According to the science channel "we live in a world with three spatial dimensions (length, width and depth) and one dimension of time. This means that it only takes three numbers to determine our physical location, which on Earth breaks down to longitude, latitude and altitude/depth. Time naturally comes into play by identifying when we're at that particular point in space. Some physicists, such as string theorists, believe that additional dimensions also exist but are folded away in each point of space and are invisible to the human eye."
On Earth, these coordinates break down to longitude, latitude and altitude representing the dimensions of length, width and height (or depth). Slap a time stamp on those coordinates, and you're pinpointed in time as well.
In string theory(/theories) the additional dimensions are "wrapped" on very small length scales, so small that our senses cannot experience them. I do not share the enthusiasm about these theories, because apparently they cannot be proved nor disproved: in this case they remain a mere mathematical exercise.
But the general idea of additional dimensions is not, in my opinion, to be rejected. Just like our senses cannot register great part of the electromagnetic radiation spectrum, maybe they are not able to "see" many other things (without entering in the realm of spirituality).
By the late 1980s and very early '90s, string theory was definitely the theory that everyone felt would eventually lead to the TOE. There were just two basic problems with it.
- Physicists had developed five different versions of string theory. Without spending the next five chapters telling you all about them, I'll just give you their names. We have Type I, Type II, Type IIB, Heterotic O, and Heterotic E. They are all fundamentally the same, but the way that they incorporate supersymmetry and explain the vibrational patterns vary from theory to theory.
- These five versions each ended up having many possible solutions to the equations that defined them. There were different possible ways to curl up the extra dimensions with each solution corresponding to a universe with different properties. What lies at the heart of this problem is that the equations in string theory are so complicated that no one knows their exact form.