this is the u.s. Treasury Department's explanation of what underpins the worth of a u.s. dollar since it came off the gold standard...
"Federal Reserve notes are not redeemable in gold, silver or any other commodity, and receive no backing by anything... The notes have no value for themselves, but for what they will buy. In another sense, because they are legal tender, Federal Reserve notes are "backed" by all the goods and services in the economy".
In other words, they're worth nothing.
conversely, gold has some intrinsic value. and surely in currency terms it will be a lot more than U.S.$900 in the coming months.....