A mere 19 months after dethroning the world’s top human Go player, the computer program AlphaGo has smashed an even more momentous barrier: It can now achieve unprecedented levels of mastery purely by teaching itself. Starting with zero knowledge of Go strategy and no training by humans, the new iteration of the program, called AlphaGo Zero, needed just three days to invent advanced strategies undiscovered by human players in the multi-millennia history of the game. By freeing artificial intelligence from a dependence on human knowledge, the breakthrough removes a primary limit on how smart machines can become.

Earlier versions of AlphaGo were taught to play the game using two methods. In the first, called supervised learning, researchers fed the program 100,000 top amateur Go games and taught it to imitate what it saw. In the second, called reinforcement learning, they had the program play itself and learn from the results.

AlphaGo Zero skipped the first step. The program began as a blank slate, knowing only the rules of Go, and played games against itself. At first, it placed stones randomly on the board. Over time it got better at evaluating board positions and identifying advantageous moves. It also learned many of the canonical elements of Go strategy and discovered new strategies all its own. “When you learn to imitate humans the best you can do is learn to imitate humans,” said Satinder Singh , a computer scientist at the University of Michigan who was not involved with the research. “In many complex situations there are new insights you’ll never discover.”

After three days of training and 4.9 million training games, the researchers matched AlphaGo Zero against the earlier champion-beating version of the program. AlphaGo Zero won 100 games to zero.

To expert observers, the rout was stunning. Pure reinforcement learning would seem to be no match for the overwhelming number of possibilities in Go, which is vastly more complex than chess: You’d have expected AlphaGo Zero to spend forever searching blindly for a decent strategy. Instead, it rapidly found its way to superhuman abilities.

The efficiency of the learning process owes to a feedback loop. Like its predecessor, AlphaGo Zero determines what move to play through a process called a “tree search.” The program starts with the current board and considers the possible moves. It then considers what moves its opponent could play in each of the resulting boards, and then the moves it could play in response and so on, creating a branching tree diagram that simulates different combinations of play resulting in different board setups.