It's always a pleasure to read a well-written book authored by a leading scientist. Such is the quality of Jayant V. Narlikar's book "The lighter side of gravity." One of the risks associated with writing any book on the leading edge of science, however, is that it will be obsolete almost before leaving the presses. Narlikar's book suffers somewhat from this problem. The book has an original publication date of 1982, and revised publication of 1996. Consequently, it misses some recent discoveries about black holes, experimental evidence of neutrino oscillation and its implications for neutrino mass, the mass of the universe, and the nature of dark matter.
The book offers a nice historical perspective, from Aristotle to Galileo and on to Newton and his laws of motion and gravitation. I particularly enjoyed the clear explanations surrounding the insight and possible clues that led Newton to the discovery of his law of gravitation.
The book's promotional litera! ture presents it as a layperson's guide to gravity, but without over-simplified (and erroneous) information. This is a high goal, and generally met, though the book's brevity might lead to some false notions. For example, the book portrays hydrogen burning as the fusing of four protons, with a helium-nucleus byproduct, two positrons, two neutrinos, and some energy. There is no mention of what theorists initially thought was the inadequacy of thermal energy to initiate fusion. There is no discussion of the importance of quantum tunneling, or the formation of helium 4 in stages (two protons form deuterium, from which helium 3 is formed, and then helium 4). Narlikar's book is not very long (only a little more than 200 pages) and could easily accommodate the extra detail.
From solar models the book digresses slightly to discuss curved space, which Narlikar does very well without equations, and with the aid only of simple diagrams and examples. There is a brief though tru! ncated discussion of supernova. Other books such as John G! ribbin's "Blinded by the Light," and Laurence A. Marschall's "The Supernova Story" offer far more insight for the weekend physicist.
The discussion about black holes, even without the most recent discoveries, is nicely done. As with any subject as broad as that of gravity, there are missing elements (there is no discussion of Hawking radiation, for example). Just the same, the discussion about black holes is about as complete as a non-technical book on the subject can be.
Narlikar finishes his book by describing the big bang theory of cosmology, its weaknesses (some of which have been at least partially resolved since 1996) and his alternative theory of quasi-steady-state. For the most part he has been admirably forthright about the scientific debate, with the possible exception of a closing comment in chapter 8:
"In spite of these questions regarding white holes of a limited size, astronomers have, paradoxically, given an uncritical acceptance to the hypothesis of ! the biggest white hole of them all: the Universe!"
Although one may disagree with the big-bang theory, it seems remarkable that anyone would claim it has been accepted uncritically. Narlikar's comment seems even more remarkable since chapter 9 proceeds to describe the wealth of scientific data supporting the big-bang model.
Overall, however, I really enjoyed this book. The closing chapter, though perhaps controversial, helps us understand that science is a progressive system of thought. Even our most cherished ideas -- perhaps especially our most cherished ideas -- are subject to review and critical examination in light of the most recent experimental evidence. If Narlikar is right about his model of the universe, we are on a threshold in cosmology. If Narlikar is wrong, we are on a threshold in cosmology. Either way, it's a wonderful universe. Read Narlikar's book. It will help you understand it a little better.