The spectacular increase and recent plunge in the price of Bitcoin and other cryptocurrencies have raised concerns that the bursting of the Bitcoin bubble will cause financial markets to crash. They probably won’t, but the Bitcoin bubble should finally destroy our faith in the efficiency of markets.

Since the 1970s, economic policy has been based on the idea that financial market prices reflect all the information relevant to the value of any asset. If this is true, market prices are the best estimates of the value of any investment and financial markets should be relied on to allocate capital investment.

This idea, referred to in the jargon of economics as the efficient market hypothesis (technically, the strong efficient market hypothesis), implicitly underlay the deregulation of financial markets that started in the 1970s. Although rarely stated now with as much confidence as it was during its heyday in the 1990s, the efficient market hypothesis remains a background assumption of much central-bank and economic policy.

The hypothesis survived the absurdities of the dot-com bubble in the late 1990s and early 2000s, as well as the meltdown in derivative markets that led to the global financial crisis in 2007 and 2008. Although the hypothesis should have been refuted by those disasters, it lived on, if only in zombie form.