[Hugh the Scot]

I’m in agreement. It’s a theory... A well supported one, in fact, but not beyond question by reasonable and intelligent people.

[Telepathic Intruder]

In science nothing really progresses beyond a theory, even something as basic as gravity. Some think they become "laws", but laws are just mathematical relationships that themselves aren't really proven. A theory contains laws but theories don't become laws.

We're reasonably certain that the universe is expanding, and predictions generally match what we see today, but no one knows how the universe originally started. There are competing alternative theories to the standard model, such as the Brane concept, but we don't have the physics or the observational data to say what really happened at "the beginning". It's anyone's guess, basically.