When an asset rises by almost 30% in a few weeks, it tends to attract attention. Recently, that asset was bitcoin (BTC). Are these cryptocurrencies mere fads? Or are they potentially game-changing alternatives to the conventional currencies such as the U.S. dollar, Chinese RMB, Japanese yen or European Union euro? There’s no lack of skeptics and critics of bitcoin and other cryptocurrencies; yet despite concerns about security, criminal use and volatility, cryptocurrencies have proliferated at a dizzying pace. So what are those who can't follow the technical arguments supposed to make of all this?