The only thing that they can do that is legal is to raise interest rates. Since they are the biggest borrower out there they would be adding billions to their interest payments. Assetts do not go up in value, it is fiat currency that looses it's value. An ounce of gold will always be an ounce of gold and a barrel of oil will always be a barrel . Unfortunately I think all of the talk about asset bubbles is an attempt to keep scared investors in paper assets, so they can slowly take our wealth away without us noticing.