‘Quantizing international relations’: The case for quantum approaches to international theory and security practice

Introduction

This special issue emerged from a shared belief that recent developments in quantum theory, science and technology have important, potentially profound implications for international theory and security. Quantum ideas first mooted independently over a decade ago by the editors have gained considerable traction in international relations, with a growing body of international scholars now coalesced around a singular intent: to ‘quantize international relations’, in the sense of applying the fundamental concepts of quantum theory to the discipline. ¹

‘Quantizing international relations’ is sure to trigger mixed responses, an effect multiplied by the complex and indeterminate nature of quantum theory itself. Since its inception at the turn of the last century, quantum has generated as many interpretations, schools and cosmologies as there are religious sects, and the equivalent of a Peace of Westphalia to mediate these differences within or between academic disciplines is unlikely to materialize any time soon. ² We have chosen a less-than-grand strategy, which is to follow the developmental path of quantum mechanics itself, seeking to reintroduce quantum ideas incrementally to the social sciences through a series of conferences, workshops and published papers in a manner similar to the Gedankenexperiments or thought experiments of the 1920s. We note that these early experiments were followed by laboratory and other proofs that made quantum mechanics the most successful theory in the history of physics, even if one narrowly measures success by technologies derived from quantum mechanics, like transistors, televisions, lasers, laptops, mobile phones and, somewhat more ambiguously, the atomic bomb. Indeed, our efforts are compelled by a shared apprehension, that a new generation of quantum innovation will have a disruptive effect on security practices, as well as by a shared belief, that we had better be fluent in the ways of quantum theory before rather than after such developments come to pass.

The numbers of publications and participants might still be relatively small, but the idea of a ‘quantum international relations’ is definitely in the ether. It remains to be seen whether quantum international relations is received as just another short-lived ‘turn’ in international relations’ long and winding disciplinary road. ³ As the fundamental theory of physical reality, quantum is not going away; the question is how will it travel outside of physics. We believe that quantum international relations will prove more transformative and lasting than a host of other theoretical imports because of a consilience of theoretical approaches and a combination of technological drivers that will only intensify in the future. This special issue focuses on three forces of change that we believe most profoundly call into question classical and endorse quantum approaches to international relations: quantum technology, quantum theory and quantum science.

Quantum technology

The most concrete stimulus to international security is quantum technology – in particular, an accelerating race to build the world’s first quantum systems for computing, communications, control and artificial intelligence. ⁴

There are currently at least four different pathways to the development of quantum computers, but fundamental to all is the quantum bit, or ‘qubit’, which, entangled in all possible states of superposition, provides an exponential advantage over classical computers based on digital bits in binary states of either 0 or 1. The almost unimaginable increase in the rate and order of calculation would provide profound advantages in strategically vital areas, including encryption and decryption, radar and sensors, navigation and targeting, simulation and data-mining, machine learning and pattern recognition. Google, IBM, Microsoft and other hi-tech giants have been in competition over the past several years to achieve ‘quantum supremacy’, the somewhat hyperbolic term coined by theoretical physicist John Preskill to describe the moment when a quantum computer proves capable of executing tasks impossible for the most powerful supercomputer, like large-number prime factoring (the basis of most classical encryption), multivariable optimization (like the ‘Traveling Salesman Problem’) or the simulation of complex many-body systems (like trapped ions and astronomical bodies). ⁵

For better or worse, the number of players in this game is limited by the staggering cost of developing quantum technologies, which commonly involves supercooling, shielded facilities, rare materials and intellectual capital. This leaves the geopolitical field primarily open to great powers like the USA, China, Europe and (lagging behind considerably) Russia. However, middle powers like Australia, Canada, Japan and Singapore, pursuing comparative advantages through collaborative research and development projects, are clearly in pursuit of a step change through quantum technology that might well register as an increase in geopolitical status. Alongside, and in some cases out ahead of the US tech firms, Alibaba, Baidu and Quantum CTek in China are pouring billions into quantum computation and communication, often in concert with state-financed initiatives based at leading universities. ⁶

