What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.

What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.

那么时间是什么呢?如果没有人问我，我知道那是什么。如果我想向问我的人解释，我不知道。

-- Augustine of Hippo 河马的奥古斯丁