 Sachs described how quantum mechanics, first in relativistic two-component spinor form, and then under low energy-momentum as Schrödinger's equation emerges therefrom.Quoting Sachs, "...by dropping the (unnecessary) space and time reflection symmetry elements from Einstein's field equations, they factorize from 10 independent relations to 16 independent relations.This generalization then yielded a unified field theory of gravitation and electromagnetism.