Saturday, 13 July 2013

Newton, Gravity, and How People Weren't Total Idiots

There's an unfortunate reality about getting a university degree in science: you end up knowing essentially nothing about the history of science. I was reminded of this recently because there was a relatively large history of science conference happening in the city I live in, sponsored by the school I attend. You would think it might be of some interest to some people in the physics department. You would be wrong. It wasn't mentioned once in the numerous emails I get describing the events of interest going on each day, wasn't discussed by any of the graduate students I ran into that week, and when I did bring it up, I got strange looks, as if, why would someone in physics care about the history of physics.

I'm not saying the state of affairs is all physics' fault; looking over the talks scheduled at this conference made me realize that the academics in the field, like all other fields, are mainly concerned with impressing their colleagues in their subfield, rather than building bridges across related disciplines. Still, it's sad, and these types of divisions mean, among other things, that you can get multiple degrees in science while maintaining a complete lack of understanding or appreciation of how your field came to be.

So hopefully I can do a small part, occasionally, to remedy the situation. Starting with Newton and gravity.

Isaac Newton, as everyone knows, invented gravity. Or discovered gravity. Something to do with gravity. There's two versions of the story. The first one, the one that is vaguely in the heads of non-scientists when they are asked about Newton, goes something like this: Newton was sitting on the ground one day when an apple fell on his head. This made him realize that gravity was a thing, so he told other people about it. They then realized that gravity was a thing and so declared Newton to be a genius.

This version of the story seems to imply that people back then were complete and utter idiots; that no one had ever noticed that things fall down, or commented on it, or thought about why this might be. Clearly, a little bit of though shows that this cannot be a true story.

The version that you get in first year physics is more like this: Ha ha, normal people are dumb, there was no apple. Newton realized that gravity is a force that is proportional to the inverse of the square of the distance between two objects, and also to the objects' masses. That is why he is famous for gravity.

This, while being closer to the truth, in that Newton did propose an inverse square law, doesn't fully explain Newton's fame and lasting influence. Hooke also proposed an inverse square law independently, and neither was the first person to make mathematical statements about gravity and the planets.

Newton's lasting influence arises from a bold claim he made with this theory (and others): that there is a single law of gravity, which applies to apples, and the Earth, and Mars, and Jupiter, and the Sun, and every single body that we can see, regardless of whether it lives in the heavens or the earth. It is this universal nature that sets Newton apart from the people who came before him, and it is that attitude that is perhaps his most influential contribution. Even if you don't remember a single law of motion, or how gravity works in a mathematical way, you know that things on Mars obey the same laws of physics as things on earth, and you believe, without needing it to be proven, that if we ever sent a probe to a planet in another star system, that the same laws of physics would apply there as well. That you believe that is Newton's most lasting contribution to science.

Why does that matter? Well, for one thing, it's always worth remembering that people in the past didn't necessarily think the same way we do now, and there's a lot we take for granted that would have been foreign to them. Prior to Newton (and yes, I know I'm simplifying things by implying it was all due to him), the idea that the universe operated under a set of consistent rules that applied everywhere was wouldn't have occurred to most people. In fact, if you go back far enough, you lose the distinction between the supernatural and the natural completely.

Secondly, in general I think that the more we educate ourselves about how science has worked, and how it works now, the better able we will be to make decisions about the many, many issues that science touches on today.

So there's the history lesson. For more on Newton, I. Bernard Cohen is a place to start. For more on pre-scientific world-views, the opening chapters of The Evolution of God offer a fantastic description.

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