Customer Reviews

A Journey into Gravity and Spacetime (Scientific American Library)

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4 star:		(1)
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This is truely an amazing book. Wheeler does for General Relativity what Hawking did for Cosmology in "A Brief History of Time", and in some sense they are similar books. However Wheeler has a unique, quirky style of writing that makes the book an entertaining adventure to read.

Wheeler is able to pull off a major accomplishment: He explains Einstein's General Relativity in a clear, straightforward manner, with a minimum of math. It's "conventional wisdom" that General Relativity is seriously serious stuff, the domain of hardcore Physics geeks. That doesn't faze Wheeler. He leads the reader along, gleefully pointing out the scenery, making it all look quite simple and understandable. And then all of a sudden, when you least expect it, you find he's derived and presented Einstein's field equations with only a teensy-tiny bit of algebra! Even if you know this stuff already, his presentation makes you think about it with a new perspective.

And did I mention the illustrations? They are really exceptional.

If you have any interest or dealings with GR, ya gotta have this book!

The interrelation of gravity and spacetime is a formidable subject to describe; the author does so with excellence. The diagrams and charts reinforce the understanding.

Unfortunately when a key subject left me rather clueless, (Boundary of a Boundary) I spent quite a few frustrated hours being uncertain on whether or not to continue reading without the support of the material on those pages. As it turned out, the subject became clearer once I read on and returned again. I never did grasp it as completely as the rest of the book.

The book contains the most enlightening description of transverse wave propagation I've ever seen. It also helps solidify one's understanding of interval and relativity.

Not a book to be read overnight.

This author is one of the most briliant, the most optimistic, and the most enthusiastic writer in all of physics, and in this book, his competence as a physicist and his deep fascination with the physical world is brought out dramatically. He is clearly a man who is feeling a powerful sense of exhiliration of the discoveries now taking place in all areas of knowledge. His foundation and his theme in the book is a simple geometric principle, namely that the boundary of a boundary is zero. He then guides the reader, assumed to have a rudimentary knowledge of mathematics, in a splendid presentation of the power of this principle in gravitational physics.

The first chapter is an overview of the history behind the subject, via the work of people who contributed to our current understanding of gravity. And then, with a masterfull use of diagrams he gives the reader a taste of the simplicity of the equivalence principle and the need to tack on an additional dimension (time) to the 3-dimensional space of everyday experience. The Pound-Rebka experiment is discussed as one that illustrates the idea of the spacetime interval, and the role of time dilation is discussed via the possibility of practical space travel. And such enthusiasm in his dialog: "the universe will grow ever more exciting", he says, and looking at the developments now taking place in today's science, he is indeed correct.

Chapter 4 gives a fascinating overview of what the author calls the boomerang, which illustrates the action of curvature on nearby test masses. This thought experiment involves the motion of a spacecraft through an imaginary tunnel through the Earth. The author analyzes the motion from the standpoint of Newtonian physics and general relativity. Curvature as the "grammar of gravity" is the topic of the next chapter, with illustrations of the paths of ants on spaces of zero, positive, and negative curvature. A very intuitive treatment of parallel transport around a closed path on a curved surface is given. The tides are discussed as a natural manifestation of the gravitational influence of the Moon on Earth.

Must difficult for a layman to understand is how spacetime acts on masive objects, but the author explains it brilliantly in the next chapter, taught via the concept of "momenergy". This entity is a 4-vector, and the author uses it to show how its creation in a spacetime region can be written as the sum of 8 terms, reflecting the fact that the "boundary" of a four-dimensional block in spacetime consists of eight three-dimensional cubes. That the contents of these cubes sum to zero is the famous "boundary of a boundary is zero", which is discussed in the next chapter. This chapter is one of the best explanations ever given (at this level) of the physics behind spacetime curvature and massive objects. The actual mathematical quantification of curvature is detailed in chapters 8 and 9, using elementary mathematics. The author discusses nicely the famous Scharwzschild geometry.

Concepts of a more concrete nature are discussed in chapter 10, wherein the author discusses the famous Pound-Rebka experiment and planetary motion. This is followed by a discussion of the elusive gravitational waves in chapter 11. Again with a clever use of illustrations, the author explains the transverse property of gravitational waves, and compares gravitational waves with electromagnetic waves. The role of the quadrupole moment in the creation of gravitational waves is brought out briliantly by the author. He discusses briefly various attempts to detect gravitational waves.

Black holes are the topic of chapter 12, wherein the famous Penrose process for extracting energy from a black hole is discussed, and the "no-hair" theorem for black holes. A neat symbolic representation of the Bekenstein number of a black hole is given. The role of the Hawking process, connection quantum processes with the physics of black holes is briefly discussed. The author ends the book with a look at the expansion of the universe, the missing mass problem, and another very interesting topic that has gained much attention recently: the concept of gravitomagnetism. This is a "weak-field" prediction of general relativity, and predicts that the rotation of the Earth should influence the motion of orbiting satellites. This topic is currently bringing together ideas such as the quantum Zeno effect, Mach's principle, and the notorious "frame dragging" effect in general relativity. Experiments do measure it are currently in play and in the proposal stage, namely the LAGEOS and LAGEOS II experiments, which measure the gravitomagnetic orbital perturbation, which is known as the Lense-Thirring effect.

This is a beautiful, poetic, and generous book. I found that after reading and mulling over each section, I could eventually visualize how space was behaving under the influence of mass, and could also see why one needed to choose one's point of view carefully to understand the physics.

The book is intended as an introduction to general relativity, without much tensor formalism, but it does not neglect the geometrical underpinnings. It presents a very nice way to get at the physics, with creative and light-hearted diagrams.

I'm not so sure that Wheeler's own poems, which introduce many of the chapters, are a great success, but I admire and salute him for including them. Even his poetry helps to open additional doors to understanding general relativity.

A book that is truly beautiful.

Usually, science books are either for laymen (that don't know math very deeply) or for expert readers (which are working on the subject and have high math skills). I think the problem with this book is that it is neither.

John Wheeler (author of "Spacetime Physics", together with Edwin Taylor, which is quite a good book on Special Relativity, and also on the basis of General Relativity) tries to explain Gravity (so, General Relativity) in an sort of poetic way. However, even though it is an original way that works well in the first chapters, it stops working after those initial chapters, when the subject starts to get a little bit harder.

As a laymen (although with an Engineering degree - so, with some math and physics background), I got lost after the initial chapters and was unable to fully understand the last chapters. For an expert, I think the book is too "poetic" to be of any practical interest.

If you want to know about Special Relativity and have a glimpse on General Relativity, I think "Spacetime Physics" is a better choice.