Time invariance is usuallyTime invariance is usuallybroken within a lifetimebroken within a lifetime

Nel mezzo del cammin di nostra Nel mezzo del cammin di nostra vita...vita...

Midway upon the journey of our Midway upon the journey of our life…life…

My dear Jean-Paul,

You have reached the ripe age of 60 which endows you not only with a past but also with a long future. This is the age which Dante described as:

Nel mezzo del cammin di nostra vitaMidway upon the journey of our life

Generations of physicists arise and disappear much faster than human generations, in spite of the fact that physicists show definite signs of being human. It takes about fifteen years for a woman to produce a reasonable human being. It takes barely three years to make a physicist. You may not realize it yet, but you have already lived through many generations of physicists.

1969 (circa)

Jean-Paul

You had a startling beginning. Indeed you were most successful in school. The preceding picture shows a picture of your class in Tours. We clearly distinguish one man in the front row who is not looking into the camera and who is Jean-Paul. But let us take a closer look.

Bernard Bigot

Jean-Paul Blaizot

We see Jean-Paul in the front row. He was going to become the director of the Service de Physique Théorique, the theory group in Saclay. But two rows behind him is standing Bernard Bigot, who is presently the head of the French Atomic Energy Commission, to which Saclay belongs. So where are the signs predestination?

Jean-Paul, you are not looking into the camera. You are no doubt looking into the future. What future did you actually see?

Was it physics?

Or were you looking forwards to your next vacation when you could take your girlfriend to the beach?

You were then admitted to the Ecole Normale Supérieure, the most difficult school to be admitted to in France. And yet this was only a beginning. I had the privilege to witness your official birth as a physicist. You turned up one fine day at the end of a physics exercise session at the Ecole Normale telling me that you were interested in doing a bit of research in nuclear physics. This was in the early seventies at a time when mean field calculations of nuclei were just beginning and I suggested that you calculate the normal vibrations of nuclei in order to see if one could relate their energies to the compressibility of nuclear matter. Indeed the monopole excitations of several nuclei had just been identified and measured for the first time. After suggesting this, you simply disappeared for a while, and then suddenly you turned up with the results. Am I not right in saying that the only bit of advice you sought from me was whether it was better to plot the monopole excitation energies as a function of the compressibility or, instead, the compressibility as a function of the excitation energy? I cannot recall which was chosen and published. But I do recall that your evaluation of nuclear matter compressibility was what we believe it to be today and that you published a most quoted Physics Report on this work which was also the subject of your PhD. And I wish to add that you felt no need to dwell further upon the problem. Nor did you ever become, as so many other theoretical physicists, a slave to your computer programme.

19751975

This is what you looked like when you were a nuclear physicist. In those days, the fashion required all nuclear

physicists to wear a casquette on the head:

But fashions change and today you can be seen But fashions change and today you can be seen in Venice all dressed up to see La Tosca at La in Venice all dressed up to see La Tosca at La Fenice, looking more elegant than Pavarotti!Fenice, looking more elegant than Pavarotti!

In 1977 you spent a year at the Niels Bohr Institute in Copenhaguen and in 1980 two years in the Physics Department of the University of Illinois in Urbana Champaign, where you studied the quark-gluon plasma and high energy collisions of heavy nuclei, applying relativistic hydrodynamics. This is where you met Gordon Baym, with whom, together with Frank Laloe and Dominique Vautherin, you later solved the notoriously tough problem of determining what change in the critical temperature of a Bose-Einstein condensate, is produced by the interaction between the particles. In the following picture we are in Urbana with Gordon Baym, Bengt Friman, Pandharipande, Usmani and the terrorist on the right is Jean-Paul.

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In 1985, you published a book on the Quantum Theory of Finite Systems. I read it and I can - objectively - say that it is a very good book! Then in 1997 you published another book in French on symmetries in microscopic physics.

Let us take a glance on the subjects you have worked on. I will not show a list of your publications. That would take too long. I simply wish to illustrate the variety of subjects to which you have made important contributions. I also show the names of several people with whom you collaborated at the time and who, for the most part, are present at this diner.

1975-1984 Nuclear compressibility and breathing modes (including a Physics Report) Quantization of time-dependent self-consistent fields (with Marshalek) A variational principle for transition amplitudes (with Ripka).

