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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.
(Some authors alternatively use the negative metric signature of (− + + +), with =, = = =.) Lorentz transformations leave the Minkowski metric invariant, so the d'Alembertian yields a Lorentz scalar. The above coordinate expressions remain valid for the standard coordinates in every inertial frame.
The Poincaré group consists of all coordinate transformations of Minkowski space that do not change the spacetime interval between events.For example, if everything were postponed by two hours, including the two events and the path you took to go from one to the other, then the time interval between the events recorded by a stopwatch that you carried with you would be the same.
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 difference between this and the spacetime interval = in Minkowski space is that = is invariant purely by the principle of relativity whereas = requires both postulates. The "principle of relativity" in spacetime is taken to mean invariance of laws under 4-dimensional transformations.
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.
Calculating the Minkowski norm squared of the four-momentum gives a Lorentz invariant quantity equal (up to factors of the speed of light c) to the square of the particle's proper mass: = = = + | | = where = is the metric tensor of special relativity with metric signature for definiteness chosen to be (–1, 1, 1, 1).
This form is invariant under the Lorentz group, so that for S ∈ SL(2, C) one has , = , This defines a kind of "scalar product" of spinors, and is commonly used to defined a Lorentz-invariant mass term in Lagrangians. There are several notable properties to be called out that are important to physics.