The Universe According to Eastern Philosophy

Eastern Concepts of the Universe in Ancient and Medieval Times

By the end of the 5th century, the “Astronomical Records” distinguished three schools of thought regarding the structure of the universe. These are the “Cái Thiên” theory (Heaven has a lid), “Tuyên Dạ” theory (the darkness spreads everywhere, the void is infinite), and the “Hồn Thiên” theory (the vast heavens encompass the Earth). These philosophers aimed to create a “Heavenly Road” for the Emperor to ascend to heaven, so although these theories had a scientific goal to explore the universe, they still reflected metaphysical and astrological influences.

The “Cái Thiên” theory, the oldest, depicts the sky as a hemispherical lid with the Earth as an upside-down bowl at its center. The underside of the Earth is not round but square, resembling a chessboard, perhaps reflecting the belief in the four cardinal directions (east, west, south, and north). Rain falls from the sky, where the stars are, and lands in the four corners of the Earth, forming four seas. Today, we understand that raindrops condense in the Earth’s atmosphere, rather than falling from the universe. The sky rotates, carrying the Moon and the Sun along with it. These two celestial bodies move slowly, counter to the rotation of the sky. In the “Great Heavenly Theory” written in the 3rd century, the sky is compared to an eggshell containing “original qi,” hence it does not sink into the four seas. The sun moves like a lamp across the sky, illuminating one area at a time. The “Three Wonders,” namely the Sun, Moon, and stars, appear and disappear, creating day and night. In fact, the “Cái Thiên” theory has two stages: during the Eastern Zhou period (5th century BCE), the “Heaven Round Earth Square” theory proposed a stationary Earth with the Moon, Sun, and stars moving across the sky. By the Warring States period, this theory evolved into one that recognized the sky as a hemispherical dome and the Earth as a bowl. The transition from a flat Earth to a spherical Earth marks a significant advancement in the “Cái Thiên” theory.

The “Hồn Thiên” theory by Zhang Heng (78-139) of the Eastern Han dynasty likens the sky to a round egg, with the yolk symbolizing the Earth. The sky contains “qi” and at the horizon, there is water, with the Earth floating on this surface. Three “deities” possibly represent the Sun, Moon, and stars, while the Earth has three “forms” that could be earth, water, and air. Both the deities and forms are observable. The Sun is compared to a wheel that never stops turning. The space outside the sky is limitless (infinite), referred to as “the universe,” and is considered mysterious. Thus, the “Hồn Thiên” theory envisions that beyond the Sun, Moon, and stars, there exists an immense universe that remains unexplored.

The “Tuyên Dạ” theory posits that the sky is an empty (non-material) void that is vast and expansive (infinite). The Sun, Moon, and stars are accumulations of energy (qi) that rise into the atmosphere. The seven celestial bodies (the Seven Luminaries), which include the Sun, Moon, and five visible planets, do not attach to the sky but move freely back and forth. These five planets are the ones visible to the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. The North Star remains fixed in place (as it is near the axis of the sky). The concept of an infinite void may relate to the “nothingness” in Daoism and the “emptiness” in Buddhism. Although the sky and Earth are vast, they are merely like a grain of rice compared to the void, which may contain other heavens and earths.

From the 6th century onward, the concept of two hemispheres containing “qi,” symbolizing Heaven and Earth from the “Hồn Thiên” theory, gained acceptance. However, questions arose about only observing half of the sphere, which means seeing only half of the truth. In subsequent centuries, the model of the universe gradually improved. For example, stars and planets are not attached to the sky but are lifted by a stream of “hard wind” (firm wind), akin to the compressed air of a jet engine. The sky has nine layers of air with different pressures and speeds, similar to nine levels. The cyclical movements of the Earth and tides are governed by the forces of yin and yang.

The Sun is considered “Thái Dương” (Thái means great) while other stars are “Tiểu Dương” (Tiểu means small). The Moon is referred to as “Thái Âm” and other planets as “Tiểu Âm.” The Earth also belongs to the yin category. Today, we know the Moon is a satellite of the Earth. The Sun and stars are very hot and emit energy due to nuclear fusion occurring within them. In contrast, the Earth, Moon, and planets are cold and do not emit energy but reflect sunlight. Thus, categorizing the Sun and stars as yang, while the Earth, Moon, and planets as yin holds some truth. The Sun is a star like the tens of billions of other stars in the Milky Way, and the Moon is one of the planets in the Solar System. Because the Sun and Moon are close to the Earth, they appear large and are referred to as “Thái Dương” and “Thái Âm.”

The evolution of astronomy in ancient China was influenced by Confucianism from Confucius (6th century BCE) and Buddhism. According to Confucianism, the universe was initially nebulous in a state called “Tai Chi,” transforming into “yin” and “yang.” Although the two entities of yin and yang oppose each other, they are harmonized and relative, resulting in the elements of metal, wood, water, fire, and earth (the Five Elements). Human life in society is also based on the yin-yang entities in the universe. One can liken the abstract yin-yang entities to two fundamental particles in modern physics, particles and antiparticles that can annihilate each other upon contact. Although Confucianism has a rational aspect, it does not particularly focus on nature. Daoism, while addressing nature extensively, lacks rationality. Zhuangzi (4th century BCE) questioned why the sky rotates while the Earth remains still, and why the Sun and Moon alternate in the sky.

The ancient thoughts on the universe, while mystical and metaphysical, sometimes reflect events that can be explained by modern scientific reasoning. Through observation and calculation, modern astrophysics posits that the universe was created about 15 billion years ago by a Great Primordial Explosion known as the Big Bang. The primordial universe was merely a nebulous cloud (as described in Confucianism). Wang Chong, a famous philosopher of the Eastern Han dynasty, believed that the Earth formed from the condensation of a mass of gas. This hypothesis was not further developed due to a lack of physical and mathematical foundations. According to modern research theories, celestial bodies like stars and planets formed from colossal gas clouds collapsing and condensing under the gravitational pull within the gas. According to the Buddhist cycle of reincarnation, creation rotates like a wheel. The chaotic states of all things can recur after periods of normalcy. Theories studying the structure and evolution of the universe (cosmology) based on current scientific understanding suggest that the universe may also undergo cyclical expansion and contraction and that the primordial universe existed in a chaotic state.

In summary, ancient Eastern astronomers did not possess an accurate model of the universe and the orbits of the planets in the Solar System, as the fields of physics and mathematics, particularly geometry, had not yet developed.

However, their notions of the universe hold a relative accuracy to reality. Thanks to the evolution of science over the ages, we now understand that the Earth is one of nine planets in the Solar System. The Earth orbits the Sun with a cycle of about 365 days in an almost circular elliptical orbit with the Sun at one focal point. The Moon is a satellite that orbits the Earth. Stars do not attach to the sky but are distant from the Earth at varying distances. The universe contains hundreds of billions of galaxies, each with tens of billions of stars like the Sun. Each star has tens of planets. The Milky Way is one of these galaxies, distinguished by harboring the Solar System and our Earth. Therefore, the Milky Way is also referred to as “our galaxy.” The center of the Milky Way is approximately 30,000 light-years from Earth. The Earth orbits the Sun at a speed of 30 km/s and moves with the entire Solar System around the center of the Milky Way at a speed of 250 km/s. Despite this high speed, due to the vastness of the Milky Way, it takes the Earth about 200 million years to complete one orbit around the center of the Milky Way.