Alternate universes

While watching an episode of Stargate that revolved around (somewhat) an alternate universe I decided that it is highly feasible that they exist. Bare with me here, for every choice we make it effects our lives. Here's a hypothetical, let's say my parents forget to buy cereal and I am therefore forced to eat toast for breakfast (god forbid), I use a old jam thats hiding away in some dusty cupboard and get ill from some sort of bacteria (like I said hypothetical) and because of this I don't go on holiday to the the US, but because of this I don't die because the plain I was going to go on crashed. (this is all starting to sound a bit Final Destinationish) So essentially I live a longer life because I forgot to buy some cereal. Now this was a more drastic example but every choice we make can effect how our lives turn out. I for one find it extremely interesting, so when thinking about it like "what if I had done so and so, could I be doing this?" it begs the question, how can there not be alternate universes? Course I'm sure someone could come up an extremely good answer to that. Maybe I should stop taking everything quite so seriously and go back to enjoying parallel universe episodes of Stargate, Star Trek and other Star related franchises. Sorry for this random and slightly pointless first post, I'll get better as I go along I swear.