Personnal Recollections about the Birth of String Theory * 1 Factorizing the Pomeron with Joël Scherk at Cern 2 Combining and Splitting Strings with Jean-loup Gervais in Orsay 3 Compactifying Strings with Joël Scherk at Lptens

1 In 1969, I was finishing my Ph.D. in Orsay under the supervision of Michel Gourdin on phenomenological works related to e + e − annhilations. These works allowed me to deepen my knowledge in particle physics as well as to learn mastering difficult calculations. However, I was more attracted by more formal research (that we would like being able to say more fundamental !). The theoretical physics laboratory in Orsay was also hit by the explosion of activity which followed the paper of Veneziano, and a group of people began to work on dual models: Bouchiat, Gervais, Nuyts, Am-ati who was spending a sabbatical in Orsay, as well as younger researcher Neveu, Scherk and Sourlas. My first encounter with dual models was to rebel against this too fashionable growing activity. With Jean Nuyts I asked if there could be some other example of a s-t dual amplitude with only poles in both channels: we found an example with poles lying on a logarithmic trajectory instead of a linear one [1]. However this amplitude led to many unsatisfactory physical conclusions and I joined the main stream. In 1970, much work was devoted to the dual multiloop amplitude, in particular by Kaku and Yu [2]. Lovelace [3] and Alessandrini [4] showed the relation between these amplitudes and the Neumann function associated with a sphere with handles. I then began a rather technical work, the study of a multiloop operator and its dual properties [5]. I had the chance to get a fellow position at the theory division at CERN for 2 years (1971 and 1972). This was the first chance of my career. The second one was to " integrate " the dual group at CERN which was led by Daniele Amati. In this group, there was not only a very stimulating scientific atmosphere, but also a very friendly one. At that time the theory division had more than a hundred people and the fellows who were not associated with a group could easily stay isolated. Then arrived my third and most important chance, the venue of Joël Scherk and the beginning of our collaboration. I knew of course Joël from Orsay and had had discussions with him although not belonging to the same " team " (Bouchiat-Meyer for Joël, Gourdin for me), but I had had no opportunity to work with him. As early as that stage, Joël was a …