A Short History of Nearly Everything by Bill Bryson.
It's great. In a 545-page book, Bryson manages to describe everything from how the universe was born to how some old geezers in the 1700's managed to determine the mass of earth. It's funny, it's smart, and best of all, you can understand it. Even if you aren't interested in science, you will appreciate the amount of research Bryson did, and will come out knowing more about the world the next time you're at a pub quizzing your friends. The best part is, it's concise, but not to the point where it's boring. It's not too much information, but enough to make you feel like you know everything.
here's an excerpt:
"Being you is not a gratifying experience at the atomic level. For all their devoted attention, your atoms don't actually care about you--indeed, don't even know that you are there. They don't even know that they are there. They are mindless particles, after all, and not even themselves alive. (It is a slightly arresting notion that if you were to pick yourself apart with tweezers, one atom at a time, you would produce a mound of fine atomic dust, none of which had ever been alive but all of which had once been you.) Yet somehow for the period of your existence they will answer to a single overarching impulse: to keep you you.
The bad news is that atoms are fickle and their time of devotion is fleeting--fleeting indeed. Even a long human life adds up to only about 650,000 hours. And when that modest milestone flashes past, or at some other point thereabouts, for reasons unknown your atoms will shut you down, silently disassemble, and go off to be other things. And that's it for you."
This book is great. Highly recommended.