October 15, 2018

Will key theories of modern science, including Darwinian evolution in biology and Einsteinian relativity in physics, survive future discoveries? Some people think such survival is impossible, because they believe that new scientific theories always overthrow the previous theories. This misunderstanding has been fostered in part by a famous book first published in 1962—Thomas Kuhn’s The Structure of Scientific Revolutions, which argued that scientific research proceeds for long periods of time within a certain manner of thinking (a “paradigm”), until too many pieces of evidence have turned up that are unexplainable or even paradoxical. Then suddenly there is a great leap (a “paradigm shift”): The old theory is abandoned for a new theory that explains much more, and the old paradoxes disappear. The concepts of the new theory are so different from the concepts of the old one that they are “incommensurable,” because the implicit assumptions have changed. For example, after the Copernican Revolution, when scientists abandoned the idea that the Earth was the immovable center of the universe, the Earth became a planet and the status of the Sun and Moon changed. The old theory was overthrown and never again taught as science.

Kuhn, whose first book was on the Copernican Revolution, appears to have assumed that all scientific revolutions are like that one. His argument implies that no scientific theory can ever be considered true, because it will eventually be overthrown by a bigger and better theory. Because the new theory will eventually be overthrown in its turn, it is ultimately no truer than the old one (even though it is temporarily more useful), so it is questionable whether science actually progresses; perhaps it just keeps changing. 

But revolutionary scientific theories do not have to overthrow their predecessors except in the earliest stage of a science, when a scientific theory is replacing earlier ideas that were not well supported by evidence. Once a field of science undergoes the revolution that creates for it a solid intellectual foundation—like the ones that Newtonian mechanics gave physics and Darwinian evolution gave biology—that foundational theory can stand forever. Science then progresses by encompassing the foundational theory in a new and larger theory that explains things beyond the ken of the older theory. An encompassing theory does not overthrow the older theory—instead, it defines the limits within which the older theory is reliably true. Science does not simply toss one theory out for another: it makes real progress toward ever-larger truths. But there is a built-in enforcer of humility in science: We cannot regard something as true until we know about something bigger.  

Have you encountered science skeptics who say that scientific research can’t be trusted because its theories are constantly changing? If so, what has been your response? Let me know at executiveoffice@sigmaxi.org.

Joel Primack, 
Sigma Xi President