Interesting idea perhaps of capital that has an accelerating half-life - invest it or lose it. I can imagine technology and society would develop at a much faster pace.
"A negative interest rate means the central bank and perhaps private banks will charge negative interest: instead of receiving money on deposits, depositors must pay regularly to keep their money with the bank. This is intended to incentivize banks to lend money more freely and businesses and individuals to invest, lend, and spend money rather than pay a fee to keep it safe."
Too bad the capital stock isn't determined by individuals but rather the Fed; who knows what the interest rate would be in real life if there wasn't massive money printing. Sorry, "quantitative easing"
A microcosm of the global economy: we're awash with capital, hence no one is willing to pay much in the way of interest rates.