Physics

Gilles Cohen-Tannoudji: "The History of Materiality Remounts the Time of the History of Matter"

Wednesday, 25 December 2013 11:11By Jérôme Skalski, l'Humanité | Interview

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Translated Friday 20 December 2013, by Henry Crapo.

Some days before the official presentation of the Nobel Prize in Physics to François Englert and to Peter Higgs for the theory of the so-called Higgs boson, Gilles Cohen-Tannoudji, physicist and philosopher, explains what is involved in this discovery and in this human adventure.

Huma: Among those things that are said about the Higgs boson 
is the assertion that it is that by which the constituents of matter acquire their mass. But isn’t mass 
an immutable property of matter ?

Gilles Cohen-Tannoudji: In Physics, matter is characterised with the help of three concepts : energy, mass and what may be called "quantity of movement", or momentum. In classical physics, the physics with which we are most familiar, mass is indeed an immutable property of matter. There is no matter without mass, on the one hand, and, on the other hand, there is no energy without movement. Furthermore, there is a relationship that tells us that energy is the square of the momentum divided by twice the mass. This is called kinetic energy. Finally, a moving body may in principle be accelerated indefinitely.

With the theory of relativity, the foundation of elementary particle physics, things change. This theory takes into account the fact that light always propagates at the same speed, regardless of the position or motion of the observer who describes the motion, and this speed can not be exceeded. Moreover, it involves a different relationship between acceleration and mass. When a body approaches the speed of light, you can no longer increase its speed. You can only increase its mass or inertia. Ultimately, if you could reach the speed of light, the inertia of the body would become infinite. The relationship between mass, energy and movement is completely changed. This is the famous "E equals m c-squared" of Einstein.

It also means that, even at rest, a particle contains some energy, a potential energy. But it also means that the mass may be zero. This is the case when the particle goes at the speed of light, as does light itself. It has zero mass, but it has energy. In classical physics, there is no matter without mass, and no energy without movement. In relativity, there is no matter without energy and mass may be zero. This is an extremely non-intuitive, but essential, notion. We had always imagined that matter was mass, and that if there was no mass, there was nothing. In the theory of relativity, this is not true. Energy precedes mass. This also means that one can easily imagine a state of the archaic universe in which no particle had mass. That is to say, we had sorts of particles of light everywhere. Compared to the current state of the universe, there was necessary a mechanism that would make particles massive.

Huma: And this is where the Higgs boson comes in, a particle whose discovery, so to speak, poses the keystone of the standard model in physical theory?

Gilles Cohen-Tannoudji: Yes, but also to meet the challenge of uniting two of the four fundamental interactions that describe the physics of electromagnetic interaction, which is responsible for the light, and the weak interaction, responsible for the lives of the stars, thermonuclear fusion that powers their energy, and certain radioactive decays. It was a very big challenge for Physics, because without this unification we have no theory for the weak interaction.

Now there was a contradiction when we wanted to unify the electromagnetic interaction and the weak interaction, because the particles that carry the weak force, the W +, W- and Z0, have mass, while the photon, which carries electromagnetic interaction, has not: it was necessary to resolve this point. From a scientific standpoint, the mechanism of the Higgs boson is a trick to overcome this contradiction. It is a theoretical or epistemological solution, but not an ontological solution.

But the discovery of the Higgs boson comes at a moment when Cosmology and particle Physics are collaborating more effectively to compose a grand narrative of the universe, which acquires a truly ontological dimension: that is to say that the universe has a history and that it is in the history of the universe that things happened like that. This story tells us that, indeed, there was a moment in the history of the universe, near the big bang, when particles had no mass, and that then they became massive. This is a turning point.

Huma: A turning point also philosophically, in that this discovery can be seen as a return of materialism, of Epicureanism for example, which argues the idea of ​​the historicity of nature, the idea that the universe has a story that derives from its very nature ?

Gilles Cohen-Tannoudji: Yes, it’s a great moment. This is a great moment for materialism. This is a monumental contribution to philosophy. What we have come to understand, and to have placed on an experimental basis, is that matter has a history, really. The scientific conception of matter is materiality. To say it with a formula, in the discovery of the Higgs boson, the history of materiality gives depth in time to the history of matter. This is a great philosophical lesson.

Yes, the idea of the ​​historicity of nature is Epicurean but it had a defect because this idea was dualistic. With on one hand, atoms (the matter) and the void, and, on the other hand, the clinamen, a spontaneous small declination of atoms in a void. For example, Einstein always refused the idea of dualism. Well, we have overcome this dualism: we should not have a substantialist vision of matter considered in the philosophical sense. The term particle is not very adequate. Particle, it seems to mean little thing. Matter is not made ​​up of small things. In fact, at first, it is not particles, but fields. This is a very important point. A concept of Gilbert Simondon can be evoked in this regard, that of individuation. In quantum theory, the fields can individuate in the form of particles or of waves; this is how it was possible to overcome the dualism that Einstein refused without being able to overcome it. That’s what is more like the way we have to see things. One of the first stages of individuation is the acquisition of mass. This is what we have brought to light experimentally, with the Higgs boson.

Huma: However, some have spoken of the "God particle." In your book [1], following Michel Serres, who wrote the afterword, you yourself seem to adopt the saying "Let there be light — and there was light" from the biblical narrative, as an adequate expression to describe the first moment of the grand narrative of the universe, and in support of its discovery. But if energy precedes mass and if mass comes from energy, is it not rather the formula by Goethe that should be highlighted? In the beginning was action?

