In January 2009, a Japanese programmer known as Satoshi Nakamoto invented Bitcoin, an online currency system that allows people to trade anonymously and securely, without incurring the transaction fees normally charged by banks.

Many commentators consider the system’s use of a decentralized peer-to-peer network to verify transactions to be ingenious, but some economists point out that it is built on unsound economic principles.

The software limits the total supply of Bitcoins to 21 million; there are currently about 7.3 million Bitcoins in existence. Each Bitcoin carries an embedded security code that prevents tampering and copying while keeping users’ identities completely anonymous.

Bitcoins can be earned by users who lend their computer’s capacity to the Bitcoin network. They can also be purchased on the network’s Web site with dollars, and because of their unregulated, restricted supply, the price of a single bitcoin has fluctuated from a few cents to a high of $32 in early 2011, to $5.55 on Sept.

12. This level of fluctuation is evidence that Bitcoins are commonly used for speculative investment rather than for currency.

Although Bitcoin trading has flourished in certain niches, its future depends on its adoption as a currency. As Benjamin Friedman, a Harvard economist, explained on National Public Radio in July, the dollar is legal tender, meaning that it must be accepted by all businesses operating in the United States. Since there is no such guarantee backing Bitcoins, a majority of consumers are unlikely to abandon the dollar for the virtual currency.

These issues pose a dilemma for Bitcoin. Central banks exist to provide a stable means of economic exchange through a standard currency.

But Bitcoin’s purpose as an alternative currency with a decentralized network may prevent the system from achieving just that.