Brute force vs. humans in chess

Chessmaster 10th edition running on Windows XP

It remained an open question whether any amount of brute force computation would ever be adequate to defeat the expertise of top humans. In 1968, IM David Levy made a famous bet that no chess computer would be able to beat him within ten years. He won his bet in 1978 by beating Chess 4.7 (the strongest computer at the time), but acknowledged then that it would not be long before he would be surpassed. It is well that Levy didn't renew his bet for another ten years, because in 1989 he was crushed by the computer Deep Thought in an exhibition match, and would probably have lost even to earlier, lesser computers.

Deep Thought, however, was still considerably below World Championship Level, as the then reigning world champion Gary Kasparov demonstrated in two sterling wins in 1989. It wasn't until a 1996 match with IBM's Deep Blue that Kasparov lost his first game to a computer at tournament time controls in Deep Blue - Kasparov, 1996, Game 1. This game was, in fact, the first time a reigning world champion had lost to a computer using regular time controls. However, Kasparov regrouped to win three and draw two of the remaining five games of the match, for a convincing victory.

In May 1997, an updated version of Deep Blue defeated Kasparov 3.5-2.5 in a return match. While not an official world championship, the outcome of the match is often taken to mean that the strongest player in the world is a computer. Such a claim is open to strong debate, as a truly fair human-machine match is difficult to arrange.

Firstly, in one of the games, Kasparov was not defeated over the board. He resigned in a technically drawn position, perhaps distraught that Deep Blue was playing such human-like moves. He angrily accused the Deep Blue team of feeding human input to the computer as the game was in progress. Thus this defeat should be reckoned more as a psychological loss than an indication of inferior chess ability.

Secondly, there are other players whose playing style is recognised as more effective against computer opponents. Kasparov's strength lies in overwhelming opponents tactically and psychologically, both of which play to the strength of computers, whereas Vladimir Kraminik, who recently defeated Kasparov in a World Championship match, is more content to defend a tenable position, probe for weaknesses, and accumulate small advantages.

Thirdly, it was impossible for Kasparov to prepare to play the machine as he would against a human opponent, as the computer's programming was adjusted between prior matches and the Kasparov match. That incarnation of Deep Blue had no tournament record before the match, whereas the Deep Blue team was able to study and prepare against hundreds of Kasparov's public games.

Finally, a six-game match was too short for Kasparov to adjust to any potential weaknesses of Deep Blue. One great advantage of humans over computers is adaptability. In all his previous encounters with computers Kasparov had finished more strongly than he began, and it is reasonable to suppose that he would have fared better in a twenty-four game match, the traditional length of World Championship matches.

IBM retired Deep Blue after the match and it has not played since. However, other "Man vs. Machine" matches continue to be played. In October 2002, Vladimir Kramnik and Deep Fritz competed in the eight-game Brains in Bahrain match, which ended in a draw. Kramnik won games 2 and 3 by "conventional" anti-computer tactics - play conservatively for a long-term advantage the computer is not able to see in its game tree search. Fritz, however, won game 5 after a severe blunder by Kramnik. Game 6 was described by the tournament commentators as "spectacular". Kramnik, in a better position in the early midgame, tried a spectacular piece sacrifice to achieve a strong tactical attack, a strategy known to be highly risky against computers who are at their strongest defending such attacks. True to form, Fritz found a watertight defence and Kramnik's attack petered out leaving him in a bad position. Kramnik resigned the game, believing the position lost. However, post-game human and computer analysis has shown that the Fritz program was unlikely to have been able to force a win and Kramnik effectively sacrificed a drawn position. The final two games were draws. Given the circumstances, most commentators still rate Kramnik the stronger player in the match.

In January 2003, Kasparov played Deep Junior, another chess computer program, in New York. The match ended 3-3.

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