[scapp]

Spaces like this (manifolds) are usually classified by which Euclidean space they look like locally. So, for example, the surface of a sphere is two-dimensional since it locally looks like a plane (whence flat-earthers). A two-dimensional torus can be visualized as the surface of a doughnut, but also as a square where going off an edge brings you to the opposite edge.

As explained in the article, the torus in question is locally three-dimensional, and you might mistake it for ordinary 3d space at first. The specific geometry we're visualizing is the 3d analogue of the square from above: it's a cube where going off an face brings you to the opposite face.

[lproven]

After much debate on Twitter, I understand this better now.

https://twitter.com/lproven/status/1564613978155802631

For a post that claims to be explaining something, I have to say, I think it's really quite stunningly poor at explaining itself.

This is not about living on a torus. As others have said, a torus is a perfectly possible 3D object in our universe, and SF has many toroidal habitats, including the original Larry Niven Ringworld and Iain M Banks' "Orbitals" as used in several Culture novels, and as also used in the videogame Halo (I believe -- not played it; not a gamer).

Since the article is called:

> Living on a Torus

Note: on

And begins:

> life in a three-dimensional torus that measured only several metres in each dimension

That to me implies inside an object. A toroidal habitat is an absolutely standard part of SF and has been since before 2001: A Space Odyssey in 1969.

The article is in fact about living inside a spacetime continuum, a universe, which is toroidally shaped, and strangely small. (What you are on is unspecified.) It doesn't say so but it seems to be.

Since I have never really wondered about the shape of spacetime, I could not even begin to parse the essay.