According to the existing theory, planets or celestial bodies will cause depressions in time and space, and such depressions are the chief culprit of gravity. Objects that always attract dark matter will attract dark matter into the depression, which will form the flow field of dark matter, that is, gravity.

Black hole is one of the best black holes. The black hole itself has great gravity, and even light can't escape from its clutches. So black holes will attract dark matter continuously, and it will gradually become stronger, causing more and more depressions and forming more gravitational fields. For a long time, black holes may absorb the whole universe. It is no exaggeration to call a black hole the Thanos of the universe.

Therefore, in space travel, because there is no gravity, astronauts can roam freely in Aoxiang space, but they will also be highly vigilant against some planets. Once pulled by the gravity of other planets, it is difficult to come back. The depression that produces gravity can only be realized by the existence of matter, which also confirms the statement that there were planets before gravity. After all, only the existence of matter can lead to depression and the emergence of gravity.

Theory of relativity

Modern physics (general relativity) believes that gravity is caused by the bending of time and space. As we all know, the line segment between two points is the shortest, which is an axiom in plane geometry. This line segment is the shortest straight line. However, in the curved four-dimensional space-time, geodesics are also curved.

Therefore, under the action of gravity, the planet approaches the sun along the short-distance line, and because of the mass coincidence (including the velocity coincidence) and the inertia of the planet (many people understand it as centrifugal force, which is wrong. Centrifugal force is just an illusion, so there is no centrifugal force in the universe, so it is not found), so it revolves around the sun in an elliptical orbit. When the masses do not coincide, there will be a gravitational springboard phenomenon or a collision with the sun. Among them, the main reason of celestial system is not gravity, but the distortion of time and space caused by mass.