Passage 20 Time

好好学习，美到极致！

[11:42.59]Time
[11:44.30]If you can read a clock, you can know the time of day.
[11:48.90]But no one knows what time itself is.
[11:52.93]For all our success in measuring the smallest parts of time,
[11:57.58]time remains one of the great mysteries of the universe.
[12:01.81]One way to think about time is to imagine a world without time.
[12:07.45]There could be no movement,
[12:09.58]because time and movement cannot be separated.
[12:12.90]A world without time could exist only as long as there were no changes,
[12:19.63]for time and change are linked.
[12:22.37]We know that time has passed when something changes.
[12:27.12]In the real world with time, however, changes never stop.
[12:32.60]Some changes happen only once in a while, like an eclipse of the moon.
[12:39.03]Others happen repeatedly, like the rising and setting of the sun.
[12:44.16]Humans always have noted natural events that repeat themselves.
[12:49.29]When people began to count such events, they began to measure time.