Gravity’s Shadow: The Search for Gravitational Waves

Gravity’s Shadow: The Search for Gravitational Waves Harry Collins U. of Chicago Press, Chicago, 2004. $100.00, $39.00 paper (870 pp.). ISBN 0-226-11377-9, ISBN 0-226-11378-7 paper

Gravity’s Shadow: The Search for Gravitational Waves , by Harry Collins, is an account of the experimental search for gravitational waves, from the quest’s beginnings around 40 years ago to the very recent past. Collins, a research professor of sociology at Cardiff University in the UK, is particularly concerned with the sociology of doing science and the growth from small-scale research to some of the current large-scale research projects. He also covers many aspects of the development and interpretation of gravitational-wave research in unprecedented detail. The book is impressive and contains material that will interest many scientists and other readers.

The book’s 900-page mass may be a deterrent to some, but even individual chapters are unusually engaging. The gravitational waves referred to in Collins’s book are traveling disturbances in spacetime, believed to be generated by accelerating masses in such astrophysical phenomena as a supernova outburst or a rapidly rotating and slightly asymmetrical neutron star. Gravitational waves are a longstanding prediction of Albert Einstein’s relativity theory, but the expected observable effects on Earth are so minute that some physicists had thought these effects to be practically undetectable. Detection of the waves could be very valuable as a new tool for studying astrophysical processes, particularly those hidden by the absorption of the electromagnetic or other radiations emitted.

In the 1960s, Joseph Weber began publishing results of experiments involving measurements of small vibrations in large, isolated aluminum bars. He claimed some of the vibrations he observed were caused by gravitational waves. His claims stimulated a first generation of experimental attempts around the world to detect gravitational waves. A careful account of Weber’s work, and of related experiments and interpretations elsewhere, forms an important part of Collins’s book. The author describes interviews he had with Weber up to the physicist’s death in 2000, as well as those with Weber’s former graduate student Joel Sinsky, who provides some interesting experimental details.

Taken all together, I think the parts of the book that deal with Weber give the best account of his work I have read. The author’s experiences with Weber are in good accord with my own. Collins paints a fascinating picture of a scientist who has had an enormously stimulating and overall beneficial influence on the field despite the fact that his interpretations of his own results are now nearly universally regarded as erroneous. Weber’s work did demonstrate a possible way of looking for gravity waves, and it triggered the development by other groups of more sensitive versions of bar gravity-wave detectors, including several operating at low temperatures to reduce thermal noise. Experiments that use bar gravity-wave detectors continue, but they are largely being superseded by a different technique using laser interferometers, an approach that is revolutionizing the field.

The basic idea behind the newer approach is to look for the relative motion of two or more separated masses by using a sensitive optical interferometer rather than by studying the two ends of one bar. The advantage is that the masses can be placed kilometers apart so that a gravitational wave induces larger relative motions. The problem, however, has been to obtain the unprecedented sensitivity required from optical techniques. A succession of new ideas, combined with technical developments in lasers and low-loss mirrors and practical laboratory experiments over baselines of tens of meters, demonstrated that the technique would have great promise if expanded in scale. The expansion would require correspondingly large high-vacuum systems, which would increase the overall cost significantly and could change the nature of the research from that of a small research group to that of a larger entity, such as a consortium that constructs and operates a large accelerator.

Such growth did occur in a particularly dramatic way at Caltech, where laser interferometers were being developed. The change had unfortunate effects for all concerned. I was personally involved, having been invited to lead the research at the institute and having originated several of the key optical and other techniques used. In my view, Collins, who devotes a small chapter to that particular situation, has done a careful job of summarizing some of the sociological problems that arose during that time and the overall effects on the management and execution of the research. He has refrained from giving full details but has summarized enough to give an impression of the extent and seriousness of the disturbances that took place. What is more important is the final outcome: The project, called the Laser Interferometer Gravitational-Wave Observatory (LIGO), led by Caltech and MIT, is now a major research endeavor involving several hundred collaborators around the world. It looks as though LIGO, in its current, initial form, has a reasonable chance of allowing researchers to observe gravitational waves.

For the next stage in the project, researchers have proposed plans to further significantly enhance the chances of detecting gravitational waves. Similar or slightly smaller projects in Europe and Japan are in operation, under construction, or proposed.

Gravity-wave detection is a good topic for Collins to use in examining the sociological aspects of certain types of scientific research. The author has done a very careful and responsible job. I do not completely agree with all of his conclusions or interpretations, but that is to be expected in a book of this scale. Although Gravity’s Shadow is indeed dense, Collins has made it more readable by including anecdotal accounts of his experiences in visiting some of the scientists and experimental sites. He spent many years on his effort, attending numerous specialist conferences and interviewing a large number of the researchers involved. The book will be valuable to readers who desire a detailed account of this growing field and its sociological aspects, and to those interested in the history of science. It will also be helpful to students and others who wish to get firsthand accounts of what experimental physics can be like in practice.

I do not know of any other book quite like Gravity’s Shadow. Collins has publicly announced his plan to produce a sequel when gravity waves have been unambiguously detected on Earth. I hope he does not have too long to wait.