The mysteries of the universe: the movement of celestial bodies: Why are they rotating? And how do they rotate?

Absolute stillness does not exist in the universe. All matter, whether macroscopic or microscopic, is always in motion.

Among all the motions, the most common one is rotation. Everything from a planet to a star to the entire galaxy is rotating all the time. Even the interior of an atom is also rotating, although the rotation in the microscopic structure is different from the rotation in the macroscopic structure. So why does the universe rotate? This is indeed a mystery. No one knows why the universe rotates, but if there is no rotation, the universe will lose its vitality, because rotation is the basis for the birth of life.

The earth rotates, so there is a distinction between day and night, which avoids the situation where one side of the earth is always facing the sun while the other side never sees sunlight all day.

If that were the case, one side of the Earth would face constant high temperatures, while the other side would be in eternal darkness and cold. Such a planet would certainly not be able to be a home for life. If rotation is the basis for the nurturing of life, then revolution is the guarantee for the complexity of species on Earth. Because of the Earth's own inclination and its revolution around the sun, the Earth can have the change of seasons, which is crucial to the establishment of the Earth's ecosystem. It can be seen that without rotation, life would be difficult to appear, and wisdom and civilization would not develop. Who would observe and think about the rotation of the universe?

Although we don’t know why the universe rotates, we know that rotation is very important to the universe and to us.

So how did the universe start to rotate? 13.8 billion years ago, the universe was an extremely dense point with infinite density and infinite volume, which we call a "singularity". At a certain moment, the balance was broken for some unknown reason, and an explosion occurred. In an instant, time, space, and matter gushed out. At first, there were only some elementary particles, and then the lightest elements began to form. So the early universe was composed of hydrogen and a small amount of helium.

From the law of universal gravitation, we know that any objects with mass have mutual gravitational forces, so the matter in the universe moves closer to each other under the influence of gravity and gradually condenses into larger and heavier matter.

However, matter in the universe is not evenly distributed. Matter in some areas is denser, while matter in other areas is sparser. This makes the gravitational influence on matter uneven, so it is impossible for matter to move completely in a straight line and approach each other. Under the influence of this gravitational difference, rotation occurs.

It can be said that the early universe was filled with countless whirlpools composed of interstellar matter. These whirlpools constantly collided and merged, and thus stars were born.

By the same token, the celestial bodies in the universe are large and small, and the distances between them are near and far. So when two celestial bodies, or more celestial bodies approach each other, they rarely move in a straight line. They will attract each other at a certain angle, which is determined by their initial momentum and non-uniform distribution structure. Therefore, the process of their approach to each other will form a rotating trajectory. As more and more celestial bodies join this rotating system, a huge structure is formed.

Once a rotating structure is formed, it will begin to accelerate, which is determined by the conservation of angular momentum.

Because of the conservation of angular momentum, when the radius of rotation becomes shorter, the speed of rotation will increase, which can be seen from the change in speed when a ballerina opens and closes her arms. Therefore, as the distance between the stars decreases, the speed of a rotating structure will become faster and faster, and the entire structure will accelerate. The rotation structure of the universe is determined by the physical laws of the universe, so why do such physical laws exist in the universe? This is a more elusive question, but it is precisely because the universe is full of infinite puzzles that we find it so beautiful.