Time slows down (why the greater the gravity, the slower time)

In 1905, Einstein published four groundbreaking papers, including the famous special theory of relativity and the theory of mass-energy equivalence. The photoelectric effect is also one of the basic theories of quantum mechanics. That is to say, he made great contributions to the two edifices of modern physics within one year, which can only be matched by Newton in the entire history of science. Therefore, Newton’s 1666 and Einstein’s 1905 are called Newton’s Miracle Year and Einstein’s Miracle Year in the history of science respectively.

Einstein’s special theory of relativity is quite subversive. When he published it, many physicists could not even understand its physical significance. Thus, Einstein was only famous in a small academic circle in 1905. Even in 1915, when Einstein proposed his general theory of relativity, he still had little influence in the minds of the general public at the time.

It was not until 1918 that the British astronomer Eddington led a team to observe the total solar eclipse and the deflection of the sun’s rays in the coronal sequence. Zheng learned from the resource network that Einstein’s theory is more universal than Newtonian mechanics, and Einstein became a world-renowned physicist. But even at this time, not to mention that people do not understand relativity very well, many people in academia cannot understand this theory.

So someone once interviewed Eddington and said: Are there only three people in the world who really understand the theory of relativity?

Eddington asked, who is the third person?

Then why do many people not understand the theory of relativity?

In fact, the theory of relativity has a wide range of applications, considering that the entire scale is beyond the macroscopic low-speed world in which human beings live. Therefore, it is extremely subversive to the three views, especially the view of time and space. The so-called view of time and space refers to the understanding between time and space. Why do you say that?

To understand this question and the theory of relativity, we need to step outside the definition of time itself.

# What time is it?

In fact, from ancient times to the present, scholars have been thinking about many ultimate questions, among which “what is time?” is a key question. The ancient Greek master Aristotle once believed that time passed equally. When it came to Newton, he believed that time and space were separate, and time and space were the same for everyone. Your second is the same as mine, it doesn’t change because of our state of motion.

But having said so much, you should be able to find that this is a change in time, but what is time?

Objectively speaking, no one has been able to directly define time. Although we can’t say exactly what the time is.

But we can change the way. This method is defined by measuring time, also called measurement definition. What exactly does that mean?

ItIn fact, this method has been used for a long time. We can think about it: what is a day, a month, a year?

In fact, one day is the time for the earth to rotate once. In ancient times, because it was the center of the earth, they thought it was the time when the sun rose in the east and set in the west. A month is the time it takes for the moon to orbit the earth once. A year is the time it takes the earth to revolve around the sun. In ancient times, it was the time when the sun revolved around the celestial sphere at the same time.

The reason why the ancients are mentioned here is actually to say that the ancients discovered this rule a long time ago. So this method of measurement definition is the basis for human understanding of time, not a product of modern science. If we use the method of measurement definition, we will find that time changes periodically. More essentially, we will find that time is actually a kind of movement. The clocks we use also use periodic vibrations to measure time. Today’s most sophisticated cesium atomic clocks also use vibrations to keep time.

# The subversion of cognitive relativity

Based on the above understanding, Einstein returned to the definition of time to think about the relationship between time and space. Since it is a kind of motion, time will actually be affected by the motion state of the object. In fact, this is the most basic problem of dynamics. Therefore, Einstein took up the basic theory of dynamics – Galileo transformation, combined with the principle of the constant speed of light, and derived the basic framework of the entire theory of relativity.

Then the passage of time should be affected when the object is at a high speed; for example, we regard the periodic motion of light as a time (for example, light goes up and down for one second). Then, if a person is on the ground and a person sits in a light-speed spacecraft in space, then we will find that the clock on the ground will be much faster than the one on the spacecraft.

That is to say, the people on the spacecraft have time dilation relative to the people on the ground. (Letâ€™s say that the passage of time is the same for each of them.)

Similarly, since it is a basic dynamics problem, Then in the accelerated state, under the action of gravity, the passage of time will also be affected. In fact, this is what general relativity describes. Of course, the general theory of relativity actually has to consider the problem of space, so it will involve complex mathematical operations.

Through general relativity, we know that the essence of gravity is actually the curved space of time. The reason why the moon revolves around the earth is that the earth bends the surrounding space-time, and the moon sticks to the geodesic space of time (that is, the space of the shortest distance between two points in four-dimensional time). ) in motion.

So the gravitational field also acts on light, making time dilate. In other words, time slows down near a black hole. Let me say a little more here. For myself, time still passes as before, but it expands compared to those who are not near the black hole.

Thus, time around the gravitational field slows down. In fact, relatively speaking, subjective time isThere are changes. It’s just others watching your time slowly passing by.