without the benefit of telescopes operating in multiple bands of light we might still declare the space between the galaxies to be empty. Aided by modern detectors, and modern theories, we have probed our cosmic countryside and revealed all manner of hard-to-detect things: dwarf galaxies, runaway stars, runaway stars that explode, million-degree X-rayemitting gas, dark matter, faint blue galaxies, ubiquitous gas clouds, super-duper high-energy charged particles, and the mysterious quantum vacuum energy. With a list like that, one could argue that all the fun in the universe happens between the galaxies rather than within them.

without the benefit of telescopes operating in
multiple bands of light we might still declare the space between the galaxies to be
empty. Aided by modern detectors, and modern theories, we have probed our
cosmic countryside and revealed all manner of hard-to-detect things: dwarf
galaxies, runaway stars, runaway stars that explode, million-degree X-rayemitting
gas, dark matter, faint blue galaxies, ubiquitous gas clouds, super-duper
high-energy charged particles, and the mysterious quantum vacuum energy. With a
list like that, one could argue that all the fun in the universe happens between the
galaxies rather than within them.