Special theory for relativity (狹義相對論)
動動腦筋，計計數。只需用到兩條簡單的算式。
以下是一個例子解釋了為何在光速之下，時間會得到延長 (time dilation):
Situations:
Observer O’ sitting on the train (velocity v) with a mirror and a light source. A light pulse travels from O’ to the mirror on the roof and then travel back to O’. For observer O’ , what is the time taken (△t’) for the light to travel back to observer O’?
Also, for observer O, what is the time taken (△t) for the light to travel back to observer O’?
Given: c = speed of the light, d = the distance to the mirror
Hints:
Only using two formula
And
Pythagoras Theorem
also,
△t’ is in terms of c and d only
△t is in terms of d, c and v only
當計算後，就會發現兩者之所用時間不同，而比較之下，就會得到 (time dilation)。亦可以初步了解到火箭在光速飛行下，回到地球時，太空人比生活在地球的人會老得慢。(p.s. 此解釋不是正確的，因為解釋此現象需要用到廣義相對論)。
