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Tim A. Koslowski (New Brunswick) gives a talk at the Mini-Workshop on the Foundations of Shape Dynamics (23 June, 2014) titled "Shape Dynamics". Abstract: Based on the introduction to shape dynamics by Sean Gryb, I will discuss the question: "Given that gravity (from the perspective of shape dynamics) is fundamentally the evolution of spatial conformal geometry and not spacetime: How is the arrow of time generated? How is the illusion of a spacetime generated? What are the limitations of the spacetime description? I will give explicit answers to several aspect of these questions and I will explain where the uncharted territory begins.

Detlef Dürr (LMU) gives a talk at the MCMP Colloquium (23 January, 2013) titled "Bohmian Mechanics, speakable quantum physics". Abstract: I introduce Bohmian Mechanics, which is a theory of particles in motion. The law of motion is not classical, i.e. the particles do not move on Newtonian trajectories. As this is often not appreciated I shall discuss some features which will help to sharpen one's intuition about this theory of nature.

Karim Thébault (MCMP/LMU) gives a talk at the MCMP Colloquium (9 January, 2013) titled "Quantisation as a guide to ontic structure". Abstract: The ontic structural realist stance is motivated by a desire to do philosophical justice to the success of science, whilst withstanding the metaphysical undermining generated by the various species of ontological underdetermination. We are, however, as yet in want of general principles to provide a scaffold for the explicit construction of structural ontologies. Here we will attempt to bridge this gap by utilising the formal procedure of quantisation as a guide to ontic structure of modern physical theory. The example of non-relativistic particle mechanics will be considered and, for that case, it will be argued that, modulo certain mathematical ambiguities, a consistent candidate structural ontology can be established.

Igor Khavkine (Utrecht) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Gravity. An exercise in quantization". Abstract: The quantization of General Relativity (GR) is an old and chellenging prob- lem that is in many ways still awaiting a satisfactory solution. GR is a partic- ularly complicated field theory in several respects: non-linearity, gauge invari- ance, dynamibal causal structure, renormalization, singularities, infared effects. Fortunately, much progress has been made on each of these fronts. Our under- standing of these problems has evolved greatly over the past century, together with our understandig of quantum field theory (QFT) in general. Today, the state of the art in QFT knows how to address each of these challenges, as they occur in isolation in ohter field theories. There is still an active research program aiming to combine the relevant methods and apply them to GR. But, at the very least, the problem of the quantization of GR can be formul

Thomas Pashby (Pittsburgh) gives a talk at the MCMP Colloquium (28 May, 2014) titled "Against Dogma: Locality, Conditionalisation, and Collapse in Relativistic Quantum Mechanics". Abstract: I argue here against the widespread view (due to David Malament) that the non-commutativity of non-instantaneous localisation projections implies the existence of act-outcome correlations in relativistic QM. There are two facets to my argument: first, I claim that the interpretation of collapse as a process brought about by the experimenter is mistaken; second, I contend that a fully relativistic model should not condition on the occurrence of spacelike separated instantaneous events. This leaves the door open to define a relativistically invariant (but non-commuting) system of localization, which I interpret in terms of conditional probabilities for the occurrence of events. In accord with Tumulka (2009), I conclude that non-local correlations of events in a relativistic quantum theory need not imply the sort of action at

Sean Gryb (Nijmegen) gives a talk at the Mini-Workshop on the Foundations of Shape Dynamics (23 June, 2014) titled "An Introduction to Shape Dynamics: a New Perspective on Quantum Gravity". Abstract: Shape Dynamics is a theory of gravity where the fundamental ontology is that of evolving conformally invariant spatial geometry. This implements a notion of local spatial scale invariance such that what is seen to be physically meaningful is the information about the local "shapes" (as opposed to size) of a system. Perhaps surprisingly, this theory can be proven to reproduce a vast number of the solutions to the Einstein equations. However, black hole solutions are known to differ from those of GR past the horizon and do not lead to singularities. Shape Dynamics, thus, provides an intriguing new starting point for a theory of quantum gravity. In this introductory chalkboard talk, I will try to give some motivations for Shape Dynamics and will describe the basic structure of the theory, outlining how one can prove

