Secrets of Universe Run Hot and Cold and in Between
A MATTER OF DEGREES
What Temperature Reveals About the Past and Future of Our Species, Planet and Universe
By Gino Segre
Viking
320 pages, $24.95
“Rectal readings” is not a phrase encountered on the opening pages of many books, but in “A Matter of Degrees,” physicist Gino Segre lightly informs us that in the human body “oral and rectal readings differ,” the latter typically exceeding the former by about one degree. From this most intimate standpoint, Segre branches into a wide-ranging discussion of temperature, examining the ways in which temperature affects everything from animal physiology to the evolution of life, from the functioning of our planet’s atmosphere to the life cycle of the sun and the history of the universe.
Humans are exquisitely engineered to function at a specific temperature, 98.6 degrees. If your body temperature rises by the merest 2% you feel sick: “If it rises and falls by much more than 5% you should consider heading for the emergency room,” Segre writes. Just why this particular temperature is a matter of much speculation, but doing the math Segre explains that 98.6 degrees ensures an optimal rate of heat dissipation under the conditions most likely encountered by our hunter-gatherer ancestors. Were the primal environment hotter, it is likely, says Segre, that so too would be human body temperature.
A significant part of our physiology has evolved to keep us at the right temperature and Segre delivers a fascinating disquisition on the physics of sweating: Want to know why you feel so exhausted at that spinning class? On a stationary bike in a windowless room, there is no airflow over the body, thus no evaporative cooling takes place and you overheat. It isn’t just you; even champion cyclists cannot keep up the pace in such conditions.
Physics is Segre’s “family business.” His uncle was the famous particle physicist and Nobel laureate, Emilio Segre; his brother is a physicist, so is his nephew, a bunch of cousins and his father-in-law. Unlike many of his colleagues, however, Segre knows how to communicate with nonspecialists, and this is one of the most deft and accessible physics books I’ve read in a long while.
Though humans have been measuring space and time for thousands of years, no one attempted to quantify heat until the early 17th century. “Temperature” is just a concrete measure of the intuitive experience we call heat. While there appears to be no limit to how hot things can get (in the final stage of a star’s collapse the temperature can reach billions of degrees), there is a limit to coldness. Minus 460 degrees Fahrenheit or minus 273 degrees centigrade is as low as the temperature scale goes, a point known as “absolute zero.”
But what exactly is being measured by a thermometer? What is it that increases when we heat a pot of water or forge a bar of iron? Throughout the 17th and 18th centuries most scientists believed that heat was some kind of substance that was destroyed, or used up, when a body burned: “Phlogiston,” they called it, from the Greek word for “combustible.” In the early 19th century, the great French chemist Antoine Lavoisier demonstrated decisively that no matter was lost during burning. Still, he and other scientists thought heat must be some kind of fluid that became more concentrated when the temperature rose.
The signal achievement of 19th century physics was the development of an understanding of heat as a byproduct of the mechanical motion of atoms and molecules. Though the science of thermodynamics remains perhaps the least glamorous branch of physics, it has impacted on our lives probably more than any other. The laws of thermodynamics led to insights about how to make more efficient steam engines, making a foundation of the Industrial Revolution. Thermodynamics remains a key science today; when designing cars and planes and computers, heat is one of the biggest problems engineers must wrestle with. That’s because any time a machine does work, it generates heat, which needs to be dissipated or the engine will overheat.
One of the great insights of thermodynamics is that heat is just a particular form of energy that can neither be created nor destroyed but only transformed from one type to another (as when coal is burned to generate steam that drives a piston and powers a weaving mill.
The statistical approach to understanding heat and energy inherent in thermodynamics infected other sciences as well; in biology it led to a shift in focus from individuals to groups. An understanding of heat flow is also critical for climate models. In a chapter on the environment and the problem of global warming, Segre describes the complex exchange of heat between the oceans and atmosphere. It’s a superb introduction to one of the most important issues of our times, and for this chapter alone the book is worth its price.
Segre’s two final chapters deal with temperature in the cosmological and quantum realms. For those with some awareness of physics, these will be a highlight, especially the section on approaching absolute zero. As the temperature is lowered toward this nadir, bizarre effects manifest such as superconductivity and superfluid flow, where a liquid can actually climb up the walls of a container. The zero point itself is like the event horizon of a black hole; here everything comes to a standstill. Beyond this there is nothing.
