We tend not to dwell on the fact that we exist in three dimensions. Forwards-back, left-right, up-down; these are the axes on which we navigate the world. When we try to imagine something else, it ...

Yes, OK, four dimensions – time is a dimension too, albeit an oddly unidirectional one (see “Cosmic uncertainty: Does time go both ways?“). But we’ve long thought there might be more large-scale ...