On the earth, human beings are influenced by the gravity of the earth. If they jump from a height, they will fall to the ground involuntarily. Why can the earth be suspended in the universe instead of falling into the "cosmic abyss"?
After Newton put forward the law of universal gravitation in 1687, we really understand why human beings can keep their feet on the ground and explain the motion between celestial bodies with knowledge. For this reason, the law of universal gravitation is called the most practical scientific law.
In fact, before Newton put forward the law of gravity, human beings had the concept of "gravity", but Newton's explanation of gravity was simpler and more direct, and at the same time, the concept of gravity could be extended to the universe to explain the motion between celestial bodies. In fact, the earth is not still suspended in the universe, but is constantly moving.
There is no distinction between "up, down, left and right" in the universe, nor between up, down, left and right, nor between southeast and northwest, because the direction of human beings is based on the concept created by the gravity of the earth. After leaving the earth, if there is no reference, the direction will lose its meaning.
Of course, all concepts are defined by human beings, and there is always a bigger reference in the universe. When you leave the earth, you can use the sun as a reference for the direction of gravity, and when you leave the solar system, you can use the Milky Way as a reference for the direction. Everything in the universe is meaningless, but human beings subjectively give it all meaning.
The earth itself, in fact, has been in constant motion and does not stop somewhere in the universe as imagined. First of all, the earth is influenced by the gravity of the sun. In the process of approaching the sun, due to the great mass of the earth itself, the balance of inertia and gravity will eventually lead to the revolution of the earth around the sun.
The relationship between most celestial bodies in the universe is the same. Smaller celestial bodies will be captured by the gravity of larger celestial bodies, and they will form revolutions in the process of movement. Some lighter objects will be "tidal locking", while smaller objects may collide with the gravitational source.
The above picture shows the trajectory of the solar system in the Milky Way and the real motion mode of celestial bodies in the solar system. When the earth goes around the sun, it also goes around the center of the galaxy with the sun. As mentioned earlier, the "direction" of human beings is based on the concept of gravity.
So what is "gravity"? Einstein pointed out in his general theory of relativity that gravity is not a force, but a "bending" of space and time. The mass and energy of any object are "equivalent". Energy is hidden in the mass of a static object, which will have an impact on time and space, just like putting a heavy object on a sponge, which will cause the surface of the sponge to bend.
Entering the bending range of time and space will naturally "slide down" to the center, which is the essence of gravity. If there is only one celestial body in the universe, then the earth will indeed be "suspended" in the universe, because the concept of "falling" will be generated when gravity attracts it, and it will move slowly in the direction of force when there is no gravity attraction.
The earth weighs about 6 trillion tons, but the sun weighs about 200 billion tons Under the gravity of the sun, the earth can't leave, but can only follow the sun, which moves around the Milky Way, which is a part of a larger celestial structure.
"Ju Yuan" is a gravitational anomaly area in the local supercluster. Galaxies in the range of hundreds of millions of light years, including the Milky Way, are moving to this area under the great source gravity. However, because the universe itself is expanding, the Milky Way may never get close to this gravitational source.
The universe has no so-called direction. All celestial bodies move because of gravity. Without the influence of gravity, celestial bodies would indeed float slowly and directionless in the universe. There is no so-called "abyss" in the universe, because the universe itself is constantly expanding, and the expansion speed has already exceeded the speed of light. Even if the earth has been "falling", it will never end, which is no different from floating in the air.
What is the biggest source of gravity in the universe? No one can give an answer. The celestial bodies in the universe are combined by gravity and form a "fiber web" under the action of dark matter. On the macroscopic cosmic scale, the distribution of matter in the universe should be uniform, but in the Hubble volume 90 billion light years away, the distribution of matter is not uniform, so there is a wider space outside the Hubble volume and there may be a greater source of gravity.