According to Mises's Monetary Regression Theorem, the value of money today depends on its value yesterday, the origin of that value being its direct use as a commodity in barter.Money substitutes like the dollar can then come into existence based on actual money, which are gold and silver.Bitcoin's value then must be based on the dollar, which had value in the past as a gold substitute and still has value because it can still buy some gold.Bitcoin is not a medium of exchange at all. It's merely a new method for transacting in dollars, and we know this because Bitcoin-denominated prices change based on the dollar price of Bitcoin.If and when the dollar falls, Bitcoin must lose all value. People will run to gold and silver in that case, and not to Bitcoin.