Curved space-time in a matter-dominated, closed universe during the middle half of its expansion-compression phases. At each instant of time t, the space axis forms a closed loop with radius R(t), the so-called radius of the universe, in an unobservable fourth dimension.

From F.H. Shu, The Physical Universe (1982); University Science Books

Gilles Nullens

Arundel, September 2006