Andreas Barrels (Bonn) gives a talk at the MCMP Colloquium (7 May, 2014) titled "How to Bite the Bullet of Quidditism - Why a Standard Argument against Categoricalism in Physics Fails". Abstract: Categoricalism is the statement that fundamental properties of physics are categorical, i.e., they have their dispositional characters not with metaphysical necessity. According to Black (2000), Bird (2005, 2007), and Esfeld (2009), categoricalism entails quidditism, the possible existence of properties which are not exclusively individuated by their dispositional characters. If quidditism is true, we cannot know, in principle, whether it is property F or its “Doppelgänger” G that shows up by exhibiting a certain set of dispositional characters. Since we cannot accept our metaphysics of properties to condemn us to necessary ignorance of fundamental properties, we must reject quidditism. Therefore, categoricalism fails. I argue that the possible epistemic situation revealed by quidditism is a case of empirical un

Michael Stöltzner (South Carolina) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Best Possible Worlds and Random Walks: The Principle of Least Action as a Thought Experiment". Abstract: Over the centuries, no other principle of classical physics has to a larger extent nourished exalted hopes of a universal theory, has constantly been plagued by mathematical counterexamples, and has ignited metaphysical controversies than has the principle of least action (PLA). The aim of this paper is first to survey a series of modern approaches, among them the structural realist readings of Planck and Hilbert, a neo-Kantian relativized a priori principle, and more recent discussions about modality within the context of analytic metaphysics. But these considerations seem outrun by the broad applicability of the PLA beyond classical physics. In the case of Feynman’s path integral, the PLA does no longer amount to the distinction of the act

Carlo Rovelli (Aix-Marseille) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Physics without Fundamental Time". Abstract: Rivers of ink have flown on the basic conceptual structure of quantum gravity -a theory where we expect the notions of classical spacetime, particles, fields, energy and momentum to require substantial revision-. I discuss a specific solution to these questions and apply concretely it to a physical calculation, the tunneling time of a Hajicek-Kiefer black-to-white hole transition. This is a quantum gravitational effect that might have some chance to be actually observable, or could have even been already observed in the "Fast Radio Bursts" observed by the Arecibo and Parkes radio-telescopes.

Donald Salisbury (Austin) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "The Intrinsic Hamilton-Jacobi Dynamics of General Relativity and its Implications for the Semi-Classical Emergence of Time". Abstract: The quantization of the general theory of relativity is notoriously difficult, in particular on account of the underlying general covariance and the consequent appearance of constraints in the classical Hamiltonian theory. The notion of time in the quantum theory is especially troubling since differing ideas of time suggest themselves depending on the quantum rules that are employed and the interpretations given to time in the classical theory itself. I will address the problem of time from a perspective in which constraints are implemented in a Hamilton-Jacobi framework through the use of intrinsic coordinates. The canonical approach is especially suited for this task. The decisive result is that the problem of time is even greater than one might have expected

Francesca Vidotto (Radboud) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Discrete Time in Quantum Gravity". Abstract: We study the quantization of geometry in the presence of a cosmological constant, using a discretiza- tion with constant-curvature simplices. Phase space turns out to be compact and the Hilbert space finite dimensional for each link. Not only the intrinsic, but also the extrinsic geometry turns out to be discrete, pointing to discreetness of time, in addition to space. We work in 2+1 dimensions, but these results may be relevant also for the physical 3+1 case.

Henrique Gomes (Perimeter Institute) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Timeless Quantum Mechanics in Configuration Space: an Outsider View". Abstract: In this talk, I will explore a timeless interpretation of quantum mechanics of closed systems, solely in terms of path integrals in non-relativistic timeless configuration space. What prompts a fresh look at the foundational problems in this context, is the advent of multiple gravitational models in which Lorentz symmetry is only emergent. In this setting, I propose a new understanding of records as certain relations between two configurations, the recorded one and the record-holding one. These relations are formalized through a factorization of the amplitude kernel, which forbids unwanted 'recoherence' of branches. On this basis, I show that in simple cases the Born rule is consistent with counting the relative density of observers with the same records. Furthermore, unlike what occurs in consistent his

Sean Gryb (Radboud) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "In Favour of a Schrödinger Evolution of the Universe". Abstract: In the canonical formulation of reparametrization invariant systems, time evolution on phase space is generated by a fully constrained Hamiltonian. On the orthodoxy view, the quantum formalism for such systems is constructed through Dirac quantization, which leads to a real, time-independent constraint on the quantum state. The question then remains how to extract a notion of time evolution from this frozen formalism. On one predominant view, the system is to be split in terms of ''partial observables'' -- which may be used as internal clocks -- and a set of ''complete observables'' -- which are understood to evolve in terms of the former. This has led to a controversy around the interpretation of the partial observables within the formalism. In this talk, we will provide a negative argument against the orthodoxy view that clarifies t

Bianca Dittrich (Perimeter Institute) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "The Consistent Boundary Formulation". Abstract: I will introduce the consistent boundary formulation which allows to express renormalization flow in a background independent context. I will discuss consequences of this formulation for the Hamiltonian framework and explore in which sense Hamiltonian constraints do actually exists in this context and how this influences the notion of time.

