E = mc2 is a formula that shows, in mathematical terms, the relationship between energy and mass. In this formula, E is energy, m is mass, and c is the speed of light. The number 2 to the upper right of the c means that c is squared, or multiplied by itself.
This formula, first devised by Albert Einstein, shows how much energy would be produced if a quantity of matter could be completely changed into energy. Suppose that just one gram of matter, or 1/28 of an ounce, were converted into energy.
To find out how much energy would be produced, we would multiply one gram times c2. The speed of light is about 30 billion centimeters per second, so the speed of light times itself equals 30 billion times 30 billion, a number that consists of 9 plus 20 zeroes!
This is the number of ergs (a very small amount) of energy that would be produced from the one gram of mass. But the number of ergs produced by converting one gram of matter into energy is so large that this amount of energy could power an ordinary light bulb for some 35,000 years!