Anyone with a control systems background or even just audio experience will recognise what happens when you have an undamped feedback loop: it oscillates.
Technology can make the problem worse by reducing the time taken to economic changes, exaggerating the feedback loop. However there has been one big success of formal macroeconomic control modelling: inflation. Almost all the Western economies have a good system for controlling interest rates in order to maintain an inflation target.
I don't think anyone has really invalidated Keynes' work on business cycle theory, although it is recognised that it doesn't quite cope with a heavily financialised economy and there is huge political opposition to counter-cyclical fiscal policy.
Technology can make the problem worse by reducing the time taken to economic changes, exaggerating the feedback loop. However there has been one big success of formal macroeconomic control modelling: inflation. Almost all the Western economies have a good system for controlling interest rates in order to maintain an inflation target.
I don't think anyone has really invalidated Keynes' work on business cycle theory, although it is recognised that it doesn't quite cope with a heavily financialised economy and there is huge political opposition to counter-cyclical fiscal policy.