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Now, the stowaway man has become an honorable auditor at the "Friedrich-Wilhelms-Universität Berlin"!

Today, the auditor sat at the end of the class early. Because just today, Professor Albert Einstein from the Department of Physics will come to class rarely.

Because Professor Einstein is also a fellow of the Royal Institute of Physics. Therefore, people generally do not take the usual classical physics courses.

There are really quite a few people who came to occupy seats to attend the lecture early this morning! It is estimated that by the time the class comes, the seats will be full! After all, the theory of relativity is really a novelty for college students in 1916!

Professor Albert Einstein showed up at the classroom podium at 10 o'clock sharp.

"Huh, his hair is standing on end by this time!"

"It's almost the same as in the later photos! It's just that the hair hasn't turned gray yet, it's still black!"

"I finally know why his hair is always standing on end! Dare to love the family is naturally curved, and he always pits his fingers into his hair! Alas!

"If it's smooth, it's not Einstein!"

Einstein in front of the blackboard could not hear the sound of discussion in a button on the clothes of an auditor sitting in the last row. Let's get straight to the point:

"My name is Albert Einstein, and I'm a professor of physics! Why do I need to introduce myself? Because I found that there are a lot of people named Einstein. There are a few in my neighborhood, Einstein who makes bread, Einstein who repairs leather shoes, Einstein who sells fruit pulp, and I, Einstein who lectures!"

"Boom!ha!" made a self-deprecation, bringing up the atmosphere of the classroom!

"Today's talk is the theory of relativity! I will talk about the early special theory of relativity together with the recently completed general theory of relativity. I hope you don't let me scare you away!"

"Special relativity is based on two basic assumptions:

First, the principle of narrow covariance: all inertial reference frames are equal, that is, the form of physical laws is the same in any inertial reference frame.

This means that the laws of physics are the same for an observer at rest in a laboratory as for an electron moving at high speed and uniform speed relative to the laboratory.

Second, the principle of invariance of the speed of light: the speed of light in a vacuum is constant in any frame of reference, which can be expressed in geometric language as the world line of photons in space-time is always light-like. It is precisely because of the experimental nature of photons that the International System of Units uses "the distance traveled by light in a vacuum in 1/299,792,458 second" to define the unit of length "meter" (meter).

The principle of invariance of the speed of light is the embodiment of the symmetry of space-time in the universe, and the superluminal phenomenon of neutrinos may only be a symmetry break in the symmetry of space-time and can never overturn the theory of relativity.

Before the special theory of relativity, people thought that time and space were independent and absolute!

This concept of absolute space-time has been established since the time of Galileo, and Newton's classical mechanics and classical kinematics founded by Newton were founded on the basis of the absolute view of space-time. ”

Professor Einstein is explaining the basis for the formation of the special theory of relativity, and the button is lively:

"No, he said that planes are connected. But the space-time array we get can be divided! Time stops, space freezes, and drops can be cast separately!"

"Einstein is talking about time and space in the law environment of the earth world! It is not the same law environment as the time and space of the flood world, and there is no comparison!"

"That's not right! The boss can use the electromagnetic divine sense to cast a time pause to keep Louis XVI's soul alive! We can also use the electromagnetic divine sense to cast space freezing to save endangered species from the small flood! This shows that the earth law environment is allowed!"

"I don't understand!"

Albert Einstein on the stage did not hear the "I don't understand" sound in the back row of the auditors. Otherwise, it is estimated that it will overturn its own theory of relativity. Separate space is divided, there is wood?

"Before the special theory of relativity was proposed, there was a lot of attention paid to the problem that Maxwell's equations were not covariant under the Galilean transformation.

Of course, there were others, such as Poincaré and Lorenz, who noticed the experiments on which I proposed the special theory of relativity. Such as the Michelson-Morey interferometer experiment.

Some people have deduced mathematical expressions similar to me, such as the Lorentz transform!

However, I combined these factors with the classical physics view of space-time to propose the special theory of relativity, which has greatly changed our view of space-time.

At this point, special relativity is revolutionary. ”

"I don't understand again!" "I haven't graduated from elementary school yet, and if I can understand, I must be bragging!

"I'm the same! The first part is okay, at least I know that time and space are related, and I don't understand what this part says. "Tell me the truth.

"I guess there aren't many people who come to listen to the lecture and can understand it!" This means that I have about the same IQ as most people! It's not that I'm so stupid that I can't understand drops!

The teacher can't care about the muttering in other people's buttons. Column after column of equations on the blackboard appeared under the chalk in Einstein's hand.

"As for the system of general relativity that I have recently established, in essence, all physics problems involve the question of which view of space-time to adopt.

In classical physics before the twentieth century, Newton's view of absolute space-time was adopted. The theory of relativity changed this view of time and space.

As a result, the formulas of classical physics had to be rewritten according to the requirements of the theory of relativity so that they had the Lorentz covariance required by the theory of relativity instead of the previous Galilean covariance.

In the three major fields of classical theoretical physics, electrodynamics itself is Lorentz covariant and does not need to be rewritten; statistical mechanics has a certain particularity, but this particularity does not bring many difficulties in principle that need to be solved urgently; and most of classical mechanics can be successfully rewritten into the form of relativity, so that it can be used to better describe objects in high-speed motion.

However, only Newton's theory of gravity could not be rewritten within the framework of special relativity, which directly led to the fact that I had to expand his special theory of relativity to obtain the general theory of relativity.

First, the experimental facts of the weak equivalence principle: the gravitational mass is equal to the inertial mass.

This fact can also be understood to mean that all test objects with a sufficiently small mass (i.e., a negligible effect of their own mass on the gravitational field) move in the same way in the same gravitational field when no force other than gravity is present.

In this case, it is worth thinking that gravity is not actually a "force", but a space-time effect!"

"Is gravity a space-time effect?" the smuggling man looked confused.