Michael
It is not a given that Space is empty since it is not yet known if it is itself discrete, especially at the Planck Scale. There are as yet deep problems correlatiing scale which seems necessary to understand why gravity is so weak let alone the full nature of the Universe. One of the major problems is formulating a theory that is background independent.
Quantizing the Universe » American Scientist
As for distance calculations this might help
http://en.wikipedia.org/wiki/Distanc...res_(cosmology)
Distance calcs may be revised sometime soon as The Planck Telescope intends to duplicate WMAP in much higher resolution. Pretty damned exciting!
