I wondered about this on the subway a few days ago:

A train is stopped at the station. Its position is well-determined and its velocity is zero. You check your wristwatch. At some point you realize the train is moving. Then you wonder: at what time did the train start moving? What was the time in your watch when the train went from "stopped" to "moving"?

This is a very interesting question (and somehow related to the "infinity" thing in a post below). The problem is, there is no point in time in which the train's velocity changes from zero to non-zero. At time t, v = 0; at time t', v > 0; there is absolutely no time between t and t'. Time is granular/quantum/not-infinitely-divisible by definition!

Three issues immediately come to my mind:

- Why do we consider time to be continuous when define it otherwise?
- How do we calculate the "minimum time" (t' - t)?
- When you think about the two issues above, you realize something amazing. But you have to see that for yourself.

Have fun

• correction - aurino__ - November 28, 2003 - 14:49 UTC
  • It's in LQG theory - yanniru - November 28, 2003 - 16:11 UTC
    • Actually.... - aurino__ - November 28, 2003 - 17:26 UTC
      • The difference between Aurino and me - kantolfir2 - November 28, 2003 - 18:54 UTC
        • I see I forgot to hide kantolfir2 (what kind of stupid alias is - aurino__ - November 28, 2003 - 19:10 UTC
          • clarification - aurino__ - November 28, 2003 - 19:17 UTC
          • Reprise - kantolfir2 - November 28, 2003 - 22:57 UTC
            • Oh yeah, Aurino - I forgot to close with "Warm Regards" - kantolfir2 - November 29, 2003 - 05:40 UTC
    • A question that was never answered - kantolfir2 - November 28, 2003 - 23:16 UTC
• uhh - sagefr0g - November 28, 2003 - 15:24 UTC
  • You have to try harder - aurino__ - November 28, 2003 - 17:25 UTC
    • i'll try... - sagefr0g - November 29, 2003 - 14:06 UTC