the big bang theory is religeous (i.e. we all started as one being). It was even developed by a priest, in 1927
There are loads of theories around. The most interesting are quite bonkers
Howards Bloom´s Global Brain theory (similar to Jung´s universal conciousness theory)
Amit Goswami´s Self aware universe theory (quantum and meta physics)
Michael Cremo´s Devolusion theory (elements of Vedic stuff here)
Darwin´s own Descent of Man theory, different from his 1853 OofS thesis
Zechariah Sitchin´s alien astronaught theory
etc. I studied this at university decades ago. We have no answers, but I think it lies somewhere in meta-quantum theory.
btw, what is gravity? sure, we know the equasion to calculate it, but why does this exist in the first place? We need a better "string" theory.
I´m reading a book written in 1910 about meta physics right now. Rare and interesting.