38 of 44 people found the following review helpful:
3.0 out of 5 stars
Not the best book out there, June 8, 2002
This review is from: How to Build a Time Machine (Hardcover)
First of all, If you have already read some books on black holes and worm holes/time travel, you probably won't learn much from the book as it is non-mathematical (the only equation is E=mc^2) and introduces only the fundamental aspects of time, space and time travel. Otherwise you might want to take a moment and read on before buying it.
I understand that most authors spend a lot of time on their books, even though the books themselves might not stand out in the end. As such, I am really reluctant to give their books any low grade. But this book really has little to deserve my praise, so I give it a 3.
The book is rather short. English is not my native language, but I still finished it in 3 hours in a bookstore.
I feel the book is divided into 3 parts: first part introduces relativity (including things like light and gravity) and black holes; second part discusses how to construct (at least in theory) a worm hole that can be used as a time machine; and the last part deals with the paradoxes and implications of time travel.
I think the author was not sure what level of audience he's targeting. The first part is easy to understand for everyone. But that is not what audience want to learn from the book--they want to know about time machines. So they turn to the last two parts, which may be a bit hard for them. For instance, the author mentioned rotating black holes, but nowhere in the book he explained what they are. He also mentioned their ring-like singularity but he didn't even put a drawing to help readers to understand. I am quite serious about science and I read a few books on the subject so I know what rotating black holes are like. But I really don't think everyone knows about them and the author shouldn't assume thate either because the first part limits the book to general audience. There are many more examples like this in the book.
This actually is embedded in a more serious problem: the book is generally lacking much needed information and explanation. When I read about black hole I expect to find the words "event horizon" and "singularity". Actually I found the latter, but the first is only vaguely described and never stated directly. When the book talks about gravitational lensing, it would be really helpful to include a drawing to show how it works, but you can't find that either. How about the Casimir Effect that creates negative energy? (negative energy is explained in the book.)The author says it relates to virtual photons, but what are those? And honestly I don't think the author clearly explains the Casimir Effect either. He simply states the things he needs and expect you to take them for granted. But if you give a little thought on the subject, I am sure that you will have tons of questions unanswered. So after reading it you might not have a firm grasp on the subject.
Also around page 15 (might be 13 or 17), I believe the author made a mistake. The book says if you half the diameter of the earth the gravitational force on the surface of the earth is 2 times as strong. This is NOT true. It should be 4 times as strong because force F is inversely proportional to the square of the distance. [F=GMm/(R^2), where G is the gravitational constant and M's are the attracting masses, R is the distance between the masses, which in this case is halved] I am sure the author overlooked this, but since it is such a fundamental thing and he highlighted the paragraph in the book, there is no excuse for the mistake.
The reason that I am giving it 3 stars and not less is because the last two sections of the book are interesting to me and I learned something (although not much) from reading them. I am not saying that you will not like it, in fact many reviews before mine gave it a 5 star. But I strongly recommend that you first take a look at it, in a bookstore perhaps. Maybe you can finish the book like I did if you have the time.
Because I didn't read that many books on the subject, I can't tell you which ones are the best. But for a better description on the subject (black holes/worm holes/time travel) you might find Clifford Pickover's "Black holes: a Travelers Guide" interesting.(New York: John Wiley & Sons, Inc. 1996.) It has some equations but they are not that hard to understand, the book introduces probably everything you ever need to know about black holes. You can find more about black holes from Stephen Hawking's "A Brief History of Time", and from the time travel authority: Kip Thorne's "Black Holes & Time Warps" (but this one is a bit harder). I also liked Brian Greene's sections on general relativity and quantum mechanics in his "The Elegant Universe", he explains the subject so clearly and provides so many insights. (If you have a question then you can be sure to find the answer in the next paragraph. A perfect 5 star if I were to rate it) John D. Hawley & Katherine A. Holcomb's "Foundations of Modern Cosmology" (New York: Oxford UP, 1998.) is also an excellent book, but I suggest you borrow it from library since it is rather expensive ($50 I believe, it has a section on black holes, probably like 30 pages, it also has a chapter on relativity).
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23 of 27 people found the following review helpful:
5.0 out of 5 stars
Short, easy, deep and beautiful. What else?, March 2, 2002
This review is from: How to Build a Time Machine (Hardcover)
Paul Davies is a great author. But some readers may find some of his books long as books usually are. This one not. It is short, but clear cut goal-oriented and conceptually deep. You will understand some concepts that seemed so confusing too you. Most of all, you will see things under a different light. Physics at its best. Just a warning: you can read it in an afternoon, but you will probably become so interested that you will want to spend a lot more time with wonderful books and subjects like these. The fun will last only about 150 pages.
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10 of 12 people found the following review helpful:
4.0 out of 5 stars
a valuable starting point, May 29, 2003
Davies has attempted a very difficult task: how to write a brief and easily understood account of the physics and mathematics underpinning the idea of time travel.
In the main part Davies succeeds admirably. It is clearly not that simple to condense highly complex mathematical equations, and concepts of and about quantum physics to a level that the ordinary person will not only grasp but perhaps think about.
The book is effectively divided into two parts. The first is a synopsis of the theories underpinning time travel. In this section Davies provides a speedy overview of the history of thinking about time travel, the development of the theories, and he attempts to at least conceptually work through the possibilities and problems associated with the main theories that hold currency.
In the second part, Davies sets out the mechanics of how to build a time machine. The content contained in is part, not matter how hard Davies tries, and despite its brevity, was very difficult for this reader to understand. Having no background in pure physics, I became a bit lost in places. But struggling through out, it is still informative and challenging.
Overall, the book is a valuable starting point for the general person to get a grip on this though provoking topic.
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