This book develops an astonishing conceptual connection between many concepts in modern physical sciences and related technologies, all of which have their roots in the Interferometer, a spectroscopic instrument created by Albert Michelson in 1880. After describing the place of the Interferometer amongst other historic, technical inventions, the book discusses the Michelson-Morley experiment (the basis of Einstein’s relativity theories) and the fine details of atomic spectral lines observed by Michelson (the basis of quantum mechanics and Dirac’s relativistic equation). It then covers nuclear magnetic resonance and applications such as atomic clocks, Global Positioning Systems and Magnetic Resonance Imaging, all derived from Michelson's discoveries. It also describes the recent detection, with a km-size Michelson’s Interferometer, of gravitational waves emitted by the merger of neutron star and black hole binaries.