Brad DeLong asks: At what time scale, if any, does the long run come?
Some other answers besides the 3-6 years discussed by Krugman and DeLong:
- It's already here in the IT model (we're back on trend, just not the trend you were thinking of , ). The time scale governing nominal shocks is really short; the time scale for unemployment is a bit longer (probably governed by matching theory).
- Never if the current state is defined by expectations at infinity (unless we change them). This (oddly) encompasses the liquidity trap and neo-Fisher views.
- Whenever the central bank really wants it to come (Green Lantern theory).