From Steam Engines to Life?
What is the state of thermodynamics on the 100th anniversary of the death of Lord Kelvin?
The Shock of the New
Kelvin and Clausius had grasped the essence of energy, heat and temperature—with, however, certain caveats. Kelvin's thermodynamics was a science of equilibrium: fine for systems going from one stable state to another, but saying little about systems that lacked this stability. It was also an isolated science: Kelvin's theories applied only to so-called closed systems, which are, by definition, unaffected by their surroundings (such as a steam engine that used heat to do work). And it was a "science of the large," one that described practical hunks of material such as boilers. Early thermodynamics was adequate for predicting the behavior of billions upon billions of atoms, but no good for tiny systems—such as the complex molecules found in living things.
Modern thermodynamics is all about stepping beyond these limitations to understand processes and systems that are far from equilibrium, inextricably tied to their surroundings, and at least a million times smaller than industrial-scale engines. Consider one such molecular engine: the protein. In converting stored chemical energy to useful work—such as transporting cargo, catalyzing chemical reactions or pumping ions across membranes—proteins do for life just what the big engines of Kelvin's day did for industry. As current research in thermodynamics conquers the limitations of 19th-century theory, it is faced with one of the great challenges of modern science. The new goal is a second transformation more profound, perhaps, than Kelvin's: to go beyond the thermodynamics of the inert world toward the thermodynamics of life.