A good feature of teenagers is that they sometimes sleep in. So Emily and I can chat on a quiet Saturday morning about wearable tech (remember 1988?), and how 2013 feels a bit like 1997 or 2007 or 1923. The times when technological change seems to rev up again. To be followed, if recent history is any guide, by yet another crash.
I suspect that DeLong, and even Krugman, believe that the fundamental drivers of our economic instability are the simultaneous and related rise of both digital technologies and China and India (RCIIIT). Both DeLong and Krugman, have, at various times, written about the disruptive impact of "smart" robots (including robot/human pairings) and the related rise of 'mass disability'. Both, I suspect, share my opinion of the economic consequences of artificial sentience.
These aren't however, topics they can discuss in the context of models and mechanisms. How do you measure technological disruption? Economists still struggle to describe the productivity impacts of typewriters. Corporations can't make an internal business case for products like Yammer. We can't measure technological disruptions, and what we can't measure we can't model. What Economists can't model they can't discuss, and so they look through a keyhole into a dimly lit room and see monsters, but can't speak of them.
But the situation for Economics is even worse than that. There is a reason Krugman rants about economists who cling to models when all their predictions fail and yet retain academic respect. A discipline without falsifiability can be scholarly, but it can't be a science. It can't progress.
Economics thus lies between the Scylla of the monsters than can't be mentioned, and the Charybdis of the non-falsifiable.
No wonder Economists are dismal.