Physicists and Philosophes Hold Peace Talks

“Theory has detached itself from experiment. The objects of theoretical speculation are now too far away, too small, too energetic or too far in the past to reach or rule out with our earthly instruments.”

“Today, most physicists judge the soundness of a theory by using the Austrian-British philosopher Karl Popper’s rule of thumb. In the 1930s, Popper drew a line between science and non-science in comparing the work of Albert Einstein with that of Sigmund Freud. Einstein’s theory of general relativity, which cast the force of gravity as curves in space and time, made risky predictions—ones that, if they hadn’t succeeded so brilliantly, would have failed miserably, falsifying the theory. But Freudian psychoanalysis was slippery: Any fault of your mother’s could be worked into your diagnosis. The theory wasn’t falsifiable, and so, Popper decided, it wasn’t science.”

“Physicists’ preoccupation with Popper “is really something that needs to stop,” Pigliucci said. “We need to talk about current philosophy of science. We don’t talk about something that was current 50 years ago.””

“Popperian falsificationism has been supplanted by Bayesian confirmation theory, or Bayesianism, a modern framework based on the 18th-century probability theory of the English statistician and minister Thomas Bayes. Bayesianism allows for the fact that modern scientific theories typically make claims far beyond what can be directly observed—no one has ever seen an atom—and so today’s theories often resist a falsified-unfalsified dichotomy. Instead, trust in a theory often falls somewhere along a continuum, sliding up or down between 0 and 100 percent as new information becomes available. “The Bayesian framework is much more flexible” than Popper’s theory, said Stephan Hartmann, a Bayesian philosopher at LMU. “It also connects nicely to the psychology of reasoning.””

“the 19th-century vortex theory of atoms. This “Victorian theory of everything,” developed by the Scots Peter Tait and Lord Kelvin, postulated that atoms are microscopic vortexes in the ether, the fluid medium that was believed at the time to fill space. Hydrogen, oxygen, and all other atoms were, deep down, just different types of vortical knots. At first, the theory “seemed to be highly promising,” Kragh said. “People were fascinated by the richness of the mathematics, which could keep mathematicians busy for centuries, as was said at the time.” Alas, atoms are not vortexes, the ether does not exist, and theoretical beauty is not always truth.”

“Except sometimes it is. Rationalism guided Einstein toward his theory of relativity, which he believed in wholeheartedly on rational grounds before it was ever tested. “I hold it true that pure thought can grasp reality, as the ancients dreamed,” Einstein said in 1933, years after his theory had been confirmed by observations of starlight bending around the sun.”

“The question for the philosophers is: Without experiments, is there any way to distinguish between the non-empirical virtues of vortex theory and those of Einstein’s theory? Can we ever really trust a theory on non-empirical grounds?”

“Popper called speculation that did not yield testable predictions “metaphysics,” but he considered such activity worthwhile, since it might become testable in the future.”

“This was true of atomic theory, which many 19th-century physicists feared would never be empirically confirmed. “Popper was not a naive Popperian,” Kragh said. “If a theory is not falsifiable,” Kragh said, channeling Popper, “it should not be given up. We have to wait.””