  The 3-space of a universe model is defined at a certain simultaneity. Hence
space depends on which time is used. We find a general formula generating all
known transformations to conformally flat spacetime coordinates, and work out
the physical interpretation of conformal coordinate systems in different
universe models. We show that continual creation appears when conformal time is
used in Friedmann-Robertson-Walker models with negative spatial curvature, and
in universe models where the inflationary era started as a quantum fluctuation
at t > 0, for example at the Planck time. A general procedure is given for
finding coordinates to be used in Penrose diagrams.
