Retrofuture: The Age of Paradox

You can learn a lot from looking at a light bulb. Just over 100 years ago physicist Max Planck did just that, and wondered what the steady, yellow glow around the bulb was caused by. The glow defied existing theories of the behaviour of light, and to explain it Planck had to invent the idea of the 'quantum', a tiny 'packet' of energy at the heart of light itself. Planck's solution soon had physicists the world over discussing the 'duality' of light – the idea that it functions both as a wave and as a particle. Out of this duality was born Quantum Theory – on which much of the science of the 20th century has been based.