'Can a robot sin?" the journal Christian Today asks readers. That, in essence, is what we are asking when we consider, for example, how the artificial intelligence (AI) driving a driverless car programmed to avoid accidents, can consider such ethical questions as what to do when faced with a choice between two accidents? Or how we are to control self-learning machines like the Twitter "chatbot" which had to be deactivated last year after it started posting increasingly racist, sexist and xenophobic messages, based on what it had "learnt" online. The questions raised by the likes of HAL 9000 and Isaac Asimov are now mainstream. Worries about the ethics and control of new so-called "autonomous weapons", which select and kill targets without human intervention, have led to calls for a ban from, among others, the likes of billionaire Elon Musk and Stephen Hawking.