If history is to be the judge, new asymmetries will result with the emergence of new ‘quantum haves’ and ‘quantum have-nots’; and, as with every new powerful technology, the effort to weaponize quantum has already begun. Deep in defence departments and under the darkness of classified programmes in spy agencies, memos are probably already circulating about the coming ‘RQMA’ or ‘Revolution in Quantum Military Affairs’. ⁷

It is by no means certain which corporation, state, university or synergy thereof will achieve the first major breakthrough and come out on top in the quantum race (not always, as we learned from the digital revolution, one and the same). Nor is it clear who will benefit from or be harmed by a ‘quantum revolution’ – or even that the correlation of social, strategic and technological forces will amount to a revolution. Two to twenty years have been mooted for the building of a functional quantum computer with – and this is a key qualification – adequate error-correction to overcome the natural tendency of qubits to decohere in noisy environments. Nonetheless, given the enormous investments committed and progress achieved so far, we consider it better to pose cautionary questions now, rather than after quantum technologies go online – and, if not by concerned scholars, who else? The networked vulnerabilities, potential accidents and ethical challenges of new quantum technologies are unlikely to be high on the agenda of profit-driven corporations, polarized political elites and short-term governments.

The concepts of quantum theory

As part of making the case for the relevance of quantum mechanics to international relations, we wish to highlight the multifold approaches shared by most of the contributors to this special issue: a quantum worldview (from multiple perspectives), a conceptual heuristic (to ‘quantize’ everything) and a pragmatic attitude (what does quantum bring to international relations?). ⁸ Although we do not pretend this adds up to a grand or unified field theory of international relations, we do believe this assemblage of quantum approaches has a comparative advantage over others that are largely derived, often unselfconsciously, from Newtonian or classical physics. Because of the inherent complexity as well as the oft-mentioned ‘weirdness’ of all things quantum, we do feel obligated to explicate some of the central concepts that inform quantum international relations, many of which may be unfamiliar or appear paradoxical for those coming from a classical worldview (i.e. most of international relations).

First, however, there is the matter of how or even whether quantum concepts might ‘travel’ outside physics. This was not always a concern: During quantum’s originary moments, from Max Plank’s coinage of ‘quantum’ in 1900 to the breakthrough gathering of the leading theorists at the Solvay Conference in 1927, physics was only just divorcing from its disciplinary cohabitation in universities as a subfield of ‘natural philosophy’ (Victor Frankenstein was an early if aberrant example of an experimental natural philosopher who got carried away by the new science of electricity). Physicists literally shared university hallways with philosophers, and key thinkers regularly exchanged views about new discoveries in quantum physics, continental philosophy and psychology that defied classical explanations or hermeneutics. Disruptive ideas crossed disciplines with an alacrity now lost – from Albert Einstein to Henri Bergson, Martin Heidegger to Werner Heisenberg, Søren Kierkegaard to Niels Bohr, Alfred North Whitehead to David Bohm, Carl Jung to Wolfgang Pauli – that served to inspire, inform and reform a shared worldview that burned brightly if briefly in the interwar period. ⁹ Physicists also cited the influence of holistic Eastern philosophies on the early formulations of quantum mechanics. ¹⁰ During this period, even the nascent field of political science at the authoritative level of the president of the American Political Science Association acknowledged the significance of the new discoveries in quantum theory. ¹¹ In his provocative essay ‘Bringing the world back in: Revolutions and relations before and after the quantum event’, Jairus Grove presents a revisionist history of this febrile period, upending the traditional version of philosophy as secondary or epiphenomenal to physics and, in the process, subverting the critique that quantum international relations represents the latest instance of ‘science envy’ in the social sciences.

Seeking to explain phenomena that were considered nonsensical and counter-intuitive in classical terms, the early quantum physicists realized that their findings, proven through mathematical formalism, would not be easily translatable into everyday language. Bohr, Heisenberg and most of their peers considered this good reason to reach out to other disciplines of learning rather than to quarantine quantum to physics. Bohr’s papers on the philosophical implications of quantum theory fill, literally, volumes; a short quote from Heisenberg (1971: 213) captures the essence of their argument:

The positivists have a simple solution: the world must be divided into that which we can say clearly and the rest, which we had better pass over in silence. But can anyone conceive of a more pointless philosophy, seeing that what we can say clearly amounts to next to nothing? If we omitted all that is unclear we would probably be left with completely uninteresting and trivial tautologies.

