I recently finished reading Why Does E=mc2? (And Why Should We Care?) by Brian Cox and Jeff Forshaw. The book has a very direct goal: explain why energy equals mass times the universal speed limit squared, and why it matters to us. The authors take an approach that only mildly boarders on the classical way of teaching science. While they do discuss relevant scientists and history as you would find in a science class, they only do so in a limited fashion and only when they need to show the previously-existing information and concepts that Albert Einstein stood upon to derive his famous equation, and then general relativity. The style of the book is somewhat easy to follow, and is aimed at presenting the path to E=mc2 to a layman without diving to far into math.
Cox and Forshaw used Pythagoras to arrive at the famous equation, which I have seen done before. However, they take the time to spell out the argument, showing why the specific mathematical path is chosen. For example, the Euclidean (flat-space geometry) version of Pythagoras is h2 = a2 + b2. The authors show why this version cannot be used because of causality (the flow of time), and graphical show why the non-Euclidean h2 = a2 – b2 must be used instead. From there they proceed, step by step, to derive E=mc2.
This drive towards Einstein’s most famous equation takes the first half of the book, and for the most part the authors take a slow, steady approach. But at the critical juncture when many abstract concepts such as spacetime, and vectors in space and time are being split, the procedure seems rushed. In just a couple of page they throw away the cautious, explanatory approach and introduce new mathematical terms which are not immediately obvious. They are not nearly verbose enough about the steps being taken, or about why new equations are being introduced. I really felt I was reading a 5-star book up until this point. I would use the analogy of going on vacation by flying to a tropical destination on a luxury private jet, then having to unload your own baggage from the plane when you got there. I really wished the authors had spent at least another page or two explaining the final pieces. But they didn’t and I had to reread the last section several times, and even consulted Wikipedia to try and figure out the mathematical tricks they were using.
The rest of the book dove off into the world of general relativity and quantum mechanics. This was a good overview, but I real felt like the book went downhill after E=mc2 was derived. One big problem I had with the sections on quantum mechanics was the introduction of a “master equations”, which relates the various types of particles and forces at the elementary particle level. Instead of reprinting the equation occasionally when discussing it, and perhaps highlighting the portions being discussed, the book simply referred to the one place it was printed. This was very inconvenient and I finally got tired of going back to the equation again and again, switching between pages trying to follow along. I would imagine that if the equation has simply been reprint 5 or 10 times where being discussed, with relevant portions highlighted, that the book would have gained a page or two. That seems a small price for clarity on a very difficult subject.
What saved this book for me was the clarity of writing by the authors, and their obvious love of the subject. I would like to find a better work on the subject to recommend to a layman, but this is still probably the best treatment I have read on E=mc2. Perhaps a second edition can make these editorial changes to improve the book. But if you are not concerned with every single mathematical step to the equation, then this is probably the book for you.






