Why do we remember the past but not the future? Why is it that we can decide what to do tomorrow but not what we did yesterday? Theoretical physicist Carlo Rovelli revels in asking such questions about the nature of time — they might seem trivial at first but they force one to look deeper, revealing new aspects of reality. He has been pursuing answers to questions like these for years, and eventually, came across work by SFI Professor David Wolpert on how time works in different memory systems.
“The breadth and the kinds of questions asked at SFI resonate with me," he says. "There’s a focus on fundamentals without being trapped in a research program.” Last fall, Rovelli joined the Institute’s Fractal Faculty.
In the world of physics, Rovelli is known for his work on loop quantum gravity — a theory that builds on Einstein’s general relativity and seeks to understand the quantum aspects of spacetime. The theory shows that the fabric of spacetime is woven by tiny loops built into a network. Beyond the world of physics, he is known as the author of popular science books such as Seven Brief Lessons on Physics and The Order of Time, which have been translated into more than 40 languages.
Born in 1956 in post-WWII Italy to a family that held knowledge in high regard, Rovelli grew up surrounded by books. During his adolescence, he felt acutely aware of the widespread hypocrisy of the world and rebelled. In his hometown of Verona, he had also to confront a lingering nostalgia for fascism. He learned not to trust common opinions around him.
“It was not an easy phase, but that’s when I learned to question. I wanted to know better and I knew I wouldn’t find answers in Verona,” he says. He chose to drop out of school. As a consequence, his father cut him off financially.
At age 16, Rovelli hitchhiked from Europe to the Soviet nations and, at the height of the Cold War, learned to be critical of narratives produced by both sides. A few years later, he traveled alone, hitchiking coast-to-coast in the US and Canada, finding jobs when he ran out of money, inspired by the people he met.
“It was a way for me to take my life in my hands, to learn about the diversity of humans, our visions and perspectives,” says Rovelli.
To delay being drafted into the military, he enrolled in the University of Bologna. There, he became involved in politics and wrote his first book — Fatti Nostri or “Our Business” — about the ‘70s uprising in Italian universities. The book, published in 1977 by a small, politically engaged Italian publisher, became a hit.
But times were changing and his generation’s radical dreams of a world without weapons, class divisions, boundaries, and wars, were fading. Rovelli turned to books for solace and fell in love with science.
He studied quantum mechanics, mostly on his own, occasionally sitting in class for an exam or journal activity. He asked his professors for books to read. If they recommended one, he would buy three on the same topic. He wanted to learn different perspectives and spent hours doing calculations. Enamored by the ideas of Einstein and quantum physics, he decided to study quantum gravity. Rovelli signed up for a Ph.D. but the university had no professors well versed enough in the subject to teach him. So, Rovelli came up with a course to systematically teach himself everything about quantum gravity.
“I wanted to immerse myself in the subject. I didn’t care about publishing papers and getting a job, which is why it was a long time before I published anything,” he says.
After his Ph.D., he received a scholarship from the Italian government and moved to the University of Rome, where he was given a little office in a basement and forgotten. From that basement, he wrote letters to theoretical physicists elsewhere working on quantum gravity asking if he could visit them.
One of his visits was to Chris Isham, a leading figure on quantum gravity. Another was to Abhay Ashtekar who created Ashtekar variables to explain a different way of understanding how gravity works in the universe. A crucial visit was to meet Lee Smolin at Yale.
Rovelli and Smolin became friends, hanging out to solve equations and discuss ideas late into the night. Together, they started loop quantum gravity, a quantum theory of gravity that, unlike other theories of gravity, didn’t rely on a fixed background. They used loops, which are closed paths, to describe the behavior of gravity on a tiny scale. They gave talks in the U.S., Europe, and Asia that generated enormous interest, and Rovelli began writing his first papers.
Rovelli was finally being noticed. Back in Italy, universities now offered him a job, but he decided to join the University of Pittsburgh’s physics department. There, he worked with pioneers in general relativity, such as Ted Newman, and engaged in discussions with philosophers of science, such as John Earman. It was a decade before he returned to Europe and, together with Smolin, developed the ideas of loop quantum gravity into a fully formed theory.
“The quest for quantum gravity is to ask what time and space are. The main result, which took so long to develop, is that if you take general relativity, apply quantum mechanics, and calculate, what comes out is the granularity of space — there is no continuous space. This, I consider to be a physical result of loop quantum gravity,” says Rovelli. The theory has not been empirically verified yet, but it represents a possible solution to the problem of quantum gravity.
“Studying quantum mechanics is about relationships, systems, structures, and orders that make the world,” says Rovelli. As in, meaning is created in relation to surroundings and is not inherent in individual things. He sees quantum mechanics as a way to challenge how we perceive reality and so he stays on course to question temporality, entropy, and the asymmetry of time in our universe. After all, who knows what the future holds?