Zero player game

The term zero player game generally refers to games that do not have human players, but also to games that do not have any player, human or non-human.

Most video games can be set up so that the computer plays against itself through the use of artificial intelligence (AI): a classic example is chess. Since these games already have artificial intelligence, the possibility of letting the computer play against itself is usually added as an extra that does not take much additional programming time. In many cases, this can reveal AI issues, when all players employ similar strategies. In some video games like the classic shareware Scorched Earth, AI-controlled players continue to play even after all human players have lost.

Entirely computer-controlled video games are also used to expose graphics or gameplay, especially in arcade games.

Genetic programming can be used to develop more or less successful strategies against other players through natural selection. Most video games used in game theory are zero-player games in their common definition, where many iterations of the simulated player's actions are used to determine the optimal strategy for a particular problem such as the prisoner's dilemma. This simulation does not have to take place on a computer, but it is a common case in complex problems with many iterations and strategies.

The movie War Games popularized the idea of using computers to examine strategy. In said film, a computer controlling the US defense arsenal played many iterations of a "global thermonuclear war" against himself using all possible strategies, taking time to play them so he is replaced to play "three in a row" with zero players and came to the conclusion that "the only winning move is not to play".

The classification of programs as games that do not have players is more problematic. John Conway's Game of Life is probably the best known game that meets the definition, along with other cellular automata, but even here it can be debated whether it is a game and whether it has players (cells). Complex simulated worlds such as the Creatures and Sim Earth video games when there is no human intervention are often included in this category. Perhaps the evolutionary games classification is more appropriate. Screensavers are not usually interactive, but in each case it is doubtful whether they can be classified as games.

The first program capable of winning a ranked match against a professional player (first Fan Hui 2dan, then Lee Sedol 9dan) on a 19x19 goban, AlphaGo improves his game level by facing himself.