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. Albert Einstein photographed by Oren J. Turner in 1947. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein. ... In general English usage, length (symbols: l, L) is but one particular instance of distance – an objects length is how long the object is – but in the physical sciences and engineering, the word length is in some contexts used synonymously with distance. Height is vertical distance; width (or breadth... Cherenkov effect in a swimming pool nuclear reactor. ... Frame of reference - Wikipedia, the free encyclopedia /**/ @import /skins-1. ...

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, i.e. 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 length measured when the object is stationary and L₁ is the length measured when the object is travelling at velocity v. An observer at rest viewing an object travelling at the speed of light would observe the length of the object in the direction of motion as zero.

Physical Origin of Length Contraction

Length contraction as a physical effect on bodies composed on atoms held together by electromagnetic forces was predicted by Oliver Heaviside and George Fitzgerald in the 1880s and worked out in more detail by Hendrik Lorentz (1895, 1899) and Joseph Larmor (1987, 1900). The following quote from Larmor is indicative of the pre-Relativity view of the effect: Oliver Heaviside (May 18, 1850 – February 3, 1925) was a self-taught English engineer, mathematician and physicist who adapted complex numbers to the study of electrical circuits, developed techniques for applying Laplace transforms to the solution of differential equations, reformulated Maxwells field equations in terms of electric and magnetic... George FitzGerald George Francis FitzGerald, or Fitzgerald, (3 August 1851 – 22 February 1901) was a professor of natural and experimental philosophy (i. ... Painting of Hendrik Lorentz by Arnhemensis Hendrik Antoon Lorentz (July 18, 1853, Arnhem – February 4, 1928, Haarlem) was a Dutch physicist and the winner of the 1902 Nobel Prize in Physics for his work on electromagnetic radiation. ... Sir Joseph Larmor (July 11, 1857 - May 19, 1942), an Irish physicist and mathematician, researched electricity, dynamics, and thermodynamics. ...

"... if the internal forces of a material system arise wholly from elctromagnetic actions between the system of electrons which constitute the atoms, then the effect of imparting to a steady material system a uniform velocity of translation is to produce a uniform contraction of the system in the direction of motion, of amount (1-v²/c²)^1/2" Joseph Larmor (1900) Aether and Matter (Cambridge University Press)

The extension of this specific result to a general result was (and is) considered "ad hoc" by many who prefer Einstein's deduction of it from the Principle of Relativity without reference to any physical mechanism which might produce it. Apparently Lorentz did not agree as this draft of a letter to Einstein in 1915 shows (see Fitzgerald contraction, unfortunately no source is given) Galilean relativity Historically, the first principle of relativity that was formulated was a principle of relativity of uniform motion suggested by the observation that there doesnt seem to be a phenomenon in dynamics that will allow an observer to establish a zero point of velocity, nor a preferred direction. ... The Lorentz-FitzGerald contraction hypothesis was proposed by George FitzGerald and independently proposed and extended by Hendrik Lorentz to explain the negative result of the Michelson-Morley experiment, which attempted to detect Earths motion relative to the luminiferous aether. ...

"... the interpretation given by me and FitzGerald was not artificial. It was more so that it was the only possible one, and I added the comment that one arrives at the hypothesis if one extends to other forces what one could already say about the influence of a translation on electrostatic forces. Had I emphasized this more, the hypothesis would have created less of an impression of being invented ad hoc." (empahsis added)

See also:

• time dilation
• Fitzgerald contraction
• Relativity of simultaneity