Of Minds & Money

David Orrell

In 2017, when the ESRC announced that it was setting up a network of experts from different disciplines to “revolutionise” the field of economics, I thought it sounded like a very good idea. But in the spirit of that disruptive mandate, what if the revolution has already happened – and economics just needs to recognise it? I am talking about the quantum revolution which overturned physics at the start of the last century.

Of course, the thought that economics has anything to do with quantum physics will sound to many economists (or physicists) like a particularly severe case of physics envy. But my point is not that economics can be reduced to quantum physics (in my book Economyths I argue against such reductionist approaches). Nor is to assert that we can use quantum physics as a fuzzy metaphor to understand the economy. Instead, it is to say that the economy is a complex quantum system in its own right and should be treated as such. This recognition has the potential to disrupt all the pillars of mainstream economics, including its models of human behaviour, markets, and the macroeconomy.

To see why (and starting with the obvious), recall that quantum physics grew out of the empirical discovery by scientists that energy is transmitted, not continuously, but in discrete chunks they called quanta, from the Latin for “how much”. This violated the basic principle that nature makes no sudden leaps (Natura non facit saltum), as the epitaph of Alfred Marshall’s Principles of Economics read at the time (and until the final 1920 edition). But of course the same is true of money. When you pay for an item with a card, the money doesn’t drain out in a continuous flow, it goes as a discrete transmission.

Quantum objects can magically appear out of the void, and disappear back into it. In the economy, we have the creation of money by private banks issuing loans, and its destruction when loans are repaid. Again, these are discrete processes that take place “instantaneously and discontinuously” as a 2015 Bank of England working paper observed, so don’t fit easily with the continuous nature of conventional models – one reason they are typically excluded.

Another discovery of quantum theory is that matter has two complementary aspects, a “real” particle aspect and a “virtual” wave aspect. Money too combines the virtual properties of a number, with the real properties of an owned object – a bitcoin seems pretty virtual, unless you lose the computer it’s on – and it is this dualistic nature which gives money its confounding properties.

In quantum mechanics, a particle doesn’t have a well-defined location or momentum. In the economy, prices of something like a stock, or a house, are similarly indeterminate, and there is no unique intrinsic value (or eigenvalue in the quantum jargon). This is why some traders, along with researchers in the field of quantum finance, model the markets as a quantum system, with its own version of an uncertainty principle.

One of the more mysterious features of quantum reality is that subatomic particles can become entangled so that a measurement on one instantaneously affects the state of the other. Suppose I take a mortgage out with a bank. If I choose to default, then from that moment on the state of the loan has changed. Of course it will take time for the bank to learn what happened and settle the matter, but it takes time to measure particles too, during which other effects may come into play. It is a financial version of the social entanglement studied in quantum social science (see for example the 2015 book Quantum Mind and Social Science by political scientist Alexander Wendt).

Finally, another key property of quantum systems is interference: as in the double-slit experiment, where shining a light beam through two slits produces an interference pattern on the other side, even if only one photon passes at a time. Of course, money objects don’t interfere with each other, which is good because otherwise they might cancel out in your pocket. But the purpose of money is to put a number on the idea of value, and dissonance between these two things – objective number and subjective value – does produce interference patterns in our minds, of the sort modelled by researchers working in the area of quantum cognition.

In fact, instead of following classical logic when making decisions, it turns out that we are better described as following a version of quantum logic. As physicists Vyacheslav Yukalov and Didier Sornette note, “It is the appearance of interference terms that makes the structure of quantum expressions richer than the related classical ones and that allows one to explain those psychological phenomena that, otherwise, are inexplicable in classical decision making.”

As an example of a quantum economics phenomenon, suppose that you come under financial stress and are deciding whether to pay the latest installment on your mortgage, or default. Your mental state – and that of the loan – can then be treated, following the methods of quantum cognition, as being in an indeterminate superposition of two states. The emergent consequences in the entangled economy can be modelled at a societal level using complexity methods, including quantum agent-based models, though as always the system eludes reduction or exact computation.

Until now, money has played no more role in the quantum social sciences than in neoclassical economics, where it has traditionally been treated as an inert medium of exchange. But as seen above, quantum ideas are perfectly suited to things like the creation of money, entanglement through loans and other contracts, and credit default – all of which were at the heart of the 2007/8 crisis, but nowhere in the macroeconomic models.

As I argue in a discussion paper and in more detail in a forthcoming book, the quantum approach has implications not just for finance, or macroeconomic modelling, but for all the basic assumptions and conclusions of mainstream economics; and points the way to a new economics which is to its neoclassical version what quantum physics was to its classical version. Economics isn’t physics, but can learn from it; and if the intention is to rebuild macroeconomics, the natural place to start is with the quantum, dualistic nature of both mind and money.