Relative Realities: Reframing Quantum Measurement

Author: Denis Avetisyan

A new perspective on the Wigner’s Friend paradox proposes that quantum states are always defined relative to an observer’s frame of reference, offering a potential path toward resolving the measurement problem.

This review connects quantum indefiniteness to symmetries in physical systems and argues that quantum reference frames, rather than absolute states, are fundamental to understanding quantum reality.

The persistent challenges surrounding the measurement problem in quantum mechanics stem from ambiguities in defining objectivity and the role of the observer. This paper, titled ‘Wigner’s Frame’, proposes a resolution to the Wigner’s Friend paradox by grounding quantum indefiniteness in the symmetries of physical systems and framing quantum states as relative to specific reference frames. By distinguishing between observer-independent facts and relational properties, this approach avoids an infinite regress of relativization and suggests a potential link between quantum mechanics and the emergence of objective scales. Could a deeper understanding of reference frame transformations ultimately illuminate the foundations of quantum measurement itself?

The Quantum World: Uncertainty as a Fundamental Truth

Quantum mechanics departs dramatically from classical physics by positing that certain properties of a quantum system – such as position or momentum – do not possess definite values until they are measured. This isn’t merely a limitation of current technology, but an inherent characteristic of the quantum realm; a quantum state exists as a superposition of multiple possibilities, described mathematically by a wave function. Before measurement, the particle doesn’t have a specific value for these properties, but rather exists in a probabilistic blend of all potential values. This ‘indefiniteness’ isn’t about a lack of knowledge; it’s a statement about the fundamental nature of reality at the smallest scales, where properties are intrinsically uncertain and only become defined through the act of observation. The probability of finding the particle in any particular state is determined by the square of the amplitude of its wave function, $ |\psi|^2 $, highlighting the probabilistic nature of quantum reality.

Quantum systems exist in a probabilistic state, described by a superposition of possibilities, until a measurement is performed. This isn’t merely a limitation of detection; the very act of observing-of interacting with the quantum system to determine a specific property-appears to force the system to ‘choose’ a definite state. Prior to measurement, quantities like position or momentum aren’t fixed but exist as a range of potential values, mathematically represented by a wave function. The measurement process, however, isn’t a passive recording; it fundamentally alters the system, collapsing the wave function and yielding a single, concrete outcome. This ‘collapse of the wave function’ is not understood as a physical disruption, but rather a transition in the system’s description from probabilistic potential to definite actuality, raising profound questions about the interplay between observation and reality at the quantum scale.

The implications of quantum measurement extend far beyond practical applications, prompting deep philosophical inquiries into the very fabric of reality. If a quantum system exists in a superposition of states – a probabilistic blend of possibilities – until observed, what constitutes an “observation” and what role does the observer play in defining reality? Some interpretations suggest consciousness itself is integral to wave function collapse, while others posit that any interaction with the environment, regardless of a conscious observer, constitutes a measurement. This debate challenges classical notions of objectivity, suggesting that the properties of a quantum system are not inherent but rather emerge through the act of observation, blurring the line between the observer and the observed and raising questions about whether a definite reality exists independent of measurement. The enduring mystery lies in understanding if quantum mechanics reveals a fundamental limit to what can be known about the universe, or if it points to a more nuanced relationship between existence and observation than previously imagined.

Relativity of Definiteness: The Observer’s Frame

The Wigner’s Friend scenario illustrates the relativity of definiteness through a thought experiment involving two observers, conventionally labeled ‘W’ and ‘F’. Observer F performs a measurement on a quantum system, potentially collapsing its wavefunction and establishing a definite outcome from their perspective. However, observer W, unaware of F’s measurement, continues to treat the system as being in a superposition. From W’s frame of reference, the system remains indefinite, even after F’s measurement has occurred. This implies that the definiteness of a quantum state is not an absolute property of the system itself, but rather depends on the specific observer and their associated reference frame. The scenario highlights that different observers can legitimately assign different, mutually exclusive, states to the same system without contradiction, challenging the notion of an objective, observer-independent reality.

The Relational View of quantum mechanics posits that physical properties are not inherent attributes of a system itself, but instead exist as relationships between that system and an observer or another system. This means a property, such as position or momentum, is not a pre-existing value waiting to be measured, but is defined only upon interaction and relative to the observer’s frame of reference. Consequently, different observers, potentially in different states of motion or possessing different information, may legitimately assign different, and even incompatible, properties to the same system without contradiction; the system does not possess a single, objective value independent of observation. This perspective fundamentally shifts the focus from intrinsic properties to relational properties, resolving issues arising from the assumption of observer-independent reality.

