# Spacetime

In physics, spacetime (or space–time, space time or space–time continuum) is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as existing in three dimensions and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions. From a Euclidean space perspective, the universe has three dimensions of space and one of time. By combining space and time into a single manifold, physicists have significantly 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.

In non-relativistic classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, time cannot be separated from the three dimensions of space, because the observed rate at which time passes for an object depends on the object's velocity relative to the observer and also on the strength of gravitational fields, which can slow the passage of time.

In cosmology, the concept of spacetime combines space and time to a single abstract universe. Mathematically it is a manifold consisting of "events" which are described by some type of coordinate system. Typically three spatial dimensions (length, width, height), and one temporal dimension (time) are required. Dimensions are independent components of a coordinate grid needed to locate a point in a certain defined "space". For example, on the globe the latitude and longitude are two independent coordinates which together uniquely determine a location. In spacetime, a coordinate grid that spans the 3+1 dimensions locates events (rather than just points in space), i.e. time is added as another dimension to the coordinate grid. This way the coordinates specify where and when events occur. However, the unified nature of spacetime and the freedom of coordinate choice it allows imply that to express the temporal coordinate in one coordinate system requires both temporal and spatial coordinates in another coordinate system. Unlike in normal spatial coordinates, there are still restrictions for how measurements can be made spatially and temporally (see Spacetime intervals). These restrictions correspond roughly to a particular mathematical model which differs from Euclidean space in its manifest symmetry.

Until the beginning of the 20th century, time was believed to be independent of motion, progressing at a fixed rate in all reference frames; however, later experiments revealed that time slows at higher speeds of the reference frame relative to another reference frame. (Such slowing, called time dilation, is explained in special relativity theory.) Many experiments have confirmed time dilation, such as the relativistic decay of muons from cosmic ray showers and the slowing of atomic clocks aboard a Space Shuttle relative to synchronized Earth-bound inertial clocks. The duration of time can therefore vary according to events and reference frames.

When dimensions are understood as mere components of the grid system, rather than physical attributes of space, it is easier to understand the alternate dimensional views as being simply the result of coordinate transformations.

The term spacetime has taken on a generalized meaning beyond treating spacetime events with the normal 3+1 dimensions. It is really the combination of space and time. Other proposed spacetime theories include additional dimensions—normally spatial but there exist some speculative theories that include additional temporal dimensions and even some that include dimensions that are neither temporal nor spatial (e.g. superspace). How many dimensions are needed to describe the universe is still an open question. Speculative theories such as string theory predict 10 or 26 dimensions (with M-theory predicting 11 dimensions: 10 spatial and 1 temporal), but the existence of more than four dimensions would only appear to make a difference at the subatomic level.

### Other articles related to "spacetime":

Spacetime Topology
... Spacetime topology, the topological structure of spacetime, is a subject studied primarily in general relativity ... This physical theory models gravitation as a Lorentzian manifold (a spacetime) and the concepts of topology thus become important in analysing local as well as global ... The study of spacetime topology is especially important in physical cosmology ...
Privileged Character of 3+1 Spacetime
... triangulation (CDT) theory is a background independent theory which derives the observed 3+1 spacetime from a minimal set of assumptions, and needs no adjusting factors ... but rather attempts to show how the spacetime fabric itself evolves ... It shows spacetime to be 2-d near the Planck scale, and reveals a fractal structure on slices of constant time, but spacetime becomes 3+1-d in scales significantly larger than Planck ...
Special Relativity (alternative Formulations) - Minkowski Spacetime
... Minkowski space (or Minkowski spacetime) is a mathematical setting in which special relativity is conveniently formulated ... and Einstein) could be elegantly described using a four-dimensional spacetime, which combines the dimension of time with the three dimensions of space ... of ways in which the four-dimensions of Minkowski spacetime are commonly represented as a four-vector with 4 real coordinates, as a four-vector with 3 real and one complex coordinate ...
Space Time (software) - SpaceTime Browser
... SpaceTime 3D Screenshot Original author(s) Eddie Bakhash Developer(s) SpaceTime 3D, Inc ... SpaceTime developers are currently working to port the product to the OpenGL framework in order to support the Linux and Unix operating systems ... Images, Yahoo!, Yahoo! Image, eBay, and Flickr, SpaceTime loads the first ten results as a stack of pages ...
Caloron - Finite Temperature and Instantons
... the theory under consideration, and which are furthermore localized in Euclidean spacetime ... Yang–Mills field equations in Euclidean spacetime (i.e ... This changes the overall structure of spacetime, and thus also changes the form of the instanton solutions ...