An obvious method for controlling high-speed trading (M. Buchanan Nature 518, 161–163; 2015) is a global financial-transaction tax of the kind proposed by the European Union in 2011.

Such a tax, originally designed to raise revenue, could be set to lead to a typical trading time. There would be no need to regulate trading times explicitly: it would simply not be profitable to trade on the tiny, rapid fluctuations that now trigger transactions. This solution would be simpler — and, with its revenues, more beneficial — than technical approaches such as 'speed bumps' that delay transactions.

The non-equilibrium, complex systems that correspond to economies often operate at the threshold of instability. Adding taxes ('friction') should not be seen as creating inefficiency, but as a stabilizing influence that can avoid the costs of dramatic crashes.