This weeks we spent a bit of time learning about interest rates/bond yield curve. The difference in yields for dissimilar maturities demonstrates markets response to the supply and demand for loanable funds and assessment of risks associated with liquidity, inflation, risk of default, etc. These models foretell that yield on longer term maturities tend to be higher than the yield on short term yields, giving the yield curve is usually upward sloping form

. So, How can interest rates be negative?

How can markets experience an inverted yield curve?

What is behind low interest rates (flat yield curve), as we now experience, for such an extended period of time?