Main Question or Discussion Point
Why should time be considered as a 4th dimension?
It's the fact that the speed of light is an invariant, a truly fundamental quantity. because of this, if you take any two events and you assign them coordinates (as measured in some specific frames), the quantity [tex] c^2 (\Delta t)^2 - (\Delta x)^2 - (\delta y)^2 - (\Delta z)^2 [/tex] gives a number that will be the same as measured by any other observer (using the intervales measured in their own frames). This is what unifies time and space into a four-dimensional manifold.Why should time be considered as a 4th dimension?