Irrational decisions might be the result of quantum theory, mathematicians say

New theory might be able to answer why humans make irrational and surprising decisions

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The Independent Online

If you’ve ever made a decision that didn’t make any rational sense, you might now have a great excuse for why. New research has taken a step forward in modelling human judgement and decision making using mathematics.

If you’ve ever seen the game show Golden Balls you will have watched judgements and decisions made with uncertainty and under conflict. Whether choosing to steal or to split, you have a risk of going home with nothing. Quantum theory may be able to explain the irrational decisions made on the show.

 “Quantum cognition” may explain our decisions when we don’t have a definite feeling about which option to choose or which decision to make, according to researchers at Indiana University and Ohio State University. Jerome Busemeyer and Zheng Wang propose that all options we could possibly make co-exist and have varying potential to be chosen. Once a choice is made, all other possible options no longer exist in our minds.

Wang suggests that in quantum theory the superposition principle allows uncertainty where classical models only allow changes from one definite to another. “Our beliefs don’t jump from state to state, instead we experience a feeling of ambiguity about all of the states simultaneously,” according to Wang. Quantum theory allows the mind to move between each option in a state of indecision until the moment the decision is made.

Quantum theory is generally thought of as describing the behaviour of sub-atomic particles rather than human behaviour. Our current probability models come from Newtonian physics, not necessarily suited to modelling the ambiguity of the human mind. In contrast, the possibility of uncertainty in a quantum system more adequately describes some aspects of cognitive behaviour.


Since various options regarding a decision to be made can easily be imagined to exist simultaneously, quantum theory more easily fits behavioural patterns of the mind than even the subatomic particles with which it is primarily concerned.

Other researchers are looking into the idea that our brain is an actual quantum computer, but Wang and Busemeyer are using the quantum model to explain how our decision making might work, without suggesting that the brain can actually perform real quantum information processing.