“To explain the origins of physical order, Ludwig connected phenomena occurring at different spatial scales, mainly atoms and gases.1 Although it makes sense today, in Ludwig’s time working across spatial scales was a practice that violated an implicit contract among scientists. Many of Ludwig’s colleagues saw science as a hierarchy of Russian nesting dolls, with new structures emerging at each level. In this hierarchy, transgressing boundaries was thought unnecessary. Economics did not need psychology, just as psychology did not need biology. Biology did not need chemistry, and chemistry did not need physics. Explaining gases in terms of atoms, although not as preposterous as explaining human behavior in terms of biology, was seen as a betrayal of this implicit deal.”