Carlo Rovelli: “French science education is too rigid”

TTheorist of quantum loop gravity (with Lee Smolin), a professor at the University of Aix-Marseille, but also in Canada, Carlo Rovelli is not only one of the most important scientists of his time, he is also a detailed author. In 2015 he published Seven short physics lessons to Odile Jacob, before dedicating a biography to Anaximander of Miletus (Dunod), a pre-Socratic scholar formed by Thales who confronted the concept of infinity in VI.i century before the Christian era. After a light test, The order of time (Flammarion), Carlo Rovelli recounts today, in a new book *, the conditions in which quantum physics was born. Designed in the manner of a historical novel, where pages of philosophy would have slipped, his book makes us discover in an educational way one of the most complex notions of contemporary physics.

Point: It all started in the summer of 1925 on the island of Helgoland in the North Sea. Werner Heisenberg, then 23, conceived the idea that electron jumps from one orbit to another respond to a logic dictated not by a constant physical variable, but by an evolving table of numbers that predicts these ends. now. incomprehensible movements more satisfactorily. What do you think is the trigger?

Carlos Rovelli: I think the “click”, as you say, was the combination of several ingredients: first Heisenberg’s total mental immersion in the problem, but also his very physical and concrete way of tackling this riddle based on not in sophisticated mathematical demonstrations, but rather in his free imagination and examination of the very nature of reality. Heisenberg’s openness to radical philosophical ideas (especially those of Ernst Mach) was also important. I will add the influence of Max Born and indirectly of Albert Einstein, who understood the need for a big step in physics. But we could add the physicophilosophical conversations with Niels Bohr, the father of the quanta, and also, most likely, Werner’s young age … All these parameters are an explosive mix. It was this cocktail that allowed Heisenberg to take a fresh look at the problem he was facing.

This discovery is the culmination of the reflections of a group of scientists, among whom, as you said, are Albert Einstein and Max Born, but also Erwin Schrödinger and Wolfgang Pauli. What do these men have in common?

They share a burning passion: to seek understanding. Another common denominator is the absence of fixed ideas. Everyone is ready to change their minds. For the rest, they have very different personalities, abilities and skills from each other.

Is it in spite of their common way of apprehending the world that allows them to explore this path of the few?

On the contrary! It is their differences that allow the success of a great collective influence.

Werner Heisenberg’s discovery, which we will soon call “quantum mechanics,” opens the door to a whole host of inventions: the domain of the atom, quantum computing, to name just two. Which do you think is the most impressive?

More than a particular invention, it is the fact that all the properties of the elements, including the very structure of the periodic table of the elements, follow a single equation!

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Quantum physics takes its name from these quanta, or energy grains, that would explain the strange behavior of electrons. They also dictate the amazing way electromagnetic waves propagate. Richard Feynman wrote that no one could understand how much …

Richard Feynman did not write that no one can understand how many, he wrote that no one understands them. The difference is in the weight. It’s one thing not to understand, it’s another not to be understood at a given time. In this second case, it is still possible to understand …

If you don’t understand them, how would you represent them if you were asked for an analogy? So why?

It depends. Photons are large in light. The gravitational field quanta are then from space. Granularity is not the hardest part to understand: sand is granular. The hardest part to understand is their “relationship.” These are not entities. These are things that manifest: light manifests itself in granular form, like photons.

This way of appreciating reality by resorting to a more subtle approach than the observation of the simplistic materialism of particles in space makes the mind admit (like Anton Zeilinger) that complex relationships can unite entities sometimes separated by immense distances.

Yes, that’s right.

How, then, can this scientific truth be considered without falling, at one time or another, into seemingly irrational considerations: one of them is the coexistence of parallel worlds where different events would take place (at the same time)? that they could interact with another; the other is the fact that hidden variables prevent us from reading our reality. We pour it Matrix… Does this mean that only imagination, dreams, and fiction can enable us to understand quantum mechanics?

I think science has often revealed seemingly strange new things to us, but then you develop a good intuition and get used to it. It is the strength of the habit. No one is shocked today by the fact that the Earth moves, that it revolves around the Sun. However, it was difficult to digest at the time it was theorized. I think the same will happen with quantum theory. We will assimilate it … little by little.

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The quantum entanglement at the heart of the reality of this “new” physics, however, opens up dizzying prospects that result from seemingly inconceivable correlations. We must accept an idea that is not at all obvious: indeterminacy, or at least the subjective interpretation of probability by virtue of this “quantum Bayesianism” that gives its name to QBist theory. Does this mean that we must resolve a form of absolute relativism where the truth would be different for each observer, depending on the point of view it embraces? That would be scary, wouldn’t it?

I think you’re exaggerating there. When we discovered that the Earth was moving, we found it much more frightening. Quantum rationalism is not subjectivism and does not challenge the usual notions of objectivity. A stone falling on our heads will hurt us as before.

The story of the famous Schrödinger cat locked in a box and alive and dead forces us to consider the possibility that several realities coexist at the same time!

Bohr spoke of “the impossibility of clearly separating the behavior of atomic systems from the interaction with the measuring apparatus that serves to define the conditions under which the phenomenon appears.” This observation explains the discovery at the heart of quantum theory: the impossibility of separating the properties of an object from the interactions during which these properties manifest and from the objects near which they manifest.

On the way to the knowledge of the quanta, we meet very few French (Louis de Broglie is the most famous). Because ? Is it tied to the same Cartesian way in which our engineers are trained?

I think French science education is too rigid. “Formative” mass. He produces good engineers, good calculators and even very good mathematicians. But they are not good theoretical physicists. Therefore, we need less formalism, more freedom of spirit.

Quantum physics owes much to scientists trained in philosophy, often also highly politically engaged (Adler or Bogdanov, to name just two). Did you have to be idealistic to give birth to this quantum mechanics?

Probably yes. You have to know how to dream. Perhaps this is why the most fruitful period for French science was the Revolution.

* Helgoland, the meaning of quantum mechanicsby Carlo Rovelli, Flammarion editions, 249 pages, € 21.90.

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