I read this book while falling asleep nearly every night for the last few months. It isn’t terribly quotable and it put me to sleep very well, but that doesn’t mean it isn’t fascinating.
What did I learn?
There is far, far more dark matter in the universe than baryonic matter. In fact it is the distribution of dark matter that determines the visible distribution of matter that we see. Understanding the properties of dark matter is essential to understanding large-scale structure formation in the universe.
There is plenty of stuff, intergalactic gas and such, between galaxies. I had somehow imagined that it was all pure voids between them. Even metals make it out into intergalactic clouds. This makes perfect sense when one considers that galaxies collide and form clusters.
Quasars were far more common in the early universe. It may be that most galaxies pass through a phase of having active nuclei.