If you feel you want something like A Brief History, but more mathsy (if you can cope with maths up to degree level, or early degree level, and can remember it all. He starts out quite benignly), I could recommend The Road to Reality: A Complete Guide to the Laws of the Universe
by Roger Penrose
It's a thick volume that's quite heavy going in the later chapters. If you understand it all completely you should probably think about getting tenure as a Physics Professor. However, if you're looking for more of a challenge than Brief History, it's a good read...
But if you do get though it, you'll have a much
more profound understanding of modern thinking on the universe than BHOT
or a book written in Layman's English could ever supply.
Another suggestion for people who are interested in the nature of computing, information theory, and some of the more obscure parts of mathematics... Godel, Escher, Bach: An Eternal Golden Braid
by Doug Hofstadter
is an excellent, intriguing page-turner. It's a bit out-of-date (predicting that a computer will never beat a human at Chess!), but nonetheless, well worth a read in paperback form...