An Etymological Dictionary of Astronomy and Astrophysics
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According to → general relativity, → space-time is curved by the presence of → matter. The curvature is described in terms of → Riemann's geometry. In → cosmological models three types of curvature are considered: positive (spherical, → closed Universe), zero (Euclidean, → flat Universe), and negative (hyperbolic, → open Universe). See also → curvature constant.

→ curvature; → space-time.

A completely flat four-dimensional space, which contains no gravitating matter, used in the theory of special relativity.

→ Minkowski metric; → space-time.

A physical entity resulting from the union of space and time concepts. In its most simple version space-time is the four-dimensional continuum, having three spatial coordinates and one temporal coordinate, in which any → event or physical object is located. In → special relativity it is Minkowski's flat space-time. In → general relativity, it is described by a curved entity characterized by a → metric. Free-fall motion describes the → geodesic of this curved space-time. It may have additional dimensions in the context of speculative theories, such as → string theory.

→ space; → time.

→ curvature of space-time.

→ space; → time; → curvature.

A simple way of representing the → space-time continuum, usually including time and only one spatial dimension. The curve of a particle's equation of motion on a space-time diagram is called a → world line. Same as → Minkowski diagram.

→ space; → time; → diagram.

1) In Einstein's → theory of relativity, ds² = c²dt² - dx² - dy² - dz².
2) In → Newtonian mechanics, time interval: dt; space interval at fixed time: dl² = dx² + dy² + dz².

→ space-time; → interval.