Here's my theory as to why time is the fourth dimension:

	Imagine a 3-D cube.  It is defined by a unique set of coordinates.  One
corner of this cube is at the origin of an imaginary set of axes.  Now,
let's say this cube moves a certain distance from its original
orientation and time has **not** passed.  This object violates our
original definition of the object.  This NEW object is defined by a
unique combination of two sets of coordinates.
	In order for our original object to move in three-dimensional space, a
new dimensional quantity has to exist, i.e. time.  Here's a brain teaser
I've been working on for a bit.  You know of Einstein's famous
equation:  E=mc^2.  Take it one step further.  If mass is a quantity
relating to the third dimension, then what would be a suitible equation
for the conversion of a unit of time to energy?

					- Ron III
					  Don't ask how I came up with this,
                                          my mind just wanders sometimes.
                                           ;)