I've gone through my "getting bearings" reading of this book, meaning a chapter a day just so I can get the trajectory of everything and maybe during my next read-through, which will be much slower, things will make sense. The first thing that has to be said is that this book definitely gives the reader a good perspective of the modern state of theoretical physics: though Penrose does take some positions which are controversial, such as his take on string theory (but then again touching the state of attempts at theories of everything is guaranteed to lead to controversy in the scientific sense), he shows deep knowledge and insight into physical problems and what barriers have to be overcome in order to reach our next physical revolution. He brings the reader through the perspectives of general relativity, quantum field theory, and thermodynamics, each time clearly making a case for what problems in each area need to be considered or explained by a unification of general relativity and quantum mechanics. This is no small accomplishment; I have not seen any books which have done nearly as good a job in putting all these things together as this one.<br><br>So why four stars instead of five? Check the title of this review. I have my bachelor's in math and physics (good school, poor student) and a large portion of this book looks like it will take a long time to digest, with the chapters on differential geometry looking like a few months of work and many secondary sources. Somebody without knowledge of those fields would have to treat the entire book that way. In short, the book is far less self-contained than it appears to be, and I would say less than the author thinks, as well. For example, in the second chapter he apologizes for having to use logarithms. This is in a book where, a dozen chapters later, we're taking the Lie derivative of tensors. Apologizing for using logarithms, yet somehow the reader is supposed to understand pseudo-Riemannian geometry a few hundred pages later. Either that's some sort of twisted joke or he really thinks that we can get it that quickly.<br><br>For all the complaining about the difficulty of some parts of this book, it's still a good one to pick up: even somebody who has to skip a great deal of the math could still learn a lot about the state of modern physics through the more qualitative descriptions of reality. Maybe after putting a bit more time into really reading closely I'll find that I was being too harsh on it all along, but we'll see in a few months.