What if we found a 10th dimension?

When someone mentions "different dimensions," we tend to think of things like parallel universes - alternate realities that exist parallel to our own, but where things work or happened differently. However, the reality of dimensions and how they play a role in the ordering of our Universe is really quite different from this popular characterization.

Does string theory excite you?

Mathematically, it holds up. Aspects about it suggest not one but several different dimensions, ones we're not generally privy to, though we may be interacting with some of them all the time completely unaware. Were it true, what would these dimensions look like and how might they affect us? And what is a dimension anyway?

Two dimensions is just a point. We may remember the coordinate plane from math class with the x and y- axes. Then there's the third dimension, depth (the z-axis). Another way to look at it is latitude, longitude and altitude, which can locate any object on Earth. These are followed by the fourth dimension, space-time. Everything has to occur somewhere and at a certain time. After that, things get weird.

Superstring Theory, one of the leading theories today to explain the nature of our universe, contends that there are 10 dimensions. That's nine of space and one of time. Throughout the 20th century, physicists erected standard model of physics. It explains pretty well how subatomic particles behave, along with the forces of the universe, such as electromagnetism, the stronger and weaker nuclear forces and gravity. But that last one standard physics can't account for. 

Even so, this model has allowed us the startling ability to peer back to the moments just after the Big Bang took place. Before that, scientists believe that everything was condensed into a single point of infinite density and temperature, known as the singularity, which exploded, forming everything in the observable universe today. But the problem is, we can't peer back beyond that point. That's where string theory comes in. The  innovations it provides can account for gravity and help explain what existed before the Big Bang.

So what are these other dimensions and how might we experience them?

That's a tricky question, but physicists have some idea of what it might be like. Really, other dimensions are related to other possibilities for our world open up.

You'd be able to move forward or backward in time, just as you can in space, say while walking down a corridor. You'd also be able to see the similarities and differences between the world we inhabit and other possible ones. In the sixth dimension, you'd move along not a line but a plane of possibilities and be able to compare and contrast them. In the fifth and sixth dimensions, no matter where in space you inhabit, you'd witness every possible permutation of what can occur in past, present and future. 

In the seventh, eight and ninth dimensions, the possibilities of other universes open up, ones where the very physical forces of nature change, places where gravity operates differently and the speed of light is different. Just as in the fifth and sixth dimensions, where all possible permutations in the universe are evident before you, in the seventh dimension every possibility for these other universes, operating under these new laws, becomes clear.

In the eight dimension, we reach the plane of all possible histories and futures for each universe, branching out into infinity. In the ninth dimension, all universal laws of physics and the conditions in each universe become apparent. Finally, in the tenth dimension, we reach the point where everything becomes possible and imaginable. 

For the string theory to work, six dimensions are required for it to operate in a manner that's consistent with nature. Since these other dimensions are on such a small scale, we'll need another way to find evidence of their existence. One way would be to peer into the past using powerful telescopes which can hunt for light from billions of years ago, when the universe was first born.

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. 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 to time or go to different futures.

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 from the very beginning of time. 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.

In the ninth dimension, we can compare all the possible universe histories, starting with all the different possible laws of physics and initial conditions. In the tenth and final dimension, we arrive at the point in which everything possible and imaginable is covered. Beyond this, nothing can be imagined by us lowly mortals, which makes it the natural limitation of what we can conceive in terms of dimensions. The existence of these additional six dimensions which we cannot perceive is necessary for String Theory in order for there to be consistency in nature. The fact that we can perceive only four dimensions of space can be explained by one of two mechanism: either the extra dimensions are compacted on a very small scale, or else our world may live on a three dimensional submanifold corresponding to a brane, on which all known particles besides gravity would be restricted (aka. brane theory).

String theory has an answer for what came before the Big Bang. The universe was made up of nine perfectly symmetrical dimensions, the tenth being time. Meanwhile, the four fundamental forces were united at extremely high temperatures. The structure was under high pressure. It soon became unstable and broke in two. This became two different forms of time and led to the three dimensional universe we recognize today. Meanwhile, those other six dimensions shrunk way down to the subatomic level.

As for gravity, string theory contends that the basic units of the universe are strings infinitesimally small, vibrating filaments of energy. They're so tiny, they'd be measured on the Planck scale- the smallest scale known to physics. Each string vibrates at a specific frequency and represents a certain force. Gravity and all other forces are therefore a result of the vibrations of specific strings.

One problem is that this theory is hard to test, outside of advance mathematical equations. Some experiments have been done using supercomputers, which can run simulations and make predictions. That isn't exactly enough to prove that it's true, but it's helpful and lends support. Besides astronomical observations, physicists are hopeful that experiments with the Large Hadron Collider at CERN, on the Franco-Swiss border, may offer evidence of extra dimensions, lending string theory greater credence.

Some scientists believe that the multiverse has only 10 dimensions while others put that number at 11. However, a universe cannot have more than 11 dimensions because of self consistency- they become unstable and collapse back down into 11 or 10 dimensions. At this point, anything is possible. There are all futures, all pasts, all beginnings and all ends, infinitely extended, a dimension of anything you can imagine. 

String theory also has an answer for the mysterious moment before the Big Bang occurred. The universe then consisted of nine perfectly symmetrical dimensions and one time dimension. The four fundamental forces- which I cover in my Quick Summary of Universe- gravity, weak nuclear, strong nuclear and electromagnetism were held together under extremely high pressure and temperature. When it became unstable, it broke into the dimensions of time and space we know today. The first four are perceptible to us while the last six or seven were reduced down to a size smaller than an atom.

While the idea of a multiverse is fun in terms of science fiction and daydreaming, it's also mathematically sound and would provide the framework for a theory of everything- which is exactly what string theory attempts to be. It would be a beautiful coming together of science, math, and mysticism.