What follows is our attempt to recapture in international relations something like the transnational, transdisciplinary, even transcendent moment of quantum mechanics at its inception. We offer in this special issue ‘traveling documents’ for key quantum concepts, in the hope that these concepts will not only visit but stay awhile in international relations. We are fully aware from our previous transgressions of traditional international relations that there will be opposition to this effort, from scientists on the grounds that quantum concepts cannot possibly scale up to the macrophysical level, as well as from social scientists who belittle quantum concepts as mere metaphors. We and other quantum international relations authors deal in depth with the scaling problem; as for the metaphorical issue, our short answer is: too late to worry and too soon to say. Quantum effects once thought confined to the subatomic have already scaled up to the biological and cognitive levels; and, in the absence of a better theory, humans could also join plants and birds as consciously exhibiting quantum behaviour. Even at the metaphorical level, as when former US secretary of state George Shultz speaks of a new ‘quantum diplomacy’, or the current president of Armenia Armen Sarkissian (who happens to be a theoretical physicist) of a globalizing ‘quantum politics’, these and similar statements attest to the superior heuristics of quantum theory for understanding quantum-like phenomena. Or, put another way: when observational practices and visual imagery transmitted in near simultaneity through densely networked systems of multiple media produce powerful superpositional effects as well as entangled affects, the heuristic advantage of quantum over classical approaches becomes increasingly difficult to refute. ¹² And to preempt the predictable retort: come the day of a quantum convergence between human and artificial intelligence, shall we deem it ‘quantum-like’ or ‘human-like’?

These are admittedly speculative propositions, but with potentially revolutionary outcomes. If quantum technology goes online, quantum science continues to scale up and quantum consciousness proves measurable at the macrophysical level, a quantum approach could well become the most realist of social scientific theories. It will then fall upon those in the social sciences upholding worldviews based on the motions of planets, pulleys and billiard balls to defend their concepts – or to recognize them as metaphors whose metaphorical nature has been forgotten. At this emergent stage, we believe it best to practice an open pluralism on the critical question of when, how and at what scale quantum behaviour is actual, potential or ‘merely’ metaphorical. Practically all of the investigations undertaken in the special issue directly address this issue; and, we believe, they do a good job of demonstrating how networked, complex or emergent aspects of human systems can be quantum in their own right, giving quantum theory a heuristic advantage over classical approaches. The authors challenge us to reinterpret the overfamiliar in international relations, as does David Orrell in his essay ‘The value of value: A quantum approach to economics, security and international relations’, which offers a counter-history of money as a non-classical object in superposition that only takes on distinct value through authoritative and institutional acts of measurement or observation. Similarly, in their essay ‘To “see” is to break an entanglement: Quantum measurement, trauma and security’, K. M. Fierke and Nicola Mackay identify hidden quantum effects of trauma on security practices that only become observable when toxic political entanglements collapse as speech acts. We would not be the first to say such quantum investigations can sound weird – right up until the moment that they make better sense than classical explanations. ¹³

We cannot in this introduction explicate every weird element or adjudicate every controversial aspect of quantum. We do believe the special issue as a whole makes a credible case for reintroducing quantum concepts into international relations (as well as into other social science disciplines). ¹⁴ Our task, at the risk of mimicking the bias of the Nobel Prize for the genius of a few individuals, is to elucidate what we believe to be the quantum concepts that are most adaptive to international relations. We try to stick as closely as possible to the ‘show, don’t tell’ style of documentary film, as we conceive of this introduction as a short teaser for the full features that follow.

Let us start with a long take of a brief version of quantum mechanics, which emerged from a series of conceptual breakthroughs by Niels Bohr, Max Born, Werner Heisenberg, Wolfgang Pauli, Louis de Broglie, Paul Dirac, Erwin Schrödinger and a handful of other physicists who would intuit, posit, model, debate, disagree and eventually agree and prove both mathematically and experimentally that quanta in the form of atoms, photons and electrons exist as both waves and particles until the point of collapse or observation; that their position and velocity could not be simultaneously measured; that they could correlate non-locally across vast distances; that they could pass through seemingly impermeable barriers; and, yes, that Schrödinger’s cat could potentially, simultaneously and absurdly be both alive and dead at the same time – until we opened the box.

