Some scientists believe that the Universe began with a Big Bang about 13.8 Billion years ago. I say it began with a Big Bang a lot earlier... maybe a billion, billion years ago. In the beginning there was this something the size of a marble but it was a bigger marble than the size described by on-line astronomer/physicist Neil deGrasse Tyson... (maybe TV personalities a billion, billion years ago were bigger than they are today.) At any rate, the big marble Banged Big, inflated and eventually the universe that it expanded into over billions of years became less and less dense as it expanded (just as our universe is doing) until the black holes in that universe were so far apart from each other that to any observer each black hole, which, by the way, were larger than the black holes we find today, seemed to be alone in the vastness of forever.
Now over a great many billions of years, black holes go through a process where they eventually come to a point where they form themselves into a marble, a marble which eventually ends itself in a Big Bang... a big bang which any observer in the vicinity of that big bang about 13.8 billion years later would think of itself as being in a universe. So in reality there are many universes, each one beginning as a marble after having gone through a process that was once a black hole. Now a billion, billion years ago, a universe was bigger than a universe is today, so big that the universe we live in today still appears to us as being a very, very big universe. The background noise that scientists talk about today are not microwaves left over from our big bang, but microwaves from other big bangs which are in the process of creating new universes outside our own observable universe. Now as far as who created the first marble a billion, billion years ago, well... God is real and not a myth.