Längdförkortning

Längdförkortning, also known as length contraction, is a phenomenon in special relativity where the length of an object moving relative to an observer is measured to be shorter along the direction of motion than its proper length. Proper length is the length of the object as measured in its own rest frame. This effect is only noticeable at speeds approaching the speed of light.

The formula describing length contraction is L = L₀√(1 - v²/c²), where L is the contracted length, L₀ is the proper length, v is the relative velocity between the observer and the object, and c is the speed of light. As the velocity v approaches c, the term √(1 - v²/c²) approaches zero, causing L to approach zero. Conversely, if v is much smaller than c, the term is very close to 1, and the contracted length is almost identical to the proper length, meaning length contraction is negligible at everyday speeds.

Length contraction is a consequence of the postulates of special relativity, particularly the constancy of the speed of light for all inertial observers. It is a real physical effect, not an optical illusion, and has been experimentally verified. For example, muons created in the upper atmosphere reach the Earth's surface despite their short lifespan because their internal clocks run slower from our perspective, and from their perspective, the distance to the Earth is length contracted.