The Trouton–Rankine experiment was an experiment designed to measure if the

Lorentz–FitzGerald contraction Length contraction is the phenomenon that a moving object's length is measured to be shorter than its proper length, which is the length as measured in the object's own rest frame. It is also known as Lorentz contraction or Lorentz–FitzGeral ...

of an object according to one frame (as defined by the

luminiferous aether Luminiferous aether or ether ("luminiferous", meaning "light-bearing") was the postulated medium for the propagation of light. It was invoked to explain the ability of the apparently wave-based light to propagate through empty space (a vacuum), so ...

) produced a measurable effect in the rest frame of the object, so that the ether would act as a "

preferred frame In theoretical physics, a preferred frame or privileged frame is usually a special hypothetical frame of reference in which the laws of physics might appear to be identifiably different (simpler) from those in other frames. In theories that apply ...

". The experiment was first performed by

Frederick Thomas Trouton Frederick Thomas Trouton FRS (; 24 November 1863 – 21 September 1922) was an Irish physicist known for Trouton's rule and experiments to detect the Earth's motion through the luminiferous aether. Life and work Trouton was born in Dubli ...

and Alexander Oliver Rankine in 1908. The outcome of the experiment was negative, which is in agreement with the principle of relativity (and thus

special relativity In physics, the special theory of relativity, or special relativity for short, is a scientific theory regarding the relationship between space and time. In Albert Einstein's original treatment, the theory is based on two postulates: # The laws ...

as well), according to which observers at rest in a certain inertial reference frame, cannot measure their own translational motion by instruments at rest in the same frame. Consequently, also length contraction cannot be measured by co-moving observers. See also

Tests of special relativity Special relativity is a physical theory that plays a fundamental role in the description of all physical phenomena, as long as gravitation is not significant. Many experiments played (and still play) an important role in its development and justifi ...

Description

The famous

Michelson–Morley experiment The Michelson–Morley experiment was an attempt to detect the existence of the luminiferous aether, a supposed medium permeating space that was thought to be the carrier of light waves. The experiment was performed between April and July 188 ...

of 1887 showed that the then-accepted aether theory needed to be modified.

FitzGerald The FitzGerald/FitzMaurice Dynasty is a noble and aristocratic dynasty of Cambro-Norman, Anglo-Norman and later Hiberno-Norman origin. They have been peers of Ireland since at least the 13th century, and are described in the Annals of the ...

and

Lorentz Lorentz is a name derived from the Roman surname, Laurentius, which means "from Laurentum". It is the German form of Laurence. Notable people with the name include: Given name * Lorentz Aspen (born 1978), Norwegian heavy metal pianist and keyboar ...

, independently of each other, proposed a length contraction of the experimental apparatus in the direction of motion (with respect to the

) that would explain the almost null result of the Michelson–Morley experiment. The first attempts to measure some consequences of this contraction in the lab frame (the

inertial frame of reference In classical physics and special relativity, an inertial frame of reference (also called inertial reference frame, inertial frame, inertial space, or Galilean reference frame) is a frame of reference that is not undergoing any acceleration. ...

of an observer co-moving with the experimental apparatus) were made in the

experiments of Rayleigh and Brace The experiments of Rayleigh and Brace (1902, 1904) were aimed to show whether length contraction leads to birefringence or not. They were some of the first optical experiments measuring the relative motion of Earth and the luminiferous aether which ...

(1902, 1904), though the result was negative. By 1908, however, the then-current theories of electrodynamics,

Lorentz ether theory What is now often called Lorentz ether theory (LET) has its roots in Hendrik Lorentz's "theory of electrons", which was the final point in the development of the classical aether theories at the end of the 19th and at the beginning of the 20th cen ...

(now superseded) and

(now generally accepted, and lacking any aether at all), predicted that the

is not measurable in a co-moving frame, because these theories were based on the

Lorentz transformation In physics, the Lorentz transformations are a six-parameter family of Linear transformation, linear coordinate transformation, transformations from a Frame of Reference, coordinate frame in spacetime to another frame that moves at a constant velo ...

, (after conducting the

Trouton–Noble experiment The Trouton–Noble experiment was an attempt to detect motion of the Earth through the luminiferous aether, and was conducted in 1901–1903 by Frederick Thomas Trouton and H. R. Noble. It was based on a suggestion by George FitzGerald that ...

in 1903), instead did the calculations using his own interpretation of electrodynamics, calculating the length contraction according to the velocity of the experimental apparatus in the aether frame, but calculating the electrodynamics by applying Maxwell's equations and Ohm's law in the lab frame. According to Trouton's view of electrodynamics, the calculations then predicted a measurable effect of the length contraction in the lab frame. Together with Alexander Oliver Rankine, he set out to verify this in 1908 by attempting to measure the change of the resistance of a coil as they changed its orientation to the "aether velocity" (the velocity of the lab through the luminiferous aether). This was done by putting four identical such coils in a

Wheatstone bridge A Wheatstone bridge is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component. The primary benefit of the circuit is its ability to provid ...

configuration which allowed them to precisely measure any change in resistance. The circuit was then rotated through 90 degrees about its axis as the resistance was measured. Because the Lorentz–FitzGerald contraction is only in the direction of motion, from the point of view of the "Aether frame" the length of the coils depended on their angle with respect to their Aether velocity. Trouton and Rankine therefore believed that the resistance as measured in the rest frame of the experiment should change as the device was rotated. However their careful measurements showed no detectable change in resistance. This showed that if the Lorentz–FitzGerald contraction existed, it was not measurable in the rest frame of the object – only theories containing the complete

, like

, are still valid.

References

External links

On the Electrodynamics of Moving Bodies
Einstein's 1905 paper * Electromagnetic phenomena in a system moving with any velocity smaller than that of light Lorentz's 1904 paper {{DEFAULTSORT:Trouton-Rankine experiment Tests of special relativity 1908 in science