The contravariant four-vector arising in special and general relativity, x^μ = [x^0 x^1 x^2 x^3] congruent [c t x y z], where c is the speed of light and t is time. Multiplication of two four-vectors gives the spacetime interval I | = | g_μν x^μ x^ν | = | (x^0)^2 - (x^1)^2 - (x^2)^2 - (x^3)^2 | = | (c t)^2 - (x^1)^2 - (x^2)^2 - (x^3)^2.

four-vector | Lorentz transformation | quaternion