Google and Facebook are worth a combined $2 trillion, with the vast majority of their revenue coming from advertising. In our previous episode, we learned that TV advertising is much less effective than the industry says. Is digital any better? Some say yes, some say no — and some say we’re in a full-blown digital-ad bubble. And: the endless pursuit of G.D.P., argues the economist Kate Raworth, shortchanges too many people and also trashes the planet. Economic theory, she says, “needs to be rewritten” — and Raworth has tried, in a book called Doughnut Economics.