KentuckyFC writes "The problem of free will is one of the great unsolved puzzles in science, not to mention philosophy, theology, jurisprudence and so on. The basic question is whether we are able to make decisions for ourselves or whether the outcomes are predetermined and the notion of choice is merely an illusion. Now a leading theoretical physicist has outlined a 'Turing Test' for free will and says that while simple devices such as thermostats cannot pass, more complex ones like iPhones might. The test is based on an extension of Turing's halting problem in computer science. This states that there is no general way of knowing how an algorithm will finish, other than to run it. This means that when a human has to make a decision, there is no way of knowing in advance how it will end up. In other words, the familiar feeling of not knowing the final decision until it is thought through is a necessary feature of the decision-making process and why we have the impression of free will. This leads to a simple set of questions that forms a kind of Turing test for free will. These show how simple decision-making devices such as thermostats cannot believe they have free will while humans can. A more interesting question relates to decision-makers of intermediate complexity, such as a smartphone. As the author puts it, this 'seems to possess all the criteria required for free will, and behaves as if it has it.'"