According to Hindu tradition, time is divided into four yugas named Satya, Tretā, Dvāpara and Kali. The span of these yugas is extremely long. For example, Kali is 432,000 years long, Dvāpara goes for 864,000 years. Tretā is 1,296,000 years while Satya is 1,728,000 years long. Many interpret these numbers to mean that Śrī Rāma appeared nearly a million years ago (he appeared in Tretā yuga).

The four yugas (caturyugas) add up to 4,230,000 years. There are 1000 such caturyugas in one day of Brahmā, which adds up to 4 billion, 230 million years. And then there is his night. And, Brahmā lives for 100 years. There are 14 manvantaras in a day of Brahmā, with each manvantara containing 71 caturyugas. We are in the Kaliyuga of the 28th caturyuga of the 7th manvantara of Vaivasvata Manu. We are currently in the first day of the 51st year of Brahmā’s life span. Here is some simple Math.

Days and nights in 51 years = 360x51x2=36,720

Duration of a day of Brahmā = 4.32 million years per caturyuga x1 000 caturyugas = 4.32 billion years.

[by comparison, the age of the universe according to science is roughly 14 billion years, and the age of the earth around 4.5 billion years. As the Bhagavad-gita explains, there is a total devastation at the end of Brahmā’s day and creation at the beginning of Brahmā’s day. Brahmā’s day is less than half done, so the age of the universe should be around 2 billion years according to the yuga calculation]

Since the birth of Brahmā, roughly 158.6 trillion years have passed.

Beyond this, the life span of individual human beings is incredibly long in Satya yuga- 100,000 years, followed by Tretā – 10,000 years, then Dvāpara- 1000 years and then Kali – 100 years. The height of individuals also decreases starting from nearly 30 ft in Satya (!) to nearly 6 ft in Tretā. Fossil evidence strongly argues against such large humans!

Śrī Babaji sent me an article from Dr. Jayasree Saranathan who has part of it on her website here: https://jayasreesaranathan.blogspot.com/2018/01/divya-and-dharma-two-sides-of-yuga.html

The full article is published here- https://www.academia.edu/36652239/Yuga_classification_how_Yuga_must_be_understood

Babaji generally agrees with the article, and also indicated some verses from the Bhāgavata that support her thesis. Below, I present the essence of Dr. Saranathan’s thesis along with my own views and with some supporting verses from the Bhāgavata.

The durations of the yugas and life spans of humans are not literally applicable to the earth.

If one insists that the yuga calculation applies to the earth, that is, human beings walked the earth millions years ago practicing meditation or fighting wars (as many literalists in modern Caitanya sects do), the idea is ridiculous given what we know about the history of the earth. Geological and climatic conditions were totally different even a million years ago. Anatomically modern beings were not around in their present form for much more than 300,000 years ago – the fossil evidence is clear on this.

Bodies of animals, dinosaurs and of humans simply cannot live for 100,000 years – the biology does not permit it. And there is clear evidence that bodies of animals millions of years ago were made of the same substances, organs and related anatomies as modern beings. So the incredible life spans of humans are also not true.

Dr. Saranathan points out that it is clear from the Vedas that the ṛṣis were not deluded about human life spans. No prayer asks for a life as long as 100,000 years. And there is prayer after prayer in the ṛg-veda, the Upaniṣads, the Mahābhārata, the Rāmāyaṇa and so on for a life span of 100 years.

Dr. Saranathan further explains that the notion that Rāma literally ruled for 11,000 years is wrong. The Mahābhārata mentions that one day of vow for exalted kings like Yudhishitra is like one year on earth. Then, Rāma can be understood to only have ruled for 11,000/360 ~ 31 years. She makes the same point that I have made before on this website- that one needs to understand the essential message of the scriptures, and not take everything literally.

How to understand the large times of yugas?

