zhihau said:
bro,
the definition of a universe encapsulates everything that's possible and everything that's impossible.
the notion of parallel universes and multiple universes may well be contained within this observable universe.
I believe multiverse actually refers to a system of parallel universes or universes in other dimensions, universes that we cannot be observed directly but their existence do not directly contradict existing laws of nature and in particularly the String Theory or M Theory, if these are a true representation of the true state of things, which implies the existence of multiple universes. This is very much like square-rooting a negative number. You get a real and an imaginary component. At the beginning, the imaginary part was thought as just a useless imaginary by product of the maths. But we now know that we can use that to derive useful physical relationships to describe the real physical world. The mathematics in String Theory is like Tensor Calculus during Einstein's time when he propounded his General Theory of Relativity. During Einstein's time, no more than 10 people could follow him. Today a lot more could understand String Theory, anyone who takes up a formal university education on this module. But I am not one of them as I am from an earlier era.
But imagine the scenario if this is true. Our core concepts of conservation can be thrown out of the window or at least out of this observable universe and new conservation laws encompassing multiple universes must be developed. Energy-mass can be destroyed if conservation laws are broken.