As we all know, Hawking spent his whole life studying black holes. So what is a black hole? Let’s discuss it together.
The first proposer of black hole was Einstein, who proposed the equation of gravitational field in his general theory of relativity. General relativity is a powerful tool for us to study the universe.
Then there was a German astronomer, Schwarzschild, who solved the equation of gravitational field in Einstein’s general relativity and got a solution. But he found that the solution of this equation is very strange and has many wonderful properties, so he called this solution “black hole”.
Schwarzenegger thinks that there may be such a strange celestial body in the universe. At that time, no one knew whether black holes existed or not, so the only way was to find them.
After that, Hawking made some attempts to solve this problem. On the basis of Einstein’s general theory of relativity, Hawking introduced quantum field theory. Through the analysis of quantum field theory, Hawking has a more detailed description of the properties of black holes.
But so far, these theories are still speculation, that is to say, whether black holes exist or not, people are still in the stage of doubt.
What are the properties of black holes?
First, black holes are so massive that even light cannot escape.
What is escape? Let’s give an example. Newton once said that if you have a shell that is launched on the ground, and the speed is relatively slow, then the shell will fall back to the ground.
But if the velocity of the projectile reaches a certain value, it will not land, but will move around the earth, so this velocity is called the first cosmic velocity of 7.9km/s.
If the speed continues to increase to 11.2km/s, the projectile will never return to the earth, but will escape to infinity, which is called escape speed.
In classical physics, the expression of escape velocity V2 is 2gm / R under the root sign, where m is the mass of the planet and R is the radius of the planet.
From this formula, we can find that if the mass of the star is larger and the radius of the star is smaller, then the escape velocity V2 will increase. We know that the fastest speed is the speed of light. If even light can’t escape, then no one can escape.
So we can get the radius of the planet r = 2gm / C ^ 2 by using 2gm / R under the speed of light C = root, which is called Schwarzschild radius.
In other words, if the radius of a star is smaller than this value, even light can’t escape. But we should note that in this process, it is an analogy process. The equation of wasey radius is finally obtained from general relativity. Although it seems to us that they are similar, their meanings are different.
If we substitute the mass of the earth 6 × 10 ^ 24kg into the formula, we will find that the Schwarzschild radius is 0.01M, that is to say, when the radius of the earth is less than 0.01M, it is equivalent to the size of a ping-pong ball, then the earth will become a black hole.
Another property of black holes is the curvature of space-time. We all know that a large mass object will cause the curvature of space-time. The curvature of time and space is not easy to understand. Let’s give two more examples.
If there is a celestial body with great gravity and there is a circle outside, this circle is called the horizon.
If someone approaches the horizon gradually and goes in again, he will have a chance to escape outside the horizon. Once he enters the horizon, even if he moves at the speed of light, he will not be able to escape. The final result is that he will only encounter the center point (singularity) of the black hole.
When he moves forward with a certain speed and uniform speed, if there is a person nearby to see him, what will be the result? The former thinks that he is moving in a uniform and straight line, but the latter thinks that the former is slower and slower. Finally, when the current person approaches the singularity, the latter will find that the former is still. This is the time slowing effect caused by gravity.
What happens when you go into a black hole?
When you go into space-time, because the curvature of space-time is very strong, it will change space-time.
Outside the black hole, time is unidirectional and space is bidirectional. Unidirectional time means you can’t go back to the past, and bidirectional space means you can go forward or backward.
But when you enter the black hole, space and time can be exchanged. That is to say, time becomes two-way, you can go back to the past, you can go to the future, and space becomes one-way, so you can only go to the “singularity” in the middle.
So when you enter a black hole, you can never get out. Even light can’t escape, let alone people.
What do you think of this? Welcome to comment area.