the voids between superclusters of galaxies is not a void in the sense that has been discussed so far, which seems to be more discussion on philisophical aspects of nothingness and/or semantics. all good discussion points.
so even if there is no matter or electromagnetic waves, etc. in the voids there is not "nothing" there as there is space-time.
(where I say "space-time" with no real understanding of it but only based upon comments from other threads. )
why are there voids? well, i though that it had something to do with fluctuations during the big bang, clumping matter together.
or are my comments "vacuous"...
