E = Mc2: A BIOGRAPHY OF THEWOELD'S MOST FAMOUS EQUATIONBy David Bodanis, Macmillan, £ 3.60 Biography by definition is restricted to reconstructing the life of an individual. The biography of an equation is a novel idea. Bodanis chooses what is without doubt the best known equation in the world. Even those who are clueless about physics are aware of Albert Einstein's famous equation that revolutionized modern physics and perhaps began the process which put into human hands the worst weapon of human destruction. Bodanis's book is emphatically a biography of the equation and not of the scientist who discovered, or of those who took the equation forward. Here, the scientists are flitting figures contributing to the development of the three key terms of the equation, energy, mass and velocity of light. Bodanis divides the book into birth, ancestry, early years, adulthood and a section entitled till the End of Time. The birth is, of course, directly related to Einstein's moment of epiphany on a beautiful spring day in 1905 in the medieval city of Berne. In a three page supplement to his famous article that he had sent to Annalen der Physik, Einstein derived the famous equation. A new idea was born. But the idea had a prolonged and convoluted gestation. Michael Faraday in the 19th century showed that apparently disparate forces are related and linked by the overarching notion of energy. Einstein would change all this and show that the amount of energy available in the universe was not fixed and could be increased many times over. Similarly, Antoine-Laurent Lavosier showed that different forms of mass were not only interconnected but could be conserved. But the domains of energy and mass were seen to be totally separate. Einstein linked the two, but he did so by looking at the speed of light. The letter 'c' is used to denote the speed of light (from celeritas, the Latin for swiftness.). The speed of light was first calculated by a Dane, Ole Roemer in the 17th century. Einstein began with this value and looked at light's inner properties. James Maxwell's equations had proved that light moved in waves. Einstein took this forward and concluded that 'light can exist only when a light wave is actively moving forward'. This changed everything for the speed of light became the fundamental speed limit in our universe. The speed of light explains the transformation of energy into mass. But why did Einstein have to square the velocity of light? There are two cameo chapters in the book. One on the development of the 'equal to' sign and the other on 'squaring'. Physicists, over time, had become used to multiplying an object's mass by the square of its velocity to arrive at an indicator of its energy. 'If the velocity is raised as high as it could go...it's almost as if the ultimate energy an object will contain should be revealed when you look at its mass times c squared.' The equation had been born. But its early years were spent away from the father, in the company of scientists like John Rutherford, James Chadwick, Enrico Fermi, Otto Hahn and Lise Meitner. The equation grew in their researches which showed how the atom could be opened, and the compressed and frozen energy that the equation spoke about let out. They had found the nucleus and the particle called the neutron and had found that when extra neutrons were pushed into overstuffed atoms such as uranium, the whole nucleus wobbled, trembled and then exploded. The adult life of the equation is better known because of its involvement in the making of the atom bomb. But as Bodanis shows, the equation has no second childhood. The researches and insights of scientists like Fred Hoyle and Subrahmanyan Chandrasekhar have used its principles to understand the stars, the sun and even perhaps the origins of the universe. The equation has changed the world and our perceptions of it. It has taken human beings to inconceivable frontiers. Had its father foreseen the future?