Ever since the “Great Recession” of 2007-2009, the world’s major central banks have kept short-term interest rates at near-zero levels. In the US, even after the Federal Reserve’s recent increases, short-term rates remain below 1%, and long-term interest rates on major government bonds are similarly low. Moreover, major central banks have supported markets at a record level by buying up huge amounts of debt and holding it.

Why is all this economic life support necessary, and why for so long?