Sky curtain cosmology
Gaitian theory is China's ancient cosmology. It is thought that the sky is like a round pot cover on the earth, hence the name "Gai Tian Lun".
According to "Jin Shu Tian Wenzhi" records: "His words are like a hat, the earth is covered by law, and the heaven and the earth are high and low. Below the North Pole, among the heavens and the earth, the earth is the highest, while the four or three lights are hidden, thinking it is day and night. In the sky, it is 60,000 miles higher than the winter solstice. The Arctic is 60,000 miles higher than the external elevation, and the external standard is higher than the Arctic Wan Li. The height of heaven and earth is 80,000 miles from heaven to earth. "
Gaitian said that it first appeared in the Western Zhou Dynasty. At that time, it was thought that the sky was low and round, "the sky was round as a cover and the earth was round as a chess", and the dome-shaped sky covered the square flat soil. This is the embryonic form of Gaitian's theory. Later, in the process of development, several different opinions appeared. Because the dome-shaped sky is not comparable to the square edge of the earth. Then it was suggested that the sky is not connected with the earth, but hung high on the earth like a big umbrella, supported by eight pillars around the earth, and the shape of the sky and the earth is like a pavilion with a dome at the top. * * * Workers can't touch Zhoushan, and the myth of the goddess mending the sky is based on this. By the Warring States period, the above-mentioned theory of covering the sky began to be doubted, so it was revised to "the sky is like a hat and the earth is like a dome", which means that the sky is spherical and the earth is spherical. It is believed that the North Pole is located in the center of the sky and the sun, moon and stars revolve around it endlessly.
In the Western Han Dynasty, some people still insisted on this statement. At that time, Zhou Kuai Shu Jing was a masterpiece of Gaitian's theory.
Gaitian said that the appearance of the sun, the moon and the stars is usually explained by the change of their running distance. Far out of sight, near in sight, shining. This explanation is far-fetched. Gaitian theory is denied by more and more astronomical observation facts. In the Western Han Dynasty, Yang Xiong put forward eight difficulties to cover the sky and denied the theory of covering the sky.
However, Gaitian theory still had some influence in ancient China. Yu Zhuo of Jin Dynasty put forward the theory of vault heaven, which is the inheritance and development of the theory of covering heaven. During the Northern and Southern Dynasties, there was also the theory of the unification of muddy cover and cover.
In the last century, the position of the earth in the universe was expanded, and this understanding was fundamentally expanded. At first, the earth was considered as the center of the universe, but at that time, the understanding of the universe only included those planets visible to the naked eye and seemingly fixed stars on the celestial sphere. Heliocentrism was widely accepted in the17th century. Later, William Herschel and other astronomers discovered that the sun was located in a disk galaxy composed of stars.
By the 20th century, the observation of spiral nebulae showed that our Milky Way was just one of billions of galaxies in the expanding universe. 2 1 century, the overall structure of Hubble volume began to become clear-supercluster formed a huge network structure containing large-scale fibers and holes. Supergalaxy clusters, large-scale fiber structures and holes may be the largest coherent structures in the universe. On a larger scale (more than one billion parsec), the universe is homogeneous, that is, its parts have the same density, composition and structure on average.
The universe has no "center" or "boundary", so we can't mark the absolute position of the earth in the whole universe. The earth is located in the center of Hubble volume, because observability is determined by the distance from the earth. At various scales, we can give the relative position of the earth with a specific structure as the frame of reference. Whether the universe is infinite is uncertain.
References:
Baidu Encyclopedia-Earth