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In general relativity, the metric tensor (in this context often abbreviated to simply the metric) is the fundamental object of study.The metric captures all the geometric and causal structure of spacetime, being used to define notions such as time, distance, volume, curvature, angle, and separation of the future and the past.
The metric tensor is an example of a tensor field. The components of a metric tensor in a coordinate basis take on the form of a symmetric matrix whose entries transform covariantly under changes to the coordinate system. Thus a metric tensor is a covariant symmetric tensor.
Writing the coordinates in column vectors and the Minkowski metric η as a square matrix ′ = [′ ′ ′ ′], = [], = [] the spacetime interval takes the form (superscript T denotes transpose) = = ′ ′ and is invariant under a Lorentz transformation ′ = where Λ is a square matrix which can depend on parameters.
Specifying a metric tensor is part of the definition of any Lorentzian manifold. The simplest way to define this tensor is to define it in compatible local coordinate charts and verify that the same tensor is defined on the overlaps of the domains of the charts. In this article, we will only attempt to define the metric tensor in the domain of ...
In these coordinates, the Euclidean metric tensor is given by = +. This can be seen via the change of variables formula for the metric tensor, or by computing the differential forms dx , dy via the exterior derivative of the 0-forms x = r cos( θ ) , y = r sin( θ ) and substituting them in the Euclidean metric tensor ds 2 = dx 2 + dy 2 .
Proper time is defined in general relativity as follows: Given a pseudo-Riemannian manifold with a local coordinates x μ and equipped with a metric tensor g μν, the proper time interval Δτ between two events along a timelike path P is given by the line integral [12]
A geodesic between two events can also be described as the curve joining those two events which has a stationary interval (4-dimensional "length"). Stationary here is used in the sense in which that term is used in the calculus of variations, namely, that the interval along the curve varies minimally among curves that are nearby to the geodesic.
Hermann Minkowski (1864–1909) found that the theory of special relativity could be best understood as a four-dimensional space, since known as the Minkowski spacetime.. In physics, Minkowski space (or Minkowski spacetime) (/ m ɪ ŋ ˈ k ɔː f s k i,-ˈ k ɒ f-/ [1]) is the main mathematical description of spacetime in the absence of gravitation.