Length contraction, according to Albert Einstein's special theory of relativity, is the decrease in length experienced by people or objects traveling at a substantial fraction of the speed of light. It is experienced only in the direction in which the body is travelling and not transverse to this direction, which in turn is dependent on the frame of reference relative to which that motion is being measured.

It is important to note that this effect is negligible at everyday speeds, and can be ignored for all regular purposes. It is only when an object approaches speeds on the order of 30,000,000 m/s; 1/10 of the speed of light, that it becomes important. As the magnitude of the velocity approaches the speed of light, the effect becomes dominant, as we can see from the formula:

Where L₀ is the distance travelled measured by a stationary observer and L₁ is this distance measured by an observer travelling at velocity v. From this simple maths which is part of the Lorentz transformations, we can see that an observer travelling at the speed of light (which, according to general relativity, is impossible for any object with a non-zero rest mass) would measure all distances in the direction of motion as 0.

See also:

• time dilation