Nuclear energy is released when heavy nuclei are broken or when light nuclei are crushed together into new elements. The first is called fission, and this is how the atom bombs and nuclear reactors work. Fission is dangerous and it produces radioactive waste. Fusion can be done safely, and it creates only hydrogen and water. Nuclear fusion powers the stars and it needs star-like conditions to work. A fusion reactor needs powerful, correctly shaped magnetic fields to safely maintain star-like conditions. So far, the energy-in to power those magnets is greater than the energy-out from fusion. A breakthrough in low-energy electromagnets promises to make the energy-in less than the energy-out. If fusion became viable, it would transform the world