The movement of an object is a change in its spatial and temporal location. The measurement of a movement by a ratio apart from direction is either a speed or a pace. Speed is a change in distance per a given duration. Pace is a change in duration per a given distance. If direction is combined with the ratio, it is either a velocity or a celerity. Velocity is a speed with direction. Celerity is a pace with direction.

There is a relation between measures of movement and dimensions. If movement is measured by velocity, the denominator is a vector of space, which means space is considered multidimensional. But if movement is measured by celerity, the denominator is a vector of time, which means time is considered multidimensional.

Max Tegmark in his 1997 letter *On the dimensionality of spacetime* gives his judgment concerning the number of space and time dimensions in a chart:

The chart indicates that one space dimension with three time dimensions (1+3D) includes only tachyons (objects traveling at more than the speed of light) and not bradyons (or tardyons, objects traveling at less than the speed of light). Bradyons exist in 1+3D, see *Subluminal and superluminal Lorentz transformations*.

The statement “We are here.” for 3+1D reflects its status as a cultural commonplace and the use of velocity. There is however equal justification for using 1+3D and celerity. Minkowski showed the way to use either 3+1D or 1+3D by using hyperbolic geometry.

*Related*