E Equals m c Squared

Posted by Paul A. Heckert Feb 6, 2008

Einstein's famous equation, E=mc2, is arguably the most famous equation in the history of physics. At least one entire popular book has been written on this equation: E=mc2 by David Bodanis, Berkely, 2000.

The preface of this book begins by quoting a magazine interview with Cameron Diaz, in which the actress said that one thing she really wanted to know was the meaning of E=mc2. Apparently even Hollywood celebrities wonder about this equation.

This equation stems from Einstein's special theory of relativity, which he published in his miracle year, 1905. About a decade later Einstein published his general theory of relativity.

What does this equation mean? In simple terms it means that mass, m, and energy, E, are equivalent. Energy can be converted into mass and mass into energy. The equation tells us how much energy is equivalent to a certain amount of mass. Because c, the speed of light, is so large a very small amount of mass converts into a very large amount of energy.

Prior to this equation physicists had separate laws for conservation of energy and mass. These laws stated that the total amount of both mass and energy in the universe is constant. After Einstein's work, these laws were modified to a single law of conservation of mass and energy. Mass and energy can interchange, but the total amount of mass-energy in the universe is constant.

The American Institute of Physics has an interesting recording of Einstein himself explaining the meaning of his equation. If you want to hear it directly from the source, check it out. If you happen to see Cameron Diaz, let her know about it too.