In 1915, Einstein predicted gravitational waves, presented the quantum theory of electromagnetic radiation and completed his concept of photon. In one hundred years, gravitational waves were directly detected through the interference of lasers, which are exactly based on Einstein's quantum theory of electromagnetic radiation. The techniques of gravitational wave detection are also related to Einstein 's concept of photons and theory of Brownian motion. The first direct detection of gravitational waves was a commemoration of the centenaries of both contributions of Einstein, one being general relativity and prediction of gravitational waves, the other being quantum theory of radiation. After a review of the “Einsteinian elements” in gravitational detection techniques, that is, the lasers, the photons and the thermal noises, we survey Einstein's research activities in 1916 and look for the historic connections between Einstein's work on gravitational waves and his work on quantum theory of electromagnetic waves, by analyzing the first-hand materials, especially the correspondence of Einstein during that period.

Einstein  /  gravitational wave  /  quantum theory of electromagnetic radiation