If you flew out in a spaceship and parked in a spot between the Milky Way and Andromeda, what else would be there?
New observations directly show that there is an intricate "cosmic web" of gas filaments flowing into galaxies like highways. This has been theorized for decades, but the Cosmic Web Imager has just given us some amazing 3D maps that show filaments of the web in great detail.
Scientists approximate that the universe is composed of 96% dark energy and dark matter; the other 4% is normal matter. Of this remaining 4% a mere 1% is the bright matter of stars, planets and galaxies, and the IGM “dim matter” makes up the rest.