Starts With A Bang

Why Does E=mc^2? (Synopsis)

Image credit: Einstein deriving special relativity, 1934, via

“Science is global. Einstein’s equation, E=mc^2, has to reach everywhere. Science is a beautiful gift to humanity, we should not distort it.” -A.P.J. Abdul Kalam

Over 100 years ago, Einstein shook up the physics world with a number of groundbreaking discoveries: special relativity, brownian motion, the photoelectric effect, and his most famous equation, E = mc^2. This mass-energy equivalence underlies everything from antimatter to atomic bombs to the process that powers the Sun.

The longer a photon’s wavelength is, the lower in energy it is. But all photons, regardless of wavelength/energy, move at the same speed: the speed of light. Image credit: NASA/Sonoma State University/Aurore Simonnet.

Yet our Universe didn’t have to have this relation; energy could have been equal to any constant times mass times the speed of light squared. Yet if you demand that both energy and momentum are conserved in any interactions, that freedom goes away, and E = mc^2 becomes, once again, your only option.

Mass-energy conversion, with values. Image credit: Wikimedia Commons user JTBarnabas.

Come get the story on why Einstein’s most famous equation is the way it is, and can’t be otherwise!