Theory of Relativity: This is a concept developed by Einstein that describes gravity not as a force but as a consequence of the curvature of spacetime caused by mass and energy.
E=mc^2: This famous equation from Einstein's theory shows that energy (E) equals mass (m) times the speed of light (c) squared, indicating that mass and energy are interchangeable.
Quantum Mechanics: A branch in physics dealing with phenomena at very small scales where the action is on the order of Planck constant. It departs from classical mechanics primarily at quantum realm scale.