Why Does E=mc2?

"This book, written by Brian Cox and Jeff Forshaw, is wonderful. Brian, who is a friend of mine, is a physicist in England. By exploring the equation “energy equals mass times the speed of light squared”, this book helps you to understand why the universe is what it is. It walks you through how Einstein came up with the equation, and why the universe behaves the way it does. I have a PhD in astronomy so the material was familiar to me, but Brian and Jeff do a brilliant job of walking the reader through Einstein’s equation. If you make just one assumption – that light travels at a certain speed, and you give that a number you call “c” – then everything falls into place in the universe. You find that mass and energy are two sides of the same coin. One can be converted to the other. And the amount of energy you get out of a handful of matter for some reason depends on the speed of light. If you read this book – and I’ll admit some of it is a little tough – you will understand how the universe works. That we’re not making this stuff up. Science isn’t an encyclopedia of facts to memorise. It’s alive, and it’s the process of how we expand our understanding of what goes on here on Earth and beyond. Even if the average reader doesn’t grasp every detail, they will see that there was a step-by-step way of achieving this understanding about our universe. That, to me, is the goal of teaching people about science."