There are four fundamental forces in nature, namely electromagnetic force, weak interaction force, strong interaction force and gravitational force, among these four fundamental forces, gravity is the weakest force, and it is also a long-range force that can act on infinity.
However, although it is the weakest force, it can dominate the entire universe, for example, gravity can cause heavy elements to gather to form planets, nebulae to collapse to give birth to stars, and galaxies to evolve all rely on gravity.
The discoverer of gravity was the famous Isaac Newton, who proposed the law of universal gravitation in 1687, which tells us that there is a gravitational force between any object, and its gravitational force is directly proportional to their mass and inversely proportional to the square of the distance. That is, the greater the mass of the object, the stronger the gravitational force, and conversely, the smaller the mass, the smaller the gravitational force.
Through the law of gravitation, we can know the laws of motion of celestial bodies, as well as calculate the mass of celestial bodies, and how objects get rid of the gravitational field of celestial bodies, etc., such as calculating the orbital velocity and escape velocity of objects around the earth.
However, although Newton discovered the existence of gravity, he did not know how gravity is generated, in short, what is the nature of gravity.
It was not until 1916 that the greatest scientist of the 20th century, Albert Einstein, published a **, that is, the general theory of relativity, that people did not know how gravity was generated, in the general theory of relativity, it is believed that gravity is actually not a force, but a geometric phenomenon of mass causing space-time curvature, the greater the mass of the object, the greater the curvature of space-time, and this bending phenomenon is the root of gravity.
We can imagine the invisible space-time as a film, when put into a mass object, the film will form a depression, and this depression is the space-time curvature caused by the mass, and with the increase of mass, the degree of the depression will become stronger, for example, the reason why the earth revolves around the sun is because the mass of the sun is huge, which makes the surrounding space-time have a serious bending, which causes the earth and other celestial bodies to move along the geodesic.
Through the general theory of relativity, Einstein also predicted many phenomena, such as the existence of black holes, which is that the mass of the black hole bends the surrounding space-time to the limit, resulting in light in the curved space-time and cannot escape.
There are also gravitational waves, which are when an object with mass accelerates in space-time, and the curvature of space-time changes with position. And this resulting distortion will propagate outward at the speed of light in the form of waves, creating ripples in space-time, just like if you throw a stone at a pond, it will create ripples on the surface of the pond and propagate outward at the point where the stone enters the water.
In addition to the above, there is also the gravitational lensing effect, etc., which are all predicted in the general theory of relativity, and now these have also been confirmed, in summary, the essence of gravity is actually a geometric phenomenon caused by the curvature of space-time!