1984-1994 Hydrodynamics of ultra-relativistic heavy ion collisions. Skyrme model and effective chiral action for QCD. Quantum theory of finite systems (book, with Ripka) Jets in expanding quark-gluon plasmas (with McLerran) Similarity flow in relativistic hydrodynamics (with Ollitrault) Non-linear distortions of rotating solitons (with Ripka) The fate of a J/Psi produced in a nucleus-nucleus collision (with Ollitrault) Soft pion emission in high energy heavy ion collisions. (with Krzywicki) Quantum mechanical model of colour transparency. Kinetic theory and quantum electrodynamics at high temperature (1993) (with Iancu) Soft collective excitations in hot gauge theories (with Iancu) Non-Abelian excitations in the quark gluon plasma.

1995-2005

Gauge structure and semi-classical aspects of hard thermal loops Quasiparticles in hot gauge theories A Boltzmann equation for the QCD plasma The transition temperature of the dilute interacting Bose gas (with Holzmann, Laloe, Baym and Vautherin) Symétries et physique microscopique (book with Teledano) The quark gluon plasma: collective dynamics and hard thermal loops (with Iancu, Physics report) Gross Neveu model at finite temperature at next to leading order in the 1/N expansion (with Wschebor) Renormalization of phi derivable theories in scalar field theories (with Iancu and Reinosa) Duality and Pomeron effective theory for QCD at high energy and large Nc (with Iancu and Trantafyllopoulos)

2005-2009

High energy collisions in the color glass approach (with Gelis and Venugopalan) Isolating vacuum amplitudes in quantum field calculations at finite temperature (with Reinosa) A new method to solve the non perturbative renormalization group equations. (with Wschebor and Mendez Galain) The Landau-Pomeranchuck-Migdal effect in a quark gluon plasma and the Boltzmann equation (with Baym, Gelis and Matsui) Confinement, turbulence and diffraction catastrophes (with Nowak)

We see successively appearing Jean-Yves Ollitrault, who is now the deputy director of the IPht, the Saclay theory group, Edmond Iancu, Francois Gelis and Urko Reinosa. They all, except François Gelis, began as your PhD students. You certainly deserve some credit for the fact that your students all became important physicists in their own right. Much of their work is being discussed in the present meeting and so I need not dwell on their achievements.

Nowadays that publications have become so numerous, it has become fashionable to keep count of the number of publications of every physicist. I believe it is time for a change. It would be far more useful not to quote the number of his publications nor the number of citations of his papers, but, instead, one should calculate, for each physicist, the entropy of his publications. My dear Jean-Paul: I have calculated the entropy of your publications, and I found it was wonderfully low! May I remind you that information is neg-entropy or, to put it another way, low entropy is rich in information. And your low entropy is real cool! What occasionally exasperates your friends and colleagues is that you always remain cool. You excel in the art of maintaining low entropy, as most real stars do.

You consecrated 6 years of your life as director of the Service de Physique Théorique in Saclay. And after that 4 more years as director of ECT* in Trento. This is simply to say that you have given a lot, both to physics and to physicists. In your research but also in the time you have devoted to several labs, you have interacted with others and I believe that you have improved the physics (allow me to say the life) of all those who came in contact with you. The following picture shows the instant when ECT* in Trento became directed by Achim Richter, who is also at this meeting.

20082008

But you still have a long way to go. It is like mountain climbing in which you also excel. One is always mislead in believing that one has reached the summit, when in fact another always pops up behind. The trouble with summits in research is that they are not indicated on the maps. How could they be? They are sometimes hard to identify even after reaching them. Looking back one can easily picture a life as a straight line trajectory because every cause has been followed by its effect. But your future, dear Jean-Paul, or any other for that matter, cannot be viewed this way. Dante was quite right in continuing his story thus:

Nel mezzo del cammin di nostra vitaNel mezzo del cammin di nostra vitaMi ritrovai per una selva oscuraMi ritrovai per una selva oscuraché la diritta via era smarrita.ché la diritta via era smarrita.

Midway upon Midway upon the journey of the journey of our life, I found our life, I found myself within a myself within a dark forest, dark forest, bbecause the ecause the straight path straight path had been lost.had been lost.

Our future is possibly embedded in this dark forest. Under these circumstances, I invite you now to raise our glasses and thank this Lord (JPB) for being among us!