Quantum mechanics has given scientists and engineers a new and deeper understanding of physical reality. It explains the behaviour of electrons, atoms and molecules, the nature of chemical reactions, how light interacts with matter, the evolution of stars, the bio-chemistry of life and the evolution of mankind itself. Despite its successes it remains an intensely controversial theory. It suggests that very small objects such as electrons or photons behave in ways that contradict the common sense ideas. Yet many scientists to this day refuse to accept the fact that contradiction is an essential part of all matter.