KentuckyFC writes: One of the extraordinary features of quantum mechanics is that one quantum system can simulate the behaviour of another that might otherwise be difficult to create. That's exactly what a group of physicists in Australia have done in creating a quantum system that simulates a quantum time machine. Back in the early 90s, physicists showed that a quantum particle could enter a region of spacetime that loops back on itself, known as a closed timelike curve, without creating grandfather-type paradoxes in which time travellers kill their grandfathers thereby ensuring they could never have existed to travel back in time in the first place. Nobody has ever built a quantum closed time-like curve but now they don't have to. The Australian team have simulated its behaviour by allowing two entangled photons to interfere with each other in a way that recreates the behaviour of a single photon interacting with an older version of itself. The results are in perfect agreement with predictions from the 1990s--there are no grandfather-type paradoxes. Interestingly, the results are entirely compatible with relativity, suggesting that this type of experiment might be an interesting way of reconciling it with quantum mechanics.