Vaclav Smil - Energy: A Beginners Guide

Illustrations

All figures copyright Vaclav Smil, except where indicated.

The word energy is, as are so many abstract terms (from hypothesis to sophrosyne), a Greek compound. Aristotle (384322 B.C.E. ) created the term in his Metaphysics , by joining (in) and (work) to form ( energeia , actuality, identified with movement) that he connected with entelechia , complete reality. According to Aristotle, every objects existence is maintained by energeia related to the objects function. The verb energein thus came to signify motion, action, work, and change. No noteworthy intellectual breakthroughs refined these definitions for nearly two subsequent millennia, as even many founders of modern science had very faulty concepts of energy. Eventually, the term became practically indistinguishable from power and force. In 1748, David Hume (17111776) complained, in An Enquiry Concerning Human Understanding , that There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion , of which it is every moment necessary for us to treat in all our disquisitions.

In 1807, in a lecture at the Royal Institution, Thomas Young (17731829) defined energy as the product of the mass of a body and the square of its velocity, thus offering an inaccurate formula (the mass should be halved) and restricting the term only to kinetic (mechanical) energy. Three decades later the seventh edition of the Encyclopedia Britannica (completed in 1842) offered only a very brief and unscientific entry, describing energy as the power, virtue, or efficacy of a thing. It is also used figuratively, to denote emphasis in speech. Little has changed in popular discourse since that, or indeed since Humes, time, except the frequency of the terms misuse. At the beginning of the twenty-first century energy, its derivative verb (energize) and its adjective (energetic), are used ubiquitously and loosely as qualifiers for any number of animated, zestful, vigorous actions and experiences, and energy is still routinely confused with power and force. Examples abound: a powerful new chairman brings fresh energy to an old company; a crowd is energized by a forceful speaker; pop-culture is Americas soft power.

Devotees of physical fitness go one step further and claim (against all logic and scientific evidence) they are energized after a particularly demanding bout of protracted exercise. What they really want to say is that they feel better afterwards, and we have a perfectly understandable explanation for that: prolonged exercise promotes the release of endorphins (neurotransmitters that reduce the perception of pain and induce euphoria) in the brain and hence may produce a feeling of enhanced well-being. A long run may leave you tired, even exhausted, elated, even euphoric but never energized, that is with a higher level of stored energy than before you began.