Preferred frame
Encyclopedia
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 (simpler) 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 is even the same in all frames under the general principle of relativity.
, a preferred frame would be a frame in which this aether would be stationary. In 1887, Michelson and Morley
tried to identify the state of motion of the aether. 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, the aether 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 aether theory the Galilean transformation
was replaced by the Lorentz transformation
. However, in Lorentz aether theory the existence of an undetectable aether is assumed and the relativity principle holds. The theory was quickly replaced by special relativity
, which gave similar formulas without the existence of an unobservable aether. All inertial frames are physically equivalent, in both theories. 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.
In general relativity, some cosmological models have a preferred frame that allows motion to be defined.
, 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.
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, a preferred or privileged frame is usually a special hypothetical frame of reference
Frame of reference
A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
in which the laws of physics might appear to be identifiably different (simpler) from those in other frames.
In theories that apply the principle of relativity
Principle of relativity
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference....
to inertial motion, physics is the same in all inertial frames, and is even the same in all frames under the general principle of relativity.
Preferred frame in aether theory
In theories that presume that light travels at a fixed speed relative to an unmodifiable and detectable luminiferous aetherLuminiferous aether
In the late 19th century, luminiferous aether or ether, meaning light-bearing aether, was the term used to describe a medium for the propagation of light....
, a preferred frame would be a frame in which this aether would be stationary. In 1887, Michelson and Morley
Michelson-Morley experiment
The Michelson–Morley experiment was performed in 1887 by Albert Michelson and Edward Morley at what is now Case Western Reserve University in Cleveland, Ohio. Its results are generally considered to be the first strong evidence against the theory of a luminiferous ether and in favor of special...
tried to identify the state of motion of the aether. 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, the aether 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
Null result
In science, a null result is a result without the expected content: that is, the proposed result is absent. It is an experimental outcome which does not show an otherwise expected effect. This does not imply a result of zero or nothing, simply a result that does not support the hypothesis...
. As a consequence, within Lorentz aether theory the Galilean transformation
Galilean transformation
The Galilean transformation is used to transform between the coordinates of two reference frames which differ only by constant relative motion within the constructs of Newtonian physics. This is the passive transformation point of view...
was replaced by the Lorentz transformation
Lorentz transformation
In physics, the Lorentz transformation or Lorentz-Fitzgerald transformation describes how, according to the theory of special relativity, two observers' varying measurements of space and time can be converted into each other's frames of reference. It is named after the Dutch physicist Hendrik...
. However, in Lorentz aether theory the existence of an undetectable aether is assumed and the relativity principle holds. The theory was quickly replaced by special relativity
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
, which gave similar formulas without the existence of an unobservable aether. All inertial frames are physically equivalent, in both theories. 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.
In general relativity, some cosmological models have a preferred frame that allows motion to be defined.
Inertial frames preferred above noninertial frames
Although there is no preferred inertial frame under Newtonian mechanics or special relativitySpecial relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
, 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.
See also
- Tests of special relativity
- Modern searches for Lorentz violationModern searches for Lorentz violationImportant motivations for modern searches for Lorentz violation are deviations from Lorentz invariance predicted by some variations of quantum gravity, string theory, and some alternatives to general relativity...
- Cosmic microwave background radiationCosmic microwave background radiationIn cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
- Test theories of special relativityTest theories of special relativityTest theories of special relativity give a mathematical framework for analyzing results of experiments to verify special relativity.An experiment to test the theory of relativity cannot assume the theory is true, and therefore needs some other framework of assumptions that are wider than those of...