From a scientific and theoretical physics pov I think the singularity (marble, cosmic rubber ball, or whatever it was) came from another universe. Maybe it was the singularity of a black hole in that universe. Maybe black holes in our universe "pinch off" singularities or bubbles to create a new universe.
In Hinduism there's a belief that a lotus sprang from Lord Vishnu's navel. One of his epithets is
Padmanābha, "lotus navel". Sitting in that lotus flower was none other than Lord Brahmā, who actually did the work of creation. I know ... our stories are nothing if not colorful and trippy.
That's the mythological and puranic explanation. But I think it's interesting that it sounds like a metaphor or allegory for the Big Bang being kickstarted by God. The
Nāsadīya Sūkta (Hymn of Creation) of the Rig Veda says "Who knows and who cares?"
because we
are here.