by houserichichi » Wed Jul 12, 2006 2:56 am
Spacetime is a four dimensional manifold with 3 dimensions of space (that we all know and love) and one dimension of time (that is either always going too fast or never going fast enough depending on situation). Some differentiate a 4-dimensional manifold from our 3 spatial and one temporal dimensional manifold by referring to spacetime as a 3+1-dimensional manifold rather than a 4-dimensional one.
In spacetime you need 4 numbers to specify a point: x, y, z, and t. Four numbers means 4 dimensional. All assuming you can set up a coordinate system to begin with, of course. Thankfully, spacetime is locally flat.