When short-term interest rates reach zero, traditional monetary policy stops working. Central banks then move to what some economists call MP3: creating money to purchase financial assets directly.
MP3 raises the price of the assets being purchased — government bonds, mortgage-backed securities, and indirectly equities and real estate. It also suppresses yields available to ordinary savers.
The effect is allocative: holders of financial assets gain, while holders of cash and fixed-rate savings lose purchasing power. This is the mechanical reason wealth gaps tend to widen during sustained MP3 regimes.