In The Grand Design, Stephen Hawking has apparently grown so smart he can claim on the first page that philosophy is dead and that truth belongs to the scientists. The rest of the book is more or less an updated equivalent to A Brief History of Time. It recounts some of the major discoveries in quantum physics and cosmology, extending all the way back to the moment before the Big Bang, when the universe emerged from nothing. This is an area usually left to philosophers and theologians, but Mr. Hawking clearly knows everything.
If you're not on Stephen Hawking's level, maybe you can fake it by reading the entire Encyclopedia Britannica. In The Know-It-All, A.J. Jacobs records his valiant effort to plow through all 33,000 pages of the honored text. He combines a running commentary on various articles with constant worrying over the effect his epic quest is having on his marriage, his social life and his sanity.
But why bother with the Encyclopedia Britannica when you could simply consult John Hodgman? Known chiefly as a Daily Show correspondent and as the PC in Apple's Mac vs PC ads, he's also given us all world knowledge in a trilogy of books: The Areas of My Expertise, More Information Than You Require and That Is All. I'm a fan of the audiobook version of More Information Than You Require, which includes a number of cameos and a live recording of John Hodgman reading the names and professions of 700 Mole-men.
And once you've listened to a near endless recording about Mole-men, you can truly say you've learned enough. At least for now.