Wednesday, January 21, 2009

the world revolves around you

I've been thinking about geocentric cosmology today.

geocentric universeNowadays we all know that the Ptolemaic/Aristotelian model of the universe is silly. The earth (and the other planets) go around the sun. Copernicus was so awesome not because he discovered something truly profound, but because he (and Brahe and Galileo) provided the arguments and data that eventually forced a bunch of stupid reactionary authorities to stop setting fire to astronomers and to start acknowledging really obvious facts. What kind of moron would put the dinky little earth at the center of the universe?

But pretend you've never been taught anything about astronomy. Go outside and look at the moon and the sun and the stars for a couple days. Go ahead - I'll wait.

Okay, notice anything? The sun and the moon and the stars move. They move, and the earth doesn't move. You can tell it's not moving, because very rarely you do feel the earth move, especially in southern California. But most of the time you don't feel any earth movement. So all those things up in the sky move, and they somehow disappear over one horizon and then reappear over the other horizon later on.

Now, if you're really gullible and superstitious, you might think that the sun and whatnot do something magical, like teleporting back to where they started, or they die and are reborn every day. Or whatever. But, no, we're being scientific. So here's an experiment: get your friend to run around you in a circle while you keep your head still. Notice that she disappears at one side of your visual field but reappears at the other side... because... she's moving in an orbit while you observe from a stationary position! That's it - the sun and moon and stars go in a circle around the earth! This is scientific progress!

Hang on though, some friendless little nerd has an objection. Try a different experiment, he says: have your friend stay stationary, while you run around her in a circle. And while you are running, spin around, so that your back is sometimes toward your friend and your front is sometimes toward your friend. Notice that your friend disappears on one side of your visual field, and reappears on the other. But you are moving, not your friend. Couldn't the earth's relation to the sun or moon be like that? Couldn't the earth be moving?

What a lame idea! Why would I want to spin while running around my friend? I'd trip and hurt myself! And why would the earth - which certainly doesn't feel like it's spinning to me! - do something so stupid? This is a needlessly complicated theory, when good old common sense tells us that the earth is holding still. This idea is obviously the sort of babble you get from crazy people, or troublemakers.

Galileo before the holy office
Galileo before the Holy Office, Joseph-Nicolas Robert-Fleury (via wikicommons)

Here's my point: geocentric cosmology was not an obviously false and stupid dogmatic position. It was, in fact, a scientific improvement upon earlier theories of planetary motion. And it was incredibly satisfying on an intuitive level. Copernicus and his friends were only able to overturn the view by providing a tight explanatory framework, and an increasingly demanding amount of data that finally overwhelmed extant accounts. Geocentric cosmology is the simplest explanatory theory when you're idly watching the stars one night, but it stops being simplest when you look at hundreds of nights' observations of all the celestial bodies. Which is to say - heliocentric theory is the best theory, but not at an intuitive level.

Except it certainly feels intuitive to us now. Of course the earth goes round the sun! But it only feels this way because we were raised on colorful planetarium displays. We were taught a heliocentric cosmology before we were able to develop an independent intuitive sense of the universe. That's why it now seems so obvious that Copernicus was right and the prevailing authorities were idiots. But they did not have the benefit of building a diorama of the solar system in elementary school.

So I wonder, now, which contemporary ridiculous and counter-intuitive views will be utterly obvious in the future. For what lapse of scientific common sense will our distant ancestors mock us? And who among our lunatic fringe will someday be a hero of rational progress? Just how much will we come to resemble the Inquisition berating Galileo? We are, after all, still plenty arrogant, even if we're no longer the center of the universe.

top image: Min Su Yun


  1. You are my intellectual hero of the day for this! The supposedly stupid do generally start from someplace that is more or less reasonable. I feel as if I spend so much of my life trying to point that out to the supposedly smart.

  2. It's amazing how much of our intellectual energy is devoted to convincing ourselves that what we already believe is so right that anyone who doesn't believe it must be stupid or evil.