A recent no-go theorem (Frauchiger and Renner in Nat Commun 9(1):3711, 2018) establishes a contradiction from a specific application of quantum theory to a multi- agent setting. The proof of this theorem relies heavily on notions such as ‘knows’ or ‘is certain that’. This has stimulated an analysis of the theorem by Nurgalieva and del Rio (in: Selinger P, Chiribella G (eds) Proceedings of the 15th international conference on quantum physics and logic (QPL 2018). EPTCS (...) 287, Open Publishing Association, Waterloo, 2018), in which they claim that it shows the “[i]nadequacy of modal logic in quantum settings” (ibid.). In this paper, we will offer a significantly extended and refined reconstruction of the theorem in multi-agent modal logic. We will then show that a thorough reconstruction of the proof as given by Frauchiger and Renner requires the reflexivity of access relations (system T). However, a stronger theorem is possible that already follows in serial frames, and hence also holds in systems of doxastic logic (such as KD45). After proving this, we will discuss the general implications for different interpretations of quantum probabilities as well as several options for dealing with the result. (shrink)

We present an analysis of the Frauchiger–Renner Gedankenexperiment from the point of view of the relational interpretation of quantum mechanics. Our analysis shows that the paradox obtained by Frauchiger and Renner disappears if one rejects promoting one agent’s certainty to another agent’s certainty when it cannot be validated by records from the past. A by-product of our analysis is an interaction-free detection scheme for the existence of such records.

In 2018, Daniela Frauchiger and Renato Renner published an article in Nature Communications entitled ‘Quantum theory cannot consistently describe the use of itself.’ The argument has been attacked as flawed from a variety of interpretational perspectives. I clarify the significance of the result as a sequence of actions and inferences by agents modeled as quantum systems evolving unitarily at all times. At no point does the argument appeal to a ‘collapse’ of the quantum state following a measurement.

The Frauchiger–Renner Paradox is an extension of paradoxes based on the “Problem of Measurement,” such as Schrödinger’s Cat and Wigner’s Friend. All these paradoxes stem from assuming that quantum theory has only unitary physical dynamics, and the attendant ambiguity about what counts as a ‘measurement’—i.e., the inability to account for the observation of determinate measurement outcomes from within the theory itself. This paper discusses a basic inconsistency arising in the FR scenario at a much earlier point than the (...) derived contradiction: namely, the inconsistency inherent in treating an improper mixture as a proper, epistemic mixture. This is an illegitimate procedure that is nevertheless endemic if quantum theory is assumed to be always unitary. In contrast, under a non-unitary account of quantum state reduction yielding determinate outcomes, the use of a proper mixture for measurement results becomes legitimate, and this entire class of paradoxes cannot be mounted. The conclusion is that the real lesson of the FR paradox is that it is the unitary-only assumption that needs to be critically reassessed. (shrink)

Constructivist epistemology posits that all truths are knowable. One might ask to what extent constructivism is compatible with naturalized epistemology and knowledge obtained from inference-making using successful scientific theories. If quantum theory correctly describes the structure of the physical world, and if quantum theoretic inferences about which measurement outcomes will be observed with unit probability count as knowledge, we demonstrate that constructivism cannot be upheld. Our derivation is compatible with both intuitionistic and quantum propositional logic. This result is implied by (...) the Frauchiger-Renner theorem, though it is of independent importance as well. (shrink)

According to QBism, quantum states, unitary evolutions, and measurement operators are all understood as personal judgments of the agent using the formalism. Meanwhile, quantum measurement outcomes are understood as the personal experiences of the same agent. Wigner’s conundrum of the friend, in which two agents ostensibly have different accounts of whether or not there is a measurement outcome, thus poses no paradox for QBism. Indeed the resolution of Wigner’s original thought experiment was central to the development of QBist thinking. The (...) focus of this paper concerns two very instructive modifications to Wigner’s puzzle: One, a recent no-go theorem by Frauchiger and Renner, and the other a thought experiment by Baumann and Brukner. We show that the paradoxical features emphasized in these works disappear once both friend and Wigner are understood as agents on an equal footing with regard to their individual uses of quantum theory. Wigner’s action on his friend then becomes, from the friend’s perspective, an action the friend takes on Wigner. Our analysis rests on a kind of quantum Copernican principle: When two agents take actions on each other, each agent has a dual role as a physical system for the other agent. No user of quantum theory is more privileged than any other. In contrast to the sentiment of Wigner’s original paper, neither agent should be considered as in “suspended animation.” In this light, QBism brings an entirely new perspective to understanding Wigner’s friend thought experiments. (shrink)

