What are X-rays, Anyway: A Modern View of the Nature of Light and its Implications for the Future of X-ray Science

摘要

Few problems in physics have received more attention than the complex nature of light. The historical roller coaster of its description dates back to Huygens and Newton around 1700 and seemed to have been resolved by Young and Fresnel around 1800 in favor of the wave theory of light. Another 100 years later, in the wake of Planck’s black body radiation formula, Einstein put forward the idea in 1905 that light is granular and that such light “quanta” can transfer their energy to electrons and emit them from solids [1]. In 1909, Einstein first suggested the existence of an inherent wave-particle duality, by deriving a fluctuation formula for Planck’s blackbody radiation which contained separate wave and particle term [2]. As reviewed by Wolf [3], the schizophrenic wave-particle duality has been upon us ever since. It has lingered on in the scientific community to this day, despite the development of quantum mechanics in the late 1920s and even its extension in the late 1940s to quantum electrodynamics (QED) by Feynman, Schwinger, and Tomonaga, who received the Nobel Prize in Physics for their work in 1965. In QED, today considered the complete theory of light, the wave-particle duality does not exist since light is fundamentally granular and composed of photon building blocks.