13 January 2008

Does a Theory Somehow Become a Law?

In a recent post I expressed a certain befuddlement over a notion that there is some sort of progression from hypothesis to theory to law. Not being a scientist myself I could only fall back on what I learned back in my school days. While stumbling about the internets looking for something or other I fell upon a Scientific American piece by John Rennie that observed:

Many people learned in elementary school that a theory falls in the middle of a hierarchy of certainty--above a mere hypothesis but below a law.

Somehow I missed that bit; I remember that stuff about forming hypotheses, testing them, and developing theories from hypotheses that panned out--whether that came up in elementary or junior high school I no longer recall--but nothing about theories being between hypotheses and laws. If it ever came up in school I must have spaced it out completely, because that whole idea was absolutely new to me when I read it in a critique of a biology textbook, complaining that the author should have written of Newton's "Law" of gravitation rather than "Theory" of gravitation. John Rennie goes on to confirm what I thought I understood:

Scientists do not use the terms that way, however. According to the National Academy of Sciences (NAS), a scientific theory is "a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses." No amount of validation changes a theory into a law, which is a descriptive generalization about nature. So when scientists talk about the theory of evolution--or the atomic theory or the theory of relativity, for that matter--they are not expressing reservations about its truth.

The rest of the commentary on this point was also interesting:

In addition to the theory of evolution, meaning the idea of descent with modification, one may also speak of the fact of evolution. The NAS defines a fact as "an observation that has been repeatedly confirmed and for all practical purposes is accepted as 'true.'" The fossil record and abundant other evidence testify that organisms have evolved through time. Although no one observed those transformations, the indirect evidence is clear, unambiguous and compelling.
All sciences frequently rely on indirect evidence. Physicists cannot see subatomic particles directly, for instance, so they verify their existence by watching for telltale tracks that the particles leave in cloud chambers. The absence of direct observation does not make physicists' conclusions less certain.

Nice to have a little common sense for a change. I've probably been reading too much of this creationist/ID stuff for too long.


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