Time, simple enough from the everyday aspect, yet so allusive to define scientifically, metaphysically or otherwise, in sufficient terms. It should be difficult – men far smarter than I have pondered time for hundreds if not tens of thousands of years.
In physics, spacetime (or space–time continuum) is a 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. In the past 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.
Prior to 1900 non-relativistic classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant. In spacetime, a coordinate grid that spans the 3+1 dimensions locates events. These restrictions correspond roughly to a particular mathematical model that importantly manifest symmetry.
At the beginning of the 20th century, 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.
Much of this is rehashed, but presented in a a different light. We need these building blocks to define a path to greater enlightenment, as a Buddhist may say.