Integral said:
The number of variables required to completely specify the state of your system is the number of dimensions of the system.
It takes 3 numbers to specify the location of a object in space, therefore we speak of 3 spatial dimensions. If you throw in time you get a 4th dimension.
If you are tracking the fluid level of 100 different tanks you have a system with 100 dimensions.
I absolutely disagree.
The fluid level of 100 different tanks is a function of one dimension (i.e., height) in a universe which contains that dimension, as well as others.
Each tank is not a universe unto itself.
The level of fluid contained within the 100 tanks is a function of the single dimension of height. The volume of fluid contained within a tank is a function of three dimensions: height, depth, and breadth. Add the fluctuation in the fluid levels within the various tanks over time and you have the three spatial dimensions plus the only observed temporal dimension.
I don't know exactly what dimensions are, but I know some of their properties. Dimensions within our universe are the framework which contain eletroweakness and gravitation. They constitute the box which contains stuff. That the box is independent of the stuff it contains is obvious from the fact that space expands faster than stuff (i.e., faster than the speed of light in a vacuum, as per last year's Nobel prize winners), and the fact that gravitation, although motivated by mass, only acts upon dimensions by warping dimensions, as per general relativity. Thus gravitational lensing, in which massless photons, themselves immune to the immediate effects of gravitation, nevertheless travel circuitous paths along spatial dimensions bent by the gravitational force motivated by objects which possesses mass.
Dark Matter and Dark Energy may well be enclosed within alternative spatial dimensions or even alternative temporal dimensions, or even within dimensions which are neither spatial nor temporal within our understanding.
Anyways, here's a fun video showing the difference between the box and the stuff within, in that the unhappy children receive beautifully wrapped boxes which contain nothing except dimensions and air. (It's actually a commentary upon the politics of a certain province within a certain country very near where I live, hut it also just so happens to illustrate my physics point, even as it shows off a couple of lovely young ladies (Hey! I'm a bachelor, so I get to say that!))
http://www.youtube.com/watch?v=k1WQ-srZX8k
So, that's my point. Dimensions are neither matter nor energy, but they contain matter and energy, and gravitation acts upon them.
Acceleration is not a dimension, but is simply a function of the three observed spatial dimensions plus the single observed temporal dimension, and requires the positing of no additional dimensions to explain it. Newton described acceleration quite well without the slightest knowledge of strings.