Principle of relativity: Encyclopedia II - Principle of relativity - General relativity

Principle of relativity - General relativity

When accelerated motion is involved, there are phenomena that will allow an observer to establish a zero point, there are phenomena that determine a preferred reference frame. For example the case of rotation: the astronomer Schwarzschild had noted that in the solar system the lines connecting the aphelia and perihelia of the planets do not rotate with respect to each other and with respect to the background of the fixed stars (apart from an unexplained precession of the perihelion of Mercury). Also it could be seen from astronomical observation of double stars that the lines connecting the aphelia and perihelia of those distant systems do not rotate either with respect to the overall background of the fixed stars.

General relativity unifies the description of gravitation and the description of inertia. General relativity is a theory of gravitation that describes the properties of the mediator of gravitational interaction, in general relativity the mediator of gravitational interaction is deformation of space-time geometry. Gravitation is that the presence of mass and/or energy alters the rate of progression of time in the vicinity of that mass-energy.

For an object to move inertially is to remain in the same Lorentz frame. To be accelerated by a force is to be accelerated with respect to the local Lorentz frame. If viewed sufficiently locally, the situations of being accelerated by a force and of gravitation being opposed by a force are fundamentally the same physics. (To be precise: it is completely the same only in the limit of infinitesimally small volumes of space-time.) The hypotenuse of the squares of the velocity and the normal vector are inversely proportional to the gamma factor. At larger size-scales this equivalence does not hold. The deformation of space-time due to gravity decreases in proportion to the inverse square of the distance to the center of gravity. When viewed from a sufficiently large distance the local deformation of space-time due to gravitation is recognizable and thus can be accounted for as gravitation in a description that is based on as much relevant data as possible.

Einstein's original aim was to show that a theory can be formulated in which the same type of relativity as in special relativity also holds for non-inertial motion; this he called the general principle of relativity. In the end, following where demands of consistency led him, Einstein formulated a theory that moves the descriptions of gravitation and inertia to a deeper level, and unifies them. The name 'general relativity' reflects Einstein's original aim, not the way it eventually was interpreted.

See also general relativity

Adapted from the Wikipedia article "General relativity", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki