AND THEN THERE'S IMAGINARY GOLD:

Cryptocurrency: The bitcoin, a virtual medium of exchange, could be a real alternative to government-issued money--but only if it survives hoarding by speculators. (James Surowiecki, September/October 2011, Technology Review)

Bitcoin is not going to make government-backed currencies obsolete. But while the system's virtues, such as anonymity and the lack of bank fees, may not matter much to most consumers, one can envision it being useful in a variety of niche markets (some legal, others not, like recreational drugs). Where anonymity is valuable, where trusted third parties are hard to find or charge high rates, and where persistently high inflation is a problem, it's possible that bitcoins could in fact flourish as an alternative currency.

Before they become such an alternative, though, the system will have to overcome a major, and surprising, problem: people have come to see it primarily as a way to make money. In other words, instead of being used as a currency, bitcoins are today mostly seen as (and traded as) an investment. There's a good reason for that: as people learned about Bitcoin, the value of bitcoins, in dollar terms, skyrocketed. In July 2010, after the website Slashdot ran an item that introduced the currency to the public (or at least the public enthusiastic about new technologies), the value of bitcoins jumped tenfold in five days. Over the next eight months, the value rose tenfold again. This attracted an enormous amount of publicity. More important, it also made people think that buying and holding bitcoins was an easy way to make a buck. As a result, many--probably most--Bitcoin users are acquiring bitcoins not in order to buy goods and services but to speculate. That's a bad investment decision, and it also hurts Bitcoin's prospects.

True believers in Bitcoin's usefulness prefer to deny that speculation is driving the action in bitcoins. But the evidence suggests otherwise. The value of the currency has been tremendously volatile over the past year. A bitcoin has been worth as little as a few pennies and as much as $33, and after seeming to stabilize at around $14 over the summer, the bitcoin's value tumbled by almost 50 percent in a matter of days in August. Media coverage has had an outsized impact on the value of bitcoins, even when it has not had a major impact on the number of transactions conducted. Blog posts in which people talk about buying bitcoins because of how much they've increased in value are common. In May, Rick Falkvinge, founder of the Swedish Pirate Party, which focuses on patent and copyright reform, posted that he had decided to put all his savings into Bitcoin. Although he had previously published a series of posts arguing for the bitcoin's viability as a currency, his first listed reason for investing in bitcoins was that their value had risen a thousandfold against the U.S. dollar in the previous 14 months. That's classic speculative thinking.

The problem with having the Bitcoin economy dominated by speculators is that it gives people an incentive to hoard their bitcoins rather than spend them, which is the opposite of what you need people to do in order to make a currency successful. Successful currencies are used to transact day-to-day business and lubricate commerce. But if you buy bitcoins hoping that their value will skyrocket (as anyone investing in bitcoins would), you're not going to be interested in exchanging those bitcoins for goods, since then you'll lose out when the value of bitcoins rises. Instead, you're going to hold onto them and wait until you can cash out.

This kind of hoarding is made more likely by the way Bitcoin is set up. Whereas the supply of modern, "fiat" currencies is controlled by central banks, the supply of bitcoins is permanently limited; there will never be more than 21 million bitcoins in existence. (The total number of coins is a result of the system's initial rules governing how many bitcoins miners could earn, and how often.) Bitcoin's limited money supply is one of the things that people like about it: the currency cannot be debased, as money can when central bankers print more of it. But the flip side is that if the demand for bitcoins rises, for whatever reason, then the value of bitcoins will necessarily rise as well. So if you think that bitcoins are going to become more and more popular, then--again--it's foolish to spend your bitcoins today. The rational thing to do is hoard them and eventually sell them to new users. But that means there will be fewer bitcoins in circulation (and more in people's virtual wallets), making them less useful as an actual medium of exchange and making it less likely that businesses and consumers will ever see Bitcoin as legitimate.

Now, even traditional currencies can be subject to this kind of cycle, which economists call a "deflationary spiral"--although with conventional currencies, the cycle occurs when falling prices lead people to start hoarding cash in the expectation that prices will keep falling (which in turn holds down demand and makes prices fall further). The quintessential recent case is Japan after its real-estate bubble burst in the 1990s.

With ordinary currencies, though, there's a limit to how far down the spiral can go, since people still need to eat, pay their bills, and so on, and to do so they need to use their currency. But these things aren't true of bitcoins: you can get along perfectly well without ever spending them, so there's no imperative for people to stop hoarding and start spending. It's easy to imagine a scenario in which the vast majority of bitcoins are held by people hoping to sell them to other people.

Follow @brothersjudd