In 1905, Albert Einstein published his now famous formula E = mc2, where he demonstrated the amount of energy emitted by objects, such as stars, is directly proportional to the amount of mass they decrease by. In this equation, the "E" stands for energy, while the "m" is for mass, and the "c2" is the square of the speed of light. The formula basically equates the transformation of energy into matter and matter into energy. Einstein was the first to successfully explain how the sun produced its energy and did not burn out, as other things that burn here on Earth do. It was by a process called nuclear fusion, where one hydrogen nucleus is bound to another hydrogen nucleus, forming a helium nucleus and releasing a small packet of energy called a photon. Although Einstein never intended his formula to be used for war, it was the basis for the development of nuclear weapons that helped bring about a quick end to World War II, when the United States dropped atomic bombs on Hiroshima and Nagasaki, Japan.
One of Einstein's great insights was to realize that matter and energy are really different forms of the same thing. Matter can be turned into energy, and energy into matter. So, in essence, Einstein figured out that the plastic in your computer and the particles that make up the air we breathe, are made of the same type of particles. (Tiny, TINY particles) Einstein's formula tells us the amount of energy this mass would be equivalent to, if it were all suddenly turned into energy. Although we don't normally think about it, everything, including the air we breathe has a mass (weight). "M" in the equation stands for the Mass. C2 stands for the speed of light, squared. (or you can think about it as "speed of light X speed of light) (which is always 900,000,000) It says that to find the energy, you multiply the mass by the square of the speed of light. The answer will be measured in Joules, because energy is measured in joules. So, for example, the mass of Hydrogen is 1.00794, so using the equation E=MC2, it looks like this...
E= (1.00794) X (300,000,000)2 The 2 is supposed to be an exponent.
E= (1.00794) X 900,000,000
E= 907,146,000 Joules
So it means, if you changed a single atom of hydrogen straight into energy, it would be equivalent to 907,146,000 joules.