Spacetime are the arenas in which all physical events takes place. The basic elements of spacetime are events. In any given spacetime, an event is defined as a unique position at a unique time. A spacetime is the union of all events (in the same way that a line is the union of all of its points), formally organized into a manifold.
Events, such as matter and energy, bend spacetime. Curved spacetime, on the other hand, forces matter and energy to behave in a certain way. There is no point in considering one without the other.
The universe appears to be a smooth spacetime continuum consisting of three spatial dimensions and one temporal (time) dimension (an event in the spacetime of the physical universe can therefore be identified by a set of four coordinates: (x, y, z, t) ). On average, space is observed to be very nearly flat (with a curvature close to zero), meaning that Euclidean geometry is empirically true with high accuracy throughout most of the Universe. Spacetime also appears to have a simply connected topology, in analogy with a sphere, at least on the length-scale of the observable universe. However, present observations cannot exclude the possibilities that the universe has more dimensions (which is postulated by theories such as string theory) and that its spacetime may have a multiply connected global topology, in analogy with the cylindrical or toroidal topologies of two-dimensional spaces. The spacetime of the universe is usually interpreted from a Euclidean perspective, with space as consisting of three dimensions, and time as consisting of one dimension, the "fourth dimension". By combining space and time into a single manifold called Minkowski space, physicists have simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.
Spacetime events are not absolutely defined spatially and temporally but rather are known to be relative to the motion of an observer. Minkowski space approximates the universe without gravity; the pseudo-Riemannian manifolds of general relativity describe spacetime with matter and gravity.