Hi, I'm in middle school too. Before you get a fairly rude response, I'll have a go at it. 1+1=2. Fact? Yes, but humans made up math to explain why if I have one stone and add another stone to it, I get two stones. Science is just like that, because it tries to explain things (not so mythical as your examples) and is fact. Now, to the multiverse part. As a side note, be careful throwing around the term multiverse, especially around here. The multiverse theory is an interesting one, because it catches people's attention while having no exparimental evidence. Some people on PF get mad when you confuse popular science with real hard science involving lots of math. I made that mistake one too many times. If you go into the issues about spacetime (I will refer to your multiverse as spacetime) people say that spacetime did have a begining, and it did not. Saying spacetime had a beginning implies time outside of spacetime, so there has never been a time without spacetime, but at the same time, saying spacetime is infinite is not exactly correct (so in other words, according to the Big Bang which is widely accepted, there was a "begining" to spacetime, but there was never a time without spacetime). It's hard to wrap your head around, but eventually you'll get it. I hope that helps!