How definitive is the claim "the universe needs no cause, it's existence is inherent in the laws of physics"?

I'm certainly no expert on this topic, but from what I understand, this is far from a "case closed" situation. I mean, we don't even know what dark matter and dark energy are yet, and we still can't get general relativity and quantum mechanics to play nice together. And besides that, there are other hypotheses out there that have not been ruled out, and that imply an outside cause to the big bang, such as brane collision.