"[E]quations developed by Heisenberg and Schrodinger did not take... from Einstein's relativistic mechanics, but from the old mechanics of Newton. ...[E]xperimental data on atomic spectra... were so accurate that small deviations from the Heisenberg-Schrodinger predictions could be observed. So there was a strong 'practical' motivation... [A]ncient and fundamental dichotomies were in play: ...light versus matter; ...continuous versus discrete ...tremendous barriers to ...achieving a unified description of nature ...[[Special relativity|[R]elativity]] was the child of light and the continuum ...quantum theory the child of matter and the discrete. After Dirac's revolution... all were reconciled, in the... conceptual amalgam... a quantum field. Maxwell's electrodynamics is a continuum theory of electric and magnetic fields, and of light, that makes no mention of . Newton's mechanics is a theory of discrete particles, whose only mandatory properties are mass and ."