with as well. Asimov’s basis for psychohistory was applying the laws of probability to large numbers of individual humans to forecast collective human behavior, just as statistical physicists calculate probability distributions of large numbers of molecules to predict the properties of a gas or the course of chemical reactions. Like matter and energy, or space and time, game theory and physics are different sides of a coin. As Pat Benatar would say, they belong together. It’s a neat, tight fit, and it’s a mystery why it took so long for game theory and physics to mutually realize this underlying relationship.

SEPARATED AT BIRTH

Of course, game theory was conceived with fertilization from physical science, as both von Neumann and Nash applied reasoning rooted in statistical physics. Von Neumann referred to the usefulness of statistics in describing large numbers of interacting agents in an economy. Nash alluded to the statistical interactions of reacting molecules in his derivation of the Nash equilibrium. Nash, after all, studied chemical engineering and chemistry at Carnegie Tech before becoming a math major, and his dissertation at Princeton drew on the chemical concept of “mass action” in explaining the Nash equilibrium. Mass action refers to the way that amounts of reacting chemicals determine the reaction’s equilibrium condition, a process described by the statistical mechanics of molecular energies. Borrowing the physical concept of equilibrium in chemical systems of molecules, Nash derived an analogous concept of equilibrium in social systems composed of people. Nash’s math was about people, but it was based on molecules, and that math embodies the unification of game theory and social science with physics. The seed of the physics-society link resided within Nash’s beautiful mind.

That seed has sprouted and grown in unexpected ways, and its fruits are multiplying, feeding progress in a vast range of sciences, from economics, psychology, and sociology to evolutionary biology, anthropology, and neuroscience. Game theory provides the



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