“…an understanding of the infinite tree of universes seems to be needed in order to make statistical predictions about the properties of our own universe, which is assumed to be a typical “branch” on the tree.” -Alan Guth
The Big Bang is commonly regarded as the start of it all, but that’s only the birth of what we call our observable Universe. There must have been something compelling to set it up, complete with the initial conditions that our Universe began with. An idea called Cosmic Inflation fits the bill perfectly, providing those conditions and making six explicitly new predictions.
Despite the fact that five of them have been observationally verified, there are still detractors of inflation, who go as far as to proclaim that inflation isn’t even a scientific theory. It’s not a crazy claim, but it’s not entirely fair, either.