"Schrödinger's theory was not relativistic. It only applied to systems of particles like electrons... moving at low velocities... not close to the speed of light. It... did not take into account the electron's spin. ...Paul Dirac set out to remedy these shortcomings. ...to combine the Schrödinger equations for quantum mechanics, the Einstein equations for special relativity, the Maxwell equations for electromagnetism, and his own non-relativistic equations for the behavior of the electron into a single set of equations. This... described the relativistic quantum behavior of the spinning electron. ...Dirac's solution ...was a startling paper ...In the classical physics of Newton, the energy of a particle always has a positive value. ...Dirac's new equations ...had two possible solutions: an electron with positive energy, or an electron with . ...Dirac discovered that an electron with negative energy passing through a magnetic field would act exactly like an electron with positive energy—if the electron had positive instead of negative charge. To Dirac, this implied that for every particle that existed there was a corresponding mirror-image particle."