# Einstein's equation turns 100

**Tuesday, September 27, 2005**

Albert Einstein's best known equation, and probably the best known aspect of all physics, E=mc^{2}, turns one hundred today.

September 27, 1905 is generally considered the birthday of the equation because that is the day that Einstein's paper outlining the significance of the equation arrived in the offices of the German journal Annalen der Physik.

In the equation, 'E' stands for Energy, 'm' stands for mass, and 'c' stands for the speed of light.

The equation shows that matter and energy are, essentially, two aspects of the same thing, and that a small amount of matter can be converted into an enormous amount of energy. Nuclear reactions, including fusion in the sun and in nuclear weapons, are examples of large amounts of energy released from the conversion of comparatively small quantities of mass.

The United Nations declared 2005 the International Year of Physics in recognition of Albert Einstein's work in 1905. In addition to discovering his famous equation, over the course of 5 months in 1905 Einstein developed the theory of Special Relativity (which led him to the equation E=mc^{2}), proved the existence of atoms and molecules, and showed that light is made of photons. 1905 is often called Einstein's annus mirabilis, or miracle year.

The 100th anniversary of Einstein's miracle year is being celebrated in many countries around the world as the World Year of Physics. In the UK, it is called the Einstein Year.

## Sources

- John S. Rigden. "Einstein 1905, The Standard of Greatness" —
*Harvard University Press*, 2005

- "Einstein Year (UK)" —
*Institute of Physics*, 2005