Please give us a brief introduction to the theory of relativity, I am a middle school student

The key point is that the source of the internal stress of any matter is nothing more than the four fundamental forces, and the propagation speed of these four fundamental forces is the speed of light, so the propagation speed of the internal stress of matter can only be lower than the speed of light - there is no such thing as hard as you imagine.

Taking ordinary rods as an example, the essence of the molecular force or chemical bond force in the rod is electromagnetic force, and the medium particle that propagates the electromagnetic force is the photon. The speed at which the molecules or atoms in the rod propagate (i.e., the speed of mechanical waves) is obviously lower than the speed of light, because when an atom's motion changes, it can only transmit this change to neighboring atoms at the speed of light, and the neighboring atoms respond with different delay times due to the difference in the magnitude of their own inertia and the magnitude of the force transmitted by them - it cannot immediately reach the same state of motion as the atom in front of it when it receives a photon, and it will have to delay a short time to reach that state ......Only when the atomic mass is 0 or the bond force between the atoms is infinite, the propagation of the force will not be delayed for a short time on each atom, but will continue to propagate at the speed of light into the distance - the speed of the mechanical wave can reach the speed of light, but it is unrealistic to have a mass of 0 and the force is infinite, so the speed of the wave can only be lower than the speed of light.

The significance of the theory of relativity is to reveal that space-time, matter, and motion are inextricably linked—that they are far more closely related to each other than classical physics originally thought.

The theory of relativity gives a kind of limitation (mainly the Lorentz transformation and the generalized covariance), since all physical theories are to deal with space-time, motion, and matter, they must meet these constraints given by the theory of relativity, otherwise the theory should be modified (to meet the requirements of the theory of relativity) or the old theory should be discarded altogether. Newtonian mechanics became relativistic mechanics by this transformation, and the Schrödinger equation became the Dirac equation ......

If you still have any doubts, please feel free to ask ......

Pushing a stick is similar to pushing water in water, except that the speed of the waves in the stick is much greater than in the water.

Indeed, the landlord did not pay attention to the relativity of the simultaneity.

Using the theory of universal relativity to explain this problem, you can be very clear that when the train and the tail of the platform are aligned, the front of the train is also aligned, but the people at the rear of the train look like the front of the train is not yet aligned, because it takes time for the light to transmit the signal of alignment, so the people at the rear of the train seem to be shorter, and the people on the platform are the small balls thrown by the talents on the platform when the tail of the train has entered the platform, and the small balls enter the car; The people on the platform saw the front of the train aligned, threw the ball, and the ball entered the car, but at this time the rear of the train looked like it was still outside the station, because the signal for alignment had not yet come. So the people on the platform saw that the train was getting longer, not shorter.

The opposition theory only deduces that the people on the train look like the car is getting shorter, but it doesn't deduce that the people on the platform look like the car is getting longer. There is also a problem: optical media, the medium moves differently, and the state of the appearance is also different.

Einstein knew that space was not a vacuum; I don't know that air, water, glass, ice, etc. are all light mediums; It is not known that in a homogeneous and stable medium, the relative medium velocity of all waves is unchanged and has nothing to do with the wave source; He derives the theory of relativity, without touching on any wave principles; He also did not know that the definition of science is an objective law, and that the time he defined did not conform to the scientific definition. So Einstein got a lot of things wrong.

Your question itself has a problem, and the question is in this sentence "when the rear of the train aligns with the platform", so you are confused.

Why is there a problem with this statement?

When the rear of the train is aligned with the station Lu Songtai", the "alignment" seen by the people of "Station" and the "alignment" seen by the Sen Peiren of "On the Car" are not at all born at the same time.

Upstairs, LZ needs to understand the relativity of simultaneity. In the special theory of relativity, all the phenomena that seem to contradict the theory of silver can be explained.