The Theory of Special Relativity

　　In 1905, the miraculous year of Albert Einstein. He was just a patent officer(專利員) in Bern.but he published 5 papers that changed the world. Two of them are about the theory of special relativity(狹義相對論).

　　In special relativity, Einstein proposed two important basic principles.The most crucial one is the principle of invariant light speed(光速不變原理): light in vacuum(真空) propagates with the speed c,which is independent of observers. That is,everyone observe the same speed of light no matter what your motion is. The principle leads to an interesting phenomenon called time dilation(時間膨脹). In short and simple, the faster you travel(but there is no acceleration, because you must in  inertial frame of reference(慣性座標系),the speed of you must be a constant or at rest), the slower time flow in other people’s observations on you.

　　There are a lot of paradoxes about special relativity because of time dilation, but the most interesting and famous paradox is the twin paradox(雙胞胎悖論). There are a pair of twin brothers, one aboard a spacecraft for long-distance space travel(the speed is close to the speed of light), while the other is left in the Earth. Results When the traveler returns to Earth, he found himself younger than his brothers(means you are in the “future”).But motion is relative, the person in spacecraft observe his brother in the earth is also very fast. Who will be the younger one? The answer is still the person in spacecraft. Solution is that the person must return to the earth, the process must have acceleration, we can therefore judge who is in motion.

　　The big problem of special relativity is that it is just for inertial frame of reference, I will tell you how Einstein promote his theory to general relativity(廣義相對論) to describe the accelerating particles in next article.