What does E=mc2 mean?
E = mc² means that mass and energy are two forms of the same thing. Energy (E) equals mass (m) times the speed of light (c) squared, so tiny masses hold huge energy.
Albert Einstein published the equation in 1905 as part of his work on special relativity. Because the speed of light is about 300 million meters per second, squaring it gives an enormous number. That means even a small amount of mass corresponds to a vast amount of energy.
For example, converting just one gram of mass completely into energy would release about 90 trillion joules, roughly the energy of a 21-kiloton explosion. In everyday chemical reactions, such as burning wood, the change in mass is far too small to measure.
Where we see it
The equation explains how the Sun shines: in its core, hydrogen fuses into helium, and a small amount of mass is turned into energy. Nuclear power plants work in a similar way, splitting heavy atoms such as uranium and releasing energy from the small loss of mass.
Did You Know?
Einstein's original 1905 paper did not use the exact form E = mc². He wrote the idea in words and other symbols, and the famous short version became popular later.