A key point Dr. Saranathan makes in her article is that the long time scales of the yugas listed above apply not to earth’s history but to celestial objects. The yuga classification above expresses the life-spans of stars in language. For example, the age of the sun is about 4.6 billion years, and the sun takes about 230 million years to make one round through the galaxy.

The reasoning here is as follows. The scriptures differentiate between earthly years and the year of the devas, or ‘divya’ year. ‘div’ means ‘to shine’, and so the year of the deva refers to time scales related to motion and life spans of the stars. The mapping between a day of the devas and our time is such that passage of only a small time for the devas corresponds to a very long time for us. So one year of the devas is 360 years of our time. But one day of Brahmā is even longer than that, corresponding to 4.32 billion years, which is about 20 rounds of the sun through the galaxy, and to 1000 divya days or days of the devas. This reasoning is directly supported by the 12,000 year time span for the four yugas given by the sage Mārkaṇḍeya in the Mahābharata (3-187) to Yudhiṣṭhira. These are divya years because 12,000×360= 432000 years as above!

In what way does the concept of yuga apply to the earth?

Dr. Saranathan distinguishes between divya yugas which were mentioned before, that refer to very long time scales, and dharma yugas. Dharma yugas also follow the same order: Satya, Tretā, Dvāpara and Kali. But the span of the dharma yuga is determined not by the divya yuga time span, but by the time at which the qualities of individual yugas are on the ascendant. And there is no time limit set for this, nor is there a rigid span of a dharma yuga. This is clear from the fact that there can be yugas within a yuga – so in Kali, there may be Satya and in Tretā, there may be Dvāpara. The rigid time span is only applicable to the divya yugas.

What determines when one dharma yuga changes to another? The Mahābharata states that the determining factor is the king. If the king upholds all four legs of dharma, then it is Satya, and if he doesn’t, then there is a progressive change in the dharma of the yuga and so on.

By this reasoning then, Rāmāyaṇa occurred not a million years ago as the divya yuga scale would suggest, but some time before Kṛṣṇa’s appearance when dharma was about 3/4th of what it was in the preceding Satya yuga.

Now the Bhāgavata purāṇa also defines the yugas, which are dharma yugas, according to the qualities. Note that there is no mention of the divya yuga time scale in these verses! I reproduce the verses below.

prabhavanti yadā sattve mano-buddhīndriyāṇi ca
tadā kṛta-yugaṁ vidyāj jñāne tapasi yad ruciḥ

yadā karmasu kāmyeṣu bhaktir yaśasi dehinām
tadā tretā rajo-vṛttir iti jānīhi buddhiman

yadā lobhas tv asantoṣo māno dambho ’tha matsaraḥ
karmaṇāṁ cāpi kāmyānāṁ dvāparaṁ tad rajas-tamaḥ

yadā māyānṛtaṁ tandrā nidrā hiṁsā viṣādanam
śoka-mohau bhayaṁ dainyaṁ sa kalis tāmasaḥ smṛtaḥ

Visvanatha Cakravarti fully agrees with the concept that [dharma] yugas can show up inside of other yugas! Here is his commentary on the verse before the above verses:

yathā ekasyāpi grahasya sūryāder daśāyāṁ grahāṇām antardaśā bhavanti, tathaikaikasyāpi yugasya madhye catvāri yugāni tiṣṭhanty ataḥ kali-madhye’pi kadācit kadācin na dharma-hrāsas tatrāpy ekaikasmin puṁsy evaṁ draṣṭavyam ity āha—sattvam iti | ātmany antaḥkaraṇe parivartante, yātāyātaṁ kurvanti

Summary

1. There are two types of yugas- divya yuga and dharma yuga.
2. The divya yugas refer to galactic events. Their time span is fixed.
3. The dharma yugas refer to times when all four, or three, or two, or one leg of dharma remains standing.
4. The change of one dharma yuga to another dharma yuga depends on the changing of the king and/or his authority.
5. One dharma yuga can occur inside another dharma yuga- so for example, Kali can occur inside Satya and Satya can occur inside Kali.