As far as we know, we live in four dimensions, three of space and one of time. But experimentalists at the Large Hadron Collider are looking for evidence that the universe contains more than that. The existence of extra dimensions could explain some puzzling properties of the universe.
Physicists know about four forces that govern the way particles interact: electromagnetism, the strong and weak nuclear forces, and gravity. Gravity is by far the weakest. Think about sticking a magnet to a refrigerator door. The magnet can respond to the electromagnetic force that attracts it to the door. Or it can respond to the gravitational force of the Earth below. If you let it go at a short enough distance, it sticks straight to the door, ignoring the entire planet beneath it.
Physicists wonder why gravity seems so much weaker than the other three forces. One possibility is that we’re only experiencing a fraction of it. It could be that the gravitational force acts partially in another dimension, or many extra dimensions, that we can’t perceive. Knowing more about gravity could help physicists seeking to form a so-called theory of everything, a theory that combines the four forces into one.
Extra dimensions would not necessarily consist of alternate worlds, as depicted in science fiction. They could simply be too small for us to see. To understand how this would work, imagine walking along a tightrope. You are able to move only forwards and backwards without falling. In this situation, it is almost as if you exist in just one dimension of space.
However, an ant walking along the same tightrope has a different point of view. The ant is able to move forwards and backwards but also around the tightrope. To such a small creature, a tightrope exists in two spatial dimensions instead of just one.
Even if extra dimensions are small, they can still have an effect on how we experience the world. Scientists think that finding evidence of extra dimensions could help answer some of their questions about gravity, still one of the most mysterious forces in the universe.
Finding evidence of extra dimensions could also give credence to theories of physics beyond the Standard Model. Models of string theory, for example, require the existence of at least 11 dimensions.
Discovering extra dimensions could give scientists clues about the mysterious workings of gravity and could help them to unify the forces or determine the validity of string theory. It could also raise more questions about ways other dimensions shape the world around us.