Quantum mechanics is the most fundamental scientific theory known to man. It underpins modern science and technology and even provides us with a blueprint for reality itself. And yet it has been said that if you think you understand it, you quite clearly don't. But is quantum physics really so unknowable? Is reality really so strange? And just how can cats be half alive and half dead at the same time? This book untangles the weirdness of the quantum world, explains the theories, explores their consequences and presents a cutting-edge guide to the current state of the science.