I just want to say as someone with a degree in physics that this commenter is correct. Mass and energy directly relate through E=mC^2. If you remove energy (and

I just want to say as someone with a degree in physics that this commenter is correct. Mass and energy directly relate through E=mC^2. If you remove energy (and "just" energy) from a system, it now has E/C^2 less mass. Example: You have some fissible material that undergoes a nuclear reaction in a closed system and the reactants turn into products with lower mass. The mass of the system doesn't actually go down until/unless the system cools down. edit: The above commenter is still being pedantic though