So, Edwin Hubble made the idea of 'The Big Bang', which is to say energy exploding into matter continuously. It came from nothing, but then what is nothing? Does nothing contain energy and dimensions? In a vacuum, nothing does. Can there really be nothing nothing?
Another theory is - is there inflation as well as expansion? The Big Bang was caused by matter made from energy exploding, but it could have been very, very small, and then inflation happened, causing it to grow. Once this finally stopped the universe then continued expanding.
Or was there a pre existing condition which always has and always will be, and inflation just started, and when that ran out of steam, expansion continued? Was there no Big Bang at all?
Is our universe the only one, or are there more? They may coexist like holey cheese, where millions of universe exist at once, but none can ever be accessed by others? Andrei Linde says there are 10 to degree 10 to degree 10 to degree 7 amount of universes.
Another theory, which makes a lot of sense to me, is that a past universe collapsed in on itself, then rebounding to make our current universe, and when the end of ours happens, the same will happen, creating some kind of infinite universe bounce. But what started the infinite bounce?
Time did not exist before nothing, but could it have suddenly sprang into existence? Or was there an event in a pre existing universe that made ours. But then what made that?
Another theory yet again is that we live on a three dimentional membrane, and all of space is part of it. Within this there are two branes, separated by a gap which is a fourth dimention of space. The two branes then collided, remaining extended and filled with the denisty of plasma and matter. But is that the Big Bang? Or a load of nonsense?
Will we ever know what created our universe?