“The firmness of a boiled egg can be adjusted at will through the cooking time. Some decisions are, however, irrevocable – a hard-boiled egg can never be reconverted into a soft-boiled one. There would be less annoyance at the breakfast table if we could simply switch back and forth between the different degrees of firmness of the egg.
Similar issues arise in the making of structural materials such as metals and alloys. The materials properties are set once and for all during production. This forces …