These principles of complementarity, uncertainty, entanglement, tunnelling, teleportation, superposition and wave function form the fundaments of quantum mechanics. The new quantum formulation of atomic behaviour, subsequently confirmed by experiments, repudiated much of Newtonian physics at the microphysical level. It challenged classical conceptions of space and time at the macrophysicial level. And it cast into doubt philosophical assumptions about causality, determinism, prediction and an observer-independent reality at the cosmological level.

Rather than attempt a comprehensive exegesis of all of the concepts that revolutionized physics, we have picked out those that have been particularly significant in the quantum revolution and figure centrally in quantum international relations: entanglement, superposition, uncertainty, the measurement problem and the collapse of the wave function.

At the macro or classical level, the elementary parts of any science are assumed to be ‘fully separable’. By that, scientists mean that nothing about those parts logically or ontologically presupposes any other parts; every part is what it is by virtue of its own physical makeup, and only that. Of course, parts can interact causally with each other to produce emergent effects, like the motion of a car, but the parts of an engine do not depend constitutionally on each other to be what they are, and as such can be removed from the engine without changing their identity; the whole can always be broken down into self-subsisting parts.

On the surface, this seems to be true of human beings – the elementary parts of social science – as well. Even though, living in society, we are deeply dependent upon each other in a causal sense for survival, in a constitutive sense we seem to be fully separable ‘individuals’, clearly demarcated by our skins. After all, even if every other human being suddenly vanished, your body would still be there alive and well, completely unchanged. As for your mind, if you are a materialist – which is the ontology of classical physics and the orthodoxy (if increasingly embattled) in philosophy – then it is nothing more than your brain, which is also encased in your skin and thus seemingly separable from other minds. An assumption of separability is therefore the ontological foundation of the doctrine of atomism in philosophy, and of methodological individualism in social science (and from there on to liberal political theory and all the rest).

One of the greatest and still most puzzling discoveries of quantum physics is that, at the subatomic level at least, this assumption does not hold; that the elementary parts of reality are not fully separable but entangled (whereby two particles remain correlated over large distances). Although philosophers might disagree in their metaphysical interpretations, everyone agrees on the basic physical facts, which are that the behaviour and properties of entangled particles exhibit correlations (‘non-local causation’) that have no causal explanation and are inexplicable in classical terms. Indeed, it is now problematic to speak of elementary ‘parts’ at all, since the tiny but hard and separable atoms imagined to lie at the bottom of the classical universe dissolve subatomically into ghostly ‘wave functions’, which, following the principle of uncertainty, represent merely the probability of finding classical particles at a given location should we look there (and, if we don’t look, there is no certainty for saying any particles are there at all). In short, entanglement makes quantum theory fundamentally holistic: the properties, even existence, of the parts depend in top-down fashion on the whole, rather than the other way around, as in the classical worldview.

Precisely because it contradicted both classical physics and our everyday experience of material objects, the holism of entanglement was something of a scandal among early quantum physicists, with Einstein leading the first-wave charge of scientific realism against the second-wave formulations of the so-called Copenhagen or instrumentalist school of quantum mechanics. In contrast, practically all physicists today have not only come to terms with entanglement and non-local causation but are trying to exploit them to build quantum computers based on spin-up/spin-down correlations of the qubit. Yet most would still argue that, although universal in some broad sense, quantum has no significant effects at the macrophysical level and as such does not scale up to international relations.

