Segre's first book -- "A Matter of Degrees: What Temperature Reveals About the Past and Future of Our Species, Planet, and Universe" (Viking, 2002) -- moves from the blazing hearts of faraway stars to physicists' drive toward absolute zero, from global warming to heat-sensitive proteins in the human body.

"Segre combines a historical perspective and a broad command of modern science to provide a lucid and novel synthesis of the concept of temperature," said science writer John Harte, author of "Consider a Spherical Cow" and "The Green Fuse."

Of all the fundamental measures of our universe, Segre identifies temperature as the newcomer. First measured in the 17th century, millennia after time and distance were first quantified, temperature is, in Segre's view, an appropriate yardstick for measuring the progress of humanity.

"If I were to employ temperature as my record for a narrative of civilization," Segre writes, "I would cite the ever-hotter fires humans made as they moved ... from the Stone Age's first fires to charcoal and then to the bellows that produced bronze and iron.

"Going further, I would reach the steam engine, the nineteenth century's great Bessemer furnaces that made steel, and finally the Nuclear Age. ... For the past 200 years, I could use as a marker the ever-lower temperatures achieved in laboratories as, one by one, all known species of gas were liquefied. As the millennium came to an end, the low-temperature scale reached billionths of a degree above absolute zero."

Ever wonder what's so special about 98.6 degrees Fahrenheit, or why we consider room temperature to be around 70 degrees? Segre explains that people feel most comfortable in settings some 20 to 30 degrees below body temperature because that differential produces a comfortable rate of heat loss. Perhaps it is not a coincidence that humans emerged two million years ago in parts of Africa where median temperatures are in the low 70s.

In another passage linking temperature to human evolution, Segre marvels at how scattered radioactivity in the Earth's crust has essentially given rise to creatures sophisticated enough to ponder radioactivity.

"The radioactive alpha particle decay of a few kinds of nuclei heats the Earth's crust, which convectively creates fire just below the surface," he writes. "Forced up through the ocean bottom in hydrothermal vents, this activity somehow sustains life that evolves to create creatures that think about radioactivity."

Far beyond the confines of humanity, Segre describes the history of our universe in terms of its evolution from the 100-billion-degree Big Bang to the average of a few degrees above absolute zero found across today's cold, sparse universe.

Along the way, the warm interstellar dust near our newborn sun condensed into moderately sized planets, while much lower temperatures further afield froze the primordial soup into giants like Saturn and Jupiter.

Segre, a Penn professor since 1967, describes physics as his "family business." Nephew of particle physicist and Nobel laureate Emilio Segre, he is also the brother, son-in-law, uncle and cousin of physicists. He has served as director of theoretical physics at the National Science Foundation and has been honored by the Alfred P. Sloan and Guggenheim foundations.

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