[ Home - Physics - Philosophy - Archive - Reference - Authors]
Yes and no; it depends on what you are talking about. Time is the fourth dimension of spacetime, but time is not the fourth dimension of the space of places. Mathematicians have a broader notion of the term "space" than the average person; and in their sense a space need not consist of places, that is, geographical locations. Not paying attention to the two meanings of the term "space" is the source of all the confusion about whether time is the fourth dimension. The 'space' of spacetime is four dimensional and in that space, the space of places is a 3-d sub-space. But spacetime is a space of events, not a space of places.
In any coordinate system on spacetime, it takes at least four independent numbers to determine a spacetime location. In any coordinate system on the space of places, it takes at least three. That's why spacetime is four dimensional but the space of places is three dimensional. Actually this 19th century definition of dimensionality, which is due to Bernhard Riemann, is not quite adequate because mathematicians have subsequently discovered how to assign each point on the plane to a point on the line without any two points on the plane being assigned to one point on the line. Consequently, the line and the plane have the same number of points, and the line and plane must have the same dimensions according to the definition. To avoid this problem, the dimensionality of a space has been given a rather complex new definition.
[ Home - Physics - Philosophy - Archive - Reference - Authors]