In Bhagavad Gita, Lord Krishna tells Arjuna:
"All the worlds from Brahma's world (the universe) are periodic. Arjuna.
They, those who know the day and night, know that the day of Brahma is a thousand yugas long and a night is a thousand yugas long.
From the unmanifested, all the manifest things spring forth on the arrival of the day (of Brahma). On the onset of night all these sink into what is called the unmanifested.
Partha, (Arjuna), this multitude of created things having existed over and over again and helplessly destroyed at the onset of night, spring forth on the onset of day."
All this sounds a lot like the modern theory of an oscillating universe that begins with a big bang that sends all matter flying out until it comes to a halt and collapses back into a tiny speck, leading to another big bang, and so on. An entire cycle according to present-day cosmological ideas could take 10,000million to 20,000 million years. It seems incredible that the ancient Hindus could hit upon this idea thousands of years ago. Some scholars have tended to dismiss this agreement of the order of length of the cycle as a mere coincidence.