Hindu Cosmology upholds the idea that creation is timeless, having no beginning in time. Each creation is preceded by dissolution and each dissolution is followed by creation. The whole cosmos exists in two states - the unmanifested or undifferentiated state and the manifested or differentiated state. This has been going on eternally. There are many universes - all follow the same rhythm, creation and dissolution (the systole and diastole of the cosmic heart). According to the Bhagavad Gita this srishti (creation) and pralaya(dissolution) recur at a period of 1,000 mahayuga or 4.32 billion years or 4,320 million years:
For a thousand ages lasts One day of Brahma, And for a thousand ages one such night;
This knowing, men will know (what is meant by) day and night.
At the day's dawning all things manifest; Spring forth from the Unmanifest;
And then at nightfall they dissolve again, In (that same mystery) surnamed "Unmanifest"
The Rig Veda describes the origin of the universe as:
"Then was not non-existence nor existence: there was no realm of air, no sky beyond it. What covered in, and where? and what gave shelter? Was water there, unfathomed depth of water? Death was not then, nor was there aught immortal: no sign was there, the day's and night's divider. That One Thing, breathless, breathed by its own nature: apart from it was nothing whatsoever. Darkness there was at first concealed in darkness this. All was indiscriminated chaos. All that existed then was void and form less: by the great power of Warmth was born that Unit. Thereafter rose Desire in the beginning, Desire, the primal seed and germ of Spirit. Sages who searched with their heart's thought discovered the existent's kinship in the non-existent. Transversely was their severing line extended: what was above it then, and what below it? There were begetters, there were mighty forces, free action here and energy up yonder. Who verily knows and who can here declare it, whence it was born and whence comes this creation? The devas are later than this world's production. Who knows then whence it first came into being? He, the first origin of this creation, whether he formed it all or did not form it, Whose eye controls this world in highest heaven, he verily knows it, or perhaps he knows not" - (Rig Veda 10.129.1-7)
Structure of the universeThe Yugas
• Satya or Krta (1,728,000 years): Satya means "truth"; the age is also known as Krta, "action," i.e., the age in which the people did unquestioningly what their benevolent elders told them.
• Treta (1,296,000 years): Treta means "three," the third age, counting backwards from the present: also the age in which the feelings and forces of good are as three parts, and those of evil as one; also the age in which people were specially "protected," trayate, by their elders.
• Dva-para (864,000 years): Dva-para means "two-sided," hence doubt also.
• Kali (432,000 years) which rotates in succession. Kali means "discord," "struggle".
And all of these add to 4,320,000 years. Now, these four yugas, taken together, constitute one Mahayuga. One thousand Mahayugas are one day of Brahma. Brahma's one day is one Kalpa. So one day of Brahma will be 432 crores or 4,320 million years or 4.32 billion years. A similar expanse of time will make His one night, and that is another Kalpa. Our wildest imagination staggers in conceiving Brahma's life-span. This is the expansive view of time. No other culture had this unique vision of the infinity of time as well as the infinity of space.