Recent theoretical work addresses the Wigner’s Friend paradox by establishing a direct link between quantum indefiniteness and the symmetries present in different reference frames. The resolution hinges on recognizing that the lack of a definite value for a quantum property isn’t an inherent characteristic of the system itself, but a consequence of the relational perspective; an observation within one frame defines a property relative to that frame, while remaining indefinite from another. This approach avoids the infinite regress of nested observers characteristic of traditional interpretations by grounding indefiniteness in the symmetries of the measurement context, effectively preventing an unbounded chain of relative observations and maintaining consistency with the principles of relativistic quantum mechanics. Specifically, the framework leverages the symmetry between different observers’ inertial frames to demonstrate that the observed state is always definite within a given frame, even if indefinite across all frames simultaneously.

Agent-Situations: Contextualizing Quantum States

Healey’s pragmatism diverges from traditional quantum interpretations by asserting that quantum states are not intrinsic properties of systems, but are instead defined relative to ‘agent-situations’. An agent-situation encompasses the observer (the ‘agent’) and the specific apparatus used for measurement, establishing a contextual framework for defining quantum states. This perspective deliberately shifts the focus from ontological questions regarding the ‘true’ nature of quantum reality to epistemic considerations of what can be known within a given observational context. Consequently, the values assigned to quantum observables are understood as relational, depending on the agent-situation, and not as absolute properties existing independently of observation. This emphasis on practical implications allows for a consistent interpretation of quantum mechanics without requiring a commitment to the existence of observer-independent, objective quantum states.

Quantum mechanical observations are fundamentally contextual, meaning the outcome of a measurement is not solely determined by the system being observed, but is inextricably linked to the observer’s frame of reference and the specifics of the measurement apparatus. This includes factors such as the chosen basis for measurement, the spatial and temporal resolution of the detector, and any pre-existing conditions imposed on the system during the measurement process. Consequently, a given quantum system does not possess a single, objective set of properties independent of observation; rather, its properties are defined relationally, emerging only within the context of a particular measurement interaction. The selection of the measurement setup, therefore, actively participates in defining the observed reality, demonstrating that quantum observations are not passive recordings of pre-existing states, but are instead active constructions of information.

Healey’s pragmatism addresses the inherent relativity of quantum mechanics by shifting the focus from determining absolute quantum states to identifying what is knowable within a specific agent-situation. This framework posits that knowledge isn’t about uncovering an objective reality, but rather establishing correlations between observations made from a defined perspective and the corresponding quantum system. The emphasis on ‘what can be known’ circumvents the need for assigning universal values to quantum properties; instead, values are relative to the observer’s operational choices-their chosen measurement procedures and reference frames. Consequently, predictions are made not about the system itself, but about the outcomes of measurements performed by the agent, providing a consistent account of quantum phenomena without requiring an observer-independent reality.

The Limits of Relativization: Symmetry and Objective Facts

Quantum mechanics, at its core, describes properties not as absolute, but as relative to an observer or a reference frame. This presents a fundamental challenge: the potential for an infinite chain of relative descriptions, a phenomenon termed ‘Regression of Relativization’. If every property is defined only in relation to another, and that defining element is itself relative, then a complete, objective description seemingly requires an endless cascade of contextualization. This regress threatens the very coherence of the quantum framework, as it implies a lack of fixed, determinate properties and undermines the possibility of making meaningful predictions about the physical world. Without a mechanism to halt this infinite loop, the quantum state remains perpetually undefined, hindering the transition from probabilistic description to observable reality.

Quantum systems, inherently described by probabilities rather than definite states, face a conceptual challenge: an endless loop of relative descriptions where every property is defined only in relation to another, threatening the stability of measurement. Fortunately, the process of decoherence offers a resolution. This phenomenon, arising from the inevitable interaction of a quantum system with its surrounding environment, effectively ‘collapses’ the wave function, selecting a definite state from the multitude of possibilities. It doesn’t impose a single, absolute reality, but rather establishes a consistent set of properties robust enough for observation within a specific frame of reference. By dispersing quantum information into countless environmental degrees of freedom, decoherence ‘fixes’ properties not by altering the underlying quantum nature, but by rendering alternative descriptions practically inaccessible, effectively halting the infinite regress and allowing for the emergence of classical, objective facts.

The research reveals a pathway to resolving the challenges posed by the ‘Regression of Relativization’ through a focus on properties that remain constant despite changes in perspective-those invariant under symmetry transformations. This approach doesn’t attempt to eliminate relative descriptions entirely, but instead anchors objective facts within macroscopic reference frames by identifying characteristics that are fundamentally stable. Instead of seeking absolute properties, the framework prioritizes those that hold true regardless of shifts in viewpoint, effectively halting the infinite regress. This reliance on symmetry and invariance allows for the preservation of meaningful, observable quantities, ensuring that descriptions of reality, while still relative, are not endlessly deferred and remain grounded in predictable, measurable outcomes. The implications suggest a universe where objectivity isn’t about fixed points, but about patterns and relationships that endure despite continuous change.

