After Milton Friedman published a 1975 compilation of writings titled There’s No Such Thing as a Free Lunch , the phrase (lifted from Robert Heinlein’s sci-fi novel about a lunar penal colony) became something of a libertarian shibboleth. For Friedman, the “free lunch myth” was epitomized by the ostensibly “free” goods and services provided by the welfare state, which in his view were paid for by the unjustified taxation of others’ wealth. But the phrase “no such thing as a free lunch” was invoked in a radically different manner by Friedman’s contemporary, the left-wing ecologist Barry Commoner, who in 1971 identified it as one of the four central principles of ecology. For Commoner, the phrase neatly encapsulated the conservation principle of physics—that energy can never be created nor destroyed—in combination with the ecological tenet that everything is connected. It meant, in Commoner’s reading, that anything human beings took from the planetary ecosystem would eventually have to be returned to it.…