When physicists began exploring the inner workings of the atom, they uncovered a world so weird that it overturned our very concept of reality. When you journey into the quantum universe you enter a world ruled by chance. Commonsense notions of space, time and causality must be left behind as the realm of solid matter dissolves away into vibrating patterns of ghostly energy; even spacetime itself is revealed as an ephemeral froth of wormholes and tunnels. Most revolutionary of all is the way in which quantum physics interweaves mind and matter in a subtle and holistic manner. It is here that scientists make the most startling claim of all: that there exist myriads of alternative realities in parallel to our own. Are these "other worlds" just mathematical artefacts, or do they really exist?