Tuesday, July 3, 2012

E=mc2: A Biography of the World's Most Famous Equation

by Drew Martin
I recently finished reading E = mc2: A Biography of the World's Most Famous Equation, by David Bodanis. He treats the formula as a character and the descendant of each component: E, m, =, c and 2. The book was inspired oddly enough by a remark from Cameron Diaz about wanting to know what the equation means. Bodanis looks at E = mc2 from a different angle. Instead of trying to tackle relativity or create another biography about Einstein, he focuses solely on the history of the formula.

E   In the early 1800's, Michael Faraday unified disparate concepts of energy, which had previously been looked at as unlinked forces.

=   In the mid 1500's, Robert Recorde promoted the equals sign as a computational symbol because he argued that nothing could be more equal than a pair of parallel lines of equal length. There were many competing symbols, which included // and ] [ . History favored Recorde's symbol. A century after its introduction, = found its way into the  language of equations.

m   Before having his head chopped in a guillotine because of his association with Louis XVI, Laurent Lavoisier demonstrated the conservation of mass, which helped recognize the commonality of different forms of matter.

c   Most people know that the c in Einstein's equation stands for the speed of light, but why c? C stands for celeritas, Latin for swiftness. Galileo was the first person who thought about measuring the speed of light. Ole Rømer was the first to best estimate c to be roughly 670 million miles per hour even though his work was not accepted at the time (late 1600's). Compared to the speed of sound, Mach 1, the speed of light is Mach 900,000. James Clerk Maxwell's 1821 breakthrough explained the mutual embrace of electricity and magnetism, leap-frogging light across the universe. It was one of the greatest theoretical achievements of all time.

2   Émilie du Châtelet (pictured here), Voltaire's companion, objected to Newton's idea (mv1), which stated that how objects make contact is simply a product of their mass times velocity. Châtelet revived Gottfried Leibniz's competing view (mv2) and supported it with evidence from the Willem 's Gravesande that energy is equal to a mass times it velocity-squared. Gravesande's experiments were simple; measure the deep of penetration of a metal ball falling into a clay floor. A ball propelled three times as fast does not go three times deeper but nine times deeper. If the speed of light is 670 million miles per hour then c2 is 448,900,000,000,000,000 miles per hour.

E = mc2 is a conversion formula and a way to express the vast amount of energy stored in mass.