Hindu cosmology measures time on a scale almost incomprehensible by modern reckoning. The basic unit is the *yuga*; four yugas make a *Mahayuga*; 71 Mahayugas make a *Manvantara*; 14 Manvantaras make a *Kalpa* — a single day of Brahma. The four yugas — *Satya, Treta, Dvapara, Kali* — chart a steady decline of dharma over each cycle.
✦ The Four Yugas and Their Durations
The classical lengths, in human years (according to *Manusmriti*, *Mahabharata* and *Bhagavata Purana*):
- ✦**Satya Yuga (Krita Yuga)** — 1,728,000 years
- ✦**Treta Yuga** — 1,296,000 years
- ✦**Dvapara Yuga** — 864,000 years
- ✦**Kali Yuga** — 432,000 years
- ✦**Total Mahayuga** — 4,320,000 years
Note the ratio: 4 : 3 : 2 : 1. Each yuga is shorter than the previous in this proportion.
✦ The Quality of Each Yuga
Satya Yuga (the Age of Truth) — Dharma stands on all four legs. The classical metaphor is of dharma as a four-legged bull, fully balanced. Truth is universal; people are virtuous by nature; longevity is high (the texts give absurd numbers — 100,000 years — but the symbolic point is "very long"). No formal religious ritual is needed; people perceive the truth directly.
Treta Yuga (the Silver Age) — Dharma stands on three legs. Virtue declines by one-fourth. The Vedic ritual emerges as a way to maintain order. Major events: the avatars of Rama, Vamana and Parashurama. Longevity drops.
Dvapara Yuga (the Bronze Age) — Dharma stands on two legs. Virtue declines further. The Vedas are formally divided into four (this is when Vyasa is said to have done the work). Major events: the Mahabharata, the life and death of Krishna. The end of Dvapara is dated traditionally to 18 February 3102 BCE — the day Krishna left his body, which is the conventional start of Kali Yuga.
Kali Yuga (the Iron Age) — Dharma stands on one leg. Virtue is at its minimum. People are short-lived (the texts say 100 years at most), short-tempered, materialistic, and increasingly divorced from spiritual perception. By the *Bhagavata Purana's* description, this is our current age — and we are approximately 5,127 years into its 432,000-year span.
✦ The Long Cycles
Mahayuga — the four yugas together: 4.32 million years.
Manvantara — 71 Mahayugas under the rule of one *Manu* (the cosmic ancestor of humanity for that period). 14 Manus rule in succession in one Kalpa. Our current Manu is *Vaivasvata*, the seventh, ruling the seventh Manvantara. The classical name for our current Manvantara is *Vaivasvata Manvantara*.
Kalpa — 14 Manvantaras = one day of Brahma = 4.32 billion human years. Our current Kalpa is the *Shveta-Varaha Kalpa*. Brahma's day is followed by Brahma's night of equal length — when creation is dissolved and re-emerges.
Brahma's life — 100 of Brahma's years (each year being 360 days-and-nights of the kind described above). At the end of Brahma's life, the entire cosmos including Brahma himself is reabsorbed into the unmanifest.
✦ The Spiral, Not a Line
Critically, this is a *cyclical* model. When Kali Yuga ends, the cycle restarts — Satya Yuga returns. Time does not move toward an end-of-history; it moves through cycles. The pattern of decline is not a permanent slide but a repeating phase. The avatar Kalki, awaited at the end of Kali Yuga, is the cosmic principle that resets the cycle.
✦ The Decline Pattern
The yuga doctrine carries an important moral psychology: the world is not getting steadily better, contrary to the modern Enlightenment narrative. Things drift toward decline naturally; *maintaining* dharma takes active effort, and even with effort, full virtue is not sustainable across millennia. This is, in classical Hindu thought, why the avatars come — not to make things permanently better, but to reset and restart the cycle when decline goes too far.
✦ A Modern Note
Modern science measures cosmic time in scales that, in some respects, run parallel to the Puranic figures. The current age of the universe in modern cosmology (about 13.8 billion years) is roughly comparable to the cosmic times in Hindu cosmology (a Kalpa is 4.32 billion years; we are partway through Brahma's life). The agreement is partial and probably coincidental, but it is striking enough that even modern Hindu commentators have noted it.
What matters more than the literal numbers is the basic shape of the worldview: time is vast, time is cyclical, dharma drifts toward decline naturally, and the spiritual aim is realised against this backdrop, not within a flat linear history.