Contrary to the popular misconception that different dimensions are parallel universes that exist parallel to our own, dimensions are less complex than that—they are simply the different facets of what we perceive to be reality. We are always aware of three dimensions—those that define length, width, and depth of all objects in our universe. Beyond theses dimensions, scientists suggest there are many more. The theoretical framework of Superstring Theory proposes that the universe actually exists across ten different dimensions.
The first dimension is length (also known as the x-axis). A straight line is an example of a one-dimension object; it exists only in terms of length and has no other qualities. If you add the second dimension, height (the y-axis), you end up with an object that is 2-dimensional (like a square). The third dimension is depth (the z-axis), which gives all objects a sense of area—like a cube. Any dimensions beyond these three are not immediately apparent, but they still have a direct effect on reality.
Scientists widely believe that the fourth dimension is time. Knowing an object’s position in time is essential to understanding its position in the universe. It governs the properties of all known matter at any given point.
Superstring Theory proposes that the fifth and sixth dimensions are where the ideas of alternate worlds arise. If we could perceive a fifth dimension, we would see a world that is slightly different from our own. In the sixth, we would see a plane of possible worlds. If you could master these two dimensions, you could essentially time travel.
But wait—it gets deeper. In the seventh dimension, you would have access to the possible worlds, where everything is different from the beginning of time. The eighth dimensions would give us a plane of all possible universe history, each of which begins with different conditions and branches out infinitely. The ninth dimension would allow us to compare all the possible universe histories. By the tenth and final dimension, we have reached a point where everything possible and imaginable is covered. This is the natural limitation of what we can conceive in terms of dimensions.
So, if there are 10 dimensions, why can we perceive only four? The answer is quite complex. Either the extra dimensions are compactified on a very small scale, or else we may live on a 3-dimensional submanifold corresponding to a brane, on which all known particles besides gravity would be restricted. If the extra dimensions are compactified, the extra six dimensions are in the form of a Calabi-Yau manifold, meaning they would have governed the formation of the universe from the beginning—though they are imperceptible to us.
The interesting thing about string theory is that it gives us more room to accommodate both Einstein’s theory of gravity as well as sub-atomic physics. It could explain why previous attempts at unifying the forces of nature have failed—a standard four-dimensional theory is “too small” to compact into one mathematical framework. The mathematics of the 10th dimension superstring, in contrast, is both beautiful and brutally complex. It has opened up entirely new areas of mathematics, but at this time it is still above our comprehension. Physicists are anxiously awaiting a genius physicist to crack this problem.
Source: PBS, Universe Today, mkaku.org