Why is rock paper scissors a serious piece of mathematics?

Rock paper scissors is serious mathematics because it is the simplest example of a game where your best move depends entirely on what the other player does, and that is exactly what game theory studies. Game theory is the branch of applied mathematics that models interactions between several players as games of strategy, to predict and choose the moves that pay off best. And it has a crisp answer for rock paper scissors: if you pick each move uniformly at random, nobody can gain an advantage over you. The moment you get predictable, a clever opponent can spot your pattern and beat you.

The field took shape around a Hungarian-American mathematician, John von Neumann. In 1928 he proved his minimax theorem: in a zero-sum game, where one player wins only what the other loses, there is a pair of strategies that lets each side keep its worst-case loss as small as possible. In 1944 he and the economist Oskar Morgenstern published Theory of Games and Economic Behavior, and the public was so curious that The New York Times put it on its front page.

The ideas spread far beyond parlour games. Game theory is now used in economics, biology, computer science, law and political science. Biologists even use rock paper scissors to study the ecology and evolution of bacteria. And the prizes followed: John Nash and two colleagues won the Nobel in economics in 1994, and game theorists have won it five more times since.