Economists have spent years bemoaning the long-term stagnation of the advanced economies and drawing unflattering comparisons with the dynamic growth in the emerging economies, but is it time to change the tune? The US economic motor is showing signs of life, just as nervousness is sweeping across financial markets from Jakarta to Brasilia. Today's guest is leading American economist and former Obama adviser Peter Blair Henry. He has just written a book about the turnaround in relations between rich and emerging nations but is it already out of date?