A Journey into Gravity and Spacetime (Scientific American Library)

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.
January 10, 2004

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.
August 25, 2002

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.
February 03, 2002

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!
December 13, 1999