Antianlun 安天論

Antianlun 安天論 "Constant-Heaven Theory" is a cosmological theory developed during the Eastern Jin period 東晉 (317-420) by Yu Xi 虞喜 (281-356), courtesy name Zhongning 仲寧, from Yuyao 餘姚 (in today's Zhejiang province).

Although repeatedly summoned by the imperial court, he never accepted an official position and remained unattached to political life throughout his lifetime. He was highly proficient in astronomy, apocryphal studies (chenwei 讖緯), history, literature, and Confucian teachings. His greatest achievement in astronomy was the discovery of precession (suicha 歲差)—the phenomenon in which the solar year does not exactly match the period between two successive winter solstices. This correction overturned the long-standing confusion between the celestial year (tianzhou 天周) and the solar year (suizhou 歲周). He also provided a quantitative estimate, stating that the winter solstice point shifts westward by one degree every fifty years. Yu wrote many studies on the Classics, like Shangshu shiwen 尚書釋問, Maoshi shi 毛詩釋, Zhouguan bonan 周官駁難, Zan Zheng Xuan Lunyu zhu 贊鄭玄論語注, Lunyu xinshu duizhang lun 論語新書對張論 or Xiaojing zhu 孝經注, as well as books on general topics like Zhilin xinshu 志林新書, Guanglin 廣林, Shizhi 釋滯 and Tongyi 通疑.

Fragmentary thoughts of the Antianlun (original size 6 juan) are preserved in the treatise on astronomy (11-13 Tianwen zhi 天文志) in the history book Jinshu 晉書. Fragments of the text are assembled in Ma Guohan 馬國翰 (1794-1857) and are found in his series Yuhanshanfang jiyi shu 玉函山房輯佚書 and the Siming congshu 四明叢書.

The Antianlun asserts that the heavens extend infinitely high, while the earth reaches unfathomable depths. The sky is lofty above, possessing a fixed and stable form, while the earth lies below with a still and tranquil nature. Heaven and earth fit together perfectly — if one is square, the other is also square; if one is round, the other is likewise round. The sun, moon, and stars each move in their own courses, much like the tides of rivers and seas or the natural rhythms of all living things.

It is evident that Yu Xi's theory was derived from and served as a supplement to the Xuanye Theory 宣夜説. Since the Xuanye Theory denied the existence of a solid celestial shell, some people at the time feared that the celestial bodies, suspended in the sky, might one day fall or that the heavens might collapse into chaos. This concern was not uncommon. Yu Xi wrote the Antianlun in an effort to prove that the celestial system was stable, thereby reassuring people. His statement about the correspondence of squareness and roundness Heaven and the Earth was clearly a rebuttal to the belief that the Earth was flat and Heaven round (tian yuan di fang 天圓地方). However, the semi-classic Da Dai Liji 大戴禮記 also hold that "the heavens are round, and the earth is also round." The claim that "the heavens extend infinitely high" emphasized the concept of an infinite universe even more than the original Xuanye Theory. However, the idea that "the earth reaches unfathomable depths" was incorrect, reflecting the limited understanding of the Earth at the time.

The assertion that "celestial bodies are arranged in the sky and move according to their own laws" was an advancement over the original Xuanye Theory, as it acknowledged an inherent order in the motion of celestial bodies. However, overall, the Antianlun made only limited progress and lacked groundbreaking innovations. Most critically, it failed to establish a new cosmic model, preventing it from replacing the dominant Canopy-Heaven (gaitian shuo 蓋天說) and Spherical-Heaven models (huntian shuo 渾天說).

The eminent scholar Ge Hong 葛洪 (283-343 or 363) criticized Yu Xi, arguing: "If the stars and constellations were not embedded in the heavens, then the sky would serve no purpose and could simply be said not to exist. Why, then, insist that it exists but remains motionless?" Although this rebuttal was not particularly strong, it effectively ended belief in the Constant-Heaven Theory, highlighting its theoretical weakness.