Chapter 8, verse 17 in the Bhagavad Gita has reference to the concept of a 'Brahma' day and night.

Roughly translated, the Gita expounds thus : A thousand ages (yugas) taken together form the duration of Brahmā’s one day. And such also is the duration of his night.

In the subsequent verse, the Gita further notes that all creation comes into existence during the day of the Brahma, and gets annihilated during Brahma's night, and the cycle repeats.

The Gita further elaborates that At the beginning of Brahmā’s day, all living entities become manifest from the unmanifest state, and thereafter, when the night falls, they are merged into the unmanifest again.

Elsewhere in the vedic literature of Manusmriti, a yuga cycle corresponds to 4.32 million years, and a thousand such cycles, effectively making up a single Brahma day which is 4.32 billion years. A single Brahma day and night consequently is 8.64 billion years, and each Brahma year is made up of 360 such day / night cycles resulting in 3.11 trillion human years for each Brahma year. Each Brahma life further extends to 100 years made up of 360 individual Brahma days and nights. Brahma himself will live and die after 100 Brahma years, which will equate to 311 trillion human years (each Brahma year calculated as Brahma day plus night multiplied by 360, or 8.64 billion years times 360) times 100, resulting in a full life span of Brahma at 311 trillion years !

Current cosmological research pegs the current age of our universe to be around 14 billion years and is believed to be expanding, with the expansion rate that is accelerating. Future estimates of how long this expansion will last until the universe starts to cool off and eventually die or exhaust all of its energy is any scientist's guess! If scientists are currently projecting a potential trillion year possibility of our current universe's expansion, the vedic estimate of 3.11 trillion years of a Brahma year does not seem to be far-fetched. Of course, cosmologists are still unable to comprehend scales larger than trillions of years, so the cataclysmic birth and death of a new Brahma every 311 trillion years by the ancient hindus is truly mind bending !

In his book, Searching for Stars on an island in Maine, renowned MIT physicist and author, Dr. Alan Lightman claims that no other philosophical thought has comprehended cosmological scales other than ancient hindu thought and texts.

In conclusion, the Gita expounds an eternal universe with constant creation and destruction every 4.32 billion years at the dawn of each Brahma day and night, with continued colossal change every 3.11 trillion years at the dawn of each Brahma year, and a further cataclysmic rebirth of an entirely new universe every 311 trillion years with the dawn of a brand new Brahma !