Conservation of mass from chemistry and conservation of energy from physics were combined into conservation of mass and energy as special relativity proved mass-energy equivalence. In short, if we count all the mass in using E=mc^2, total sum of energy is always conserved even with nuclear fission. Then, I do not see how that can work as I thought of this question. here is the question. 1. I lifted a stone from the floor to the table. Assume 100% efficiency I spent 20 J and the stone now has 20 J of potential energy. 2. Suddenly, nuclear fission happened on the other side of the earth. a half of the Earth's mass is now converted into a massive energy, following e=mc^2. Energy is conserved as nuclear fission made the energy accordingly. 3. somehow, my stone on the table was not affected from the nuclear fission, it was not burnt or anything. But now g is a half, so the potential energy it has is a half. So it will gain only 10J when it is dropped back to the floor. Then the question is, where is my another 10 J gone ?