This image of the mushroom cloud arising from the 1952 hydrogen bomb test, Ivy Mike, released 10.4 Megatons of energy by leveraging hydrogen bomb technology. The overwhelming majority of this energy was liberated by the conversion of mass into energy: about 484 grams (1.07 pounds) worth of mass. (Credit: The Comprehensive Nuclear-Test-Ban Treaty Organization/flickr)

Why Einstein’s E = mc² is only half of the equation

Einstein’s most famous equation is E = mc², which describes the rest mass energy inherent to particles. But motion matters for energy, too.

One of the most profound insights to come about in all of physics has been what’s easily Einstein’s most famous equation: E = mc². Quiet simply, it states that energy is equal to an object’s mass multiplied by the speed of light squared. This simple-seeming mathematical relation holds an enormous amount of physics inside of it, including:

• if you have a certain amount of energy available, you can spontaneously create new matter-antimatter pairs of particles as long as their rest mass is less than the amount of energy required to create them,
• if a matter-antimatter pair of particles annihilates, they will produce a specific amount of energy given by the masses of the pair of particles that annihilated,
• and that every time you have a nuclear reaction, whether fusion or fission, if the mass of the products is less than the mass of the reactants, E = mc² tells you how much energy will be liberated in that reaction.

This one equation, E = mc², describes how much energy is inherent to any massive particle at rest, including how much…