“The principle of playing chess was actually found to be
reasonably straightforward for a computer. At any stage of the game, each
player has only a limited set of available moves, creating a small set of
alternative board positions. From each one of these, a further set of moves can
be made and board positions created; and from those again, a small set of yet
further moves is possible. At each stage, a ‘tree’ of possible board positions
is produced. Chess programs work by producing a complete set of ‘If I do this,
then you can do this, and then I can do this’ sequences of anticipated moves;
the number of future moves calculated is called the ‘depth’. For each of the
board positions then produced, the program calculates a score for itself and
for its opponent; it chooses the move which minimizes the opponent’s advantage
whilst maximizing its own. This is a strategy called ‘minimax’, created by
Claude Shannon in 1949 and perfected by Alan Turing the following year. The
first computer program written to execute minimax for chess was produced in
1956 at Los Alamos, followed two years later by a more powerful system at IBM.
Using minimax and a depth of only five moves, chess programs
can trounce all but the most experienced of club players; given a slightly
greater depth, the programs can beat all but the most experienced chess grandmasters.
In 1997, when a dedicated computer system developed by IBM (called ‘Deep Blue’
and capable of examining 200 million chess positions per second) was allowed a
depth of 14 moves, it beat the then world champion, Gary Kasparov. Although
chess is indeed a striking example of human intelligence, and although
computers are not programmed to play in anything like the same way as humans apparently
do, it seems to be at least one human-like thing that can better performed by
computers.”
That “five moves” bit is interesting, I hadn't heard that
before.
