Giorgio Parisi, Professor at the University of Rome, is a theoretical physicist of exceptional depth and scope. He has contributed at the highest level to particle physics, computer science, fluid mechanics, theoretical immunology, etc. etc. Today we honor him for his outstanding contributions to statistical physics, and particularly to the theories of phase transitions and of disordered systems. Among these many contributions, I would specifically mention Parisi's early work in which he showed how conformal invariance can be used in a quantitative way to calculate critical exponents. He was also the first to really understand that one can derive critical exponents through expansions of the beta function at fixed dimensions, avoiding the convergence problems of the epsilon-expansion. The opened the way to the current best theoretical estimates of exponents. Another important achievement concerns the mapping of the branched polymer problem in d-dimensions onto that of the Lee-Yang edge singularity on d-2 dimensions. Most recently, Parisi's work on interfaces in disordered media and on the dynamics of growing interfaces has had a large impact on these fields.

However, Parisi's deepest contribution concerns the solution of the Sherrington-Kirkpatrick mean field model for spin glasses. After the crisis caused by the unacceptable properties of the simple solutions, which used the "replication trick," Parisi proposed his replica symmetry breaking solution, which seems to be exact, although much more complex than anticipated. Later, Parisi and co-workers Mezard and Virasoro clarified greatly the physical meaning of the mysterious mathematics involved in this scheme, in terms of the probability distribution of overlaps and the ultrametric structure of the configuration space. This achievement forms one of the most important breakthroughs in the history of disordered systems. This discovery opened the doors to vast areas of application. e.g., in optimization problems and in neural network theories.

The Boltzmann Medal for 1992 is hereby awarded to Giorgio Parisi for his fundamental contributions to statistical physics, and particularly for his solution of the mean field theory of spin glasses.

Updated 18 June 1999.