EDGE
Carlo Rovelli, a theoretical physicist
Introduction
by Lee Smolin
Carlo Rovelli is a leading contributor to quantum gravity, who is also made influential proposals regarding the foundation of quantum mechanics and the nature of time. Shortly after receiving his Ph.D he did work which made him regarded as one of the three founders of the approach to quantum gravity called loop quantum gravity-the other two being Abhay Ashtekar and Lee Smolin. Over the last 25 years he has made numerous contributions to the field, the most important of which developed the spacetime approach to quantum gravity called spin foam models.These have culminated over the last five years in a series of discoveries which give strong evidence that loop quantum gravity provides a consistent and and plausible quantum theory of gravity.
A Conversation with Carlo Rovelli
I seem to be saying two things that contradict each other. On the one hand, we trust scientific knowledge, on the other hand, we are always ready to modify in-depth part of our conceptual structure about the world. But there is no contradiction, because the idea of a contradiction comes from what I see as the deepest misunderstanding about science: the idea that science is about certainty.
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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 would say, even if often je is called a philosopher: Anaximander. I am fascinated by this character, Anaximander. I went into understanding what he did, and to me he’s a scientist. He did something that is very typical of science, and which shows some aspect of what science is. So what is the story with Anaximander? It’s the following, in brief:
Until him, all the civilizations of the planet, everybody around the world, thought that 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, is something else. ‘The earth is a finite body that floats in space, without falling, and the sky is not just over our head; it is all around.’
How he gets it? Well obviously he looks 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 get to this conclusion. Except that nobody else got 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 andthe Jesuits went to China and told them. In spite of centuries of Imperial Astronomical Institute which was studying the sky. The Indians only learned this when the Greeks arrived to tell them. The Africans, in America, in Australia… nobody else got to 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 sort of 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 says why should it fall? Things fall toward the earth. Why the earth itself should fall? In other words, he realizes that the obvious generalization from every small heavy object falling, to the earth itself falling, might be wrong. He proposes an alternative, which is that objects fall towards the earth, which means that the direction of falling changes around the earth.
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