String Theory
Extract from www.universetoday.com

On a related subject click here for the wormhole (tunnel), also referred to as the Einstein–Rosen bridge, first coined in 1957 by John Wheeler as a speculative structure linking disparate points in spacetime.

We are aware of the three dimensions that surround us on a daily basis - those that define the length, width, and depth of all objects we perceive (the x, y, and z axes, respectively). The theoretical framework of "string theory", aka superstring theory, posits that the universe exists in ten different dimensions.

1. The first dimension, as already noted, is that which gives it length (aka. the x-axis). A good description of a one-dimensional object is a straight line, which exists only in terms of length and has no other discernible qualities.
2. Add to it a second dimension, the y-axis (or height), and you get an object that becomes a 2-dimensional shape (like a square).
3. The third dimension involves depth (the z-axis), and gives all objects a sense of area and a cross-section. The perfect example of this is a cube, which exists in three dimensions and has a length, width, depth, and hence volume.
4. It is posited that the fourth dimension is time, which governs the properties of all known matter at any given point. Along with the three other dimensions, knowing an objects position in time is essential to plotting its position in the universe.
5. According to Superstring Theory, the fifth and sixth dimensions are where the notion of possible worlds arises. If we could see on through to the fifth dimension, we would see a world slightly different from our own that would give us a means of measuring the similarity and differences between our world and other possible ones.
6. In the sixth, we would see a plane of possible worlds, where we could compare and position all the possible universes that start with the same initial conditions as this one (i.e. the Big Bang). In theory, if you could master the fifth and sixth dimension, you could travel back in time or go to different futures.
7. In the seventh dimension, you have access to the possible worlds that start with different initial conditions. Whereas in the fifth and sixth, the initial conditions were the same and subsequent actions were different, here, everything is different from the very beginning of time.
8. The eighth dimension again gives us a plane of such possible universe histories, each of which begins with different initial conditions and branches out infinitely.
9. In the ninth dimension, we can compare all the possible universe histories, starting with all the different possible laws of physics and initial conditions.
10. In the tenth and final dimension, we arrive at the point in which everything possible and imaginable is covered, which makes it the natural limitation of what we can conceive in terms of dimensions.

The fact that we can perceive only four dimensions of space can be explained by one of two mechanisms: either the extra dimensions are compactified on a very small scale, or else our world may live on a 3-dimensional submanifold corresponding to a brane, on which all known particles besides gravity would be restricted (aka. brane theory).

A 0-brane is a zero-dimensional object, a point; a 1-brane is a one-dimensional object, a string; a 2-brane is a two-dimensional object, a membrane; and a p-brane is a p-dimensional object, for values of p up to 9.