How Einstein Shattered the Myth of "Settled Science"

The philosopher Karl Popper pointed out that most early practition­­ers of science were justificationists. They didn’t just seek out any old knowledge; they were on the hunt for justified knowledge. Knowledge they could be certain was true—or at the very least probably true. In other words, settled science.

Unsettled science, many presumed, was risky, unreliable, insecure—in danger of one fateful day collapsing, sending hard-won practical progress built atop it crashing to the ground.

Around the time of the Enlightenment, many justificationists (notably Francis Bacon) believed science had finally found a way to deliver their prized certainty—a method known as induction. Here’s how it worked: As careful, objective scientists gathered observations that supported their theory, the probability that the theory was true went up and up and up. Provided no disconfirming instances were found, at some point, so much evidence amassed that for all intents and purposes, we could drop the cumbersome qualification of "probably" and just call the thing true. Settled science.

In the face of skepticism, justificationists had a crowning example of grade-A, justified knowledge to which they could point: Newton’s theory of gravity. Newton’s theory, which described gravity as a force that affected the motion of objects both terrestrial and celestial, had been corroborated by centuries’ worth of observations. It passed every test anyone had ever thrown at it. So successful was the theory that many believed physics itself was nearly complete.

But then came Einstein. Albert “Anything You Can Do I Can Do Better” Einstein. Guys, guys, guys, you’ve got it all wrong, he warned. Gravity is not a force. It’s a result of the fact that—and you might want to sit down for this—space and time are curved.

Einstein’s theory, absurd as it must have first sounded, not only matched the effectiveness of Newton’s theory but surpassed it, succeeding in places where Newton’s theory could not and, at the same time, granting us a far richer glimpse into the underlying structure of reality. To the disbelief of justificationists, Einstein had done the unimaginable: proven Newton’s theory wrong.

In doing so, the Einsteinian revolution highlighted, more generally, something that critics of justificationism had been pointing out for centuries: We simply can’t have settled science.

After all, how could any number of observations ever justify a theory as true, if the very next observation could always render it false? More to the point, the notion that any information might serve as a justification for some knowledge seems to lead inexorably to an infinite regress. Indeed, doesn’t any purported justification itself require justification? Even more to the point, come on. Only a zealot or sociopath could ever really with a straight face deny the possibility that they could be mistaken. We are all human, are we not?

Einstein’s impeachment of Newton’s theory, and more broadly the quest for scientific certainty, may seem frightening to those with even a remote interest in making progress. But it need not be. Because along with demonstrating that we can’t have settled science, the Einsteinian revolution showed that we don’t need settled science.

After Einstein successfully fractured Newton’s theory, some justificationists I imagine must have felt the impulse to scurry underneath their desks, waiting for theoretical and practical progress to crumble around them. But crumble it did not. Not only did Newton’s theory and its practical applications not collapse (Newton’s laws, mind you, are still used to this very day), its overthrow by general relativity amounted to one of the greatest leaps of progress in the history of science. Why were the justificationists so wrong?

Justificationists failed to appreciate a subtle, yet vital distinction: It’s not science that is unsettled that is risky, unreliable, and insecure, but rather knowledge that is untested.

Before modern science, knowledge-seekers frequently fooled themselves into thinking that their fatuous theories were true, even as they had little basis in reality. Some ancient societies, for instance, believed that human sacrifices could ward off natural disasters. When unfounded ideas like these were later revealed false, they were revealed almost entirely false, and so were indeed liable to collapse in the way justificationists feared.

But science was invented precisely as a bulwark against these kinds of delusions. Scientists subject their ideas to the most severe tests they can think of so that when a theory manages to survive, while we can’t conclude it to be entirely true, we are right to conclude that it contains some truth. In other words, it must correspond to something in reality, even if our current theory fails to represent that something with perfect clarity or precision.

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When an unsettled but well-tested scientific theory, such as Newton’s, is later revealed false, it’s likely to be revealed partially false—the truth it contains does not vanish and the theory itself does not fall.

Moreover, not only does falsifying a theory not disappear the truth it contains, but it’s the first step to expanding it. In the face of a now-erroneous theory, scientists face a new challenge: Conjecture a successor theory, one that corrects the newly surfaced error while at the same time preserves the truth embodied in its predecessor. It’s in this way that our scientific theories come to contain more and more truth over time. Not only is unsettled science not destined to collapse, but quite the contrary: It’s primed to grow.

There is one important condition for continued growth, however. We must not ever, ever, ever stop searching for errors in our theories, even our best ones: the ones that appear settled, which we can’t presently imagine being superseded.

Karl Popper speculated that justificationism is what got the project of science off the ground. Early scientists would not have been inspired by the realization that all we can have is unsettled science. But now, the very same desire for settled science that got us off the ground, I’m afraid, threatens to restrict how high we ultimately fly.