BG Chap 8 - Lifespan of Brahmā
Brahmaloka and other planets are destroyed because of limitations of time. Even if Brahmā, the master of the planet, must die, what can be said of others? The persons situated on elevated planets such as Mahar-loka know that one day of Brahmā is a thousand cycles of the four yugas by human calculations and such is the duration of Brahmā’s night also. The four yugas are Satya (lasts 1,728,000 years), Tretā (lasts 1,296,000 years), Dvāpara (864,000 years) and Kali (lasts 432,000 years). The total duration of these four yugas is thus 4,320,000 human years. One thousand of this cycle of four yugas is one kalpa or one day of Brahmā. Using a different calculation: One year of human is a day and night of the devatās. Thus 360 days of the devas (1 year of deva) is 360 human years. Twelve thousand devatā years is 4,320,000 human years, and this makes a cycle of four yugas. One thousand of these cycles makes one day of Brahmā. His night is also the same duration. One hundred of those years is the lifespan of Brahmā. After that Brahmā dies. If the Brahmā is a Vaiṣṇava, he will attain liberation. By these calculations the life of Brahmā seems fantastic and interminable, but from the viewpoint of eternity it is as brief as a lightning flash. In the Causal Ocean there are innumerable Brahmās rising and disappearing like bubbles in the Atlantic. Brahmā and his creation are all part of the material universe, and therefore they are in constant flux.