[TopQuark]

The generally accepted answer is that the fourth dimension is time. The more interesting question is "what is the fifth dimension?" (And no smart remarks about the musical group please)

No one knows, of course. I just wanted to mention that the scientists need not add dinmensions one at a time. Your remark reminded me of a model (in statistical mechanics) from long ago that calculated the behavior of a system in... 27 dimensions (yes, there were reasons for the choice of that number). You may also hear a statement along the lines, "We know this phase transition occurs above eleven and below six dimensions. What happens in between is an open question."

So, one need not assume that the next "big" change in paradigm, if it affects the dimensionality at all, will add just one dimension.

[lafroste]

You'll get no arguments from me on that one. However, my little pile of quivering grey stuff has its metaphorical hands full with just five, thank you very much.

[gjenkins]

Super string theory has us somewhere around 9 dimensions, and super membrane theory has us somwhere around 11, and my super string super string theory has us at 18 dimensions ... but that doesn't account for the 32 continuous random variables, that I have just identified, which determine what I will do in the next hour. Geez, this is getting complex.