# e = mc2 by David Bodanis

MacMillan, 2000

### Review by Alan Goss, Napier

This bestselling book, a biography of Einstein's famous equation, was inspired by an interview with the actress Cameron Diaz in a popular movie magazine. Diaz wanted to know what e = mc2 really means, a query shared with many others who are often mystified by the many books that try to explain it. David Bodanis took up the challenge and in 219 pages (excluding a detailed appendix and notes for those who want to know more) and has done a first rate job.
The book is more than a popular account of cool scientific discovery which on its own is a fascinating story. A brief account of e = mc2 gives the context. “e” is for energy, a word not used in its modern sense until about the 1850's. Einstein found a vast source of energy where no-one had thought to look. The equals symbol ("=') in his 1905 equation was like a telescope, or a tunnel, pointing or leading to mass containing other sources of energy -- right here on earth. The "m" is for mass.
Einstein found that there was a link between energy and mass and began to focus on what then looked like a complete red-herring, the speed of light. "c" (Latin celeritas) is simply the speed of light, about 670 million m.p.h., which is the fundamental speed limit in our universe. Nothing can go faster. Einstein saw, therefore, that there could be a natural transfer between energy and mass and that "c" is the conversion factor linking the two. "c2" is crucial in explaining how this link operates. The 670 million m.p.h., when squared, becomes 448,900,000,000,000,000 which when multiplied by, say, a pound of mass, gives off a phenomenal amount of energy. If this page could be converted into pure energy there would be a massive eruption! Accessing that power in uranium is a much easier process. So Einstein's equation takes the great speed of light, squares it, and multiplies that huge figure by the amount of mass you're dealing with. That represents how much energy the mass will pour out.
We learn how e = mc2 is constantly at work in our everyday life and in the universe. Its application is at the heart of the formation of mountain ranges like the Himalayas, to exploding volcanoes, the creation of electricity generating stations, and its effects are seen in smoke detectors, televisions, CAT scanners, glowing exit signs at your local theatre, and of course the sun. The sun uses the immense power of c2 to warm our planet which, when it was formed, was a comparative newcomer in the heavens.
Atomic bombs are an early direct application of e = mc2, and the book covers physicists like New Zealand's "booming, rugby-playing Ernest Rutherford" who with others helped show the potential power within the atom. The furious race between German and American based scientists to build the first death-laden bomb reads like a modern day thriller, with horrific consequences.
Sodanis reminds us that ancestors of e = mc2 like Isaac Newton, Michael Faraday and James Chadwick, were deeply religious men. Einstein in his younger years was a biblical literalist, the scientist Arthur Eddington was a quiet Quaker and pacifist.
We are also reminded that in the 17th and 18th centuries science and religion were not separate entities but were one.
The underlying message of the book is that, with such massive sources of energy at our disposal, we humans are constantly being called upon to decide how best to use it. Unless we resolve to combat the nuclear mischief now being perpetrated in high places, an uninhabitable earth is an unthinkable yet very real prospect. e = mc2 directs us to the words of Moses:
"I have set before you this day life and good, death and evil Therefore choose life."
Clearly the buck stops with us.