As the story goes, English mathematician and physicist Sir Isaac Newton (1642 - 1727) contemplates the force of gravity on seeing an apple fall in his orchard, circa 1665.Credit: Hulton Archive / Getty Images Physics equations are forms of magic. They allow us to explain the past, such as why Halley’s comet visits every 76 years, and predict the future - as far as the ultimate fate of the Universe. They place limits on the possible, as in the efficiency of an engine, and they reveal possibilities we could never have imagined, such as the energy inside an atom. Occasionally over the past few centuries, a new equation endowed the next generation with a new magical tool, and so changed the course