Didn't look at the videos, but besides absolute nothing then everything came into existence, 2 other ideas I've heard are.
1. The universe is always contracting and expanding, right now expanding but soon more and more mass, planets, galaxies, etc, will join. Each time creating a stronger gravity pull, and eventually everything compresses into one lump and explodes making another big bang with a never ending cycle.
2. Our universe is the result of a 4th dimensional star exploding and turning into a black hole. (If that's the case then just imagine one star in our entire universe spawning another universe. Means at least one other universe outside of ours.