Vidura enquired, “O worshipful one! Being the personification of the Supreme Lord, you definitely will know about the movements of time in totality. Accomplished beings of your cadre observe this world through the medium of the intellectual eye”.
In response to Vidura’s question, Maitreya Maharishi replied, “Kṛta, Treta, Dwapara and Kali are the four Yugas. Each of these Yugas has Sandhya and Sandhya-amśa i.e. the transitional period before and after the Yuga. The transitional period before starting of the Yuga is known as Sandhya and the transitional period that comes at the end of the Yuga is known as Sandhyāmśa. In other words, the period of time between Sandhya and Sandhyāśa is a Yuga.
(The set of these 4 yugas of Kṛta, Dwarapa, Treta and Kali is known as Chatur-yuga. It is one basic cycle).
One cycle of 4 Yugas together with their intermediate periods is 12000 celestial years. Among them Kṛta Yuga is made up of 4000 celestial years, Treta Yuga is 3000 celestial years, Dwarapa Yuga is 2000 celestial years and Kali Yuga is 1000 celestial years. One celestial year is 360 human years.
The transitional period before and after Kṛta yuga (Sandhya and the Sandhyāmśa) is 800 celestial years. For Treta Yuga it is 600 celestial years, Dwapara has 400 celestial years and Kali Yuga has a transitional period of 200 celestial years. The sum total of the Yugas and the transitional periods is 12000 celestial (divine) years.
Each Yuga has its own special rules of righteousness (Yuga- dharma). In the first eon called Kṛta Yuga, dharma is completely upheld by human beings i.e. dharma stands on all its four feet. Unrighteousness (adharma) increases progressively in each successive Yuga. In proportion to it, dharma decreases in each successive Yuga.
Mahar-loka is the celestial plane that exists beyond the three planes of existence (tri-lokas). The time period of one morning (daytime) in these supreme lokas beginning from Mahar-loka and up to Brahma-loka, is equivalent of 1000 Chatur-yugas. In other words, one cycle of 4 Yugas * 1000 (12000 divine years * 1000) is the day for Brahma. His night is of equal duration. During night, the creator Brahma sleeps. When night comes to an end, he once again begins the task of creation.
One night of Brahma is equal to many thousands of Yugas for us. What a long period! But to him it is as trivial as our night. Just as we go to work during the day, Brahma begins his creation during the day. This is his duty.
During this day of Brahma, the lifespan of 14 Manus and the period of their rule get complete. Each Manu rules for an approximate period of 71 cycles consisting of 4 yugas each, i.e. 71 Chatur-yugas (71*12000 divine years). This period of time is known as Manvantara.
During each Manvantara, the Manu, the kings belonging to his lineage, the Maharishis, the celestials, Indra and others Devatas who rule over these celestials, together with their assistants such as Gandharvas appear simultaneously to execute their duties and rule over the universe.
This is the daily creation of Lord Brahma. The three worlds are part of this creation. In this creation, the living beings based on their past fruitive actions take birth in the wombs of human beings, animals, birds or forefathers.
Manvantareṣu bhagavān bibhrat sattvaṁ sva-mūrtibhiḥ
Manv-ādibhir idaṁ viśvam avaty udita-pauruṣaḥ
In each Manvantara, the Supreme Lord displays his transcendental powers (pouruśah) taking the help of the traits of goodness (sattva guna). Through incarnations such as that of Manu he sustains and nourishes the universe.
At the end of the day, Brahma takes the help of his traits of inertia (tamo guna) and stopping activities pertaining to creation, he sleeps. Due to the influence of time, entire creation gets absorbed into him. His night is the time for pralaya (annihilation). Even Sun and Moon vanish. The three worlds viz., Bhu, Bhuvah and Suvah merge into him completely and get enveloped in darkness.
At such time the Lord’s energy manifests in the form of a blazing fire which emerges from the face of serpent Adishesha. This is known as Sankarśanāgni. This fire reduces the three worlds into ashes. Unable to withstand this blazing fire, Brighu and other Maharishis, who reside in Mahar-loka, now travel to Jana-loka.
The violent fiery winds of devastation begin to blow. Due to the force of these devastating winds, the waters from the ocean rise rapidly creating huge tsunami waves. In a second the waters from the ocean submerge the three worlds.
In the middle of these waters, Lord Srihari rests with closed eyes on his snake-bed. He will be in Yoga-nidra (yogic sleep). The residents of Jana-loka will be worshipfully singing his hymns at this time.
In this creation, Brahma has the maximum lifespan! He has a lifespan of 100 years as per the time calculations applicable to his plane. In accordance with the different time zones and calculations, day and night keep following one another.
Yad ardham āyuṣas tasya parārdham abhidhīyate
Pūrvaḥ parārdho ’pakrānto hy aparo ’dya pravartate
The lifespan of Brahma i.e. 100 years is divided into two. The first 50 years is known as the purva-parārdha and the second 50 years is known as dwiteeya-parārdha. In these 100 years of Brahma, the purva parardha is complete. The dwiteeya-parārdha is now going on.
In the beginning of the Purva-parādha, there was a Kalpa (time period) known as Brahma-kalpa. In the beginning of this Kalpa, Brahma who was a personification of sound (śabda-brahma) manifested in the form of Vedas.
The Kalpa that comes towards the end of that parārdha is known as Pādma-Kalpa. In that Kalpa, the lotus called the world emerged from the navel of Lord Srihari.
In this Dwiteeya-parārdha, the first Kalpa is known as Varāha kalpa. This is because in this Kalpa, Srihari incarnated as a boar (Varaha).
Kālo ’yaṁ dvi-parārdhākhyonimeṣa upacaryate
Avyākṛtasyānantasya hy anāder jagad-ātmanaḥ
Srihari is the cause for all causes. He is without beginning and end. He is the Universal Self. He is the true essence. This time period of Brahma, which consists of two parārdhas, is just a fraction of a second for the Supreme Lord. It is the taken for blinking once.