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I am a proud owner of the 1st edition of this book and purchased this one because it is the more recently released 2nd edition. It was my favorite book on the topic to date so purchasing the 2nd edition was a no-brainer. So what do I think of this book? Al-Khalili is no doubt a master at taking esoteric physics concepts and breaking them down into terms for anyone who has a genuine interest in the topics covered to understand. Another commenter here said he read the whole book in two sittings. Congratulations are in order for him. I, on the other hand, had to slowly comb through this book digesting the knowledge a little at time before I can move onto the next section. I read about twenty pages at a time for about a month. I would often reread areas to make sure I knew exactly what was going on. Not because it was difficult to understand what he was saying but because it was truly challenging for me to completely digest. It's more than just fascinating and it deserves to be chewed swallowed.
Al-Khalili brilliantly connects chapter to chapter helping you understand dimensions, gravity, the universe (so much more complex - even though he does a wonderful job explaining - than I could even have imagined), black holes, white holes, Einstein and his theory of relativity (it's a really big deal and he doesn't downplay how big of a deal it is), paradoxes, and finally a move into where physics is today and what our leading - most abstract? - theories are. All of it beautifully rendered with illustrations and real-world easy to understand examples.
Having read the first edition and now the second edition and although I'd recommend this book strongly to anyone with an interest in these topics that isn't perusing - or has - a degree in physics, I have a couple of gripes I'd like to bring some attention to. Maybe some of these are my own lack of understanding and inability to grasp what the author is saying, but, nonetheless, they left me confused and once or twice a little disappointed.
Al-Khalili admittedly wrote the first edition of this book years ago, and during that time Pluto was still a planet. Twice in this book he makes reference to Pluto being our ninth or `outermost planet'. Given, this is petty, but if you're updating older material and releasing it as a new and improved edition, shouldn't you look into all the details? It is my understanding that Pluto, although now considered a dwarf planet, is not truly our ninth planet anymore. In fact, it is one of many dwarf planets beyond Neptune.
Next there is a line from his first edition repeated in this edition explaining that the cosmological constant was the biggest mistake of Einstein's scientific career. While at the time that may have been believed to be the case this book goes on to explain that the cosmological constant is back in play and is actively being used in modern equations. So was it a mistake or not? A simple word change would get rid of some of the confusion this can create.
He then deals with the shapes of the universe from open to closed and finally flat. I understood this perfectly because of his examples of what open and closed were, but I feel he kind of jumbled it a little in the end when explaining the difference because these and a flat universe. Closed = gravity halting expansion causing a recollapse. Open = gravity not being able to slow the expansion causing it to expand forever. Got it... Now flat: "balanced on a knife's edge between a universe that will one day collapse and one that will steadily expand forever." Okay, that makes sense. It sounds like it becomes static since open means eternal expansion and closed means a recollapse. However, in the next sentence he says "Instead, the density of matter would be such that its gravity will steadily slow the expansion rate down, but never quite stop it. This corresponds to a flat universe, neither open nor closed." This is why I'm confused. Gravity cannot stop the expansion in an open universe, fine. But gravity also cannot stop the expansion in a flat universe? It just keeps expanding, just maybe slower? What then is a flat universe? What's the difference? Is it that gravity just slows it down? Wouldn't that happen anyway within an open universe? A little more explanation here would do wonders because it just doesn't appear clear enough to be easily understood.
Now he moves onto the paradox of the twins. It is beautifully explained and easy to understand. However, he injects his beliefs as to why there is no paradox here. Without going into detailed explanation, his idea defeats the paradox only if the universe is as he believes it to be; open. He explains shapes of the universe wonderfully earlier on in the book, but doesn't reference here that the paradox will still exist if the universe is positively curved and closed. He explains throughout the book his ideas and other's ideas and where they disagree, but fails to do so here, which is a little disappointing.
One last gripe on the author, and it's more of a personal preference than something I feel he did incorrectly. When he's talking about the speed of light, why it's the cosmic speed limit, and why nothing can pass it (truly fascinating and finally explained for laymen to understand) he makes the statement "to accelerate it up to the speed of light would require an infinite amount of energy, which is impossible". This book deals with the seemingly impossible in a radical way including the infinite. For example, when explaining how black holes are formed he talks about the escape velocity equaling the speed of light causing the gravitational force on the surface of the star to become infinite. Seems unreal yet he explains general relativity allows for these infinite things to happen. So to have Al-Khalili blatantly state without explanation that an infinite amount of energy is impossible seems somewhat out of character for the very book he has created.
Finally here's an extremely petty complaint that has to do with the editor and not the author. The only reason I even mention it is if there is to be a third edition at some point it should be corrected. Unless, of course, I'm mistaken and it's not wrong, in which case I apologize for even bringing it up. There appears to be typing error in the following sentence: "Namely, if the Universe is open and infinite, then what does it expands into?" Expands, not expand?
In closing, this is hands down, bar-none the absolute best book I have ever read on the introduction to these radically complicated topics for the laymen to understand. Al-Kahalili is an absolute master at communicating these extraordinarily esoteric concepts to anyone with the desire to understand them. The only reason I do not give him five stars here is because of the things I listed above. Barring those, this would absolutely be a five star book! I'd give it 4.5 stars if I could. I highly recommend it! Thank you, Al-Kahalili for putting this information together so spectacularly.