100 Years Before Quantum Mechanics, a Physicist Spotted Its Hidden Clue
100 Years Before Quantum Mechanics, a Physicist Spotted Its Hidden Clue Hamilton’s 19th-century insight connecting light and motion became a cornerstone of quantum mechanics and modern physics. William Rowan Hamilton, the Irish mathematician and physicist born 220 years ago last month, is often remembered for an unusual act in 1843, when he carved a mathematical formula into the stone of Dublin’s Broome Bridge.During his own lifetime, however, Hamilton’s standing rested on breakthroughs he made much earlier, in the 1820s and early 1830s, while he was still in his twenties. In that period, he introduced powerful new mathematical methods for analyzing the paths of light rays (or “geometric optics”) and describing how physical objects move (“mechanics”). An intriguing feature of Hamilton’s work was his use of an analogy between the trajectory of a light ray and the motion of a material particle. That comparison made sense if light were composed of particles, as Isaac Newton had argue...