"If there is such a thing as a universal speed... Newtonian physics... must be reviewed. As long as the laws of physics were concerned only with accelerations... no conceivable experiment... would lead to the selection of one particular frame of reference as fundamental. But if in empty space light propogates at the universal speed... then a careful determination of the apparent speed of light relative to laboratory apparatus should reveal the [absolute] velocity of that apparatus.... There should exist one frame of reference with respect to which light does travel everywhere at the speed c. Call this... the frame of absolute rest. ...[W]ith respect to any other frame...the apparent speed of light should be less than c in the direction in which the frame is traveling relative to the frame of absolute rest; it should be greater than c in the opposite direction."