The theory of relativity in words of four letters or less

Edit: sorry, changed wording while being replied to

Most people implicitly believe that there must be some privileged reference frame, if not mine necessarily than at least one very close to mine, and for good reason. (I'd go so far as to say that most people believe explicitly that there is a privileged reference frame, and that it is an intelligent agent called God, but leave that alone for now.) Even if they do get past this statement with a, "Uh, okay, I guess so..." they probably have not actually adjusted their entire world view to account for that powerful fact, and if they seem to understand what you have told them it is likely that they have simply memorized the right answer.

Not that there's anything wrong with trying.

Assume now the virtual particle winks out of existence. Have you suddenly stopped moving? Were you wrong/incorrect somehow to have chosen the particle as the rest frame? Has conservation of (your) momentum just been violated?

So yes, it really is meant to be talking about a self-evident fact (once you think about it).

But you're right; I'm not a physics teacher. I'm willing to concede that I underestimated the potential stickiness of this point, and/or that I failed to overcome my handicap in expressing this point.

(I was inspired in part by Douglas Hofstadter, who did something similar on a smaller scale in "Le Ton Beau de Marot".)

The two rocks land just as Bert and Dana are closest to each other. The two rocks are equally distant from that point. But as the light propagates towards them, Bert continues to move towards the light from the impact ahead of him, and away from the impact behind him. Thus he will see the light from the former impact before the latter.

(The traditional thought experiment is described in terms of trains and lightning, instead of buses and moon rocks. If you do a web search for that plus "special relativity", you should find plenty of descriptions that are closer to the original.)

Now. Bert is on the bus. It goes, let us say, from west to east on the road. Bert is half way from the west rock to the east rock when each rock hits land -- but he is on the move, and when the rays from the east rock hit his eyes he has gone some way east. The rays from the west rock have not yet got to him. Then, just a tad more time, and the rays from the west rock get to Bert's eyes.

But Dana does not move. She sits by the road. The rays from the west rock and the east rock hit her at the same time: each rock is, say, a yard from her, one west and one east.

So Dana sits and does not move; she sees the rays from each rock at the same time. Bert is on the bus, and goes from west to east; he sees the rays from the east rock and then the rays from the west rock.

And all that is fine. They both know that Dana does not move and Bert does. So they will say that each rock hit at the same time, for Dana (who did not move) saw them hit at the same time.

But (and this is the bit that may fry your mind) we can just as well say that Bert does not move and Dana does move! And then we will have to say that the east rock hit and then the west rock! How can that be?

We must say, even if you find it odd, that "did the east rock hit, then the west? or the west, then the east? or both at once?" just goes one way for Dana and not that way for Bert. Just like "is this rock to the east or to the west?" may not go the same way for both, if they are not at the same site.

(You are not dumb. This is hard. It took Al to work it out!)

I feel relatively smarter now

Best I could do.