Question: What is the meaning of e=mc2?

Euan Allen answered on 22 Jun 2016:

Hi Miss Science, that’s a great question.

The equation you are referring to is one of Einsteins most famous equations, in fact it’s probably the most famous equation in science. It describes the relationship between matter (mass) and energy, and is really telling you that they are exactly the same thing.

If we write out the equation in words it is:
energy = mass x (speed of light squared).

We use this equation a lot in physics, but I’ll just describe one example.

We know energy is conserved in the universe, but we know we can change which form it takes. At the LHC, we fire protons (which are made of atoms and therefore have mass) at each other at high speed. We can calculate using the equation above and the equations of motion, how much energy these protons have initially. When these protons hit, they break up into many other particles and some radiation (light) too. To make sure we catch all of the interaction productions, we take the mass of the particles produced, use e=mc2 to convert this to an energy, add this to the energy that the light has, and then compare this with how much energy we put into the collision in the first place. This is a good way to check that we can measure every product in the interaction.