Philipp Hoehn (Perimeter Institute) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Constraints, Dirac Observables and Chaos". Abstract: I will discuss fundamental challenges to the standard relational paradigm arising from chaotic dynamics.

J. Brian Pitts (Cambridge) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Changing Observables in Canonical General Relativity from Hamiltonian-Lagrangian Equivalence". Abstract: Is change missing in classical canonical General Relativity? If one insists on Hamiltonian-Lagrangian equivalence, then there is Hamiltonian change just when there is no time-like Killing vector field. Change has seemed missing partly due to Dirac’s belief that a first-class constraint, especially a primary, generates a gauge transformation. Pons showed that Dirac’s argument stops too soon: working to second order in time brings in first-class secondaries and hence the gauge generator G, a tuned sum of first-class constraints used by Anderson and Bergmann (1951) and recovered by Mukunda, Castellani et al. from the 1980s. I observe that trouble happens immediately: a first-class primary constraint generates an illegal change of initial data in GR, Maxwell and Yang-Mills. Dirac’s subtr

Oliver Pooley (Oxford) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "First-Class Constraints, Gauge, and the Wheeler-DeWitt Equation". Abstract: Recently, Pitts (2014) has argued that the claim that first-class constraints generate gauge transformations (hereafter “orthodoxy”) fails even in electromagnetism, which is standardly taken to illustrate its correctness. Independently, Barbour and Foster (2008) have argued that a key presupposition of the primary argument for orthodoxy (due to Dirac, 1964) is not satisfied in the important case of reparameterization-invariant theories. In assessing these claims, one needs to distinguish between, (i) transformations that relate points of phase space that represent the same instantaneous state and (ii) transformations that map curves on phase space to curves that represent the same history. Pitts shows that arbitrary first-class constraints fail to generate transformations of type (ii), but leaves untouched the orthodo

Tim A. Koslowski (Brunswick) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "The Gravitational Arrow of Time". Abstract: The arrow of time appears to always to point in one direction (i.e. we can clearly tell whether a movie is played forward or backward) although the underlying physics is time-reversal symmetric. The most widely accepted explanation for this is that the experienced arrow is the thermodynamic arrow of time (i.e. the direction of entropy growth). This scenario requires the past hypothesis, i.e. an atypical initial condition. We propose an alternative mechanism: The arrow of time is the direction in which the complexity of the universe grows. Gravity generates this arrow of time and creates subsystems with low entropy initial conditions spontaneously. I show this in detail in the Newtonian limit and discuss the extension to cosmological models in GR.

Kurt Sundermeyer (FU Berlin/MPIWG) gives a talk at the Workshop on the Problem of Time in Perspective (3-4 July, 2015) titled "Facets of Time in Physics". Abstract: In an attempt to understand slogans such as "The End Of Time", "Forget About Time", "Time Reborn", "Time Remains", I started to write an essay about the various notions of time in physics (with a glimpse to philosophy) from classical mechanics to quantum gravity. By this curiosity-driven motivation I realized that there are not only various notions of time, but that there are diverse problems with time and problems of time. In my talk I will present the structure and inputs of this still unfinished treatise, and I expect to receive valuable feedback from the competent participants of this workshop.

Miklós Rédei (LSE) gives a talk at the MCMP Colloquium (13 May, 2015) titled "A Categorial Approach to Relativistic Locality". Abstract: In the talk relativistic locality of a probabilistic physical theory is interpreted as an interconnected web of properties which express compatibility of the theory with the underlying causal structure of spacetime. Four components of this web are distinguished: spatiotemporal locality, causal locality-Independence, causal locality-Dependence, and causal locality-Dynamic. These four conditions will be specified in terms of concepts from the categorical approach to quantum field theory and results are recalled indicating the extent to which an algebraic quantum field theory satisfying the Haag–Kastler axioms is causally local.

