It is said that in the reckoning of Heaven and Earth, 129,600 years make one yuán (a cosmic epoch).

Before any story, a number. 數 (shù) is the "count" of the cosmos — the idea that time has an exact arithmetic. 元 (yuán) is the largest unit in it: 129,600 years. The whole scheme is borrowed, figure for figure, from the Northern Song philosopher Shào Yōng (邵雍, 1011–77, often called by his posthumous title 邵康節) and his 《皇極經世》. 蓋聞, "it is said," is how a classical essay clears its throat.

One yuán divides into twelve huì, corresponding to the twelve Earthly Branches: zǐ, chǒu, yín, mǎo, chén, sì, wǔ, wèi, shēn, yǒu, xū, hài.

One 元 divides into twelve 會 (huì), named for the 十二地支, the twelve Earthly Branches. Those same twelve labels name the two-hour blocks of an ordinary day — which is the trick the next few lines turn on. (Shào Yōng's full system nests four deep: 元 › 會 › 運 › 世. Wú keeps the top two and drops the small change.)

Each huì comes to 10,800 years.

該 (gāi) here means "comes to." Twelve 會 at 10,800 years each makes 129,600 — one 元 exactly. The sums are meant to balance, and the balancing is the message: this is a universe that runs like a clock.

Take a single day as the measure: at the zǐ hour the yang-breath is born; at chǒu the cock crows; at yín there is not yet light; at mǎo the sun rises; at chén, after the morning meal; at sì, things settle into their order;

Here is the idea the passage rests on. The life of the cosmos has the shape of a single day, and each Branch serves as both an hour and an age of the world. Notice how homely the hour-names are — 雞鳴 cock-crow, 食後 after breakfast, and further down 晡 the late-afternoon meal, 黃昏 dusk, 人定 "when people have settled," the hài hour. A cosmology told in the vocabulary of a farmhouse.

at noon (wǔ) the sun stands at the zenith; at wèi it slips toward the west; at the shēn hour comes the late-afternoon meal, and the sun sets at yǒu; at xū falls the dusk; and at hài people settle to rest.

天中 is the top of the sky, noon; 西蹉 has the sun slipping westward. The day is now going downhill, which is the point. The next line lets the universe follow it into the dark.

Reasoning by the same scale on the grand cosmic clock: when the xū huì reaches its end, Heaven and Earth grow dim and the ten thousand things fall into decay.

The reading matters here. 否 is pǐ, not the everyday fǒu ("not"): it names hexagram 12 of the Yijing, Obstruction — everything blocked, stalled, going bad. It survives in a phrase people still use, 否極泰來: when 否 hits bottom, 泰 (Peace) comes round again. 昏曚 (hūn méng) is dim and lightless. The world, like a day, has its evening.

After another 5,400 years, as the hài huì begins, all turns to darkness; between Heaven and Earth no beings remain at all — and this is called chaos (hùndùn).

兩間, "between the two," means the space between Heaven and Earth — that is, the world; 俱無 says nothing is left living in it. And the name for that emptiness is 混沌, the same chaos the opening poem began with. So chaos is not only the start of things. It comes round again. The universe dies back into shapelessness, then is reborn.

After a further 5,400 years, as the hài huì nears its close, the cycle turns again — "when zhēn ends, yuán begins anew" — and as the zǐ huì approaches, light gradually returns.

貞下起元 is a four-word formula out of the 《易經》. Hexagram 乾 has four virtues in sequence — 元亨利貞, beginning, growth, harvest, holding firm. Reach 貞, the winter of the cycle, and 元, the new beginning, is already starting up underneath it. This is the engine of the whole scheme: an ending is a beginning seen from the wrong side.

Shao Kangjie wrote: "At the winter solstice, the midpoint of zǐ, the heart of Heaven does not shift; where the single yang first stirs, the ten thousand things are not yet born."

The four-line poem is Shào Yōng's own, from his poetry collection 《擊壤集》. 冬至, the winter solstice, is the year's midnight, matching the zǐ hour. 一陽初動 is the first flicker of yang — in Yijing terms, hexagram 復 (Return), one unbroken line pushing up beneath five broken ones. The 天心, "heart of Heaven," is the still point the whole turn pivots on. Wú quotes a real philosopher to lend a monkey story the weight of serious metaphysics.

At this point, Heaven first has its root.

始 is "begins to." With that first stir of yang, Heaven acquires a 根 — a root, a seed of being. Everything visible grows from it.

After another 5,400 years, right at the zǐ huì, the light and clear rises upward: there is sun, there is moon, there are stars, there are asterisms. Sun, moon, stars and asterisms are called the Four Images. Hence it is said: Heaven opens at zǐ.

輕清上騰, the light and clear floating up, is the first time anything separates from anything. 辰 here means the fixed stars. Note that Wú glosses 四象, the "Four Images," loosely as sun, moon, stars and constellations, rather than as the Yijing's technical four line-pairs — he wants the night sky, not the diagram. 天開於子, "Heaven opens at zǐ," is another of Shào Yōng's famous formulas.

After another 5,400 years, as the zǐ huì draws to its close and the chǒu huì approaches, things grow firm and solid. The Book of Changes says: "Great indeed is the Creative and its origin! Perfect indeed is the Receptive and its origin! The ten thousand things draw their life from it, in obedient accord with Heaven." At this point, Earth first congeals.

The quotation splices together two lines from the 彖 (tuàn) commentary of the 《易經》: 大哉乾元 praises hexagram 乾 (qián), the Creative, and 至哉坤元…乃順承天 praises 坤, the Receptive. The pairing is the point. Heaven starts things; Earth finishes them, "in obedient accord." And only now, as zǐ turns to chǒu, does Earth thicken (凝結) into anything solid.

After another 5,400 years, right at the chǒu huì, the heavy and turbid settles downward: there is water, fire, mountain, stone, and earth. Water, fire, mountain, stone and earth are called the Five Forms. Hence it is said: Earth is opened at chǒu.

重濁下凝, the heavy and muddy settling, mirrors 輕清上騰 above; 重 reads zhòng, heavy, not chóng, repeated. Then a curiosity worth stopping on. The text says 五形, "Five Forms" — water, fire, mountain, stone, earth — where every reader expects 五行, the Five Phases (metal, wood, water, fire, earth). It is not a slip the editors missed. It is concrete where the standard term is abstract: the five things Earth actually turned into. We keep it.

After another 5,400 years, as the chǒu huì ends and the yín huì begins, the ten thousand things burst into life. The Almanac says: "The breath of Heaven descends, the breath of Earth ascends; Heaven and Earth mingle, and all things are born." At this point, Heaven is clear and Earth is fresh, and yin and yang are joined.

發生萬物 — everything bursting into life at once. The 曆, an almanac, supplies the mechanism: Heaven's 氣 comes down, Earth's goes up, the two meet, and life happens. Same yin-and-yang reciprocity as before, now creative instead of destructive. 天清地爽: a clear sky over a fresh earth, the world ready for tenants.

After another 5,400 years, right at the yín huì, humans are born, beasts are born, birds are born; this is what is meant by Heaven, Earth and Humanity — the Three Powers take their places. Hence it is said: Humanity is born at yín.

Living creatures arrive in three orders — people, beasts, birds — and that completes the 三才, the Three Powers: Heaven, Earth and Humanity, with people standing between the other two. It also completes a three-part formula every educated Ming reader knew by heart: 天開於子、地闢於丑、人生於寅. The stage is now fully built. At last the novel can narrow to one mountain and one rock.