It is therefore ironic that, despite the strong intuitions that sustain methodological individualism, in the social sciences holism has long been supported by strong intuitions of its own, and accordingly was never eliminated as a social ontology in the way it was as a physical ontology by the classical worldview. ¹⁵ The intuitions that sustain social holism revolve heavily around language and the seemingly irreducibly relational quality of meaning and practices. Consider two famous examples. One is Hegel’s analysis of the ‘master/slave relation’ – a person literally cannot be a master unless there are slaves around to ‘make’ them one, again not in a causal sense (though that matters for reproducing slavery over time), but constitutively. Accordingly, it is not just the physical states of brains encased safely inside skins that make certain people masters, but whether other people, especially slaves (sic), mutually recognize them as such. The other is Jaegwon Kim’s analysis of what happened to Xantippe when her husband, Socrates, was forced to commit suicide – she became a widow, but not, in Kim’s analytic philosophical treatment, because of a causal process, but because of a non-causal one. ¹⁶ While hardly ever discussed this way, these examples sound a lot like descriptions of entities that are distinct (masters and slaves; husbands and wives) but not fully separable (can’t have one without the other), and between which there can be non-local causation (changing one instantly changes the other). In short, in contrast to the material world, where it indeed seems ‘spooky’ and counter-intuitive, in the social world, by virtue of language, entanglement seems to be given and entirely commonplace.

Although individualism nevertheless remains the default ontology in most social science, holism is dominant in mainstream philosophy of language (and those branches of social science indebted to it). However, in the past, social or linguistic holists have never felt a need for quantum foundations, believing that it was enough to show that linguistic meaning is irreducibly relational. But, like everything else, language is physical too, and so it is either classical or quantum – but if it is classical and as such trapped in brains, then how could it be holistic? ¹⁷ There is, in our view, a tension or even contradiction here, the resolution of which could depend on the mind–body problem. If the ontology of consciousness, as we suggest below, also turns out to be quantum rather than classical, then it might not be trapped within brains, but could be the manifestation of our entanglement with the world and with each other. That would provide a completely different basis for social theorizing, both positive and normative, than the orthodoxies today, one in which there is a real (if limited) sense in which quite literally – which is to say physically – ‘I am You.’ ¹⁸

In the classical worldview, all objects and their properties are always in well-defined and non-contradictory states. Objects are, of course, also always in process, eroding, decaying, growing, and so on, and thus constantly changing (however slowly). However, classical logic tells us that, at any given instant, the musical chairs are stopped and everything is in either state A or state not-A – there are no ‘in-between’ states nor overarching ones that could encompass both possibilities. Note that this says nothing about our ability fully to know objects and their properties, especially as complexities rapidly mount the deeper inside them we probe; the point here is ontological, about what objects can be, not epistemological. And, given the materialism of the classical worldview, it should hold equally for mental objects and their properties as for material ones, since ultimately the mind is nothing but the brain. While a subjective experience like ‘ambivalence’ might feel as though we are in state A and state not-A simultaneously, in fact each of the zillions of brain states that cause and/or constitute that feeling is in one state or the other. After all, as material objects, how could they not be?

Quantum theory provides an answer with the concepts of superposition and wave function. One of the most fundamental findings of quantum physics is that, at the subatomic level, the familiar, well-defined objects of classical physics dissolve into wave functions, which, as we have seen, describe only the probability of finding classical objects (particles) when we look for them, not the objects themselves. Moreover, and crucially, unlike the back of a house, which we have no reason to doubt is there when we are not looking at it, we have no warrant for such a claim in the quantum world. A wave function describes only potentialities, not actualities – a ‘super’-position of different actual ‘positions’. While, from a classical perspective, that might make it less than perfectly real, the wave function is clearly real in some sense, and it has the virtue of being able to encompass in a unitary description not just possibilities that never end up happening, but even mutually exclusive ones, both A and not-A. ¹⁹

If reality ultimately consists of superpositions, then a key question is how it gets from many possible worlds to the one actual world we observe in the physics lab – from ghostly wave functions to well-defined, material particles hitting a screen. Known most commonly (if not precisely) as the ‘collapse’ of the wave function, how and why this process occurs is one of the deepest mysteries in the debate over the interpretation of quantum theory. ²⁰ Of what we do know and generally agree on, however, three related points stand out in the present context.

