The universe is the general name of the vast space and all kinds of celestial bodies and dispersed substances existing in it. The origin of the universe is an extremely complicated problem. The universe is a material world, which is in constant movement and development.
For thousands of years, scientists have been exploring when and how the universe was formed.
Astronomical theory
Shortly after Babylonian astronomers began to study astronomy, they put forward an astronomical model of the universe. They think that the universe is a flat plate floating in the ocean, which became the premise of early Greek maps, such as those drawn by anaximander and Miletus Hicataeus.
Later Greek philosophers observed the movement of celestial bodies and focused on developing the model of the universe more deeply based on empirical evidence. The first coherent model was proposed by Oddoxos of Cnidos. According to Aristotle's physical explanation of the model, celestial bodies move in a straight line at a constant speed around the stationary earth. Matter is completely contained within the scope of the earth.
After abandoning the concentric sphere model, this geocentric model was also improved by Calippe, and it was almost the same as Ptolemy's astronomical observation. The success of this model is largely based on the mathematical fact that any function (such as the position of the planet) can be decomposed into a set of circular functions (Fourier mode).
Other Greek scientists are Pythagorean philosopher Philolaus. According to Stobaeus, a document editor of a Greek writer, Philolaus assumed that there was a "central fire" at the center of the universe, around which the earth, the sun, the moon and the planets moved in a uniform circle.