Preferred frame
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In theoretical physics, a preferred or privileged frame is usually a special hypothetical frame of reference in which the laws of physics might appear to be identifiably different from those in other frames.
In theories that apply the principle of relativity to inertial motion, physics is the same in all inertial frames and no single inertial frame is privileged or preferred above any other.
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[edit] Preferred frame in aether theory
In theories that presume that light travels at a fixed speed relative to an unmodifiable luminiferous aether, the "preferred frame" would be the frame in which this "aether" would be stationary. In 1887, Michelson and Morley tried to identify the state of motion of this hypothetical "preferred frame". To do so, they assumed Galilean Relativity to be satisfied by clocks and rulers; that is, that the length of rulers and periods of clocks are invariant under any Galilean frame change. Under such an hypothesis, a preferred frame should have been observed.
By comparing measurements made in different directions and looking for an effect due to the Earth's orbital speed, their experiment famously produced a null result. As a consequence, within Lorentz ether theory the Galilean transformation was replaced by the Lorentz transformation.However, in Lorentz ether theory the existence of an undetectable ether is assumed and the validity of the relativity principle seems to be only coincidental. This is one reason why the theory was quickly replaced by special relativity, which changed the meanings of space and time and rejected the existence of an unobservable ether. Thus, all inertial frames are physically equivalent. More precisely, provided that no phenomenon violates the principle of relativity of motion, there is no means to measure the velocity of an inertial observer with regard to a possible medium of propagation of quantum waves.
[edit] Inertial frames preferred above noninertial frames
Although there is no preferred inertial frame under Newtonian mechanics or special relativity, the set of all inertial frames as a group may still be said to be "preferred" over noninertial frames in these theories, since the laws of physics derived for inertial motion only work exactly in this special category of frames.
[edit] No preferred frames
In theories that comply with Mach's principle, even the preference for inertial frames is removed: observations made by observers in nominally "inertial" and "noninertial" frames may seem superficially biased in favour of the inertial observer, but ultimately, a full description of the physics becomes similarly complex in either case.
[edit] See also
[edit] References
- Einstein: Relativity, the special and the general theories (1954)
