Actually, the universe is my thing. I have a few theories of my own, but I'll leave them for some other point.
The answer to your question is simple. If a being such as God can exist before the creation of the universe, why is it so impossible to believe that matter which is tangible can exist before the universe was created.
An alternate explanation is that(as has been observed) in intense vacuum subatomic particles have been formed.
My personal theory is that the matter exists because the universe once it reaches it's furthest point begins to colapse in on itself as supermassive black holes(like the one in the center of the Milky Way) enter into their feeding cycles(hey don't laugh that was how the prof explained t to me). Then the whole process starts over for the next universe... it just takes a while...
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson