The Extravagant Universe by Robert Kirschner, Princeton University Press, 拢19.95, ISBN 0691058628
BOB KIRSCHNER is one of the liveliest and most amusing lecturers in the world of astronomy so it was with great anticipation that I turned to his first popular book on astronomy. I was not disappointed. It鈥檚 wonderful. The Extravagant Universe is an entertaining and witty account of one of the biggest scientific stories of the past 10 years: how exploding supernovae show that the expansion of the Universe is accelerating.
Kirschner has worked on supernovae for the past 30 years and is one of the major figures in supernova research. Many of the most active younger astronomers working in the field are his students or postdocs. He was not only the senior member of one of the two teams searching for distant supernovae, and he also found himself on the visiting review board of the department where the rival team was based and referee of their first major paper on the subject, so he has a unique perspective on this whole story. His book gives a fascinating insight into the rivalry between scientific teams working in the same area and how they spur each other on to greater efforts.
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He begins with a brief account of the big picture 鈥� the stars, the Universe, the laws of physics, Einstein鈥檚 general theory of relativity 鈥� to convey the size and age of the Universe. Yet at the same time he is disappointed that we seem to have seen almost to the limit of the world of galaxies with the Hubble Space Telescope. As he points out, if we want to see the light from the first objects in the Universe, we have to move to a new generation of large infrared space telescopes, to see the red-shifted light from these young and distant objects.
Kirschner then moves on to the two types of supernovae, Type Ia, which are due to the explosion of a white dwarf star whose companion has dumped gas on it, and Type II, the death throes of star much more massive than the Sun. Immediately we are into a lively narrative style, in the form of a dialogue between astronomers working at the telescope. He intersperses his life history of stars and their violent deaths with amusing and self-deprecating autobiographical episodes.
Then it鈥檚 back to the larger picture of cosmology, explaining the expansion of the Universe with an analogy involving how things look to a marathon runner, the age of the Universe, Einstein鈥檚 cosmological constant and the microwave background radiation. One of many good jokes is that Kirschner compares the smoothness of the microwave background with that of a baby鈥檚 bottom, which he claims to have measured on his own children.
Finally, the systematic searches for supernovae: first relatively locally, and then at ever greater distances. Finding supernovae at cosmological distances is a huge logistic effort: observations with large telescopes, including the Hubble Space Telescope, have to be timed to the phases of the Moon. Kirschner at first doubted whether this programme would work, given the need for fabulously accurate measurements, controlling the effects of interstellar dust, and understanding whether the supernovae are all genuinely similar.
The two teams became excited as they realised their results pointed to an accelerating Universe, because that meant some kind of 鈥渄ark energy鈥� was responsible. Like most astronomers who have accepted this claim Kirschner is not particularly concerned that particle physics can鈥檛 really explain this dark energy, or why the Universe should be expanding expotentially today.
The Extravagant Universe is hugely enjoyable, though I did get thoroughly confused with the notation he uses for the densities of matter, dark energy, and the sum of the two. And I thought it was a bit mean-spirited of him to dismiss the proposed SNAP supernova mission as 鈥渢en years of boring meetings鈥�. But these are minor quibbles. Do buy this delightful book.