A strange thought has occurred to me this morning. Each piece of matter has a huge amount of gravitational potential energy stored in the universe. My thought is that during nuclear reactions the large amounts of energy that are released would be tiny compared to the loss of gravitational potential out there. Where does the energy go? I've done a little reading and from what I can gather the changes in mass aren't exactly 'real' in the regular sense. I find this concept a little hard to grasp though. So I guess the question is during a nuclear reaction does the change in mass affect the gravitational force exerted by the matter?