Question: does e really equal mc²

Varun Ramaswamy answered on 18 Nov 2019:

I love this question!

E is NOT equal to just mc^2 .. That only makes sense for something that has an “m” (which is mass) and is not moving. But when you consider things like light, then the problem is that light has no mass. That means this equation, that was originally made to describe how light behaves doesn’t really do its job at all.

The actual equation is E = mc^2 + (pc)^2; where “p” is called the momentum, that exists only when an object is moving.
So when you’re using this equation to describe something like light that has no mass, the equation becomes E = 0 + pc, which is just E = pc.
But to describe someone like me or you sitting down in one place, remember that we have a mass but no momentum. So only in our case, the equation gets simplified to E = mc^2