First, wave functions collapse, following the uncertainty principle, whenever we try to measure them. That might suggest the world would not exist but for us humans, but most interpreters resist such hubris and draw the opposite conclusion, that measurement is a highly general process, which is somehow ubiquitous in nature. Second, it is not just that wave functions collapse when they are measured, but where – where particles actualize on the screen in the famous double-slit experiment – depends on the details of the measurement. This has led some interpreters to argue that, in quantum physics, measurement is ‘creative’ or in some related way ‘causes’ collapse in a certain direction. However, that is contested by others, so the most one can safely say here is that, in an experimental setting, there is an entanglement between the observer and the observed, and the final result is ‘elicited’ by their unfolding relationship. Finally, wave-function collapse is non-deterministic, having no apparent external (or internal) cause; given the probabilities, where a particle will actually land is anyone’s guess. Although consonant with our intuitions about free will, this quantum ‘leap’ is problematic for physicists because it means they are forced to bolt together two unrelated mathematical formalisms to describe the entire process. One, the Schrödinger equation, models the (deterministic) evolution of a wave function in the absence of measurement, and then the other, Von Neumann’s ‘projection postulate’, models (after the fact) what happened in the collapse from measurement. This is surely a clunky, unsatisfactory state of affairs for physicists who crave an elegant ‘Theory of Everything’, but this is where we are – for now.

Quantum science

While it is natural that a race for quantum supremacy would transport and elevate quantum ideas into fields beyond physics, a sceptic might plausibly argue that we do not need anything as radical as quantum international relations to analyse new quantum technologies. After all, a technology race is a technology race, and security scholars have a whole host of classical concepts for comprehending complex emergent phenomena, from game to complexity to chaos theories. Frank Smith’s timely article ‘Quantum technology hype and national security’ injects a healthy note of scepticism along these lines, reminding us of how the quantum race, like all powerful new technologies caught in the securitization web, is subject to rational expectations and performative perspectives that might take on a hyperreal quality but still can be explained in classical terms. Conversely, in their article ‘Quantum and systems theory in world society: From analogy to complementarity’, Mathias Albert and Felix Barton suggest that systems might have non-classical attributes that do not necessarily require quantum approaches, although they identify a range of striking similarities between systems and quantum theories.

We believe, however, that new developments in quantum science call even advanced forms of classical and non-classical (but not quantum) thinking into question. Quantum science is conventionally understood as the application of quantum mechanics to scientific fields adjacent to and outside of physics, including quantum biology, quantum chemistry, quantum information and quantum cognition.

The first and most immediately significant implication for quantum international relations is the appearance of quantized models of cognition and decision theory, which, after rigorous empirical testing, seem to account for all of the irrational, ‘Kahneman–Tversky’ anomalies that psychologists have consistently observed using classical rationality as a normative baseline. ²¹ In our view, the empirical success of quantum decision theory is extraordinary (quantum game theory is probably next) and has helped create a thin but rapidly growing layer of highly mathematical quantum theorizing across the social sciences. ²² The second development is the unexpected birth of a new discipline, quantum biology, based on the discovery that an ever-growing number of organisms use quantum processes in non-trivial ways for survival. ²³ If birds (for navigation) and plants (for photosynthesis) can exploit quantum processes to their benefit, then it seems unlikely that evolutionary pressures would select against such a remarkable ability in the human case. And, third, there has been at least slow progress on the most controversial question of all: whether the brain is a quantum computer, in which case human beings would literally be ‘walking wave functions’. ²⁴ Their hands still full of sceptics in their own fields, most quantum biologists and decision theorists today want little to do with such a speculative idea; but if their work continues to bear fruit, it makes quantum brain theory (see below) an ever more natural inference.

So far, this is about what is going on at a very micro level; the question facing international relations scholars and social scientists more generally is whether superpositions and wave-function collapse can be found at the human or macro scale, not just by analogy, but really. Most physicists would still say no because of the decoherence problem, where microscopic quantum effects ‘wash out’ in large, wet and warm environments like the brain (Waldner, 2017). However, that opposition is clearly challenged by the emergence of quantum biology and especially quantum decision theory.

