From PowellsBooks.Blog (July 20, 2009):
Why Does E=mc2? is in some ways a simple book with a simple aim: we (Jeff Forshaw and Brian Cox) wanted to see whether we could actually derive E=mc2 in a way that any interested non-mathematical reader could understand. By derive, I mean follow a series of small steps that are well-motivated and hopefully obvious, or at least plausible, and arrive at the equation itself, assuming no prior knowledge and making the minimum possible number of assumptions. In other words, we behave exactly as we would in our professional life as research scientists, searching for equations that describe nature.
In doing this, we hope to do much more than simply present and describe the equation, however. If the reader follows the argument, we hope that he or she will experience the delight and awe that scientists feel when they explore nature and reveal its underlying simplicity and beauty. One often hears scientists describe equations as "beautiful," and we believe the best way to understand what this means is to actually see how the most iconic and simple equation of all came to be written down. We don't in fact follow Einstein's route to E=mc2, because we believe that 100 years of teaching and understanding has provided a more profound and transparent route to it — we aren't writing a history book.
There is an element of polemic in the book. We very firmly believe that science, which is synonymous with rational thought as far as we are concerned, is the route to a better future. Woolly thinking and superstition are rife, and we should strive to reduce their place in public discourse. By showing how something as useful and, as far as we can tell, correct, as E=mc2 emerges from simple thought processes that we believe are open to every interested reader, we hope to make our case for an increased respect for and use of the scientific method in everyday life.
We also describe what E, m, and c actually are. Why is the speed of light special? What is energy, and what is mass? The question of mass leads us to the Large Hadron Collider at CERN, where we both work. One of the key goals of this machine is to answer this question definitively for the first time. It is remarkable that Einstein could be led to the equation that describes how mass and energy can be interchanged freely, without actually knowing what mass is. Such is the wonder of physics!