Most paper money initially existed as a substitute for gold. That's what gave it value. But right now what gives a currency value is other currency. Most countries hold reserves and the reserves are other currencies. If you are a backing up the euro with the dollar, what's backing up the dollar? I don't think it is going to go to a point where all you have is coins and bars of gold, but I do think that we are going to have to go back to a monetary system based in gold, not based on paper.