Presentation of special relativity

I wrote long ago... very long ago, that I would publish an article about relativity theory. I will do my best. I don't have much education about relativity theory, but I can say some things about it. Listen carefuly and don't be afraid. If there is something you don't understand, ask a question.

I Principle of relativity
II Lorentz transformation
III Einstein's interpretation
IV Paradox of twins

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I Principle of relativity

The principle of relativity is one law among others that characterize the universal laws of Nature. It says :

"The laws of Nature are the same whatever the mechanical referential."

In the Sun's mechanical referential, the Earth rotates around the Sun. But in the Earth mechanical referential, we see the Sun rise in the morning and set in the evening.

There are other kinds of laws. I would say that the laws of Nature are the same whatever the size of the considered object.

Actually, the principle of relativity is rather a principle of absolute.

When he was working about making electromagnetic laws abiding by the principle of "relativity", a man called Hendrik LORENTZ found some mathematical relations.

II Lorentz transformation

When you look at something, say, an elephant eating a fruit, it takes some space and some time. This is what we call "an event", in special relativity.

Lorentz found the solution of his problem only for a part of cases. He found the solution for a mechanical referential going straight at the same speed in another referential. This looked like this.

 
Lengths and times are multiplied or divided by gamma.

If you don't understand at this point, it's OK. I just wanted to show you the classical formula, so you can think "I've seen that somewhere else.".

What do these formulaes mean ? Here comes Einstein.

III Einstein's interpretation

Three people were working on this electromagnetism problem : Lorentz, Poincaré and Einstein.

Einstein had the strongest interpretation. He said that the gamma factor changing the lengths and the times was a sign that space and time are not absolute.

The absolute came to be the speed of light, making special relativity a modern theory of light.

The strange effects of special relativity cannot be seen in the normal life. They can be seen only for things getting so fast that they nearly have the speed of light, c. Lengths seem smaller and times seem bigger. The elephant would seem smaller in size and slower to eat its fruit.

A physicist called Thierry CHAMBON said that times seem bigger and lengths smaller because of a perspective effect within the space-time.

IV Paradox of twins

Let us put ourselves in the Earth's referential. Let us imagine two twins A and B. The A twin takes a spaceship travelling nearly as fast as the speed of light ; the B twin stays on the Earth. Then A comes back to Earth. Due to the time dilatation, it would be possible for A to age 2 years whereas B ages 40 years. But

• if we consider the problem from the spaceship referential, it is the contrary : A ages 40 years and B ages 2 years ;
• we supposed that the spaceship goes straight with a constant speed. When accelerating, the problem must be considered with another theory : general relativity.

 
The physicist Vincent MORENAS said it is maybe actually the same time for both of twins (40 years for A and 40 years for B).