Thanks, Rich. But I can't take credit for it, it's an old turn of phrase, and even George Lucas is aware of it. Seemingly "empty" space is actually jam-packed with electro-magnetic radiation, including visible-light photons. As you gaze at M31, take a step to the right. You still see it. Now, take a figurative 10,000 light-year step to the right, and you still see it. Every star in the cosmos is sending out a flood of radiation, at many wavelengths and in all directions, and it only takes a tiny, immeasurably small fraction of it, for humans to not only detect it, but to wrest basic information out of it as to the conditions of it's birth. Wavefront after wavefront of visible-light energy in spherical shells is pumped out into the vastness of space, from every star that shines. A cubic meter of empty interstellar space contains wavefronts of energy from every star and galaxy in the observable universe a with line-of-sight to it. Space itself is full of information cast-off by every emitter in the cosmos. The same information M31 yields to a spectrograph on earth is available to an astronomer on a planet somwhere in M33. We exist amid an ether of information of cosmic places near and absurdly far. We are immersed in it. It flows around us, through us. Gravity is part of it; so yes, it "binds the galaxy together". That's as far as I'll take it, lol.