Obituaries: Ilya Prigogine

he divided his time between Brussels and Austin. Ilya Prigogine was the second son of Roman Prigogine, a factory owner and chemical engineer, and Julia Wichman Prigogine, who had been a student at the Conservatory of Music in Moscow. Ilya studied chemistry at ULB, although on entering the university was interested more in history, archaeology, and music, especially piano. According to his mother, he was able to read musical scores before the printed word; he once won a prestigious piano competition. From his adolescence, he read widely. A lasting influence was Henri Bergson, especially the philosopher's remark on time: " The more deeply we study the nature of time, the better we understand that duration means invention, creation of forms, continuous elaboration of the absolutely new. " His interest in chemistry developed in a rather unusual way. He and his parents had agreed that he would pursue a legal career, and he decided that the best way to begin would be to understand the mind of the criminal. While looking for books on criminal psychology, he discovered a volume on the chemical composition of the brain. His plans to study law soon gave way to a passionate interest in chemistry. At the university Prigogine was strongly influenced by two professors: Théophile De Donder and Jean Timmermans. It was De Donder who inaugurated the course in thermodynamics for engineers that would lead to the birth of the Brussels thermodynamics school. To understand the originality of De Donder's approach, Prigogine believed, it was necessary to recall the fundamental work of Clausius, and his formulation of the second law of thermodynamics as an inequality: " Uncompensated heat " —or, in more modern terms, entropy production—is positive. The inequality refers, of course, to phenomena that are irreversible, as is any natural process. Until the middle of the 20th century, the latter were poorly understood. They appeared to engineers and physical chemists as " parasitic " phenomena, which could only hinder something—here the productivity of a process, there the regular growth of a crystal—without being of any intrinsic interest themselves. The usual approach, then, was to limit the study of thermodynamics to an understanding of equilibrium laws, for which entropy production is zero. This could only make of thermodynamics a " thermostatics. " In this context, the great merit of De Donder was to extract entropy production out of this " sfumato, " relating it …