Challenging Quantum Predictions: The Extended Wigner’s Friend

The Extended Wigner’s Friend scenario represents a sophisticated evolution of the original thought experiment, dramatically amplifying its implications for quantum foundations. It intricately weaves Wigner’s Friend – where one observer’s measurement outcome seemingly remains indefinite for another – with the principles of Bell experiments, traditionally used to test local realism. By having multiple “Wigner’s Friends” perform measurements on entangled particles and then themselves become the subjects of further measurements, the scenario creates a cascading chain of indefinite states. This complex arrangement doesn’t simply question whether a single measurement defines reality; it posits a situation where consistent assignments of definite outcomes across all observers become mathematically impossible if one adheres to both locality – the principle that distant events cannot instantaneously influence each other – and the assumption that observers’ experiences should be objective and consistent. Consequently, the Extended Wigner’s Friend scenario doesn’t merely challenge quantum mechanics; it forces a re-evaluation of the fundamental assumptions underpinning both quantum theory and our classical intuitions about reality itself.

The Extended Wigner’s Friend scenario reveals a fundamental tension between quantum mechanics and seemingly reasonable assumptions about how observations occur. If one insists that an observer’s measurement outcome is objectively real – independent of any further observation – and that information cannot travel faster than light (locality), then contradictions emerge. Specifically, the ‘Local Friendliness Theorem’ mathematically demonstrates that multiple, equally valid descriptions of quantum events can exist, each claiming objectivity. This isn’t merely a philosophical curiosity; it implies that if two observers independently measure a quantum system, both can legitimately conclude their measurement determined a definite outcome, even if those outcomes disagree. The theorem highlights that maintaining both objectivity and locality forces a rejection of standard quantum predictions, suggesting a potential breakdown in our understanding of measurement and reality itself, and prompting further investigation into the foundations of quantum theory.

The Extended Wigner’s Friend scenario doesn’t simply offer another paradox; it actively compels a re-evaluation of quantum mechanics’ foundational principles. By intertwining the classic thought experiment with the complexities of Bell tests, the scenario exposes potential inconsistencies if one insists on maintaining both objectivity – the idea that measurement outcomes exist independently of the observer – and locality – the principle that distant events cannot instantaneously influence each other. This isn’t about disproving quantum mechanics, but rather about rigorously probing its limits and uncovering where our intuitive understanding of reality clashes with its predictions. The persistent challenges posed by such experiments suggest that a complete understanding of quantum reality requires deeper investigation into the nature of measurement, observation, and the very fabric of spacetime, potentially leading to revisions or refinements of the theory itself.

The pursuit of objective reality, as often framed within the Wigner’s Friend paradox, appears increasingly less a quest for a singular truth and more a mapping of perspectives. This work, by grounding quantum states in relational reference frames, doesn’t so much solve the measurement problem as reframe it – suggesting that what appears indefinite isn’t a property of the system itself, but of its description relative to an observer. As Paul Dirac once observed, “I regard quantum mechanics as a mathematical framework for describing the behaviour of the world, and not as a description of reality itself.” The emphasis on symmetry and decoherence here isn’t about revealing an underlying order, but about understanding how information – and therefore, apparent definiteness – emerges from the interaction between systems. It’s a reminder that a model isn’t a mirror of reality – it’s a mirror of its maker, and the frame they choose to view it from.

What’s Next?

The connection proposed between quantum indefiniteness and symmetry, while intriguing, doesn’t dissolve the measurement problem so much as relocate it. If reference frames aren’t fundamental, but emerge, the question immediately becomes: what dynamics govern that emergence? Simply stating a symmetry is broken feels less like an explanation and more like a renaming of the difficulty. Anything confirming expectations needs a second look, and the temptation to treat emergence as a hand-waving solution should be resisted.

Future work must grapple with the practical implications of relational quantum mechanics. Demonstrating how these reference frames actually arise within a physical system – beyond theoretical construction – is crucial. Decoherence, often invoked as a deus ex machina, requires a more nuanced treatment. It’s not enough to show that interaction leads to classicality; the specific way in which frames are established through those interactions needs careful consideration. A hypothesis isn’t belief – it’s structured doubt, and this framework needs more than just consistency; it requires predictive power.

Ultimately, the success of this approach-or any attempt to resolve the measurement problem-will hinge on its ability to connect the quantum world to the observer’s experience without invoking privileged or fundamental observers. The search for a genuinely relational quantum theory is a long one, and the current work, while promising, represents a step-perhaps a cautious one-along that path.

Original article: https://arxiv.org/pdf/2512.07101.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/