Lorentz-Fitzgeral length contraction. The effect of lengths shortening when something travels at or near the speed of light. Even things that do not travel at the speed of light will shorten, but by a smaller factor. The basic formula is L' = L√ 1 - v²/c² where L' is the length of object in a moving frame of reference (frame where the ruler is moving compared to observer), L is the length of the object in its inertial frame of reference (frame where the ruler is not moving compared to observer), v is the speed of the L' frame and c is the speed of light.