時間的speed

Since 1967, the second has been defined to bethe duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

2010-07-18 22:01:41 補充：
愛因斯坦沒有說過快過光就可以回到過去之類。
愛因斯坦只說過，沒有物體或能量的傳送可以快過光。
如果我在地球，看見你乘著光速飛船經過，我會發現你的時間（包括手錶、人體動作等等）都是停頓的。

衝你在知識+搜尋《時光倒流的問題》
因為我唔可以答相同答案，我拿過最佳。

The fundamental units in physics for mass, length and time are respectively the kilogram (kg), metre (m) and second (s).

Velocity is NOT a fundamental unit in physics, instead it is a derived unit based on two fundamental units, namely metre and second. Hence, the time unit is, in fact, embedded in the velocity unit.


2010-07-18 13:20:18 補充：
Q:愛因xx講,話快過光,就可以穿越時空...
Had Einstein ever said this?
In General Relativity, mass causes a wrapping of space-time. The time change is becuase of sapce wrapping.