General relativity: A mathematical theory relating gravity to non-Euclidean distortions in the geometry of space and time introduced by mass and energy, and reducing to the special theory of relativity in localized regions of space and time. [e]
Statistical mechanics: A theoretical model by which one can derive the laws of thermodynamics via statistical analysis of the dynamics of a large number of atoms and molecules [e]
Optics: A field of scientific, technological, and engineering study and application concerned with understanding light, — typically in the visible, ultraviolet, and infrared ranges of the electromagnetic spectrum — and harnessing it for useful tasks. [e]