The Rigveda makes references to the theories of creation of the world in several hymns from Mandala 2 to Mandala 9. In Mandala 10, for the first time, we find hymns dedicated to cosmology. The hymn 129 of Mandala 10 is a cosmological hymn, but it is a strange cosmological hymn because it states that the Gods came after the universe got created, which means that even the Gods don’t know when and how the universe was created. The hymn begins with a mention of the nonexistence where there is the ultimate source of creation, the “One,” which assumes a cosmic egg like form in the verse 3, and in the verse 4, the “primal semen,” the origin of all beings gets concretized.
Here’s a translation of the hymn 129 of Mandala 10 (The Rigveda, translated by Stephanie W. Jamison and Joel P. Brereton, OUP, 2014):
1. The nonexistent did not exist, nor did the existent exist at that time. There existed neither the airy space nor heaven beyond.
What moved back and forth? From where and in whose protection? Did water exist, a deep depth?
2. Death did not exist nor deathlessness then. There existed no sign of night nor of day.
That One breathed without wind by its independent will. There existed nothing else beyond that.
3. Darkness existed, hidden by darkness, in the beginning. All this was a signless ocean.
What existed as a thing coming into being, concealed by emptiness—that One was born by the power of heat.
4. Then, in the beginning, from thought there evolved desire, which existed as the primal semen.
Searching in their hearts through inspired thought, poets found the connection of the existent in the nonexistent.
5. Their cord was stretched across: Did something exist below it? Did something exist above?
There existed placers of semen and there existed greatnesses. There was independent will below, offering above.
6. Who really knows? Who shall here proclaim it?—from where was it born, from where this creation?
The gods are on this side of the creation of this (world). So then who does know from where it came to be?
7. This creation—from where it came to be, if it was produced or if not— he who is the overseer of this (world) in the furthest heaven, he surely knows. Or if he does not know...?
Vedic theology does not commence with stories on creation as Western theology does. The Rigveda explores the cosmological issues in its final book (the Mandala 10).