Richard Dawid (MCMP) gives a talk at the MCMP Colloquium (29 April, 2015) titled "Bayesian Perspectives on the Higgs Search". Abstract: The history of the Higgs discovery is characterized by a specific constellation: trust in the existence of a Higgs particle was very strong already before the particle's discovery. This raises the issue of a Bayesian perspective on data analysis in high energy physics in an interesting way that differs from other contexts in the field where the deployment of Bayesian strategies was proposed.

Elena Castellani (Florence) gives a talk at the MCMP Colloquium (28 January, 2015) titled "Dualities". Abstract: Dualities are a key, intriguing ingredient in mathematics, logic and physics. This talk is concerned with physical dualities, in particular those dualities that have played "a central role in mapping out the structure of theoretical physics" in the past two decades (quoting Polchinski, 2015). Despite the importance of duality in field and string theory, philosophers are just starting to pay the due attention to the subject. This talk is meant as an introduction to discussing the significance of physical dualities, by pointing out the different relevant functions they play and the kinds of philosophical issues they connect or give rise to (in particular: theoretical equivalence and ontological indeterminacy).

Rüdiger Schack (Royal Holloway London) gives a talk at the Workshop on Quantum Computation, Quantum Information, and the Exact Sciences (30-31 January, 2015) titled "QBism and the Born rule". Abstract: By adopting a strictly personalist approach to probability, QBism takes the view that quantum states, and therefore also quantum information, reflect an agent’s personal degrees of belief about the consequences of his actions on the world. The quantum formalism enables the agent to make better decisions in the light of his previous experiences. This talk focuses on the central role played in quantum mechanics by the Born rule, which in QBism has a normative character similar to the rules of probability theory.

Chris Timpson (Brasenose College, Oxford) gives a talk at the Workshop on Quantum Computation, Quantum Information, and the Exact Sciences (30-31 January, 2015) titled "Quantum Information: Conceptual and Ontological Aspects". Abstract: In this talk I will explore some ways of thinking about what quantum information is. This topic has a certain intrinsic interest, but it is also important when trying to assess in a careful way what role the concept of information might have to play in fundamental physics. I shall argue for a view which is fairly ontologically deflationary about quantum information (this has significant impact on how we should understand the slogan ‘information is physical’ and for informational immaterialist views) and which sees quantum and classical (Shannon) information both as species of a single genus.

Gia Dvali (LMU-MPI & NYU) gives a talk at the MCMP Colloquium (14 January, 2015) titled "Corpuscular structure of geometry". Abstract: We review some recent ideas on quantum-corpuscular structure of gravitational metric backgrounds, such as black holes and cosmological spaces. We show how this picture sheds light on seemingly-mysterious properties, such as, black hole information processing and evaporation, as well as how it excludes eternal de Sitter space. This picture sheds a very different light on notion of "holography" and cosmological constant problem.

Karim Thebault (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "A New Prescription for the Quantization of Refoliation Invariant Field Theories". Abstract: Imagine a loaf of bread that we can irregularly cut up into a sequence of slices. The loaf is spacetime and the slices are instantaneous spatial surfaces. A foliation is a parameterization of a spacetime by a time ordered sequence of spatial slices. In a field theory such a parametrization can be local in the sense that it is defined for every point on every spatial slice. Diffeomorphism invariance implies that spacetimes described by general relativity that are related by refoliations are physically equivalent. Classically the symmetry is therefore directly connectable to the idea that only the coordinate-free information contained in a spacetime geometry has a physical basis. The implications of this symmetry for quantization are notoriously problematic. Here we o

Ben Feintzeig (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Unitary Inequivalence in Classical Systems". Abstract: I provide an algebraic formulation of classical field theories and use this to probe our interpretation of algebraic theories more generally. I show that the problem of unitarily inequivalent representations, as discussed in Ruetsche (2011), arises in classical theories just as in quantum theories, and I argue that this gives reason to not be a Hilbert Space Conservative when interpreting algebraic theories.

Brian Padden (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Relativistic Quantum Particles the Feynman Way". Abstract: It is often believed, especially in light of theorems by Malament and others, that there is no relativistic theory of localizable quantum particles. However, an example of exactly such a theory seems to exist, and in fact occupies an important place in the storied history of quantum field theory: Feynman’s path integral approach to quantum electrodynamics. We introduce Feynman’s theory and show that, up to a few minor issues, it is satisfactory. Then, we turn to the theorems stating that such a theory is impossible and discuss which premises are violated by the Feynman theory.

