Newton v.s. Einstein:The Theory of General Relativity

　　The problem of special relativity is that it cannot cover accelerating particles. In 1915, Einstein finished his theory of general relativity(廣義相對論) by equivalence principle(等效原理).Einstein once said:”I was…in the patent office at Bern(in 1907) when all of a sudden a thought occurred to me:’If a person falls freely, he will not feel his own weight.’I was startled. This simple thought made a deep impression on me. It impelled me toward a theory of gravitation.” This is equivalence principle,which connects acceleration with gravity. Therefore, Newton’s gravitational theory is just a approximation.

Equivalence principle

 

Einstein and Tagore

　　After a long time of try and error, Einstein finally write down the”Einstein gravitational field equation.”(愛因斯坦重力場方程式) It tells us gravity is just the curvature(曲率) of spacetime. Perhaps the diagrams are the best explanations.

Einstein gravitational field equation

　　The best interpretation of general relativity is by a great physicist John Wheeler:”spacetime tells matter how to move;matter tells spacetime how to curve”

　　The most important tests of general relativity are the curved light(光的彎曲) and precession of Mercury(水星的進動),especially the test of curved light in 1919. After that, Einstein become a world-famous person.

　　Strangely, Einstein didn’t get Nobel prize by relativity but by photoelectric effect(光電效應). This is because the theory of relativity is too controversial then.

　　For further applications of general relativity, you can search some keywords:cosmological constant(宇宙常數), gravitational wave(重力波),dark matter and dark energy(暗物質與暗能量).