Science Is Not About Certainty
The separation of science and the humanities is relatively new—and detrimental to both
By Carlo Rovelli
We teach our students: We say that we have some theories about science. Science is about hypothetico-deductive methods; we have observations, we have data, data require organizing into theories. So then we have theories. These theories are suggested or produced from the data somehow, then checked in terms of the data. Then time passes, we have more data, theories evolve, we throw away a theory, and we find another theory that’s better, a better understanding of the data, and so on and so forth.
This is the standard idea of how science works, which implies that science is about empirical content; the true, interesting, relevant content of science is its empirical content. Since theories change, the empirical content is the solid part of what science is.
Now, there’s something disturbing, for me, as a theoretical scientist, in all this. I feel that something is missing. Something of the story is missing. I’ve been asking myself, “What is this thing missing?” I’m not sure I have the answer, but I want to present some ideas on something else that science is.
This is particularly relevant today in science, and particularly in physics, because—if I’m allowed to be polemical—in my field, fundamental theoretical physics, for thirty years we have failed. There hasn’t been a major success in theoretical physics in the last few decades after the standard model, somehow. Of course there are ideas. These ideas might turn out to be right. Loop quantum gravity might turn out to be right, or not. String theory might turn out to be right, or not. But we don’t know, and for the moment Nature has not said yes, in any sense.
I suspect that this might be in part because of the wrong ideas we have about science, and because methodologically we’re doing something wrong—at least in theoretical physics, and perhaps also in other sciences. Let me tell you a story to explain what I mean. The story is an old story about my latest, greatest passion outside theoretical physics—an ancient scientist, or so I say even if often he’s called a philosopher: Anaximander. I’m fascinated by this character, Anaximander. I went into understanding what he did, and to me he’s a scientist. He did something that’s very typical of science and shows some aspect of what science is. What is the story with Anaximander? It’s the following, in brief:
Until Anaximander, all the civilizations of the planet— everybody around the world—thought the structure of the world was the sky over our heads and the earth under our feet. There’s an up and a down, heavy things fall from the up to the down, and that’s reality. Reality is oriented up and down; Heaven’s up and Earth is down. Then comes Anaximander and says, “No, it’s something else. The Earth is a finite body that floats in space, without falling, and the sky is not just over our head, it’s all around.”
How did he get this? Well, obviously, he looked at the sky. You see things going around—the stars, the heavens, the moon, the planets, everything moves around and keeps turning around us. It’s sort of reasonable to think that below us is nothing, so it seems simple to come to this conclusion. Except that nobody else came to this conclusion. In centuries and centuries of ancient civilizations, nobody got there. The Chinese didn’t get there until the 17th century, when Matteo Ricci and the Jesuits went to China and told them. In spite of centuries of the Imperial Astronomical Institute, which was studying the sky. The Indians learned this only when the Greeks arrived to tell them. In Africa, in America, in Australia—nobody else arrived at this simple realization that the sky is not just over our head, it’s also under our feet. Why?
Because obviously it’s easy to suggest that the Earth floats in nothing, but then you have to answer the question, Why doesn’t it fall? The genius of Anaximander was to answer this question. We know his answer—from Aristotle, from other people. He doesn’t answer this question, in fact: He questions this question. He asks, “Why should it fall?” Things fall toward the Earth. Why should the Earth itself fall? In other words, he realizes that the obvious generalization—from every heavy object falling to the Earth itself falling—might be wrong. He proposes an alternative, which is that objects fall toward the Earth, which means that the direction of falling changes around the Earth.
This means that up and down become notions relative to the Earth. Which is rather simple to figure out for us now: We’ve learned this idea. But if you think of the difficulty when we were children of understanding how people in Sydney could live upside-down, clearly this required changing something structural in our basic language in terms of which we understand the world. In other words, “up” and “down” meant something different before and after Anaximander’s revolution.
He understands something about reality essentially by changing something in the conceptual structure we use to grasp reality. In doing so, he isn’t making a theory; he understands something that, in some precise sense, is forever. It’s an uncovered truth, which to a large extent is a negative truth. He frees us from prejudice, a prejudice that was ingrained in our conceptual structure for thinking about space.
