Werner Heisenberg’s Uncertainty PrincipleThe puzzling part of de Broglie’s theory was that the velocity of an electron related to its wave nature, whereasthe mass related to its particle-like nature. This was hard to reconcile. That is, until Heisenberg’s theory. He theorized that(Δ x ) (m Δ v) > h / 4piWhere x is the position of the electron, m is its mass, and v is its velocity. This relationship between position and velocity introduced complimentarity, the notion that an electron is either a particle or a wave, never both simultaneously.