All in A Day of Brahma
What does Krishna mean by the beginning of creation? According to the Puranas (Vedic histories), there have been innumerable creations in the course of cyclical time. The basic unit of Vedic cyclical time is the day of Brahma, which lasts 4.32 billion years. The day of Brahma (also called a kalpa) is followed by a night of Brahma, also lasting 4.32 billion years. The cycle of days and nights of Brahma toes on for Brahma's lifetime of one hundred years (36,000 nights), equivalent to 311.04 trillion of our human years. During the day of Brahma, life, including human life, is manifest. During the night of Brahma, life is not manifest.
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