Presently,the U.S. has roughly 14.5 trillion in U.S. dollar debt. Check out how many tons of gold ,collectively ,that all the G20 countries have.Those reserves of gold (that may not exist) are NOT enough to collateralize at present value of dollars,that amount of debt.As far as all the gold and silver in the world,well ,I meant refined in bars,not in the ground.That would be an answer best left to science in about 200 years.