Done! It seems unbelievable, but yesterday I managed to finish *The Road to Reality*, by Sir Roger Penrose. I must say I liked it a lot. It has its failures, of course, and it is sometimes contentious (willingly so), specially at the end. I have made a list of things I have found outstanding in the book.

**Brilliant first part on mathematics**. Even with no interests in physics, the chapters devoted to mathematics are just outstanding. The topics covered end up being very advanced, but things are always presented in the simplest possible way (ok, that’s not so simple with stuff such as fibre bundles), and great insight. A must read: chapters on complex numbers.**Big Bang and the 2nd law**. You don’t need Hoyle, just Clausius! Penrose really attacks this thorny issue with great honesty: the time arrow**is**really there, which means the Universe started in an initial state of incredibly low entropy. Things go downhill from there. (Remember: under gravity entropy*increases*when things cluster, the opposite from usual gases.)**Quantum entanglement and teleportation**. Very nice insights about quantum “paradoxes” due to entanglement, including teleportation, in which quantum information seems to be able to “go back in time”.**Information and black holes**. People seem to be very worried about information “lost” as stuff enters black holes. Penrose, not so much, since it connects with the argument of entropy increasing since the Big Bang. Alternatively (and, is seems, in contradiction), there is the wild idea that information disappears into black holes but appears a t every single quantum measurement, the “sinks” and “sources” of information cancelling in the global phase space. Would not this be a “totally out-to-lunch freaky head trip”? (In the language of this very funny article in The Onion.)**Ruthless criticism of string theory**. This seems like to be the fashion nowadays, but I take some pleasure on seeing this theory (some people would not even call it that) taking a beating from having sold us that they were*this*close to the final answer when, clearly, they were not. Plus, “*the*” final answer would be*their*final answer: Penrose is quite aware that many branches of physics (mine, for example) are completely independent on particle physics. BTW, see*stringscape*in physicsworld, for a nice assay of string theory situation.**The twistor agenda, and its criticism**. Penrose writes the book in such a way that string theory looks like an outlandish theory, while twistors would be the natural thing to do. Many particle phycisicst think the opposite, with twistors considered a mere mathematical exercise. Anyway, Penrose has the honesty to critizise the theory he has been developing for 40 years!**Almost no brain BS**. I was less than happy with Penrose’s journey into conciousness proposed in his*The Emperor’s New Mind*. The details probably deserve a whole entry, but let’s just say I was very glad that Penrose sticks in this book to what he knows best: physics and mathematics, stating clear from slippery issues of quantum conciousness. I was afraid we was going to do so in his discussion of quantum, state reduction; but no, that part is fine in my opinion (some suggestions are put forward, such as the LIGO experiment, that may be considered quite non-standard, but they definitely belong to standard physical theory.) He just briefly talks about his work in this area in one of the last sections. That honours him: it’s hard to refrain from talking about something to which you have devoted so much thought. But he does the right thing: the book benefits from this omission. (And, as I said, I think Penrose is just plainly misguided in this area, but this entry, just as his book, seems already too long.)

Hello. I’m a physics student (I’m going to start the third course this year). I’ve seen this book in a library near to my house, and I’ve thought of taking it but I think it will probably be difficult to understand (for example in topics like quantum mechanichs) if you haven’t studied them before. One thing i’ve observed is that inside the text there are not too long mathemetical developements of the theory (instead there is a lot of explainig text, which I prefer in a 1500 page book). I would like to know your opinion about if it’s possible to read the book from the beginnig to the end without looking for extra information in other books, or if it is necessary a graduate level in order not to miss a big part of the information.

Thank you for your time and congrautulations for your blog page.

Hello Antonio,

I guess my short answer would be “yes, grab a copy.” This is a remarkable book, and a keeper for anyone who is interested in physics. Will you be able to understand most of it? Probably not.

How much depends, as you suspect, on your previous knowlodge. Mr Penrose makes the point (in the Introduction) that everyone should be able to catch something, regardless of their background. That is partly true, and there is lots of knowledge to be gained in the first few chapters, and other introductory ones — one should be fearless to skip whole section of the book if needed, as the author suggests. But, as he admits, some parts of modern physics are just very abstract, and he does not want to “cheat”, as some others do.

A bonus on having previous knowledge is the fact that the book discusses some issues from very interesting and unusual perspectives. The mathematical part is outstanding in this regard, but there are some very interesting stuff in physics too, like quantum mechanics.