The equation E = m c² is perhaps the most well-known equations in physics, and was deduced by Albert Einstein in 1905. E represents energy, m represents mass, and c is the speed of light (a very large number!). The general idea of the equation is that mass can be converted into light, and light can be converted in to mass. The equation tells how much light or mass would result from such a conversion.

The sun is an excellent example of the conversion of mass to energy. As atoms in the sun undergo fusion, a very small amount of the mass of those atoms is converted to the sunlight we see every day. Einstein's equation can tell us exactly how much light is produced if we know how much mass has "disappeared" in such a reaction.