If the relativity principle, which states that the law of propagation for light has the same form for all macroscopic observers, is extended to include quantum observers, this leads directly to the quantum unified field theory which was introduced in a previous paper. This theory appears suitable for describing all known interactions. Gravitation and electromagnetism are described by the Einstein equations ${G}_{\ensuremath{\mu}\ensuremath{\nu}}=\frac{1}{2}({e}_{\ensuremath{\mu}\ensuremath{\nu}}\ensuremath{-}{K}_{\ensuremath{\mu}}{j}_{\ensuremath{\nu}}\ensuremath{-}{K}_{\ensuremath{\nu}}{j}_{\ensuremath{\mu}})\ensuremath{-}R{K}_{\ensuremath{\mu}}{K}_{\ensuremath{\nu}}$, where ${G}_{\ensuremath{\mu}\ensuremath{\nu}}$ is the Einstein tensor, $R$ is the Ricci scalar, ${e}_{\ensuremath{\mu}\ensuremath{\nu}}$ is the usual stress-energy tensor for the free electromagnetic field, and ${j}_{\ensuremath{\mu}}$ is the electromagnetic current. The vector ${K}_{\ensuremath{\mu}}$ plays a dual role. It is the electromagnetic vector potential in the covariant Lorentz gauge, and, it is also a unit timelike vector interpretable as the velocity of the observer.