Geoscience Reference
In-Depth Information
CHAPTER
4
THEORY ON TRIAL
It must be possible for an empirical
scientific system to be refuted by experience.
Karl Popper
O
F
P
REDICTION
AND
P
ROOF
By the early 1980s, the importance of impact in the solar system was
established as a fact, as was the presence of high iridium concentra-
tions in at least a few K-T boundary clay sites. That the Cretaceous
had ended with a great mass extinction was also a fact, though the
suddenness of that extinction was disputed. The Alvarezes invented
a theory that tied these facts together. To explain the observational
facts is merely the first obligation of a theory; often several do a good
job of explaining at least some of the observations. The theories that
prove to have lasting value go further: They predict new facts that
have yet to be discovered. If these predicted facts are subsequently
found, the theory gains strength. Curiously, however, a theory is
never completely proven. The possibility always exists that some
new evidence will come to light to discredit the theory, or that some
clever scientist will come up with an alternative theory that explains
more of the facts. Luis Alvarez never went so far as to claim that
the meteorite impact theory had been proven, though he came per-
ilously close. Typically he would assert only that the theory had met
a large number of its predictions (and "postdictions," which are rea-
sonable predictions that happened not to be thought of until later).
Being human, however, he was not above, in Tennyson's phrase,
"believing where we cannot prove."
2
German philosopher Karl Popper has done more than anyone to
advance the notion that scientific theories may be disproven, but
never proven. He argued that for a theory to be called scientific, it
