“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.
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.