The Sciences

Theories, laws, facts

Cosmic VarianceBy Sean CarrollSep 20, 2005 8:57 AM

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Could we just agree to tell the truth about this from now on? The New York Times has an interesting story by Cornelia Dean on the training that museums have started to give their docents and employees on how to deal with creationists. A sad commentary on our current state of affairs that such training is becoming necessary, but probably nobody reading this blog is surprised. But as a supplement to the article, the Times reprints a FAQ from a pamphlet handed out by the Museum of the Earth in Ithaca, N.Y. It includes the following question:

Is evolution 'just a theory'? A "theory" in science is a structure of related ideas that explains one or more natural phenomena and is supported by observations from the natural world; it is not something less than a "fact." Theories actually occupy the highest, not the lowest, rank among scientific ideas. ... Evolution is a "theory" in the same way that the idea that matter is made of atoms is a theory.

This is right in spirit, but the truth is not so very scary or technical that we can't just fess up to it. The truth is that the hierarchy of "hypotheses" and "theories" and "laws" and "facts" that many people are taught in elementary school (or wherever) has absolutely no relationship to how real scientists use those words. Which is, that they are completely inconsistent and sloppy with their use. There is no procedure by which an ambitious young Hypothesis accumulates some promising support, and is brought up before the Most Supreme Council of Learned Scientists to be promoted to a Theory. The reality of the situation is that it's a mess. I can invent a half-baked idea tonight and call it a "model" or a "theory" and nobody cares, or would even notice. The Standard Model of Particle Physics is much closer to objective truth than Newton's Law of Universal Gravitation, and the General Theory of Relativity is somewhere in between. And "facts"? Eavesdrop on some scientists at work. You will go years without hearing any of them talk about "facts." They'll talk about data, and measurements, and observations, and experiments -- those are things with identifiable meanings that we can work with. But call something a "fact" and you're making some absolute metaphysical claim that isn't the kind of thing scientists like to do. Likewise "proof." Mathematicians and logicians, who deal with abstract symbols independent of any connection to nature, prove things. Scientists don't. They figure out that certain beliefs should be held with greater and greater confidence, but proving something is simply outside the domain of science. Which does bring us to the one almost-subtle point in this generally easy-to-understand business. Science never gets anything 100% right; it is always working on a better understanding, improving on the best current theory (or model, or whatever). But it does get some things right enough. The Big Bang, the round earth, Newton's Laws, the Standard Model, natural selection -- none of these is "proven" correct, but they are all correct, within certain domains of validity. There comes a point when, even though you can never (even in principle) prove an idea to be a fact, it becomes well-enough established that maintaining a skeptical attitude is a sign of crackpottery, not wisdom. So let's just quit the charade and let the unwashed masses in on the truth as far as "theory" is concerned. It's a shorthand term for a model of some part of nature -- but the label implies absolutely nothing about how true that model is. (The phlogiston theory didn't stop being a theory once we knew it wasn't true.) What matters isn't whether we label something a "theory" or a "law" or a "fact," it's whether we label it "right" or "wrong." As in, Darwin was "right," the creationists are "wrong."

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