David Peat

OneQUANTUM UNCERTAINTYIn 1900 Lord Kelvin spoke of thetriumphs of physics and how Newton’s theory of motion could be extendedto embrace the phenomena of light and heat. His address wenton to mention “two clouds” that obscured the “beauty and clearness”of the theory: the first involved the way light travels through space, thesecond was the problem of distributing energy equally among vibratingmolecules. The solution Kelvin proposed, however, proved to beway off the mark. Ironically, what Kelvin had taken to be clouds on thehorizon were in fact two bombshells about to create a massive explosionin twentieth century physics. Their names were relativity andquantum theory, and both theories had something to say about light.Light, according to physicists like Kelvin, is a vibration, and likeevery other vibration it should be treated by Newton’s laws of motion.But a vibration, physicists argued, has to be vibrating in something.And so physicists proposed that space is not empty but filled with acurious jelly called “the luminiferous ether.” But this meant that thespeed of light measured in laboratories on earth—the speed with1