special relativity

(uncountable)A theory that (neglecting the effects of gravity) reconciles the principle of relativity with the observation that the speed of light is constant in all frames of reference.

Spezielle Relativitätstheorie, spezielle Relativitätstheorie

специа́льная тео́рия относи́тельностиspeciálʹnaja teórija otnosítelʹnosti, ча́стная тео́рия относи́тельностиčástnaja teórija otnosítelʹnosti

a physical theory of relativity based on the assumption that the speed of light in a vacuum is a constant and the assumption that the laws of physics are invariant in all inertial systems