find an opportunity to put your thoughts on the above website, as well as answering this blog - so pay attention!
Before you can say whether there could be more than one universe, you have to ask if there is such a thing as a universe in the first place. By this I mean, "What is the nature of Reality?" - is there, in fact, anything out there at all? This question goes back, at least, to Plato's discourse in "The Republic". A good general answer is, "We think there is, but we don't know what it is."
It is even harder to work out what may be in another universe if we're not even sure about the one we think we're in.
At the end of the day we only know what is out there by our internal and subjective senses. We can blog to each other, of course, but as far as you know I am a virtual person who may not exist outside your own head.
A pause for a moment while I think about being a figment of your imagination...
If each of us is the centre of our own universe and nothing outside each individual actually exists, then that would mean there must be a multiverse with as many universes as there are creatures capable of thought. But hang on, if there is nothing outside myself then you don't exist and nor does anyone else - most inconvenient when I want to go and buy groceries from a shop. Of course, if there is nobody out there, I could just take the groceries, the shop is, after all, only in my own mind. But if I do that I may find myself imprisoned by people who don't really exist, in a prison which is only in my own mind, but which is nevertheless most disagreeable.
So let us join the general agreement of convenience, that there really is something out there. We still don't know what it is, so let's call it Reality.
So, what is Reality?
It's obvious isn't it? It's "Life, the Universe and Everything... You know."
I'm glad we got that settled.
Now then, what else is out there?