Samuel Fletcher (MCMP/LMU) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "Classical Field Theory and Intertheoretic Reduction". Abstract: In 1986, Ehlers set out a program on how to understanding the approximative relationships between different physical theories. However, he essentially only investigated the case of classical and relativistic spacetime theories, which have a number of special features that distinguish them from broader classes of physical theories. To what extent, then, can the Ehlers program be successful? I outline some of the challenges facing the program's generalization and argue that they can largely be overcome for classical field theories.

Sarita Rosenstock (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December, 2014) titled "On Fiber Bundle and Holonomy Interpretations of Yang-Mills Theories". Abstract: In the philosophy of Yang-Mills theories, there is an ongoing debate between rival interpretations that can be grouped into two rough categories: “holonomy interpretations” (supported by, e.g., Healey, Belot, and Lyre) and “fiber bundle interpretations” (supported by, e.g., Arntzenius, Maudlin, and Leeds). I present a theorem that I interpret as providing a precise sense in which these interpretations are equivalent.

James Weatherall (UC Irvine) gives a talk at the Irvine-Munich Workshop on the Foundations of Classical and Quantum Field Theories (14 December) titled "Fiber Bundles, Yang-Mills Theory, and General Relativity". Abstract: I articulate and discuss a geometrical interpretation of Yang-Mills theory. Analogies and disanalogies between Yang-Mills theory and general relativity are also considered.

Meinard Kuhlmann (Mainz) gives a talk at the MCMP Colloquium (10 December, 2014) titled "A Trope Bundle Interpretation of Algebraic Quantum Field Theory". Abstract: Algebraic quantum field theory (AQFT) is a conceptually lucid reformulation of the conventional theory of quantum fields. I consider AQFT to be the appropriate starting point for ontological considerations about QFT because, like the philosophical discipline of ontology, AQFT strives for a clear, justified and parsimonious separation of basic and derived classes of entities. I argue that the one-category theory of particularized properties or 'tropes', which analyses all other entities in terms of the basic category of tropes, yields the most appropriate ontological reading of AQFT. Among other things I will show that trope ontology and AQFT have essential structural similarities. I argue in particular that the trope-ontological conception of objects as bundles of tropes is related to the pivotal net structure of observable algebras in AQFT. Event

Michael Esfeld (Lausanne) gives a talk at the MCMP Colloquium (26 November, 2014) titled "The Primitive Ontology of Quantum Physics". Abstract: In this talk, I will first recall the arguments why we need what is known as a primitive ontology of quantum physics and then argue that this ontology consists in primitive stuff that is structurally individuated through metrical relations (but without a commitment to absolute space). Against this background, the only reason to admit physical properties then is that they play a causal role for the temporal development of the primitive stuff. I will sketch out two metaphysical views of these properties, namely Humeanism and dispositionalism.

Christopher Fuchs (MPQ Garching) gives a talk at the MCMP Colloquium (20 November, 2014) titled "QBism: A Subjective Way to Take Ontic Indeterminism Seriously". Abstract: The term QBism, invented in 2009, initially stood for Quantum Bayesianism, a view of quantum theory a few of us had been developing since 1993. Eventually, however, I. J. Good's warning that there are 46,656 varieties of Bayesianism came to bite us, with some Bayesians feeling their good name had been hijacked. David Mermin suggested that the B in QBism should more accurately stand for "Bruno", as in Bruno de Finetti, so that we would at least get the variety of (subjective) Bayesianism right. The trouble is QBism incorporates a kind of metaphysics that even Bruno de Finetti might have rejected! So, trying to be as true to our story as possible, we momentarily toyed with the idea of associating the B with what Chief Justice Oliver Wendell Holmes Jr. called bettabilitarianism. It is the idea that the world is loose at the joints, that indeter

Tim Maudlin (NYU) meets Sebastian Lutz (MCMP/LMU) in a joint session on "Reduction and the Ontology of Physical Theories" at the MCMP workshop "Bridges 2014" (2 and 3 Sept, 2014, German House, New York City). The 2-day trans-continental meeting in mathematical philosophy focused on inter-theoretical relations thereby connecting form and content of this philosophical exchange. Idea and motivation: We use theories to explain, to predict and to instruct, to talk about our world and order the objects therein. Different theories deliberately emphasize different aspects of an object, purposefully utilize different formal methods, and necessarily confine their attention to a distinct field of interest. The desire to enlarge knowledge by combining two theories presents a research community with the task of building bridges between the structures and theoretical entities on both sides. Especially if no background theory is available as yet, this becomes a question of principle and of philosophical groundwork: If there

