A notion, not a hypothesis

 I’ve been thinking about scientific hypotheses and about what a hypothesis is.

Here’s an example of something that looks like one but is not:

About one in every thousand atoms of potassium is in the form of an isotope that has an atomic weight of 40, rather than 39. As the word “isotope” implies, it’s radioactive.

Potassium is an essential nutrient for humans. I couldn’t begin to calculate how many of those isotopes I eat with a diet that includes black beans, lentils, bananas and dark leafy greens.

Presumably, when the earth was younger and hotter with radiation, there was a lot more radioactive substances in the food chain.

Isaac Asimov suggested that the level of radiation of that particular isotope of potassium determines the window of opportunity for the development of intelligent life. Too much, and the long genomes that are characteristic of intelligent creatures would break apart. Too little, and the rate of mutation would slow. After eons, we’d still have snails rather than mammals.

It’s an ingenious and telling idea. Students learn from teachers who think aloud like that.

But that suggestion is not really a hypothesis, is it? Can you imagine going to your academic adviser with a proposal to test it? And if that suggestion is not a hypothesis, what would you call it? A bit of speculation? Just an idle notion?

Carl G. Hempel, a philosopher, used to say that one of the most common misconceptions about science is that it is driven by facts — that scientists let the facts drive their hypotheses. Actually, science is driven by minds that are imaginative, as creative as those of poets and fiction writers.

I think science is full of suggestions and speculations like Asimov’s. I wish we had a richer vocabulary to talk about those kinds of illuminating suggestions.

• Sources: A short summary of Asimov's suggestion is in Theodore Gray's The Elements; New York: Black Dog & Leventhal Publishers, 2009. For a discussion of what we ought to count as a hypothesis, see Carl G. Hempel, Philosophy of Natural Science; Englewood Cliffs, N.J.,  Prentice-Hall, Inc., 1966.