In theory, any currency should maintain its exact value over time (a day, a month, a year, a decade) in order to serve as both a medium of exchange and a storer of value.
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A digital crypto-currency should be the ideal for this, since the servers and exchanges can read various public indicators (prices of precious metals, CPI, PPI, GDP of various countries, price of oil, iron, natural gas, AMS, M2, etc) and adjust the price accordingly but adjusting the growth in the block chain.
There is a problem here. Nobody can "adjust" the value of anything you have. I mean, how do you feel about owning a house if its market value is going up and down in a real estate bubble? So, if two people believe that a certain number of coins is worth a certain other thing, they don't have to pay attention to anyone trying to "adjust" the value of a coin. The one owns the house and decides how much it is worth; the other owns the coins and decides how much they are worth.
If the servers and exchanges attempt to "adjust" the price against some currency or some commodity, you immediately get Gresham's Law, where whichever one is valued more by people than the official exchange rate allows for, goes wherever it can get an unadjusted price.
When a government overvalues one type of money and undervalues another, the undervalued money will leave the country or disappear from circulation into hoards, while the overvalued money will flood into circulation.
It is commonly stated as:
Bad money drives out good.
With Gresham's Law restated for the layman, I should ask this (of everyone who would like to chime in):
1. Is it impossible to maintain such a currency?
2. Is it impractical to maintain such a currency?
3. Is it desirable to maintain such a currency?
4. Would such an alternative really be an alternative to Bitcoin?
What do you do with the money that you can't afford to lose? In 30 years, a 2013 dollar could be worth 75 cents, 50 cents, 25 cents, or nothing. It won't be worth a dollar. You can buy gold, silver, platinum, etc, but those historically fluctuate by a factor of two over time, so you might end up with $1.50, or you may be left with 50 cents for your dollar. You could buy into a Dow Index fund, but Dow drops loser stocks over time, so you never get the same performance. Corrections have seen 30% drops compared to the dollar, which also loses up to 10% of its value in a year.
Where do I put the money that I can't afford to lose? In the old days, dollars. Dollars were backed by both gold and silver until almost WWI. Inflation stayed at 0-2% year after year. Detached from widely used currencies, silver fluctuates from about $8 to $45. Gold swings just as wildly.