Everything is relative

My wife is sitting on a plane as I type these words, flying from London to Hong Kong and then on to Australia. I’m staying at home, and from my desk I’m toying with a hypothetical question: if she gets up, strolls the length of the plane and then returns to her seat, has she come back to where she started? From her perspective, yes. From my perspective, however, both she and the plane are moving at five hundred miles per hour. Assuming her round trip took five minutes, this means she’s forty miles further away from London.

So far, so trivial. But we can extend this investigation. I’ve been sitting at my desk for five minutes, typing and tinkering with these sentences.