Then I suggest you restrict yourself to logic, Mathematics, and distilled spirits, the only realms in which absolute "proof" is possible.
Scientific theories are based on consonance with observed evidence and multiple unsuccessfull attempts at falsification. Thus, they are NEVER "proven" in the sense of metaphysical certitude. That is the nature of science, and it has seerved us very well, despite it's shortcomings.
They're going back 13 billion light years in time to see what happened then because that's how long it took for the light to reach us. But for all we know, as another poster said the universe goes on in infinity, there are probably galaxies a hundred trillion light years away, and farther. My point is, and it's a theory, fifteen billion years for the universe is like a second for us. It's been around a lot longer than that.
Now you're talking!