如果形容一个人是在另一个世界，那就表示这个人对眼前的事情心不在焉，漠不关心。

例句

Jane's on another planet – she went to buy some apples and bought lemons instead!

John really doesn't listen in class; he seems to be on another planet.

请注意

如果说一个人 living on another planet 那么意思就是说这个人一点都不现实。

例句

He thinks we'll be able to drive to Paris by tonight – he's really on another planet!

If she thinks we can afford a two-week holiday in Spain she's living on another planet!