# The shape of the universe

It’s important to know the shape of the universe. Maybe one day we’ll set off on a very long journey into space and we’d need to know whether we’re just going to end up right back where we started, which would be irritating.

This depends in part on the curvature of the universe and it’s easiest to think of this in two dimensions. Imagine a flat earth, like a sheet of A4. If you and I set off parallel to one another, we’d remain the same distance apart and our paths would never cross. If we drew a triangle on this flat surface, the angles would add up to 180 degrees. We’d say this had *zero curvature*.

Now imagine a globe. We set off parallel to one another again, but our paths would eventually cross. If we followed the latitude lines on the Earth, for example, we’d meet at the North Pole, and the angles of a triangle on this surface would add up to more than 180 degrees. We’d say this had *positive curvature*.

Finally, imagine a saddle (or hyperbola if you want to be scientific). If we walked in parallel on this surface we’d keep getting further apart. I have a policy of never lending money to anyone on a hyperbola because you’ll never see them again. Here, the angles of a triangle would add up to less than 180 degrees and we call this *negative curvature*.

It gets harder to visualise in three dimensions, which is how many space dimensions our universe has, and even harder again if we include time as the fourth dimension, but hopefully you get the idea.

There are a number of things that can influence the curvature of our universe and one of the biggest is gravity. We all think of gravity as helpfully sticking us to the planet or unhelpfully making cups of tea drop off our desks, but that pulling force also bends the fabric of space.

One of the common visualisations is to use a rubber sheet stretched over a box to represent space. Now drop a bowling ball onto the rubber sheet and you’ll see it sink into the rubber, bending it. That’s what a star or planet does to space.

For a while now, experiments have pointed to our universe being flat and having zero curvature, or as near as damn it. We get a lot of information about the shape of the universe from the Planck Space Telescope, which was launched in 2009. An instrument on that measured the Cosmic Microwave Background (CMB), which is the ancient glow of light left over from the Big Bang. Looking at that tells people with slide-rules a lot about the shape of the universe now and in the distant past.

However, three smart-arses have reanalysed a lot of the CMB data and claim the universe is 99% likely to have positive curvature, like a globe. They went as far as to call the whole thing a cosmological crisis.

Their work has however displeased many other scientists — presumably those with shares in a flat universe — and effigies of the three smart-arses may be burnt in laboratories across the world. The smart-arses’ analysis of the data is not in dispute but some scientists suggest this is an aberration, a statistical fluctuation and no doubt an abomination.

Other experiments still point to the universe being flat, which remains the prevailing opinion.

Anyway, you can read all about it in the article I link to. I’m concerned about how a curved universe might affect house prices, although I’m sure estate agents have more trickery at their disposal beyond the trusty wide-angle lens.