"This is an interesting and positive step forward, but it is really important not to exaggerate it," said Ken Goldberg, a professor at the University of California, Berkeley, who explores similar techniques. A robot that can solve a Rubik's Cube is not new. Researchers previously designed machines specifically for the task -- devices that look nothing like a hand -- and they can solve the puzzle in less than a second. But building devices that work like a human hand is a painstaking process in which engineers spend months laying down rules that define each tiny movement. The OpenAI project was an achievement of sorts because its researchers did not program each movement into their robotic hand.

Last week, on the third floor of a small building in San Francisco's Mission District, a woman scrambled the tiles of a Rubik's Cube and placed it in the palm of a robotic hand. The hand began to move, gingerly spinning the tiles with its thumb and four long fingers. Each movement was small, slow and unsteady. But soon, the colors started to align. Four minutes later, with one more twist, it unscrambled the last few tiles, and a cheer went up from a long line of researchers watching nearby.