We discuss the no-go theorem of Frauchiger and Renner based on an "extended Wigner's friend" thought experiment which is supposed to show that any single-world interpretation of quantum mechanics leads to inconsistent predictions if it is applicable on all scales. We show that no such inconsistency occurs if one considers a complete description of the physical situation. We then discuss implications of the thought experiment that have not been clearly addressed in the original paper, including a tension (...) between relativity and nonlocal effects predicted by quantum mechanics. Our discussion applies in particular to Bohmian mechanics. (shrink)

Facts happen at every interaction, but they are not absolute: they are relative to the systems involved in the interaction. Stable facts are those whose relativity can effectively be ignored. In this work, we describe how stable facts emerge in a world of relative facts and discuss their respective roles in connecting quantum theory and the world. The distinction between relative and stable facts resolves the difficulties pointed out by the no-go theorem of Frauchiger and Renner, and (...) is consistent with the experimental violation of the Local Friendliness inequalities of Bong et al.. Basing the ontology of the theory on relative facts clarifies the role of decoherence in bringing about the classical world and solves the apparent incompatibility between the ‘linear evolution’ and ‘projection’ postulates. (shrink)

Having its seeds in the 2nd International Lauener Symposium held in honour of Dagfinn Follesdal, the present collection contains a rich, kaleidoscopic ensemble of previously unpublished contributions by leading authors, representing diverse approaches to a variety of philosophical themes on which Follesdal has had a longstanding, formative impact. Follesdal himself contributes an orientating essay continuing to develop his pioneering theory of reference as well as in-depth commentaries on each of the other authors elaborated papers plus candid answers in the added (...) interview. The volume assembles a wealth of original articles containing in part direct discussions of Follesdal s work and covering a broad range of topics like subjectivity, intersubjectivity, objectivity, rationality, logics and mathematics, choice theory, values, modalities, intentionality, individuation, perception, communication, meaning, reference, the slingshot, one- and two-sorted semantics, evidence, neuropsychology, space and time, science and society, methodology, fallibilism, the relative a priori, justification, holism, the life-world, reflective equilibrium, empathy, and ethics. Moreover the book includes an incisive memoir of Follesdal the philosopher as well as a spanning interview with him, which are both critically directing toward Follesdal s subtly differentiated understanding of the dynamic philosophical horizon he shares in. With contributions from Dagfinn Follesdal, Charles Parsons, Patrick Suppes, Jon Elster, John Perry, Michael Friedman, Dag Prawitz, Wilhelm K. Essler, David Woodruff Smith, Olav Gjelsvik, Graciela De Pierris, Nils Roll-Hansen, Christian Beyer, Oystein Linnebo, Michael Frauchiger. Excerpt Open publication". (shrink)

Although evidence of teaching behaviour has been identified in some nonhuman species, human teaching appears to be unique in terms of both the breadth of contexts within which it is observed, and in its responsiveness to needs of the learner. Similarly, cultural evolution is observable in other species, but human cultural evolution appears strikingly distinct. This has led to speculation that the evolutionary origins of these capacities may be causally linked. Here we provide an overview of contrasting perspectives on the (...) relationship between teaching and cultural evolution in humans, and briefly review previous research which suggests that cumulative culture can occur without teaching. We then report the results of a novel experimental study in which we investigated how the benefits of teaching may depend on the complexity of the skill to be acquired. Participants were asked to tie knots of varying complexity. In our Teaching condition, opportunities to interact with an experienced partner aided transmission of the most complex knots, but not simpler equivalents, relative to exposure to completed products alone, and also relative to information about the process of completion. We conclude by considering the plausibility of various accounts of the evolutionary relationship between teaching and cultural evolution in humans. (shrink)

