IANAP, but those +/+/+/+ are the signs in the distance function of your universe. Specifically ++++ is an Euclidean spacetime where the distance of any point in

IANAP, but those +/+/+/+ are the signs in the distance function of your universe. Specifically ++++ is an Euclidean spacetime where the distance of any point in spacetime is the sum of the squares of the distances in each dimension (including time). Our universe is not Euclidean but Minkowski spacetime where the opposite sign is used for the time-like dimension (which gives origin to special relativity). Egan explores universes with two timelike dimensions (++--) and all spacelike dimensions (++++).