Contemporary non-representationalist interpretations of the quantum state (especially QBism, neo-Copenhagen views, and the relational interpretation) maintain that quantum states codify observer-relative information. This paper provides an extensive defense of such views, while emphasizing the advantages of, specifically, the relational interpretation. The argument proceeds in three steps: (1) I present a classical example (which exemplifies the spirit of the relational interpretation) to illustrate why some of the most persistent charges against non-representationalism have been misguided. (2) The special focus is placed on dynamical evolution. Non-representationalists often motivate their views by interpreting the collapse postulate as the quantum mechanical analogue of Bayesian probability updating. However, it is not clear whether one can also interpret the Schrödinger equation as a form of rational opinion updating. Using results due to Hughes & van Fraassen as well as Lisi, I argue that unitary evolution has a counterpart in classical probability theory: in both cases (quantum and classical) probabilities relative to a non-participating observer evolve according to an entropy maximizing principle (and can be interpreted as rational opinion updating). (3) Relying on a thought-experiment by Frauchiger and Renner, I discuss the differences between quantum and classical probability models.
Contemporary non-representationalist interpretations of the quantum state (especially QBism, neo-Copenhagen views, and the relational interpretation) maintain that quantum states codify observer-relative information. This paper provides an extensive defense of such views, while emphasizing the advantages of, specifically, the relational interpretation. The argument proceeds in three steps: (1) I present a classical example (which exemplifies the spirit of the relational interpretation) to illustrate why some of the most persistent charges against non-representationalism have been misguided. (2) The special focus is placed on dynamical evolution. Non-representationalists often motivate their views by interpreting the collapse postulate as the quantum mechanical analogue of Bayesian probability updating. However, it is not clear whether one can also interpret the Schrödinger equation as a form of rational opinion updating. Using results due to Hughes & van Fraassen as well as Lisi, I argue that unitary evolution has a counterpart in classical probability theory: in both cases (quantum and classical) probabilities relative to a non-participating observer evolve according to an entropy maximizing principle (and can be interpreted as rational opinion updating). (3) Relying on a thought-experiment by Frauchiger and Renner, I discuss the differences between quantum and classical probability models.
Quantum mechanics has transformed our understanding of reality, yet deep philosophical puzzles remain unresolved. Is there a consistent way to describe quantum measurement, the emergence of space and time, and the role of observers within one coherent ontology? This paper introduces Relational Quantum Dynamics (RQD), an interpretation that places relationships and information, not isolated objects, at the foundation of physics. Unlike traditional views, such as the Copenhagen interpretation, Everett's many-worlds theory, or hidden-variable approaches, RQD denies a single observer-independent reality, instead proposing that facts only become definite within specific observational contexts. It explicitly addresses foundational no-go results, including Bell's theorem, the Kochen-Specker theorem, and the Frauchiger-Renner paradox, by replacing absolute facts with relational, context-dependent truths. RQD rests on five interlocking principles: (1) quantum states are contextual and observer-relative, (2) time emerges from quantum interactions rather than existing as an external parameter, (3) space is constructed from patterns of quantum entanglement, (4) observers emerge as systems with highly integrated information, and (5) classical reality appears through quantum decoherence without special wavefunction collapse. Philosophically, RQD aligns with ontic structural realism, proposing that the fundamental ontology of the universe consists entirely of informational relations. It avoids collapsing into relativism or solipsism by ensuring intersubjective agreement through physical interactions. Ultimately, RQD may offer a unified picture in which quantum mechanics, spacetime, and observers are no longer separate domains but aspects of one interconnected informational web.
Quantum mechanics has transformed our understanding of reality, yet deep philosophical puzzles remain unresolved. Is there a consistent way to describe quantum measurement, the emergence of space and time, and the role of observers within one coherent ontology? This paper introduces Relational Quantum Dynamics (RQD), an interpretation that places relationships and information—not isolated objects—at the foundation of physics. Unlike traditional views, such as the Copenhagen interpretation, Everett’s many-worlds theory, or hidden-variable approaches, RQD denies a single observer-independent reality, instead proposing that facts only become definite within specific observational contexts. It explicitly addresses foundational no-go results, including Bell’s theorem, the Kochen–Specker theorem, and the Frauchiger–Renner paradox, by replacing absolute facts with relational, context-dependent truths. RQD rests on five interlocking principles: (1) quantum states are contextual and observer-relative, (2) time emerges from quantum interactions rather than existing as an external parameter, (3) space is constructed from patterns of quantum entanglement, (4) observers emerge as systems with highly integrated information, and (5) classical reality appears through quantum decoherence without special wavefunction collapse. Philosophically, RQD aligns with ontic structural realism, proposing that the fundamental ontology of the universe consists entirely of informational relations. It avoids collapsing into relativism or solipsism by ensuring intersubjective agreement through physical interactions. Ultimately, RQD may offer a unified picture in which quantum mechanics, spacetime, and observers are no longer separate domains but aspects of one interconnected informational web.
