If there’s one thing that science depends on, it’s models. From physical models of the planets orbiting our Sun to theoretical models of the behaviour of gravity, models are a necessary part of moving our understanding of the Universe forward.
Throughout the history of science, the models have become more complicated: from the humble beginnings of Ptolemy’s perfect circular orbits to the theoretical prediction of the Higgs boson, now proved true by the amazing work at the Large Hadron Collider in CERN.
Adding dimensions is just another form of modelling. The simplest models occur in one dimension: a dot moving in a straight line. Add another dimension and you’ve got interactions: parallel lines, intersections, action and reaction, the standard pool table model.
The third dimension simply makes things a little more realistic: this is the physics of the everyday, the world we experience. But nothing could actually happen in any of these theoretical worlds without dimension number four: time. Only when we move forwards (or backwards) in time can we experience the interactions, collisions, near misses, and any other physical events.
So, three dimensions in space and one in time: surely we don’t need anything extra?
To keep up with the wacky weirdness of quantum mechanics, physicists and mathematicians have had to take one (well, a few) steps further. Adding extra dimensions helps to solve problems that just don’t make sense in a four-dimensional world.
For example, adding a fifth dimension allows physicists to show that electromagnetism and gravity are just two different parts to the same force – one step further to a unified theory of everything. Adding more helps to explain more difficulties – until we reach the end of the line for now, dimension 10, where string theory comes into play.
String theory comes from physics’ grand desire to unite everything into one overall theory: if everything has the same origin and explanation, then every phenomenon in the universe can be theorised, measured and explained. The idea behind it is that the universe is made up of strings, just like those on a guitar; and the note each string plays corresponds to how it manifests itself. So a string playing an ‘A’ might be an up quark; a string playing a ‘D’ might be dark matter; and so on. Thus, everything in the universe becomes one thing, just with a single different property.
Personally, I’d prefer it if there wasn’t one grand, unified theory of everything: life is much better when there are still mysteries to be solved.