In the grand tally of cosmic constituents, galaxies are what typically get counted. Latest estimates show that the observable universe may contain a hundred billion of them. Bright and beautiful and packed with stars, galaxies decorate the dark voids of space like cities across a country at night. But just how voidy is the void of space? (How empty is the countryside between cities?) Just because galaxies are in your face, and just because they would have us believe that nothing else matters, the universe may nonetheless contain hard-to-detect things between the galaxies. Maybe those things are more interesting, or more important to the evolution of the universe, than the galaxies themselves

In the grand tally of cosmic constituents, galaxies are what typically get counted.
Latest estimates show that the observable universe may contain a hundred billion
of them. Bright and beautiful and packed with stars, galaxies decorate the dark
voids of space like cities across a country at night. But just how voidy is the void
of space? (How empty is the countryside between cities?) Just because galaxies
are in your face, and just because they would have us believe that nothing else
matters, the universe may nonetheless contain hard-to-detect things between the
galaxies. Maybe those things are more interesting, or more important to the
evolution of the universe, than the galaxies themselves