In much of the modern world we picture time as a straight arrow, flying once from a beginning to an end. The Hindu vision is grander and stranger: time turns in immense cycles, and within each turn the world passes through four ages, the yugas, descending from light toward darkness before the wheel comes round again.

The first and finest is the Satya Yuga (also called Krita Yuga), the age of truth. Dharma — righteousness, the moral order of things — stands complete. Tradition pictures dharma as a bull standing firm on all four legs; in this age there is no need of law, for virtue is natural and effortless, lifespans are immense, and the divine is close at hand.

Then begins a slow decline. In the Treta Yuga, dharma rests on three legs; sacrifice and duty must now be deliberately upheld. In the Dvapara Yuga, the bull stands on two; truth and falsehood are evenly matched, knowledge fractures, and conflict spreads. Finally comes the Kali Yuga, the dark age, dharma balanced precariously on a single leg — an age of shortened lives, scattered attention, and forgotten wisdom. By long-standing tradition, we live in the Kali Yuga now.

It would be easy to read this as mere pessimism, but the tradition holds a counterweight. The very difficulty of the Kali Yuga makes spiritual effort cheaper and more potent: what took long austerity in the golden age can be won, the texts say, by sincere devotion and even the simple chanting of the divine name. The dark age is hard, but it is also, paradoxically, generous to the earnest seeker.

These four ages together form one mahayuga ("great age"), traditionally reckoned in a 4:3:2:1 ratio — the golden age longest, each successor shorter — totaling 4,320,000 human years. And the mahayuga is itself only a small gear in a far larger machine. A thousand mahayugas make a single kalpa, a "day of Brahma," at whose end the worlds are withdrawn in dissolution, to be created anew when Brahma wakes. Different texts and regional traditions vary in the finer numbers and in how the descent is described, but the shape is shared across the tradition.

The teaching beneath the arithmetic is consoling. Decline is real, but it is never final. Nothing is wasted and nothing simply ends; the wheel that falls into darkness is the same wheel that rises again into gold.