The Most Famous Equation in History
E = mc²
Five symbols that changed the world. But what do they actually mean?
Breaking Down the Equation
- E = Energy (measured in joules)
- m = Mass (measured in kilograms)
- c = The speed of light (299,792,458 meters per second)
- c² = The speed of light squared (an enormous number)
The equation says: mass and energy are equivalent. They're the same thing in different forms.
Why c² Is So Important
The speed of light squared is approximately 90,000,000,000,000,000 (9 × 10¹⁶).
This means a tiny amount of mass converts to an enormous amount of energy.
- 21,500 tons of TNT
- Enough to power 28,000 homes for a year
- The energy of the Hiroshima bomb
Where Does This Energy Come From?
Mass doesn't just disappear. In nuclear reactions, tiny amounts of mass convert to energy:
- Nuclear fission: Splitting heavy atoms (like uranium). Used in nuclear power plants and atomic bombs.
- Nuclear fusion: Combining light atoms (like hydrogen). Powers the Sun and hydrogen bombs.
- Matter-antimatter annihilation: When matter meets antimatter, 100% converts to energy.
The Sun's Secret
The Sun converts about 4 million tons of mass into energy every second. That's where sunlight comes from.
Thanks to c² being so large, the Sun can burn for billions of years while losing only a tiny fraction of its mass.
Why Can't We Use All This Energy?
- Normal chemical reactions (like burning wood) convert virtually no mass
- Nuclear reactions convert about 0.1% of mass
- Only matter-antimatter reaches 100%, but antimatter is extremely rare and hard to store
Einstein's Insight
Before Einstein, scientists thought energy and mass were completely different things. E=mc² showed they're convertible — like ice and water are different forms of the same substance.
- Nuclear power
- Understanding stellar physics
- Particle physics discoveries
- GPS satellite corrections
Learn More
This article is based on our audio course Physics Fundamentals. Listen to Episode 7: "Special Relativity: Space, Time, and E=mc²" for the complete story of Einstein's revolutionary theory.