Quantum mechanics arose from Einstein's 1905 paper that offered a quantum-based theory to explain the photoelectric effect.
 One of the oldest and most common is the "transformation theory" proposed by Paul Dirac, which unifies and generalizes the two earliest formulations of quantum mechanics  matrix mechanics (invented by Werner Heisenberg) and wave mechanics (invented by Erwin Schrdinger)
 Quantum electrodynamics is, along with general relativity, one of the most accurate physical theories ever devised

