It's lucky you're here. But for a series of choices, accidents and coincidences - any of which could have gone otherwise - your life would have been very different. The same goes for reality. We live in just one of many possible worlds - but we can imagine parallel universes in which dinosaurs still rule the Earth, the Russians got to the moon first, everyone's a vegetarian or time itself flows backwards. And that's just for starters. What if the laws of physics were different? What if robots become smarter than us? Or, if every human on the planet simply vanished tomorrow? The answers to these questions aren't just fun to consider, but reveal deep truths about our own universe.Join New Scientist on a thrilling journey through dozens of incredible but perfectly possible alternative realities, thought experiments and counterfactual histories - each shining a surprising and unexpected spotlight on life as we know it.