As far as the universe can be said to exist at all, it probably has 10 dimensions. That’s the only way string theory makes sense. And physicists want string theory to make sense because it could be the Theory of Everything, uniting the otherwise incompatible theories of general relativity (for very big things) and quantum mechanics (for very small things) into one internally consistent package.

We don’t see the additional six, they say, because they’re just too small to notice, curled up or “compactified” in the form of Calabi-Yau manifolds. And it may be just as well, since they get pretty weird as they go on.

We’ll get to them later, but first let’s start with the basics.

### 10. The First Dimension

The first dimension is pretty simple: a straight line connecting two points, or a length without width or depth. But as Rob Bryanton (on whose work this list is based) points out, within that apparent simplicity there’s a great deal of complexity. After all, the first dimension isn’t bound by any two points that define its trajectory. It stretches to infinity beyond them.

Nor does any 1D line exist in isolation. None of the dimensions do. So a single one-dimensional line passing through any two points in your living room also passes through every other point along the same trajectory, taking in distant planets, stars, galaxies, neighboring universes even – whatever lies in its path. In other words, a line has the potential to contain an infinite stream of information within its one-dimensional confines.