Why do I think this is interesting? Because I think this is what happens at every major step, at least in physics; in fact, I think this is what happened at every step in physics, not necessarily major. When I give a thesis to students, most of the time the problem I give for a thesis is not solved. It’s not solved because the solution of the question, most of the time, is not in solving the question, it’s in questioning the question itself. It’s realizing that in the way the problem was formulated there was some implicit prejudice or assumption that should be dropped.
If this is so, then the idea that we have data and theories and then we have a rational agent who constructs theories from the data using his rationality, his mind, his intelligence, his conceptual structure doesn’t make any sense, because what’s being challenged at every step is not the theory, it’s the conceptual structure used in constructing the theory and interpreting the data. In other words, it’s not by changing theories that we go ahead but by changing the way we think about the world.
The prototype of this way of thinking—the example that makes it clearer—is Einstein’s discovery of special relativity. On the one hand, there was Newtonian mechanics, which was extremely successful with its empirical content. On the other hand, there was Maxwell’s theory, with its empirical content, which was extremely successful, too. But there was a contradiction between the two.
If Einstein had gone to school to learn what science is, if he had read Kuhn, and the philosophers explaining what science is, if he was any one of my colleagues today who are looking for a solution of the big problem of physics today, what would he do? He would say, “OK, the empirical content is the strong part of the theory. The idea in classical mechanics that velocity is relative: forget about it. The Maxwell equations: forget about them. Because this is a volatile part of our knowledge. The theories themselves have to be changed, OK? What we keep solid is the data, and we modify the theory so that it makes sense coherently, and coherently with the data.”
That’s not at all what Einstein does. Einstein does the contrary. He takes the theories very seriously. He believes the theories. He says, “Look, classical mechanics is so successful that when it says that velocity is relative, we should take it seriously, and we should believe it. And the Maxwell equations are so successful that we should believe the Maxwell equations.” He has so much trust in the theory itself, in the qualitative content of the theory—that qualitative content that Kuhn says changes all the time, that we learned not to take too seriously—and he has so much in that that he’s ready to do what? To force coherence between the two theories by challenging something completely different, which is something that’s in our head, which is how we think about time.
He’s changing something in common sense—something about the elementary structure in terms of which we think of the world—on the basis of trust of the past results in physics. This is exactly the opposite of what’s done today in physics. If you read Physical Review today, it’s all about theories that challenge completely and deeply the content of previous theories, so that theories in which there’s no Lorentz invariance, which are not relativistic, which are not general covariant, quantum mechanics, might be wrong.…
Every physicist today is immediately ready to say, “OK, all of our past knowledge about the world is wrong. Let’s randomly pick some new idea.” I suspect that this is not a small component of the long-term lack of success of theoretical physics. You understand something new about the world either from new data or from thinking deeply on what we’ve already learned about the world. But thinking means also accepting what we’ve learned, challenging what we think, and knowing that in some of the things we think, there may be something to modify.
What, then, are the aspects of doing science that I think are undervalued and should come up front? First, science is about constructing visions of the world, about rearranging our conceptual structure, about creating new concepts which were not there before, and even more, about changing, challenging, the a priori that we have. It has nothing to do with the assembling of data and the ways of organizing the assembly of data. It has everything to do with the way we think, and with our mental vision of the world. Science is a process in which we keep exploring ways of thinking and keep changing our image of the world, our vision of the world, to find new visions that work a little bit better.
In doing that, what we’ve learned in the past is our main ingredient—especially the negative things we’ve learned. If we’ve learned that the Earth is not flat, there will be no theory in the future in which the Earth is flat. If we have learned that the Earth is not at the center of the universe, that’s forever. We’re not going to go back on this. If you’ve learned that simultaneity is relative, with Einstein, we’re not going back to absolute simultaneity, like many people think. Thus when an experiment measures neutrinos going faster than light, we should be suspicious and, of course, check to see whether there’s something very deep that’s happening. But it’s absurd when everybody jumps and says, “OK, Einstein was wrong,” just because a little anomaly indicates this. It never works like that in science.
The past knowledge is always with us, and it’s our main ingredient for understanding. The theoretical ideas that are based on “Let’s imagine that this may happen, because why not?” are not taking us anywhere.
I seem to be saying two things that contradict each other. On the one hand, we trust our past knowledge, and on the other hand, we are always ready to modify, in depth, part of our conceptual structure of the world. There’s no contradiction between the two; the idea of the contradiction comes from what I see as the deepest misunderstanding about science, which is the idea that science is about certainty.
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