Yes, c² is a constant and energy is proportional to that constant. Actually, Einstein’s formula was E² = |𝐩|²c² + (mc²)². 𝐩 is the momentum vector, and we ne

Yes, c² is a constant and energy is proportional to that constant. Actually, Einstein’s formula was E² = |𝐩|²c² + (mc²)². 𝐩 is the momentum vector, and we need to square the magnitude of that vector to find the energy due to momentum. Since momentum is often zero, that term can be neglected leaving you with E = mc². When considering light, however, it is mass that is zero, leaving you with just the energy due to momentum. None of it is “PR bullshit”.