Shulou(Shulou.com)11/24 Report--

The description of any motion is relative to a frame of reference.

If a person is standing on the ground and another person is sitting on a moving train, some of the measurement results may be different because they choose a different reference frame, one using the ground as the reference frame and the other using the train as the reference frame.

Source: pexels Newtonian scientists believed that some reference systems were superior to others. Which aspects are superior? For example, in some reference frames, time passes uniformly and space is isotropic, and the equation describing motion has the simplest form, which is called inertial reference frame.

From this perspective, Ptolemy's geocentric theory takes the earth as the inertial frame, while Copernicus's heliocentric theory holds that the sun is a better inertial reference frame than the earth.

However, both still recognize the existence of an absolute, static inertial frame of reference. Bruno went a step further in this respect. He not only promoted heliocentric theory, but also developed Copernicus's cosmological theory. He put forward the idea of cosmic infinity with genius intuition. Bruno believes that neither the earth nor the sun is the center of the universe, and the infinite universe has no center at all.

In 1609, a Dutch glasses worker invented the telescope. Italian scientist Galileo Galilei (GalileoGalilei,1564-1642) modified the telescope and used it to survey the night sky, observe the sun, moon and stars, and found many new results. These new results inspire Galileo to think about some of the most basic principles of physics, the famous principle of relativity is one of his achievements.

Galileo's principle of relativity is that the laws of physics should have the same form in the reference frame of uniform linear motion.

Galileo described this principle in a passage in his 1632 Dialogue on two World Systems (DialogueConcerning the Two Chief World Systems for short). The idea is to lock you in a large cabin with several flies, butterflies, bugs, goldfish, etc., and hang a water bottle so that the water drips down one by one. When the ship is motionless, you pay attention to their movement:

The bug flies freely, the fish swings its tail, and the water droplets fall in a straight line. You can also jump with both feet, no matter which direction you jump, the distance you skip is almost the same. Then you make the ship move forward at any speed, and as long as the movement is uniform and does not wobble, you are still hiding in the cabin.

If you can't feel the boat moving, you will also find that all the above phenomena have not changed at all. The insects fly, the fish swim, the water drops fall, and the distance skipped in all directions is equal.

You can't tell from any phenomenon whether the ship is moving or standing still. Even if the ship moves quite fast, the same is true as long as it remains steady and uniform.

The phenomenon described by Galileo is similarly recorded in the ancient Chinese book Wei Kao Ling Yao in Shangshu:

"the earth is constantly moving but no one knows it. For example, if you close the boat and do not realize the luck of the boat." This passage in Chinese ancient books can be traced back to the Wei and Jin dynasties, that is, AD 220-589, which was earlier than Galileo 1000, but without follow-up expansion, Galileo opened his mind and boldly put forward the hypothesis of relativity: "the laws of physics have the same form in all inertial reference frames, and no mechanical experiment can distinguish between static and uniform inertial reference frames." This hypothesis then developed into the basic principle of classical mechanics, called the "principle of relativity".

The principle of relativity based on the fact that the laws of physics should not be changed by a frame of reference does not sound difficult to understand. The phenomenon described by Galileo in Dialogue is also the experience that each of us has experienced when traveling by train or air.

In Galileo's principle of relativity, time is still considered absolute, and the spatial position varies according to the selected reference system. In the two coordinate reference systems moving at a uniform speed in the x direction, the space-time coordinates (t, x, y, z) and ('t, x', y', z') measured respectively will have different values, and these two sets of values can be converted into each other by "Galileo transformation".

More than 270 years after Galileo's time, Einstein stepped onto the stage of history. He reconsidered this "principle of relativity". As mentioned earlier, what inspired Einstein to think about power at that time came from a dark cloud against the background of a clear sky in the magnificent building of classical physics.

The magnificent mansion of classical physics is mainly composed of classical mechanics and Maxwell electromagnetic theory, both of which have been proved by a large number of experimental facts, there seems to be no doubt about their correctness, but there is a little contradiction between them.

As mentioned above, the law of classical mechanics satisfies Galileo's principle of relativity and remains unchanged under Galileo transformation, but the Maxwell equation of classical electromagnetic theory does not have this invariance under Galileo transformation. That is to say, for classical mechanical phenomena, all inertial reference frames moving in uniform straight lines are equivalent, but this is not the case for electromagnetic phenomena, because the principle of relativity is no longer valid. Therefore, for the classical electromagnetic theory, physicists have to assume that there is a special and absolute inertial reference frame, in which the Maxwell equation can be established, which is called the "ether" reference frame.

The ether is assumed to be "motionless", so the motion of the earth relative to this fixed inertial reference frame should be observed, but physicists have found nothing in this regard.

After that, Einstein extended the principle of relativity from classical mechanics to classical electromagnetism and established the special theory of relativity. Later, the principle of relativity is extended from inertial reference frame to non-inertial reference frame, thus the general theory of relativity is established.

Source: the essence of time and Space: the Story of Relativity

Author: Zhang Tianrong

The picture in this article comes from the Internet.

The copyright belongs to the original author

Editor: Zhang Runxin

This article comes from the official account of Wechat: ID:tupydread, author: Zhang Tianrong

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.