Hundreds of science and tech luminaries are freaked out about the real possibility of robotic machines that kill on their own, without a human picking the targets and pulling the trigger, and they think you should be worried, too. On Monday, in an open letter presented at the opening of the International Joint Conference On Artificial Intelligence in Buenos Aires, physicist Stephen Hawking, Space X founder Elon Musk, Apple co-founder Steve Wozniak, and other prominent figures with ties to artificial intelligence (AI) warned about autonomous weapons and urged the world to enact a global ban on such human-free killing technology.