New Scientist | Guide to the Quantum World

New Scientist | Guide to the Quantum World: "ONCE upon a time, Newton prevailed, and the world was a safe place for all of us. When you hit a plain, old-fashioned billiard ball, you could predict how fast it would move and in what direction. And when the billiard ball came to rest, you knew exactly where it was. These simple notions seemed obvious, necessary even. Most people believed that for physics to work, it had to be based on such solid and unshakable foundations.

Then on 19 October 1900, physicist Max Planck made a ground-breaking presentation to the German Physical Society. Planck was a sober man and, at 42, a little long in the tooth for a revolutionary. But his discovery was to turn the classical physics of the billiard ball on its head. What he described was an answer to an old question: Why does the colour of radiation from any glowing body change from red to orange and ultimately to blue as its temperature increases? Planck found he could get the right answer by assuming that radiation, like matter, comes in discrete quantities. And he called his little packets of energy 'quanta' from the Latin for amount. At the time, Plank seems to have imagined that some deeper explanation of these quanta would emerge.

But it rapidly became clear that the 'quantisation' of energy -- dividing it up into individual pieces -- was actually a new and fundamental rule of nature. The classically trained Planck didn't like this conclusion one bit. He resisted it to his dying day, prompting his famous lament that new scientific theories supplant previous ones not because people change their minds, but simply because old people die."