In an economy run on Bitcoin, these things would be impossible for a central bank to accomplish. A key aspect of the Bitcoin protocol is that the total number of bitcoins is capped at 21 million, after which no more will ever be issued. This makes Bitcoin appealing to many people because something that will never increase in supply is more likely to hold its value. The problem is that in the event of a crisis, there would also be no way to add liquidity to the system, since you can’t “print” more bitcoins. The central bank could build up a stash of bitcoins that it could then funnel into the system, but that would do little good because people would know the stash was limited. And in any case, the central bank’s demand for Bitcoin would drive up its price, which would make people more likely to hold onto it and less willing to spend it—the opposite of what you want in a financial crisis.

Bitcoin would also make it hard for governments to fight recessions, which they typically do by using what economists call countercyclical monetary and fiscal policy. Central banks slash interest rates, and—as the Federal Reserve did after the 2008 financial crisis—pump money into the system by buying assets (what’s known as quantitative easing). And governments try to get the economy moving again by cutting taxes and increasing spending, typically paying for that by borrowing money, as with the Obama-era stimulus package.

Here again, a Bitcoin economy would limit the government’s options. Since the central bank would have no control over the currency, it would also have no control over interest rates, and only a limited ability (depending on the size of its Bitcoin stash) to pour money into the economy. Fiscal policy, too, would be close to impotent. Today, when the government runs a deficit, it can have the Fed print money and then borrow that money from the Fed. That adds liquidity to the system. In the Bitcoin world, the government would have to borrow bitcoins to spend. And again, this would make bitcoins more valuable, making people less willing to spend them—the opposite of what you need to fight a recession.

But don’t worry about it

The good news is that it’s an incredibly unlikely future. While the idea of making Bitcoin a universal currency may have impeccable logic to digital-age utopians, in practice it makes little sense. And the design of Bitcoin also makes it difficult to imagine. Since the supply of bitcoins is limited, if the demand for them rises, their value rises, too. But that means that if you own bitcoins, and you think they’re going to become more popular, then the sensible thing to do is hold them, since they’ll be more valuable tomorrow. That makes people less interested in using bitcoins to actually buy stuff and more interested in treating them as speculative investments—the opposite of what you want in a medium of exchange.

This doesn’t mean cryptocurrencies are useless. Buying drugs, money laundering: these are situations where they can come in handy.

You might think that the same restrictions on supply were true of gold when economies were run on the gold standard. But the supply of gold wasn’t fixed. It expanded as people mined more of it. There actually was something of an equilibrium—as economic growth increased the demand for gold, making it more valuable, the rising price encouraged people to mine it, which brought more gold into the system, ultimately keeping the dollar value of gold relatively stable. Between 1800 and 1900, the dollar value of gold gradually rose by small percentages. Bitcoin, by contrast, regularly rises and falls 5 or 10 percent in a single day, purely because of shifts in speculative sentiment. That volatility weakens its usefulness as a store of value (one of the other roles of a currency) and makes it unsuitable for use as a day-to-day medium of exchange, since no one wants to accept a currency if it might be worth 10 percent less a couple of hours from now. In other words, a financial system run on Bitcoin would have all the bad features of the gold standard and few of the redeeming ones.

There are also practical hurdles to making Bitcoin a currency people can use easily. When demand for Bitcoin is high, transaction fees soar as miners raise the price of processing those transactions. At the peak of Bitcoin mania last fall, it could cost as much as $55 a transaction. That was fine when people thought the value of their Bitcoin stash was going to double overnight. But it doesn’t work if people want to use Bitcoin to buy pizza or a new TV set. Even more important, Bitcoin cannot scale to deal with the number of transactions a modern economy needs. The system is limited to processing just 420 transactions per minute. Finally, there’s the fact that a remarkably small number of people control a remarkably large percentage of all the bitcoins in the world. That gives them the leverage to manipulate prices, and makes it harder for Bitcoin to have the reach it would need to become a real currency.

Choose your own currency!

Of course, bitcoin is far from the only cryptocurrency. Depending on how you count, there are now hundreds, if not thousands, of them. And while they’re all built, like Bitcoin, on the blockchain, some have features that might seem to make them more attractive as a potential global currency. Litecoin, for instance, can process more transactions per minute. Monero and Zcash offer genuine anonymity (as opposed to Bitcoin, where every transaction is associated with a given key that can be tracked). And not all cryptocurrencies have a rigid cap on the total number of coins. So perhaps a different cryptocurrency could replace the dollar or euro or yuan—or, more plausibly, we could end up with a system of lots of different private currencies, rather than relying solely on a single medium of exchange.

There’s something appealing about the idea of everyone choosing the currency that suits them best, and of cryptocurrencies competing against each other to win the loyalty of consumers and businesses. But in fact the proliferation of cryptocurrencies that we’ve seen over the past few years makes it less likely, not more, that they will eventually replace fiat money.