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E = mc²
Initializing
Special Relativity  ·  Albert Einstein  ·  1905

E = mc²

Four symbols. The most consequential idea in the history of physics — mass and energy are the same thing, separated only by the square of the speed of light.

1905
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The Equation

Every symbol,
decoded.

E
Energy
The total intrinsic energy of a body. Not kinetic, not potential — the raw energy contained within mass itself. The deepest reservoir in nature.
Joules — kg·m²·s⁻²
m
Mass
The measure of matter. Every kilogram of anything — a coin, a breath of air — contains an almost incomprehensible amount of latent energy.
Kilograms — kg
c
Speed of Light
299,792,458 metres per second. The absolute cosmic speed limit. Squared, it becomes an amplifier of staggering magnitude — the bridge between mass and energy.
299,792,458 m/s in vacuum
²
Squared
c² ≈ 8.99 × 10¹⁶ m²/s². This is why a paperclip contains enough energy to power a city. Small mass, astronomical multiplier.
≈ 89,875,517,873,681,764 m²/s²
By the Numbers
0
Speed of light in metres per second — the universe's ultimate constant, identical for all observers.
0 PJ / kg
Energy in a single kilogram of matter. Ninety petajoules — equivalent to 21.5 kilotons of TNT.
0 t/s
Tonnes the Sun converts from mass to energy every second through nuclear fusion.
0
Einstein's age when he published E = mc² from a patent office in Bern, Switzerland.
0%
Mass-to-energy conversion in matter–antimatter annihilation. The maximum physically possible.
0 μs/day
GPS clock drift from relativistic effects. Without correction: ~10 km positional error per day.
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Mass value
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E = mc² result
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Energy: 0 TJ
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Photons: 0
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Chronology

The road to
E = mc²

Applications

Where the equation
lives in the real world.

"Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world."
— Albert Einstein
mc²