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Loving and Sharing Science: Pierre-Gilles de Gennes

ETIENNE GUYON

École Normale Supérieure, Paris


This presentation about Pierre-Gilles de Gennes, an intimate friend and a great scientist, recently deceased, should not be too surprising in a meeting devoted to opening the Gate to Understanding, as I aim to present some of the keys he used to open this Gate. This may be of special interest, as we are dealing with a scientific genius whom the Nobel committee which awarded him the prize in 1991, described as “a Newton of the twentieth century.” At the same time, his achievements are accessible to others, as he liked to share his science as much as his love for science with others.

I will not present elements of de Gennes’ long scientific career. This has been amply done in the months following his death. Rather, I will try to share some contents of his “tool box”—his set of keys—in order that others may have access to them. Some are quite general and are (or should be) taught in school. They establish the elements of rational judgment: order of magnitude, reference data, accuracy, and estimation of errors. These elements are often expressed as numbers or as quantitative ratios.1

1

It should not be a surprise that in the midst of the French Revolution in 1790, priority was given by the elected deputies to establishing a standard of meas



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7 Loving and Sharing Science: Pierre-Gilles de Gennes ETIENNE GUYON École Normale Supérieure, Paris T his presentation about Pierre-Gilles de Gennes, an intimate friend and a great scientist, recently deceased, should not be too surprising in a meeting devoted to opening the Gate to Understanding, as I aim to present some of the keys he used to open this Gate. This may be of special interest, as we are dealing with a scientific genius whom the Nobel committee which awarded him the prize in 1991, described as “a Newton of the twentieth century.” At the same time, his achievements are accessible to oth- ers, as he liked to share his science as much as his love for science with others. I will not present elements of de Gennes’ long scientific ca- reer. This has been amply done in the months following his death. Rather, I will try to share some contents of his “tool box”—his set of keys—in order that others may have access to them. Some are quite general and are (or should be) taught in school. They estab- lish the elements of rational judgment: order of magnitude, refer- ence data, accuracy, and estimation of errors. These elements are often expressed as numbers or as quantitative ratios.1 1 It should not be a surprise that in the midst of the French Revolution in 1790, priority was given by the elected deputies to establishing a standard of meas- 45

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46 SCIENCE AS A GATEWAY TO UNDERSTANDING I will spend some time discussing the specific scientific tools that de Gennes used for his studies of magnetism, supercon- ductivity, liquid crystals, polymers, soft condensed matter, and bi- ology. Some recurrent items can be found. • His interest in order/disorder effects in condensed matter as well as the essential role of defects in such structures. These defects should be avoided in some instances. In other cases, such as semiconductor electronics or properties of metal and alloys, they play an essential role. • The use of analogy is a key that opens corridors be- tween different rooms of science. Its use requires rigor and precise comparisons between different problems and should not be con- fused with loose metaphors. A mastery of analogy helped de Gennes build strong bridges between magnetism, superconductiv- ity, liquid crystals, and polymers. • Interfaces are another theme in de Gennes’ re- search. Borders separate different entities, but they should also al- low exchanges across them. It is possible in physics to transfer properties from one layer into an adjacent layer by such proximity effects. In such cases, original behaviors will emerge from this in- terplay. This type of geometry has been often considered by de Gennes in his work. It is also the basic principle behind the Nobel prize awarded to a “normalien” (as de Gennes was), Albert Fert, in 2007: by putting together stacks of very fine layers of a good con- ductor (copper) and of poorly-conducting magnetic iron layers, he was able to obtain some very anomalous magneto-conducting ef- fects that are ubiquitous in today’s memory chips of our computers and portable phones. Quite metaphorically, we could say that these various prop- erties—dialogue between order and disorder, the presence and role of defects, and the interactions at interfaces—are all elements of society! These scientific tools, having a large scope of application ure—the meter or the kilogram—in order to provide a common reference that could be shared among all citizens.

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LOVING AND SHARING SCIENCE: PIERRE GILLES DE GENNES 47 and making recourse to mathematical treatments, should be ana- lyzed in more detail in order to identify where and how genius en- ters into the work of de Gennes. Like a magic wand, he was able to transform a simple observation of phenomenon into a new field of research that others could build upon and that would lead to practi- cal applications for many years to come. Beyond these scientific aspects, I now want to try to iden- tify some of the personal and social influences in his professional life. A first characteristic is the broader culture of which he was a part, where science is only an element of reference next to litera- ture, art, philosophy, or history. The École Normale Supérieure, where he was educated as a student, was created to train some of the best students and to encourage cultural diversity, with an equal number of students in the colleges of humanities and science. In the sciences, we enjoy the benefit of a broad perspective and inter- disciplinary approaches as keys for opening the gate toward new understandings. De Gennes often criticized the fact that our school programs and classroom curricula were too narrowly focused and left little room for such multidisciplinary opportunities. A paradoxical attitude that great creators often have is to admit a certain bit of irrationality in their process of discovery that feeds imagination and, later, organizes creation. Why refuse intui- tion or serendipity if it results in discovery? I like to imagine de Gennes as a seventeenth century explorer of the New World, func- tioning as an astronomer, anthropologist, botanist, historian, and geographer. For de Gennes, an explorer’s attitude is one of extreme curiosity to explore unknown territories of science as a leader, with an open mind and rejection of taboos and preconceived ideas. This often teaches us a new lesson: the need to recognize and make use of one’s errors. Teachers often do not dare say that they do not know something, or even worse, that they have made a mistake. This is clearly an essential part of culture and learning: to profit conscientiously from one’s ignorance when in contact with others. Sharing is not just giving but also receiving, and de Gennes always listened carefully, regardless of the difference in age or education between him and his collaborators or students. Not only

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48 SCIENCE AS A GATEWAY TO UNDERSTANDING did he have a lot of charm and charisma when he expressed in the simplest terms what he had to say, he also liked to circulate in the ranks of the classes and listen very carefully to the questions and comments of the pupils. This attitude has to be promoted to open the Gate. We are not just there to open the “good book” of knowl- edge for others but to listen to what less scientifically educated in- dividuals have to say. An important social aspect he created in his laboratories was the team spirit he instilled. Rather than publishing with sepa- rate names, he would promote joint articles with no specific names to identify the authors: “Orsay group in superconductivity,” “Orsay group on liquid crystals,” etc. Such articles mixed contributions from experimentalists and theoreticians, young and senior mem- bers—even if their partial contributions were of different impor- tance—with the largest part often coming from him. It was very stimulating and challenging for the younger members of the group, and I have also successfully tried to do it for my research groups. I hope that these personal memories and reflections in- spired by my friend Pierre-Gilles de Gennes will offer some keys to promoting science and leading to a better understanding among each other, with rigor as well as tolerance.