Length contraction is one of the primary phenomena predicted by Albert Einstein's theory of special relativity published in 1905. The theory states that the measured distance between two points in space depends upon the observer's frame of reference. In brief, an object will always appear shorter from the frame of reference of an observer moving with respect to the object. Hence, the object appears to be contracted.

An observer who is stationary with respect to an object will measure the object's proper length L. The object can never be measured to be longer than the proper length. However, a second observer, moving with a constant velocity v with respect to the object and in a direction parallel to the object's length, will measure the length of the object to be shorter. The second observer will measure the length of the object to be

where c is the...