Schrödinger’s equation was, of course, developed by Austrian physicist Erwin Schrödinger (1887–1961) in 1926. Called a wave equation, it could be applied to any physical system. The actual equation has more than one solution, and each solution (also called a quantum state, matter waves, or probability waves) to the equation is a probability wave that describes one of the possible outcomes, or behaviors, of that system. For example, looking at a hydrogen atom, each wave solution to the equations describes one of the allowed electron orbits of the atom.