# E=mc2 | The Equivalence of Mass and Energy

E=mc2 is perhaps the most famous equation in all physics, but very few people actually know what the equation means, or where it comes from.

The equation - E=mc2 - means "energy equals mass times the speed of light squared." It shows that energy (E) and mass (m) are interchangeable; they are different forms of the same thing. If mass is somehow totally converted into energy, it also shows how much energy would reside inside that mass: quite a lot.

In this video I would like to show one method for deriving this equation, as well as provide some insight into what the equation actually means.

Along the way we will also touch upon some of the most fascinating features of Einstein’s theory of special relativity, including time dilation, the reason why nothing can travel faster than the speed of light, and the relationship between energy and momentum for massless particles.