Presentation Speech by Professor Stig Claesson of the Royal Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

The discoveries for which Ilya Prigogine has been awarded this year’s Nobel Prize for Chemistry come within the field of thermodynamics, which represents one of the most sophisticated branches of scientific theory and is of enormous practical relevance.

The history of thermodynamics dates back to the early years of the nineteenth century. With the acceptance of the atomic theory – due above all to the works of John Dalton – the view began to be commonly accepted that what we term heat is merely the movement of the smallest components of matter. Then the invention of the steam engine created an increasingly urgent need for exact mathematical study of the interaction between heat and mechanical work.

A number of brilliant scientists, whose names have survived not only in the annals of science but also as terms for important units, contributed to the rapid development of thermodynamics during the nineteenth century. Apart from Dalton himself, we have Watt, Joule and Kelvin, who have given their names to the units of atomic weight, power, energy and absolute temperature calculated from absolute zero. Important work was also done by Helmholtz, Clausius and Gibbs, who adopted a statistical approach to the movement of atoms and molecules and created that synthesis of thermodynamics and statistics which we call statistical thermodynamics. Their names have been given to several important natural laws.

This process of development attained something of a conclusion in the early years of the present century, and thermodynamics began to be regarded as a branch of science whose evolution was essentially complete. However, it was subject to certain limitations. For the most part it could only deal with reversible processes, that is, processes occurring via states of equilibrium. Even an irreversible system as simple as the thermocouple, with its simultaneous conduction of heat and electricity, could not be satisfactorily treated until Onsager developed the reciprocity relations which earned him the 1968 Nobel Prize for Chemistry. The reciprocity relations were a great step forward in the development of a thermodynamics of irreversible processes, but they presupposed a linear approximation. which can only be employed relatively close to equilibrium.

Prigogine’s great contribution lies in his successful development of a satisfactory theory of non-linear thermodynamics in states which are far removed from equilibrium. In doing so he has discovered phenomena and structures of completely new and completely unexpected types, with the result that this generalized, nonlinear and irreversible thermodynamics has already been given surprising applications in a wide variety of fields.

Prigogine has been particularly captivated by the problem of explaining how ordered structures – biological systems, for example – can develop from disorder. Even if Onsager’s relations are utilized, the classical principles of equilibrium in thermodynamics still show that linear systems close to equilibrium always develop into states of disorder which are stable to perturbations and cannot explain the occurrence of ordered structures.

Prigogine and his assistants chose instead to study systems which follow non-linear kinetic laws and which, moreover, are in contact with their surroundings so that energy exchange can take place – open systems, in other words. If these systems are driven far from equilibrium, a completely different situation results. New systems can then be formed which display order in both time and space and which are stable to perturbations. Prigogine has called these systems dissipative systems, because they are formed and maintained by the dissipative processes which take place because of the exchange of energy between the system and its environment and because they disappear if that exchange ceases. They may be said to live in symbiosis with their environment.

The method which Prigogine has used to study the stability of the dissipative structures to perturbations is of very great general interest. It makes it possible to study the most varied problems, such as city traffic problems, the stability of insect communities, the development of ordered biological structures and the growth of cancer cells to mention but a few examples.

Three of the persons who have assisted Prigogine for many years, above all P. Glansdorff but also R. Lefever and G. Nicolis, deserve special mention in this context, because of the important and original contributions they have made towards the development of science.

Thus Prigogine’s researches into irreversible thermodynamics have fundamentally transformed and revitalized the science, given it a new relevance and created theories to bridge the gaps between chemical, biological and social scientific fields of inquiry. His works are also distinguished by an elegance and a lucidity which have earned him the epithet “the poet of thermodynamics”.

Professor Prigogine, I have tried briefly to describe your great contribution to non-linear irreversible thermodynamics, and it is now my privilege and pleasure to convey to you the heartiest congratulations of the Swedish Royal Academy of Sciences and to ask you to receive your Nobel prize from the hands of His Majesty the King.