Gilles Cohen-Tannoudji: Correct. That’s right, yes. And the Planck constant, the universal constant in the origin of any quantum physics, is action (product of energy per time). The essential idea is that there is emergence. This is one of the great contributions of the Higgs boson, that at the most fundamental level, there is already emergence. Emergence, usually, is considered at the macroscopic level, that is to say, we used to say that "not everything is the sum of its parts". Consider a complex system; we realize that there may arise or emerge properties that are not present when the system is analysed at lower levels of structure. But this rather naive vision is out of date. What happens is that we have a methodology that has been called the methodology of effective theories, which allows us to think of this emergence as a universal process. Everywhere there is emergence. And we can do study it in a quantitative and predictive manner. This is a quite extraordinary achievement.

That said, a few words about the beginning of your question. Although we carefully avoided talking about the "God particle", we have not been able to prevent ourselves from seeing a striking analogy between the transition triggered by the Higgs mechanism, in which light and matter separate and where each acquires the properties they have today, and the "fiat" of the biblical narrative.

Huma: Beyond its scientific and philosophical implications, you describe the discovery of the Higgs boson as both an "exemplary human adventure" and as an "antidote to Tina." Can you enlighten us on this double dimension of adventure at CERN?

Gilles Cohen-Tannoudji: The history of CERN, from its creation to its triumph with the discovery of the Higgs boson is indeed an exemplary human adventure. In the fifties, after the dramatic upheavals of the first half of the twentieth century, when Europe was devastated, when, having been first in Physics before the war, Europe lost its scientists, its facilities and major research centers, the creation of CERN met the objective of reconstructing a Europe of science, beginning with the atom. After the war, the atom, or more specifically the nucleus of the atom, is at the center of all attention, with respect to both strategic and economic planning. But the founders of CERN, some eminent scientists and some farsighted politicians, had the intelligence to understand that the atom is also central to questions of knowledge, of basic research, and by providing the CERN with the status of research center, with stable financing, guaranteed by an international treaty, which allowed it to implement a long-term strategy, exclusively motivated by the needs of basic research. It can not be excluded that the ulterior motive of the founders was to establish a scientific community that, as was the case when it was necessary to counter the mortal danger of a nuclear weapon in the hands of the Nazis, could be mobilized to deal with some other eventual global threat. I think that such a concern is still valid. We must see indeed that the extraordinary human adventure represented by this research and the discovery of the BEH ​​boson occurs in a context that is not unlike that of the early twentieth century: the current ascendancy of the standard model reminds one of classical physics in those earlier days. The tremendous growth of information technology made ​​possible by the quantum and relativistic revolution is reminiscent of the techniques of the industrial revolution in the eighteenth and nineteenth centuries. But at the same time the systemic crisis into which is plunged the world economy, the prospect of depletion of energy resources and disturbing beginnings of global climate change bring fear of the arrival, on a global scale, of convulsions comparable to those that marked the first half of the twentieth century. That an international organization such as CERN, founded in the aftermath of the tragedies of two world wars, with, as single purpose, this progress of human knowledge, has been able to meet the formidable challenges of the BEH boson search, is this not a reason for hope in the ability of human civilizations to reject the inevitability, to overcome crises, no matter how serious they may be? To borrow a phrase used by Louise Gaxie and Alain Obadia in their beautiful book We have the choice! [2] we see that the operation and strategy of CERN have shown that it is possible to refuse the injunction and Thatcher neoliberal " Tina ": "there is no alternative": "there is no alternative."

A boson named Higgs

Neutrino, muon, quark, gluon ... the names of members of the family of elementary particles may seem strange to the uninitiated. In The Boson and the Mexican Hat, a book co-authored with Michael Spiro, Gilles Cohen-Tannoudji, doctor of physics, emeritus researcher at the Laboratory for Research on Materials Science ( LARSIM ), a specialist in philosophy of science, invites us to enter into the world of these ultimate elements of matter. Postulated in the mid-1960s, the Higgs boson or BEH boson ( Brout, Englert, Higgs ), has seen its existence demonstrated experimentally July 4, 2012. This discovery, made in the particle accelerator LHC at the European Council for Nuclear Research (CERN), is a milestone in the history of physics and in our understanding of Nature. Made on the basis of unprecedented international collaboration, it testifies in favor of an alternative model of cooperation turning its back on the logic of hegemony, competition and competition. The official presentation of the Nobel Prize in Physics 2013 François Englert and Peter Higgs was held in Stockholm Tuesday, December 10, 2013.

[1] Gilles Cohen-Tannoudji and Michel Spiro, le Boson 
et le chapeau mexicain ("The Boson and the Mexican Hat), éditions Gallimard, collection « Folios essais », Paris, 2013, 544 pages, 9,90 euros.

[2] Nous avons le choix ! Penser le souhaitable 
pour ouvrir d’autres possibles, "We have a choice!
 think of what is desirable, in order to open other possibilities", Louise Gaxie
and Alain Obadia, Foundation editions Gabriel Peri, 
Pantin, 2013, 525 pages, 15 euros.

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JÉRÔME SKALSKI

Jérôme Skalski is a contributor to l'Humanité.

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