Alexander Wendt proposes a radical idea in his Quantum Mind and Social Science: Unifying Physical and Social Ontology: that we should reconsider fundamentals of the social sciences to reflect emerging research on “quantum consciousness” and cognition. He describes his aim in these terms:

In this book I explore the possibility that this [classical physics] foundational assumption of social science is a mistake, by re-reading social science “through the quantum.” More specifically, I argue that human beings and therefore social life exhibit quantum coherence — in effect, that we are walking wave functions. (3)

A keystone to Wendt’s argument is what he regards as the credibility and predictive niceness of “quantum decision theory”. The foundational text in this field is Busemeyer and Bruza, Quantum Models of Cognition and Decision. Busemeyer and Bruza argue here, and elsewhere, that the mathematics and concepts of quantum mechanics in physics have seemingly relevant application to the field of cognition and judgment as well. For example, the idea of “wave function collapse” appears to have analogy with the resolution of uncertainty onto decision by a human cognitive agent. Busemeyer and Bruza offer six fundamental analogies between quantum mechanics and cognition:

- judgments are based on indefinite states
- judgments create rather than record
- judgments disturb each other, introducing uncertainty
- judgments do not always obey classic logic
- judgments do not obey the principles of unicity
- cognitive phenomena may not be decomposable

For these and related reasons Busemeyer and Bruza argue that the mathematics, logic, and concepts of quantum mechanics may allow us to reach better traction with respect to the processes of belief acquisition and judgment that constitute human cognition. So far so good — there may be a mathematical homology between quantum states in the micro-physical world and states of knowledge acquisition at the level of acquisition.

However, Busemeyer and Bruza are entirely explicit in saying that they regard this solely as a formal analogy — not a hypothesis about the real underlying structure of human thought. They explicitly deny that they find evidence to support the idea that consciousness is a quantum phenomenon at the sub-molecular level. They are “agnostic toward the so-called ‘quantum mind’ hypothesis” (kl 156). Their use of the mathematics of quantum mechanics is formal rather than substantive — more akin to using the mathematics of fluid dynamics to represent flow through a social network than arriving at a theory of the real constitution of a domain as a basis for explaining its characteristics.

This book is not about quantum physics per se, but instead it explores the application of the probabilistic dynamic system created by quantum theory to a new domain – the field of cognition and decision making. (kl 245)

So the application is heuristic rather than realistic:

We motivate the use of quantum models as innovative abstractions of existing problems. That is all. These abstractions have the character of idealizations in the sense there is no claim as to the validity of the idealization “on the ground.” (kl 171)

Instead [our theory] turns to quantum theory as a fresh conceptual framework for explaining empirical puzzles, as well as a rich new source of alternative formal tools. To convey the idea that researchers in this area are not doing quantum mechanics, various modifiers have been proposed to describe this work, such as quantum-like models of cognition, cognitive models based on quantum structure, or generalized quantum models. (kl 156)

Given the key role this body of research plays in Wendt’s arguments about the social sciences, it is worth considering how it has been received in the relevant academic communities. H. Van Dyke Parunak reviews the work in *Computing Reviews* (link). Parunak emphasizes the point made here, that the book is explicit in declaring that it does not provide support for the idea of “quantum cognition” as a manifestation of underlying quantum physical processes. He observes that “a more accurate title, but much less exciting, would be *Hilbert space models of cognition and decision,*” emphasizing the purely formal and mathematical nature of their arguments. Quantum mechanics provides a computational model for cognition based on quantum probability theory in their work, not an ontology of the cognitive process. Here is a short piece by Trueblood, Pothos, and Busemeyer in *Frontiers in Psychology* that spells out the mathematical assumptions that are invoked here (link).

What is perhaps less known is that the ingenious physicists who developed quantum mechanics also invented a new theory of probability, since classical probability (CP) theory was inconsistent with their bold new theory of the physical world. QP theory refers to the rules for assigning probabilities to events from quantum mechanics, without the physics. QP theory is potentially applicable to any area where there is a need to compute probabilities. (“Quantum probability theory as a common framework for reasoning and similarity”)

Here is a review article that proposes a series of tests of “quantum-like” models of judgment (link). Here is how the authors describe the field of quantum-like models of cognition:

Recently, a research field that rely on so-called “quantum” or “quantum-like” models has developed to account for such behaviors. The qualifier “quantum” is used to indicate that the models exploit the mathematics of a contemporary physical theory, quantum mechanics. Note that only some mathematical tools of quantum mechanics are employed, and that the claim is not that these models are justified by an application of quantum physics to the brain. For that reason, we shall prefer to call them “quantum-like” models. Such models put into question two classical characteristics recalled above: they abandon Bayesian probabilities for others which are similar to probabilities in quantum mechanics, and they allow for preferences or attitudes to be undetermined. Quantum-like models have received much interest from psychologists, physicists, economists, cognitive scientists and philosophers. For example, new theoretical frameworks have been proposed in decision theory and bounded rationality (Danilov and Lambert-Mogiliansky 2008 and 2010, Yukalov and Sornette 2011). (2)

This description too emphasizes the purely formal nature of this theory; it is an attempt to apply some of the mathematical models and constructs of quantum theory to the empirical problems of cognition and judgment. They go beyond this observation, however, by attempting to assess the ability of the mathematics to fit the data. Their overall judgment is dubious about the applicability of these mathematical tools to the available data on specific aspects of belief formation (22). “After performing the test against available data, the result is quite clear: non-degenerate models are not an option, being not empirically adequate or not needed.”

This is all relevant to a discussion of Wendt’s work, because Wendt’s premise is solidly realist: he wants to seriously consider the possibility or likelihood of “quantum consciousness”. This is the idea that thought and mental activity are the manifestations of subatomic quantum effects.

Quantum brain theory takes known effects at the sub-atomic level and scales them upward to the macroscopic level of the brain. (31)

Hence the central question(s) of this book: (a) how might a quantum theoretic approach explain consciousness and by extension intentional phenomena, and thereby unify physical and social ontology, and (b) what are some implications of the result for contemporary debates in social theory? (29)

For the price of the two claims of quantum consciousness theory –that the brain is a quantum computer and that consciousness inheres in matter at the fundamental level –we get solutions to a host of intractable problems that have dogged the social sciences from the beginning. These claims are admittedly speculative, but neither is precluded by what we currently know about the brain or quantum physics, and given the classical materialist failure to make progress on the mind–body problem, at this point they look no more speculative than the orthodoxy –and the potential pay-off is huge. (35)

These are tantalizing ideas. It is clear that they are intended as substantive, not merely formal or mathematical. We are asked to take seriously, as an empirical hypothesis, the idea that the brain is a quantum machine and its gross behavior (memory, belief, judgment) is substantively influenced by that quantum substrate. But it is fundamentally unclear whether the findings of Busemeyer and Bruza or other practitioners of quantum probability in the field of cognition provide any support at all for the substantive quantum-consciousness hypothesis.