回複：請說說你的推理。

http://universe-review.ca/R15-17-relativity.htm#eq5    if you have time.

If you just like to short answer. Relativity is based on light speed is same to different observers! In order to make that happens, time must be variable to observer at high speed and observer at rest.  This is called time dilation. For easier understanding, check wiki. From time dilation, miloswinki space time graph, it is easier to see what Einstein conclude below

 

“The distinction between past, present, and future is only a stubbornly persistent illusion”

Albert Einstein