User:Paul Murray/Introduction to special relativity

Introduction to special relativity

Imagine a pool (or billiards, or snooker) table. A player hits a ball with a cue, which hits another ball, and so on untill a red ball sinks in the top corner pocket.

Now, if you know the exact shape of the table, the exact position of the balls, exactly what happens when balls roll along felt, exactly how hard and where the player hit the first ball, then it's possible (in principle) to predict the outcome - red ball in the corner pocket.

Abe and Betty are watching the game. They each compute the outcome of the hit, and agree that mathematically it will be red ball in the top corner. But here's the thing: Abe and Betty are moving with respect to the table. And they are moving in different directions. And both of them, when computing, work with the positions and velcities of the balls relative to themselves. That is: Abe, who is walking north at 1 m/s