In his new book What If?: Serious Scientific Answers to Absurd Hypothetical Questions, Randall Munroe tackles all the problems you've been dying to figure out. Here, he definitively answers the age-old question of how long the longest book in the world could be.
Q: Say an author announces that his or her next book will be the longest book in the world. Given the available resources of our planet, how long is the longest individual hardcover book we could publish?
A: The paper industry produces about 20 million tons of printable paper each year. If we used all that paper in our book, it would be about 12 trillion pages long, and a bookshelf wide enough to hold it would have to wrap around the Earth 15 times.
With a book that takes up that much shelf space, you might have a hard time convincing bookstores to put it in the rack up front.
If you started reading this book, and read for 8 hours a day, every day, it would take you about 70 million years to finish. If there's a new major character introduced every hundred pages or so, you'd have 100 billion main characters—which is about the same as the total number of humans who have ever lived. In other words, this book could be a biography of *everyone*.
Unfortunately, as cool as it would be, I don't think this is a good idea, for one simple reason: Since you could only ever sell one copy, you'd have zero chance of making the bestseller list.