Imagine you are living in a lake. You are a fish with eyes on either side of your head and all you know is the underwater world of sediment and vegetation and other fish swimming around you. The sunlight comes in, dimmer and refracted, through the water. You go about your life convinced that this underwater world is all there is because it’s all that you can experience. However, there exists an entirely new environment outside of your line of sight — one where animals don’t need water to breathe and flowers bloom in a far more arid world.
This is the situation physicists believe we’re in. We are those fish and those higher dimensions are the new environments we can’t perceive. In fact, string theory, which attempts to reconcile relativity with quantum mechanics (the laws of the very big with the very small), only works if we assume there are much more than the four dimensions we’re used to. Physicists believe but cannot yet prove that there exist up to 11 dimensions in the multiverse. Yes, the multiverse, where universes are bubbles that sometimes come together or split apart. This splitting apart of a universe bubble is one possibility of what might have caused the Big Bang.
Here, I attempt to simplify the ten dimensions of string theory.
A line connecting two points. There is no depth and no height, only a width. You can call this the x-axis.
Now we have added height or the y-axis. Think of any flat figure, like a triangle.
We have now added depth or the z-axis. This is the dimension in which we experience the world. It includes volume and the ability to obtain cross sections from objects. You can think of this dimension as space without time.
The fourth dimension is not a spacial one but it consists instead of time. Time helps plot an object’s location in the universe and also adds a way for the third dimension to change. Remember how the third dimension is space without time? Well now we officially have space time.
“Time is relative, okay? It can stretch and it can squeeze, but… it can’t run backwards. Just can’t. The only thing that can move across dimensions, like time, is gravity.” -Interstellar, dir. Christopher Nolan.
From here on we begin to see the higher dimensions. These are imperceptible to us, scientists believe, because they exist on a subatomic level. These dimensions are curled in on themselves in a process known as compactification. The dimensions here on out really deal with possibilities.
In the fifth dimension there would be a new world that would allow us to see the similarities and differences between our world and this new one, existing in the same position and having the same beginning as our planet, i.e. the Big Bang.
The sixth dimension is an entire plane of new worlds that would allow you to see all possible futures, presents, and pasts with, again, the same beginning as our universe.
In the seventh dimension up through the ninth, we now have the possibility of new universes with new physical forces of nature and different laws of gravity and light. The seventh dimension is the beginning of this, where we encounter new universes which have a different beginning from ours. That is, they were not born from the Big Bang.
This dimension is a plane of all the possible pasts and futures for each universe, stretching infinitely.
The ninth dimension lays bare all the universal laws of physics and the conditions of each individual universe.
The Tenth, or Eleventh Dimension
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. Everything comes together.
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 the 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.