Classical decision (‘rational choice’) theory assumes that people have a portfolio of preferences and beliefs in their minds, which ideally obey the rules of classical logic and thereby make their holders rational. Moreover, although rarely explicit, it seems clear that a tacit assumption of this model is that the brains behind the human mind are classical. If they were quantum, why would the standard of rationality be classical, given the vastly greater, almost ‘super-rational’ computational powers of a quantum brain? All of which is to say, according to the rationalist orthodoxy, the contents of our mind/brains – our ‘types’, in the jargon – will always be in well-defined states. If they are rational, then actors can be assumed to know their own types, but often not those of others; as classical states, others can be assumed to have types, but they are hidden away in other brains. Thus, the primary strategic problem facing rational actors in such a world is trying to determine others’ types so that interaction will be optimal (think security dilemma theory). ²⁵

A very different picture emerges from quantum decision theory, best explained by Ariane Lambert-Mogiliansky and co-authors in an essay suggestively entitled ‘Type Indeterminacy: A Model of the KT (Kahneman–Tversky)-Man’. ²⁶ Playing off ‘Harsanyi Man’, the ideal Bayesian rational actor operating under uncertainty, Lambert-Mogiliansky et al. represent a person’s ‘state’ as a superposition of all their potential types relevant to a given situation, each of which is modelled as a distinct vector in an n-dimensional decision space. The superposition of these vectors does not collapse into an actual type until a measurement (interaction) occurs, whether on one’s own or on someone else’s initiative. At that point, depending on the context, one vector will become what is called ‘preferred’ and a single type will emerge in the collapse of the wave function (manifested as ‘behaviour’). Note that this is the exact opposite of the standard, classical view. Rather than being an expression of underlying, well-defined preferences and beliefs, the latter become well-defined only through the act of measurement itself. Thus, whereas Harsanyi Man’s problem is merely uncertainty about others’ types, KT ‘Man’ (sic) does not even know her own type until she makes a choice. Perhaps the feeling of ambivalence is more genuine than classical metaphysics would have us believe.

Quantum international relations builds on the resonances between Lambert-Mogiliansky’s highly mathematical quantum model of human beings as collapsing superpositions and Judith Butler’s performative model of agency (which figures centrally in Karen Barad’s approach to quantum social theory as well). ²⁷ Although, as a feminist theorist, Butler’s foil is identity theory more than rational choice, her critique of the former is similar to what we have just seen – namely, gendered performances are not enacted by an intrinsically gendered subject with pre-existing desires and beliefs; rather, they make someone a gendered subject with those desires and beliefs in the first place. We would not want to overstate the affinities between these theorists, but it is striking to us that two approaches that – at least on the surface – could hardly be more different epistemologically or methodologically would arrive at such similar pictures of the human being. Call it consilience if you want, but, at the very least, in quantum social science and quantum international relations there seems to be an opportunity for a fresh and potentially very fruitful inter-paradigmatic dialogue not just about social ontology but about epistemology as well.

We acknowledge (once more) that all of these new bodies of research challenge a fundamental but completely implicit assumption of the social sciences: that quantum theory is only relevant at the subatomic scale, above which quantum effects decohere and classical physics takes over. In different ways, these new sciences suggest that, far from washing out above the molecular level, in living organisms quantum effects might actually get amplified, right on up to the human scale.

Proving all of this is another matter. Science, ultimately, is a measurement problem. At the macrocosmic level, Albert Einstein was considered by many of his peers to be an upstart patent clerk with a dubious theory of relativity – until Sir Arthur Eddington developed an irrefutable method to measure gravitational lensing during the 1919 solar eclipse. It is not without irony that, at the microcosmic level, many scientific realists shared Einstein’s dismissal of the quantum principle of entanglement as ‘spooky action at a distance’ – until a loophole-free Bell test conclusively measured quantum entanglement in 2015. In quantum, the measurement problem is further complicated, if not upended, by the uncertainty principle, which elevates an epistemological problem into an ontological paradox: until observed (or measured) we cannot know whether Schrödinger’s famous cat is dead, alive or getting a quadrillion hits on YouTube across the multiverse.

