A Matter of Degrees

What temperature reveals about the past and future of our species, planet, and universe

by Gino Segrè

328 pages, ISBN 0-670-03101-1, Viking, New York, 2002.

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Reviewed by J. M. Haile, Macatea Productions, http://www.macatea.com/

Common systems of units are usually constructed from five fundamental dimensions: mass, length, time, force, and temperature. Of these, temperature is newest and most elusive. Newest because attempts to measure and quantify temperature date only from the time of Galileo; in contrast, the others were needed to promote early trade and commerce, and so they date from antiquity. Elusive because we cannot measure temperature directly; instead, we measure the length of a column of fluid, or the voltage across a resistor, or the frequency of radiation. Elusive too because the concept is subtle: ask someone to define temperature and they will likely say it is the amount of heat in an object. But temperature does not measure the quantity of heat; instead, it refers to the degree of hotness—the intensity of heat. In molecular terms, temperature is proportional to the average kinetic energy of the molecules in an object. And so, a precise definition of temperature together with well-defined scales for quantifying it date only from the development of the molecular theory of matter, which coincides with the industrial revolution.

The concept of energy pervades much of scientific inquiry, and since kinetic energy is one form of energy, temperature crops up, explicitly or implicitly, in many disciplines, including medicine, oceanography, astronomy, thermodynamics, environmental science, quantum mechanics. Recognizing this, Gino Segrè uses temperature as the unifying thread to discuss major developments in several of these disciplines.

The book is divided into six chapters. In the first chapter, Segrè describes the effects of temperature on the human body: we can tolerate relatively large temperature swings in our environment, but we can tolerate only small temperature changes within our bodies. In the next chapter, he briefly summaries the development of 19th century thermodynamics, which was motivated by attempts to convert heat into useful work. The third chapter considers the earth and its atmosphere and describes how they respond to changes in temperature. In chapter 4, Segrè introduces us to life at extreme temperatures, especially life at very high temperatures but without photosynthesis. In the fifth chapter, Segrè considers the stars: how hot is our sun? How does a star's temperature change over its life cycle? In the last chapter, he describes something of the strange world of quantum physics, including the behavior of superconductors and superfluids at extremely low temperatures. Of these, I felt the last half of Chapter 3, on the greenhouse effect, was particularly well presented.

The book is directed toward an educated, but nonscientific audience, and as such it is informative and easy to read. The pace is somewhat brisk, but this is probably unavoidable, given the range of topics introduced. However, the tone and pacing become predictably uniform and balanced; often this signals over-editing. As a consequence, the reader is offered no help in making judgments about the relative importance of the topics presented. For example, the difficulties and confusions surrounding the definitions of temperature, heat, and temperature scales—surely of importance to a book based on the concept of temperature—are discussed in no more detail than other topics. This leaves many readers believing that what is familiar is already understood and it misses an opportunity to use familiar concepts to help readers appreciate the challenges and difficulties people face in doing science. Similarly, the book describes the design of the Einstein-Szilard refrigerator, which teaches us something about Einstein, but nothing about refrigeration. In contrast, no mention is made of the Joule-Thomson expansion, which has long been an important component of refrigeration.

More generally, the book presents a long string of scientific accomplishments, but relatively little is said about how any of those accomplishments were actually achieved. My sense is that most readers want to know not only what was done and why it is important, but they also want to know how important things were achieved: why were certain pathways to learning chosen rather than the alternatives? If the public is going to understand and support scientific inquiry, then they must be given opportunities to understand the scientific process.

Writing about science for a general audience is difficult for at least a couple of reasons. One is the large gap in knowledge between reader and writer, so the writer has to make extraordinary efforts to help the reader bridge that gap. If the writer is a scientist, then a second difficulty is that previous writing experience is of little help: the scientist must learn, on his own, the required kind of writing. When writing a technical article for his peers, a scientist rarely tells how a piece of work was done: a scientific article does not present a history of the work nor does it document the mistakes, failures, blind alleys, and frustrations that were encountered when trying to solve a difficult problem. But mistakes and frustrations are part of the human experience, and I believe more of the public would be sympathetic to science if they were aware of the passion and determination that scientists must bring to bear in overcoming setbacks.

The best popularizers of science—such as Jeans, Haldane, Gould, Wilson, Thomas—were successful, in part, because they managed to infuse their writings with the passion they felt for their subjects. Readers may not be particularly interested in, say, ants, but nevertheless, they will read Wilson, not so much to learn about ants, but to share Wilson's passion. In like manner, Segrè is at his best when he writes about the things closest to him: his family in the Introduction and his relationship to science in the last few pages of the book. He has written a good book, but I suspect there is a better book still inside him.

(jmh 02 July 06) © 2006 by J. M. Haile. All rights reserved.