Probably the most well know equation in all of science is Einstein’s famous energy, mass equation 
. What most people don’t know is that this expression is only part of the whole equation. In fact this equation only works for matter that is at rest. Most people also know that Einstein won a noble prize but it wasn’t for relativity at all. In 1921, well after his work on relativity, Einstein received the nobel prize for his explanation of the Photoelectric effect.
Equation Explained
The famous equation only represents the rest energy a particle has and is better suited written like this, 
. Eo is the rest energy, m the mass , and c the speed of light.
But that is only half the story, the entire equation consists of the rest energy plus the kinetic energy, 
. In this equation, K is defined as, 
, and gamma as, 
, where gamma is the Lorentz Transformation, and u is the velocity of a particle.
This relationship between mass and energy gives rise to the notion of massless particles that travels near the speed of light. So considering the full equation, a particle can be massless and still contain energy, but it can never be at rest.
So the next time a friend of your says something about , you can correct them and give them a dosage of information they probably don’t want.
Click the play button below to hear Einstein himself explain the equation.
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