“Let’s nuke it in the microwave,” we often say as we pull a frozen dinner out of the freezer. That figure of speech seems to express the fact that our experience with nuclear power and with microwaves goes back only a few years, while our experience with fire goes back thousands of years. We seem to be reacting to the novelty that nuclear power and microwave cooking have in common. They don’t really have anything else in common. Microwaves are electromagnetic waves, exactly the same as visible light except that microwaves have much longer wavelengths than the light our eyes detect. The first large-scale use of microwaves was in radar in the 1930’s. Now microwaves are also used to transmit telephone and television signals. Microwaves cook food by heating the liquid water it contains. Even frozen food contains some liquid water, at least on the outside surface exposed to warm air on the way from the freezer to the oven.