The differentiation of trait anxiety and depression in nonclinical and clinical populations is addressed. Following the tripartite model, it is assumed that anxiety and depression share a large portion of negative affectivity, but differ with respect to bodily hyperarousal and anhedonia. In contrast to the tripartite model, NA is subdivided into worry and dysthymia, which leads to a four-variable model of anxiety and depression encompassing emotionality, worry, dysthymia, and anhedonia. Item-level confirmatory factor analyses and latent class cluster analysis based on (...) a large nation-wide representative German sample substantiate the construct validity of the model. Further evidence concerning convergent and discriminant validity with respect to related constructs is obtained in two smaller nonclinical and clinical samples. Factors influencing the association between components of anxiety and depression are discussed. (shrink)

This collection concentrates on vital themes from Michael Dummett, one of the most influential and creative analytic philosophers of our time. The contributors, who include some of Dummett's distinguished former students, critically reflect on various concerns of Dummett's ground-breaking work in philosophy of language, metaphysics, and philosophy of mathematics and logic. The essays direct towards aspects of Dummett's pioneering work in the history of analytical philosophy, particularly his interpretations of the works of Frege and of Wittgenstein, which in conjunction with (...) Dummett’s own highly original ideas on truth and meaning have shaped decisive contemporary debates concerning notably the distinction between realism and anti-realism. Further, the volume includes a cheerfully serious excursion into popular philosophy by Dummett himself and reveals less known facets of Dummett's many-sided work and activities such as his political philosophy of immigration and asylum, and beyond that, his untiring and warm-hearted campaign for racial justice and humanity. Contributors: Michael Dummett, Eva Picardi, Crispin Wright, Timothy Williamson, Ian Rumfitt, Daniel Isaacson, Dag Prawitz, Dale Jacquette, Alex Burri, Michael Frauchiger. (shrink)

This anthology opens up new stimulating perspectives on a broad variety of Barcan Marcus s concerns ranging from quantified modal logic, identity, extensionality, direct reference, substitutional and objectual quantification, essentialism and possible worlds to epistemic and deontic modalities, belief, rationality and moral dilemmas. The contributions demonstrate that her philosophy has had a formative influence on current philosophical debates.".

H. sapiens stands out from other primates along many social dimensions; however, none seems as prominent and important as the capacity of our species for cumulative cultural evolution or, as Tomasello calls it, “the ratchet.” Although other primate species show evidence of cultural variation, there is little evidence of cumulative cultural evolution, i.e., the gradual accumulation, modification, and refinement of traditions and skills over historical time, in any primate species other than our own. This is clearly an extremely significant component (...) of the human phenotype, responsible for our unparalleled cultural, social, political, and technological achievements. However, it remains extremely controversial what sorts of cognitive capacities are necessary to trigger cumulative cultural evolution and whether any currently proposed candidates are really distinctive of humans. Furthermore, the ratchet raises a bootstrapping problem: before complex skills and technologies are present and necessary for biological success, there appear to be few advantages to high-fidelity social learning; however, without such high-fidelity social learning, it is unclear how traditions capable of generating complex skills and technologies could arise in the first place. In this chapter, we survey relevant empirical research in comparative and developmental psychology, integrating it with a novel theoretical analysis of the bootstrapping problem to defend a hypothesis about the minimal cognitive preconditions on the ratchet. (shrink)

This book collects major original essays developed from lectures given at the award of the Lauener Prize 2016 to T. M. Scanlon for his outstanding oeuvre in Analytical philosophy. In "Contractualism and Justification," Scanlon identifies some difficulties in his theory and explores possible ways to deal with them. In "Improving Scanlon’s Contractualism," D. Parfit recommends revisions and extensions of Scanlon’s theory, while R. Forst suggests in "Justification Fundamentalism" that Scanlon may want to replace reason with justification as his foundational concept. (...) T. Nagel raises fundamental questions concerning "Moral Reality and Moral Progress," and S. Mantel offers in "On How to Explain Rational Motivation" a critical discussion of Scanlon’s cognitivist theory of motivation. Z. Stemplowska does the same for Scanlon’s conception of responsibility in "Substantive Responsibility and the Causal Thesis," and S. Olsaretti suggests in "Equality of Opportunity and Justified Inequalities" an alternative to Scanlon’s arguments against economic inequalities. All contributors receive extensive replies by Scanlon. For anyone interested in Scanlon’s seminal work in moral and political philosophy, the present volume is utterly indispensable. (shrink)