The book cover doesn't lie. Carroll really does tackle the big picture, starting with the fundamental question of how to ascertain the nature of reality, to the origin and overall state of the universe, to the evolution of life, the appearance of consciousness, free will, and finding meaning in an uncaring universe. Throughout, Carroll's writing is lucid and approachable: these may be big ideas, but they can be understood.
Some of the ideas to retain are:
- There is no up or down in space. The reason we think "up" is so different from "down" or "left" is that we're very close to a planet that exerts a gravitational force on nearby objects. Likewise, there's no "before" or "after" at the level of quantum physics: you can swap a time axis for a space axis and the equations still make sense. The reason we think the past is so different from the future (or from left and right) is that we're very close to a point of very low entropy: the Big Bang.
- Planets of belief: some beliefs naturally congregate: if you think that there's an afterlife for humans, then you likely think that there's an afterlife for dogs as well. And if you think that, then you likely believe in souls. Carroll calls these systems "planets of belief" (though perhaps an analogy involving a social network might have been better).
- Poetic naturalism: this is the idea that there are many different ways of describing something that are true and, just as importantly, useful. It's true that a car is a collection of molecules obeying the laws of chemistry, or even as a collection of subatomic particles obeying the laws of quantum physics. But there are far, far too many molecules (or atoms, or fermions) to keep track of, so it's much more useful, and no less true, to consider a car as a collection of mechanical parts. What's important is that where they overlap, the different explanations be compatible.

In the end, unsurprisingly for a scientist, he sees beauty and wonder in the universe, and hope in humans. What's remarkable is the way Carroll ties together all the elements of the journey into a coherent whole.