That the binding energy curve peaks in the middle is the reason that both fission and fusion can produce energy, but the way to tap these resources leads to entirely different types of reactors. In a fission reactor, a chain reaction is sustained as neutrons created in one fission move on to split other atoms nearby. The material, uranium or

plutonium, is held in tubes which can be moved so that the number of “nearby” atoms can be controlled. If control is lost, the reaction runs away, and there is an accident. In fusion, the hydrogen fuel is heated into a gaseous, electrified state called a plasma. Since the plasma is hotter than the interior of the sun, it must be held in place by a magnetic field rather than a walled container. The problem is that this magnetic bottle leaks, and the problem is to keep the fire burning. There is certainly no possibility of a runaway reaction in this case. However, plugging these leaks has been a long and difficult journey for fusion researchers, whose story will soon unfold.

People used to confuse astronomy with astrology. With the great success of the Hubble telescope, the difference between science and fortune-telling is now clear in the public’s mind. If fusion should succeed, perhaps the difference between fission and fusion would be equally well recognized.