How Computers Play Chess Peter Barnum November 15, 2007 Artificial Intelligence 101

“This … raises the question ‘Can a machine play chess?’ It could fairly easily be made to play a rather bad game. It would be bad because chess requires intelligence.” –Alan Turing 1946

“The decisive game of the match was Game 2…we saw something that went beyond out wildest expectations…The machine refused to move to a position that had a decisive short-term advantage - showing a very human sense of danger.” – Garry Kasparov 1997

What move should we make?

How a computer decides

Uh oh!

“If I make this move, what’s the worst thing my opponent could do?” Adversarial search

Examining all possible moves … Can I make a move that will allow me to win and prevent my opponent from winning?

Wait, that’s easy! 35x35 …=35 N For a game with 6 moves per player: =3,379,200,000,000,000,000 possibilities If a computer can check one billion moves per second, it would take over 100 years

What to do? Can we avoid searching all possibilities? Can we pre-compute anything? Can we approximate the search?

Stuart Russell and Peter Norvig Artificial Intelligence: A Modern Approach Stanford Encyclopedia of Philosophy References