The history of quantum science suggests that so far there are good reasons to be sceptical about the scientific value of quantum approaches to international relations. But there are other reasons not to be dismissive. There might not yet be sufficient scientific evidence to make the leap from a micro- to a macro-quantum theory, but we strongly believe there are now compelling practico-philosophical reasons to engage quantum international relations in the kinds of thought experiments that first set quantum mechanics in motion. The absence of laboratory proofs or sufficient measurement tools should not impede an inquiry into the most perplexing questions of the human condition for which quantum science might provide the best possible answers.

We have in mind – literally – the vexing problem that is so often glossed over in the social sciences and ignored by almost everyone in international relations but for a few feminist theorists: the hard problem of consciousness undertaken by Wendt (2015) and now advanced by Leonardo Orlando in his essay ‘The fabric of agency: Navigating human potentialities through introspection’, which ventures deep into neuroscience and the philosophy of mind to explore how a quantum approach to social ontology and consciousness revalorizes the holistic aspects of human action in international politics. More precisely, these investigations seek to explain conscious actions in a way consistent with what quantum physics tells us about the nature of reality. The materialist orthodoxy – which social science has followed since Hobbes – has always assumed that the relevant physics is classical, because the brain is a macroscopic material object. Unfortunately, after centuries of hard work, this starting point has proven incapable of generating a theory of consciousness that even most materialists could agree on, and now some have drawn from their explanatory failure the only ‘logical’ conclusion: that consciousness is an illusion. In contrast to this unproven and wildly counter-intuitive claim, quantum theory is only mildly counter-intuitive, and at least has room for consciousness to play a crucial role in the collapse of the wave function, which has generated growing interest in ‘quantum consciousness theory’ as a potential solution to the mind–body problem. ²⁸

This might seem far from the world of international relations, though our own disciplinary debates between positivists and interpretivists are but localized manifestations of the mind–body question. ²⁹ There is also a growing recognition – in some quarters, an apprehension – as quantum artificial intelligence labs are set up by tech giants, as well as by aspiring and existing superpowers, that quantum consciousness will soon cease to be a merely human question. When consciousness becomes a chimera of the human and the artificial, not only new scientific but new philosophical and spiritual cosmologies of a quantum bent might well be needed if we are to be ‘at home in the universe’. ³⁰

Some concluding speculations

After a transdisciplinary inception followed by a long confinement in physics, quantum theory is now breaking out and starting to engage with other natural and social sciences. As a fundamental worldview, theory of reality and enabler of new technologies, quantum touches everything, in theory and increasingly in practice. It remains to be seen how far it will go in international relations; perhaps nowhere fast if blindly opposed or blithely ignored. However, if the effect of quantizing international relations is anything like the effect of quantum theory in physics and now in biology, chemistry, engineering, computer science and philosophy, then this will not be just another ‘turn’ but the start of a permanent revolution that warrants our close attention. There is possibly as much peril as promise in such a revolution, and, as said of war and generals, quantum is just too important to be left to scientists alone.

The other characteristic of a theory that touches everything is that there are no obvious limits to how it might relate to international relations. We already see in quantum international relations and quantum social science in general remarkable collaborative efforts to respond to diverse questions that range from physical to metaphysical, theoretical to empirical, and explanatory to normative, many of which are represented in this special issue. Although this might lead to a degree of conceptual eclecticism or even philosophical incommensurability, in our view this inchoateness is not surprising nor necessarily detrimental to the early stages of a critical inquiry.

This is also why we offer quantum approaches (in the plural) rather than propose a quantum theory (in the singular) of international relations. Our title intentionally, if ironically, invokes Hedley Bull’s (1966) noted essay in which he forcefully challenged the scientific-behaviouralist approaches to international relations then emanating from the United States, to make the case for a ‘classical approach’ of philosophical, historical and juridical inquiry. We obviously do not seek to retrieve a classical Newtonian science, in which states interact like billiard balls, humans reductively behave as rational-choice actors and power is reduced to unitary interests. Nor is this a call for another ‘great debate’ or a polemical attack on other theoretical approaches. We offer instead in this special issue a series of deep dives into a quantum world that has gone relatively unexplored in the social sciences, in the hope that our holistic efforts will advance theoretical inquiry in international relations and facilitate peaceful navigations of a quantum future.