Today we’ve published a paper showing that Bell’s inequality is violated in fluid mechanics. What has this to do with computing or security? Well, when we posted a paper back in February pointing out that hydrodynamic models of quantum physics raise questions about the scalability of quantum computing, a number of people asked for a better explanation of how this squares with the Bell tests. John Bell proved an inequality in 1964 that applies to classical particles but that is broken by quantum mechanical ones. In today’s paper we show that Bell’s inequality does not hold in classical fluid dynamics, as angular momentum and energy are delocalised in the fluid.

This may have implications for engineering, science and philosophy. On the engineering front, nine-figure sums have been poured into developing quantum computers, but even advocates of quantum computing admit they don’t really work. As our February paper argued, a hydrodynamic interpretation of quantum mechanics may suggest reasons why.

On the scientific front, the Bell tests are commonly seen as excluding not just local hidden-variable models of quantum mechanics, but local realism too. Our paper shows that the two are distinct, and thus leaves more room for research on quantum foundations. It also shows that we should be more careful in our use of terms such as ‘local’ – which might be of interest to the philosophers; the Bell tests do not draw quite as clear a dividing line between the quantum and classical worlds as many have believed.