Where Are We?

Before we leave chapter 1 (have we all got our books now?) I'd like for us to talk a bit more about the question of location.

We've talked about motion and the fact that "Who moved?" is an impossible question when everything is moving in different ways. Rosie said that made her feel like she was falling down the rabbit hole, which made a lot of sense to me.

In the book, the authors also talk about the idea of being able to plot things out on a grid. We can start with the longitude and latitude of the earth, a system which works very well, and extend it out infinitely into space. That, then, can be the box in which things move around. If we do this, then even if things are moving around, we can still say where they are.

I think this is the image we grew up with, in which we can say that Mars will be visible in the evening sky to the west, just above the horizon, or that the Big Dipper shows us true North and stuff like that. We recognize that we're moving, but we carry our imaginary grid around with us, and say where things are in relation to ourselves.

Once we give up the idea that "in relation to ourselves" is an adequate position to take, then we have to give up the idea that things really are in a particular place. If there isn't any unmoving spot at which to anchor the grid, then the grid itself becomes meaningless, and we can no longer say that something occupies a location.

I read an explanation of relativity once that talked about loud music in the park. For people, who can get up and move away easily to a place where the sound is quieter, it makes perfect sense to think of the volume as relative to your location (your location relative to the source of the sound, that is). We have no trouble with the concept of sound that is louder when you're closer to the source and softer when you move away.

But for a snail, which couldn't leave the area before the end of the music, it would seem preposterous to talk about loudness being relative.

So I guess that's why we have to think about outer space before we can grasp the idea of space and motion being relative in any useful way.