Oliver Pooley (Oxford) gives a talk at the MCMP Colloquium (22 January, 2014) titled "New Work on the Problem of Time". Abstract: A central aspect of the "Problem of Time" in canonical general relativity is the result of applying to the theory Dirac's seemingly well-established method of identifying gauge transformations in constrained Hamiltonian theories. This "orthodox" move identifies transformations generated by the first-class constraints as mere gauge. Applied to GR the strategy yields the result that the genuine physical magnitudes of the theory (so identified) do not take on different values at different times. In the context of quantum gravity, this orthodoxy underwrites the derivation of the timeless Wheeler–DeWitt equation. It is thus intimately connected to one of the central interpretative puzzles of the canonical approach to quantum gravity, namely, how to make sense of a profoundly timeless quantum formalism. This talk reviews several disparate challenges to the technical underpinning of the

Heinz-Jürgen Schmidt (Osnabrück) gives a talk at the MCMP Colloquium (27 November, 2013) titled "The Bohmian challenge". Abstract: The Bohmian extension of quantum theory claims to solve the measurement problem by re-establishing, in some sense, the classical ontology of particle trajectories on a microscopic level. In this talk I will not dwell upon the pros and cons to this claim but rather try to explain why this enterprise constitutes a challenge for philosophy of science, especially for those branches striving for rigorous methods. The Bohmian extension is empirically equivalent to standard quantum mechanics and mathematically only an extension by definitions. The main difference to other interpretations of quantum theory seems to be the belief into the reality of the Bohmian trajectories. Are the theory concepts used in philosophy of science rich enough to represent this crucial difference? In particular, I will scrutinize the theory concept of Günther Ludwig that was explicitly developed to foster h

Erik Curiel (MCMP/LMU) gives a talk at the MCMP Colloquium (18 December, 2013) titled "Are Classical Black Holes Hot or Cold?". Abstract: In the early 1970s it is was realized that there is a striking formal analogy between the so-called laws of black-hole mechanics and the laws of classical thermodynamics. Before the discovery of Hawking radiation, however, it was generally thought that the analogy was only formal, and did not reflect a deep connection between gravitational and thermodynamical phenomena. In particular, it is still commonly held that the surface gravity of a stationary black hole can be construed as a true physical temperature only when quantum effects are taken into account; in the context of classical general relativity alone, one cannot cogently construe it so. Does the use of quantum field theory in curved spacetime offer the only hope for taking the analogy seriously? I think the answer is 'no'. To attempt to justify that answer, I shall begin by arguing that the standard argument to

Karen Crowther (Sydney) gives a talk at the MCMP Colloquium (13 November, 2013) titled "Emergent spacetime in condensed matter analogues of general relativity". Abstract: It has been claimed, based on a few different lines of reasoning, that the notion of spacetime will not appear in a quantum theory of gravity. If this is the case, then spacetime is an emergent concept. Analogue models of general relativity based in condensed matter systems present us with concrete examples of emergent spacetime, and could potentially help us understand the nature of emergent spacetime in the context of quantum gravity. These models present a curved spacetime metric that is described using an effective field theory. In this talk, I explore the conception of emergence that is relevant to analogue spacetime in the condensed matter models. This is a conception of emergence that also applies more generally to other effective field theories, and, as I argue, one that is best understood without appeal to the idea of reduction. I f

Fay Dowker (Imperial College London) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Things happen, they just happen in a partial order". Abstract: In causal set quantum gravity spacetime is hypothesized to be atomic and causal order is the most basic organising principle. Fundamental discreteness brings with it novel possibilities for "dynamical laws" in which spacetime grows by the accumulation of new atoms, potentially realising within physics C.D. Broad's concept of a growing block universe in which the past is real and the future is not. That a growing block can be compatible with general covariance and the lack of a global time, is demonstrated by the Rideout-Sorkin Classical Sequential Growth models in which the “present” is identified with the growth process itself.

Jean Bricmont (Université catholique de Louvain) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "From the microscopic to the macroscopic world". Abstract: The derivation of the laws describing the macroscopic world from those governing the microscopic one is a very difficult problem. The root of the difficulty is sometimes seen as arising from the fact that the first set of laws are often time-irreversible, while the second ones are time-reversible. The goal of the talk will be to explain precisely these notions (macroscopic, microscopic, (ir)reversibility) and why this difference does not constitute an insuperable difficulty. We will also discuss the role of probability in the derivation of the macroscopic laws from the microscopic ones and criticize several misleading attempts at justifying this derivation.