Abstract The theories of pre-quantum physics are standardly seen as representing physical systems and their properties. Quantum mechanics in its standard form is a more problematic case: here, interpretational problems have led to doubts about the tenability of realist views. Thus, QBists and Quantum Pragmatists maintain that quantum mechanics should not be thought of as representing physical systems, but rather as an agent-centered tool for updating beliefs about such systems. It is part and parcel of such views that different agents may have different beliefs and may assign different quantum states. What results is a collection of agent-centered perspectives rather than a unique representation of the physical world. In this paper we argue that the problems identified by QBism and Quantum Pragmatism do not necessitate abandoning the ideal of representing the physical world. We can avail ourselves of the same puzzle-solving strategies as employed by QBists and pragmatists by adopting a perspectival quantum realism. According to this perspectivalism (close to the relational interpretation of quantum mechanics) objects may possess different, but equally objective properties with respect to different physically defined perspectives. We discuss two options for such a perspectivalism, a local and a nonlocal one, and apply them to Wigner’s friend and EPR scenarios. Finally, we connect quantum perspectivalism to the recently proposed philosophical position of fragmentalism.
We argue that quantum mechanics makes sense without such controversial postulates as the wave function collapse, the quantum probability rule and the observable postulate. We only need the existence of a wave function as a representation of a state, its dynamical evolution rule and another rather trivial postulate proposed here (Read-Off Postulate). The wave function collapse and the probability rule are replaced with intrinsic properties of the theory, i.e. decoherence and relative frequency, respectively. Interpretation of the wave function as a faithful representation of the reality naturally emerges, although quantum reality has a peculiar feature which distinguishes it from classical reality.
QBism has long recognized quantum states, positive-operator-valued measure elements, Kraus operators, and even unitary operations to be of the same type: they express aspects of an agent's belief system concerning the consequences (for her) of actions she might take upon her external world. Such action-consequence pairs have conventionally been called ``quantum measurements.'' The calculus of quantum theory is then viewed as an empirically motivated addition to Bayesian decision theory when brought to this notion of measurement. This radical approach has allowed QBism to eliminate conceptual problems that plague other interpretations of quantum mechanics. However, one issue has remained elusive: If a QBist does not believe in the existence of an ontic (agent-independent) dynamical variable evolving over time, why would there be any constraints on her quantum-state assignment in the absence of performing a measurement? Why would she introduce unitary or open-system quantum dynamics at all? Here, we present a representation theorem based on van Fraassen's reflection principle to answer these questions. Simply put, an agent's assignment of quantum dynamics represents her belief that a measurement action she is contemplating would not change her current odds for future gambles. A corollary to this approach is that one can make sense of ``open-system dynamics'' without the need to introduce an ``environment with a measurement record,'' as is common in decoherence accounts of quantum measurement. QBism's understanding instead rests more fundamentally on an agent's beliefs about the system of interest (not system plus environment) and her judgments about measurements she might perform on that system. More broadly, this result establishes QBism's contention that measurement itself is the central concept of quantum theory and thus the framework upon which any future QBist ontology must hang.
We offer a realist interpretation of non-relativistic quantum mechanics in which dynamical properties are properly possessed by the system in question, and are supposed to have definite values at any time. Like the QBists, we employ Bayesian probability, but we adopt something closer to the Bayesian statistics of E. T. Jaynes than to the subjective Bayesian statistics of B. de Fenetti employed by the QBists. Accordingly, we view calculated Bayesian probabilities as rational degrees of expectation of dynamical property values rather than as personal degrees of expectation of future (measurement) experiences. Probabilities are, for us, based on knowledge of the value of some dynamical property of the system, not on knowledge of previous experiences unassociated with system dynamical properties. As some Bayesians might, we take a probability equal to 1 not generally to indicate certainty but only (full) expectation; and we disallow probabilities of conjunctions of propositions claiming incompatible properties. Then, by reinterpreting and adding a little to the quantum formalism, we argue that we can maintain the advantages of the QBist interpretation. So, for us (as for the QBists), there is no unexplained collapse of the wave function, no need for ‘spooky action at a distance’, and no problem raised by the double slit experiment, the Kochen-Specker paradox or Bell type theorems. By holding on to a realist perspective, modelling (of ideal measurements, of system preparation processes etc.) is possible, and we can claim certain dynamical laws of quantum mechanics without leading to contradiction.