In Cosmology, the third and fourth dimensions are equivalent.

The first two are polar coordinates.  The third is distance from the origin and also elapsed time.

Local time is so small comparatively, it can be ignored.

However, local time is our most important fact, and gives us both a warning and a clue.

The failure to identify the equivalence of the 3rd and 4th gives rise to much of the  confusion in cosmology.

The warning and clue are to the existence of a separate reality.