Julian Barbour (Oxford) gives an evening lecture at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "A Dynamical Origin of the Arrow of Time".

Robert Spekkens (Perimeter Institute) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "On Causal Explanations of Quantum Correlations". Abstract: If correlation does not imply causation, then what does? Causal discovery algorithms take as their input facts about correlations among a set of observed variables, and they return as their output causal structures that can account for the correlations. We show that any causal explanation of Bell-inequality-violating correlations must contradict a core principle of these algorithms, namely, that an observed statistical independence between variables should not be explained by fine-tuning of the causal parameters. The fine-tuning criticism applies to all of the standard attempts at causal explanations of Bell correlations, such as superluminal causal influences, superdeterminism, and retrocausal influences that do not introduce causal cycles. This suggests a novel perspective on the assumptions underlying Bell'

J. Brian Pitts (Cambridge) gives a talk in the colloquium "On the Split Between Gravity and Inertia in Different Spacetime Theories" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Inertia and the Conformal-Projective Decomposition for Nordström-Einstein-Fokker, Massive Scalar, Einstein, and Massive Spin 2 Gravities". Abstract: The Ehlers-Pirani-Schild (EPS) construction, which derives a metric tensor from a projective connection and a conformal metric density, has sometimes been thought to undermine the conventionality of geometry. It might be of renewed interest due to the appearance of the dynamical or constructivist ap- proach to space-time geometry of Brown and Pooley. Constructivism shares with conventionalism the modally cosmopolitan awareness of a multiplicity of options, not all so tidy as to fit a unique geometry, leaving the ‘true’ geometry ambiguous. An EPS-inspired decomposition is applied to Nordström-Einstein-Fokker (massless spin 0) scalar gra

Eleanor Knox (London) gives a talk in the colloquium "On the Split Between Gravity and Inertia in Different Spacetime Theories" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "The Gravity-Inertia split in Newtonian and Relativistic Contexts". Abstract: Relative to Newton-Cartan theory, Newtonian gravitation involves the split- ting of a single curved connection into gravitational and inertial parts. I examine the prospects for imposing an analogous division of the connection in general relativity. It’s well-known one cannot split the Levi-Civita connection in quite the same way as one does the Newton-Cartan connection, into a symmetric connection and gravitational field. However, it is possible to divide the Levi-Civita connection into a non-symmetric connection and a part that has sometimes been held (in Teleparallel theories) to represent the gravitational field. I’ll argue that non-symmetric connections are not candi- dates for representing full inertial str

Dennis Lehmkuhl (Wuppertal) and Oliver Pooley (Oxford) give a talk in the colloquium "On the Split Between Gravity and Inertia in Different Spacetime Theories" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Against the Gravity/Inertia split?". Abstract: To make sense of talk of a frame-dependent inertia–gravity split in General relativity, one needs to relate the theory to Newtonian gravity, and to recognise that two routes to privileged frames of reference need not yield the same sets of frames. On the first route, which paths in spacetime correspond to unaccelerated (“inertial”) motions is an absolute, coordinate-independent matter. The privileged frames are those whose standard of rest corresponds to inertial motion. On the second route, privileged frames are identified via classes of co-moving coordinate systems with respect to which dynamical equations take a simple, canonical form. In Newtonian gravity, the second route yields globally-defined frames w

Sean Gryb (Radboud) gives a talk in the colloquium "Journeys in Platonia: Celebrating 50 Years Since The End of Time" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Barbour's Shape Space as an Ontology for Gravity". Abstract: I will give a personal account of the development of the conformally invariant version of ‘Shape Dynamics’. The story will be told from three perspectives: i) a historical one, highlighting the role of College Farm and the unique interactions with Julian Barbour, ii) a philosophical one, describing a simple observation about the meaning of local scale in physics, and iii) a formal one, showing how an early observation of Poincare ́ combined with York’s method for solving the initial value problem in General Relativity led a concrete implementation of Barbour’s ontology.

Edward Anderson (Paris Diderot and Cambridge) gives a talk in the colloquium "Journeys in Platonia: Celebrating 50 Years Since The End of Time" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Kendall’s Shape Statistics as a Classical Realization of Barbour-type Timeless Records Theory Approach to Quantum Gravity". Abstract: I already showed that Kendall’s shape geometry work was the geometrical description of Barbour’s relational mechanics’ reduced configuration spaces (alias shape spaces). I now describe the extent to which Kendall’s subsequent statistical application to such as the ‘standing stones problem’ realizes further ideas along the lines of Barbour-type timeless records theories, albeit just at the classical level.

