Wednesday, 01 December 2010
Ah…so here we are at the final month of the year. I’ve written a post for each day of the year so far – 336 total.
This evening, before bed, Owen and I were reading books together as we often do. Tonight, he selected a book about the universe. I told him the book was too long to read cover-to-cover, but that we could just read some excerpts from it.
Among other things, I turned to a page that showed a picture of Isaac Newton sitting on a bench in the classic thinker position. We read about how Newton realized that the same force that keeps the planets tethered to the sun is the same force that makes fruit fall from trees.
While I was reading those paragraphs, Owen asked: “But how do you know if your idea is right?”
I wasn’t sure what he meant, so I asked for clarification. He said: “Because if you think your idea is that the sun goes around the earth, then you are wrong, but how do you know you are wrong?”
I told him that was a good question (you know, to distinguish between that and all the stupid questions). I tried to explain that people used to just come up with ideas that explained what they saw (or what they think they saw). For the most part, I said, that worked out okay, but in time people decided to test their ideas.
We talked more about the sun going around the earth: we agreed that it certainly seems like the sun goes around the earth. After all, we see it move across the sky, and we don’t feel the earth moving. And we also agreed that saying the sun ‘rises’ and ‘sets’ is a pretty useful way of describing what we see.
But then I told him how people noticed that Mars, Venus, and Jupiter did not move in predictable patterns, and so people sought to find better ways of explaining things. We talked about how we need to do tests to check on our hypothesis, and to find better ways to observe our world, such as by sending up spacecraft to get a better view.
Owen agreed that Newton was pretty smart for coming up with the correct answer. There was a box below the one about Newton that discussed how Einstein figured out that Newton wasn’t exactly right…but I figured it was best to skip that box for today. It was bedtime, after all.
I thought they did have a model predicting the motion of the planets with the Earth at the center of it all. If I remember correctly, the retrograde motion was thought of as being caused by the planets moving in little circles around the Earth. I can’t remember though, did the heliocentric model make better predictions or was it favored more for its simplicity?
Anyway, that was a great teaching moment. It seems to stick better when they ask the questions.
Thanks. Yeah, I try to write about my good parenting moments a lot more than my crappy parenting moments.
I think (and this is all from memory of past book readings) there was originally just a belief that the sun, planets and stars all went around the earth (’cause that’s what it looks like). In a way, it does make very good predictions, e.g., I can predict via my geocentric theory that the sun will ‘rise’ tomorrow morning.
At some point, the bizarre movements of the planets was documented better and better and people came up with all these weird patterns of circles-within-circles (epicircles?) that attempted to explain the movements while still holding onto the geocentric model. For a long time, at least since ancient Greece, there was the idea that the sun might be at the center of it all, but it was tough to prove back then. The heliocentric model was, at some point (Kepler? Copernicus?), determined to make better predictions. Because, if you place the sun at the center, then the planets motions can be simplified into ellipses.