The Problem With Regress

I don't understand why there can't be an infinite regress. I think it depends on what kind of regress we're talking about. Craig is always, I thought about Vlanken's argument and this idea that there's a big bang,. etc. He argued that the universe always existed. And I don't see, I'm not a theoretical physicist. But even if there were, you wouldn't get that through sitting in a room and thinking about it. It would have to come from science.