It was a war of titans you likely never heard about. One year ago, two of the world's strongest and most radically different chess engines fought a pitched, 100-game battle to decide the future of computer chess. On one side was Stockfish 8. This world-champion program approaches chess like dynamite handles a boulder--with sheer force, churning through 60 million potential moves per second. Of these millions of moves, Stockfish picks what it sees as the very best one--with "best" defined by a complex, hand-tuned algorithm co-designed by computer scientists and chess grandmasters.
The eye-catching victory of AlphaZero, the artificial-intelligence program that taught itself to play chess, over the No 1 computer engine Stockfish, has evoked comparisons with human legends. Garry Kasparov has written a foreword for a newly published book in which he says AlphaZero's "dynamic, sacrificial style … mirrored my own … AlphaZero prefers piece activity and attacking chances". He also compares it to "Alexander Alekhine, with dazzling sacrifices and a fondness for unbalanced positions". The book is Game Changer by Matthew Sadler and Natasha Regan (New in Chess, £19.95) which features an in-depth analysis by Sadler, a grandmaster and former British champion, of recurrent motifs in AlphaZero's style which can be adapted by human players. Among the many themes which Sadler identifies, AZ likes Harry the h pawn to spearhead its long-term attacks with an advance to h6 which entombs a rook or bishop at h8.
The recent world chess championship saw Magnus Carlsen defend his title against Fabiano Caruana. But it was not a contest between the two strongest chess players on the planet, only the strongest humans. Soon after I lost my rematch against IBM's Deep Blue in 1997, the short window of human-machine chess competition slammed shut forever. Unlike humans, machines keep getting faster, and today a smartphone chess app can be stronger than Deep Blue. But as we see with the AlphaZero system (see pages 1118 and 1140), machine dominance has not ended the historical role of chess as a laboratory of cognition.