Scientists who focus primarily on curiosity-driven basic research—such as theoretical physics—often find their curiosity piqued by the challenge of finding a solution to a real-world problem. Albert Einstein is best known to the general public for devising the world's most famous equation: E=mc2. But his contributions to physics extend over an impressively broad range of topics, including Brownian motion, the photoelectric effect, special and general relativity, and stimulated emission, which led to the development of the laser. Less well known, even among physicists, is his work with Leo Szilard to develop an energy efficient absorption refrigerator with no moving parts.