Are voids in space empty or consist of undetected matter?
v. 5 n. 10
The intent now is to contrast some conventional and a proposed view of cosmic voids.
In the cover image the black dots represent groupings of galactic superclusters. In contrast to convention referenced above and in the footnotes, the voids in this image are considered to be composed of only marginal particulate, or visible, matter. Particularly, if the largest scale voids held substantial undetected particulate matter they would contract, instead of expand as observed.
The mass-energy of voids (and more) has been quantitatively described by
m/r^2 = A/G
where A ≈ 10^14 m/s^2. This expression was shown to be scale invariant; for example, the mass of the visible Universe given a diameter of 93 billion light years is about the conventional figure according to this relation. It was derived at the galactic supercluster scale (to include dark energy, dark matter and visible matter) where accelerated expansion is first apparent, so that acceleration A is essentially that of the Universe at large.
Typical large-scale voids vary from about ten to one hundred times the size of a typical galactic supercluster (100-300 million light years; the size of a couple of close together dots in the cover image). The mass of a typical large-scale void, then, could be
m ∝ r^2
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m = A/G r^2 ≈ A/G (200x10^6 LY x 50)^2 kg.
In conventional terminology this mass includes dark energy, dark matter and/or any particulate matter. But according to these Letters, this void is considered to be essentially composed of gravitational mass-energy stored in space(time) that is being released to cause the acceleration of the Universe (at about 10^-14 m/s^2).
To answer the title question, voids in space are not empty, nor might they be composed of undetected or transparent matter of any significance, rather voids could be essentially gravitational energy stored in space causing the observed accelerated expansion of the Universe as well as stabilizing visible matter at the smaller scales. *
[64] [astro-ph/9505088] The formation and evolution of large- and superlarge-scale structure in the universe -I: General Theory ( arxiv.org )