As computing becomes cheaper and more powerful, highly-realistic historical simulations will offer us a great tool for learning about ourselves as a society. But these things are never simple – and Melanie Swann takes a look at the potential ethical conundrums that such virtual realities will produce. For example, if you’ve created a world full of self-aware software agents with a degree of sentience, how can you ever switch it off without effectively becoming a mass murderer?