Reflections on light, basic research and innovation

The questions raised by the interpretation of Maxwell's equations were also the starting points for the theory of relativity (special and then general) and quantum physics. The presentation recalled how relativity arose from questions raised by the speed of light, and how quanta arose from the mysteries raised by the explanation of radiation from heated bodies and the photoelectric effect. Quantum physics challenged the fundamental principles of classical science by introducing the notion of wave-corpuscle dualism and superposition of states. The lesson emphasized the predictive richness of this physics, based on Schrödinger's non-relativistic wave equation (which serves as the starting point for the essentials of atomic and condensed matter physics, as well as chemistry) and Dirac's relativistic equation (which predicted the existence of anti-matter and formed the premise of quantum field theory).

In its second part, the lesson illustrated the often fortuitous links between fundamental and applied research by following the long and fruitful line of research that began in Germany with the atomic jet experiments of Otto Stern, who discovered electron spin and atomic magnetism in the 1920s. This work, taken up and developed by Isidore Rabi and his school in the United States in the 1930s and 1940s, led to the invention of nuclear magnetic resonance (NMR) by Bloch and Purcell. This fundamental research, initially motivated by simple curiosity, was to lead unexpectedly to the development of Magnetic Resonance Imaging (MRI), not to mention the importance of NMR as a probe of the properties of matter in chemistry, solid and liquid physics and biology. Another spin-off of the atomic jet method was the development of atomic clocks, following on from the work of the Rabi school, which led to a redefinition of the second and to GPS (satellite-borne clock systems whose signals enable us to find our bearings anywhere on Earth by triangulation). Another extension of the work on atomic and molecular jets was the invention of the maser, which then evolved into the laser, an extraordinary source of light still based on Einstein's idea (stimulated emission). Lasers have countless applications in fundamental and applied physics. Some of these were recalled in the lecture (applications to optical atomic clocks, see lecture five of this lecture; use of lasers to control quantum particles, see lecture four).

In conclusion, the closing lesson recalled the importance of ongoing dialogue between fundamental research and innovation, and evoked what could be some of the applications of research into lasers and light in the field of communication or quantum computing. However, it was also pointed out that research often holds surprises in store for us, and that it is difficult, if not impossible, to predict the direction in which it will take us, both in the fundamental field and in that of innovation.