If you look at the longitude and latitude lines on a globe, you may notice (if you haven't in the past) something interesting: we don't handle north-south and east-west the same way.The longitude lines are great circles that meet at the north and south poles, while the latitude lines are just horizontal (if you will) circles of varying size, like cross-sections of the planet.
I commented to Ed recently that we should try doing east-west like we do north-south, and he said, "But then, if you went east for a while, you'd eventually be going west."
"What?" I asked.
"Well, now, if you go north far enough, then eventually you start going south, so if we handled east-west the same way..."
And that was a very weird thought. At first I couldn't make any sense of the idea that if you go east for a while you'll find yourself heading west (because it's not true), and then I started wondering why it does seem to make sense for north-south. Why am I comfortable with the idea that once you're at the north pole, if you keep going, you're heading south?
Is it purely because I was educated about how latitude/longitude lines work?
Then it occurred to me that it's because I think of the north pole as "up" (the way that north is up on most maps). And so I associate it metaphorically with the direction that heads away from gravity. And clearly if you were to climb up a sphere for long enough (using your sticky gecko feet), you'd get to the top, and if you kept going, you'd be headed back down. While if you just geckoed your way sideways around the sphere, there wouldn't be any reversals.
Is it natural that we think of north as up, or is it just a convention? Clearly it's a matter of convention whether north or south is up, but could east or west be up just as easily? We would then picture the earth as rolling around through its orbit rather than spinning, and we would view the solar system as being a flat vertical plane rather than a horizontal platter.
What do you think?