Einstein's Special relativity

I want to explain Einstein's theorem "Special relativity" using two blog article. Today and next week. First week, I want to explain about basic fact of the theorem, "principle of constancy of light velocity".

There has been many experiment to measure light velocity. Galileo also had the experiment using two lamps. It is easy, two lamps are covered, one person(we call him "A") uncover the lamp, the other(we call him "B") uncovered lamps when "B" watch a lamp's light. Then  "A" measure a round trip time of light. At last We use easy math, divide distance between "A" and "B" by the time makes light velocity. But this experiment was not succeeded. Light velocity is too high to measure on Earth. 

There are some experiments of light velocity that can measure light velocity. But it is not sure what meditate light, like air meditate sound. Before 19th century, it is said "aether" meditate light,  but no one prove existence of aether. Aether meditate light, but we can't see, touch, smell, and hear that.Then, if we want to prove existence, what we have to do? 

Imagine a train, you are in front and I am in the rear. I say "Hello!" to you, then you hear that. sound velocity will be same if you say "Hello!" to me. Then, we moved to an open goods wagon, I say "Hello!"......what will be? Sound velocity is not same you say to me.because air that meditate sound is not moving with us. Sound velocity from me to you is more slow than one from you to me.

In 19th century, scientist thought that in light. If Earth and us are moving in space, we can measure of effect of aether. Light velocity from Earth to the direction of the movement of Earth is more slower than light from Earth to the right angled direction of the movement of Earth.

Michelson-Morley experiment

Albert Michelson and Edward Morley had this experiment. They wanted to know how Aether effect on light velocity. They made a skillfull laboratory equipment. Light from "coherent light source" is split to two light by semi-silvered mirrors, one goes in the direction of the movement of  Earth and the other goes in the right angled direction of the movement of Earth, reflected two light go to detector. If Aether exists, there are differences between two light velocity, then interference fringe would appear. They wanted to measure this.

But, this experiment was failure. The interference fringe size was too small to prove existence of Aether. After this experiment, there were many experiment to prove existence of Aether. But there were no good result to prove.

This experiment suggested one fact. It is "Hmm,  if this experiment is true, Aether does'nt exist? And, light velocity is constant?"

Yes it is!

I want to show abstract of Einstein's special relativity in next week using this fact.

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Now, we have more and more accurate 
result using laser equipment.  Light velocity is  
299 792 458 m/s in SI(The international System of Unit)
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Quoted from...

http://commons.wikimedia.org/wiki/File:Michelson-Morley_experiment_(en).svg?uselang=ja

ガードナーの相対性理論入門 マーティン・ガードナー著 金子 務訳 白揚社 2007/12/31