Human behaviour is often irrational if viewed through the lens of “classical” physics and probability theory.
THE CONVERSATION
Human behaviour is an enigma that fascinates many scientists. And there has been much discussion over the role of probability in explaining how our minds work.
Probability is a mathematical framework designed to tell us how likely an event is to occur – and works well for many everyday situations. For example, it describes the outcome of a coin toss as ½ – or 50% – because throwing either heads or tails is equally probable.
Yet research has shown that human behaviour can’t be fully captured by these traditional or “classical” laws of probability. Could it instead be explained by the way probability works in the more mysterious world of quantum mechanics?
Mathematical probability is also a vital component of quantum mechanics, the branch of physics that describes how nature behaves at the scale of atoms or sub-atomic particles. However, as we’ll see, in the quantum world, probabilities follow very different rules.
Discoveries over the last two decades have shed light on a crucial role for “quantumness” in human cognition – how the human brain processes information to acquire knowledge or understanding. These findings also have potential implications for the development of artificial intelligence (AI).
Human ‘irrationality’
Nobel laureate Daniel Kahnemann and other cognitive scientists have carried out work on what they describe as the “irrationality” of human behaviour. When behavioural patterns do not strictly follow the rules of classical probability theory from a mathematical perspective, they are deemed “irrational”.
For example, a study found that a majority of students who have passed an end-of-term exam favour going on holiday afterwards. Likewise, a majority of those who have failed also want to go for a holiday.
If a student doesn’t know their result, classical probability would predict that they would opt for the holiday because it is the preferred option whether they have passed or failed. Yet in the experiment, a majority of students preferred not to go on holiday if they didn’t know how they’d done.
Intuitively, it’s not hard to understand that students might not want to go on holiday if they are going to be worrying about their exam results the whole time. But classical probability does not accurately capture the behaviour, so it is described as irrational. Many similar violations of classical probability rules have been observed in cognitive science.
Quantum brain?
In classical probability, when a sequence of questions is asked, then the answers do not depend on the order in which the questions are posed. By contrast, in quantum physics, the answers to a series of questions can depend crucially on the order in which they are asked.
One example is the measurement of the spin of an electron in two different directions. If you first measure the spin in the horizontal direction and then in the vertical direction, you will get one outcome.
The outcomes will generally be different when the order is reversed, because of a well known feature of quantum mechanics. Simply measuring a property of a quantum system can affect the thing that’s being measured (in this case an electron’s spin) and hence the outcome of any subsequent experiments.
Order dependence can also be seen in human behaviour. For example, in a study published 20 years ago about the effects that question order has on respondents’ answers, subjects were asked whether they thought the previous US president, Bill Clinton, was honest. They were then asked if his vice president, Al Gore, seemed honest.
