The Knowledge Machine: How Irrationality Created Modern Science

by Michael Strevens

This might sound like just the sort of insanity that Russell feared. But Popper was no poached egg. Science, he thought, had a powerful replacement for the inductive thinking undermined by Hume. There may be no such thing as evidence for a theory, but what there can be—and here Popper recalled his youthful bedazzlement by Einstein in 1919—is evidence against a theory. “If the redshift of spectral lines due to the gravitational potential should not exist,” Einstein wrote of a certain phenomenon predicted by his ideas, “then [my] general theory of relativity will be untenable.” As Einstein saw, we can know for sure that any theory that makes false predictions is false. To put it another way, a true theory will always make true predictions; false predictions can issue only from falsehood. No assumptions about the uniformity of nature are needed to grasp that.