Harvey Brown (Oxford) gives a talk in the colloquium "Journeys in Platonia: Celebrating 50 Years Since The End of Time" at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "Leibniz, Mach and Barbour". Abstract: My comments will be concerned with the way that Leibniz's and Mach's thinking on the nature of space have influenced Julian Barbour's approach to the formulation of dynamical theories.

John D. Norton (Pittsburgh) gives a talk at the 17th UK and European Meeting on the Foundations of Physics (29-31 July, 2013) titled "The Neglect of Fluctuations in the Thermodynamics of Computation". Abstract: The thermodynamics of computation assumes that thermodynamically reversible processes can be realized arbitrarily closely at molecular scales. They cannot. Overcoming fluctuations so that a molecular scale process can be completed creates more thermodynamic entropy than the small quantities tracked by Landauer's Principle. This no go result is the latest instance of a rich history of problems posed by fluctuations for thermodynamics.

Michael Krämer (RWTH Aachen) gives a talk at the MCMP Colloquium (23 October, 2013) titled "The (philosophy of the) Higgs". Abstract: I will review the physics of the Large hadron Collider LHC, including the recent the discovery of a Higgs particle, and the search for new physics beyond the Standard Model of particle physics. While the talk focusses on the physics, I will also mention various philosophical questions which are being addressed in the context of an interdisciplinary research group on the "Epistemology of the LHC".

James Owen Weatherall (California) gives a talk at the MCMP Colloquium (19 July, 2013) titled "Inertial Motion, Explanation, and the Foundations of Classical Spacetime Theories". Abstract: There is an influential view in physics and philosophy of physics, originating with Einstein and Eddington, that holds that general relativity is distinctive in the history of physics because it can be used to "explain" inertial, or unforced, motion. In this talk, I will describe how a reformulation of Newtonian gravitation may be used to provide insight into claims concerning the (allegedly) distinctive explanatory resources of relativity theory. I will then argue that Newtonian gravitation can be understood to explain inertial motion in much the same way as general relativity. However, a careful comparative study of the status of inertial motion in the two theories reveals that neither explanation is as clean or straightforward as adherents to the view noted above believe. I will conclude by presenting a view about t

Michael Stöltzner (South Carolina) gives a talk at the MCMP Colloquium (17 July, 2013) titled "Feynman Diagrams as Models". Abstract: While Feynman considered his diagrams as pictorial representation of (real and virtual) physical processes, Dyson took then as a mere bookkeeping tool for mathematical expressions in a perturbation series. This split perspective has persisted since, especially when Feynman diagrams gradually extended their sway into modern particle physics. I argue that the modern debates on models in science can build a bridge between both perspectives by granting Feynman diagrams some explanatory autonomy and representative features. While a single Feynman diagram remains isomorph to a mathematical expression, it also represents a family of diagrams that model a measurable physical effect.

Christian Wüthrich (San Diego) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Time and space in causal set theory". Abstract: Causal set theory offers an elegant and philosophically rich, though admittedly inchoate, approach to quantum gravity. After presenting its basic theoretical framwork, I will show how space and time vanish from the fundamental picture it offers. The absence of space and time from the theory raises the serious question of whether such a theory can be empirically coherent at all, i.e, whether its truth would not undermine any justification we may heave for believing it. If it can be shown that spacetime re-emerges from the fundamental structure itn the appropriate limit, I will argue, then the threat of empirical incoherence is averted and it can be appreciated how space and time emerge from what there is, fundamentally, according to causal set theory. I shall close by sketching the prospects of the antecedent of this conditional claim.

Ioan Muntean (Fort Wayne) comments on Dean Rickles' "Dualities and the Physical Content of Theories" at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013).

Dean Rickles (Sydney) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Dualities and Physical Content". Abstract: A duality expresses a reltionship between a pair of putatively distinct physical theories. Theories are said to be dualwhen they generate "the same physics", where same physics is parsed in terms of, e.g., having the same amplitudes, expectation values, observable spectra, and so on. Hence, theories related by dualities can look very different while making exactly the same predictions about observatle phenomena. Indeed, such theories can look sufficiently different that would-be interpreters would surely consider them to be representations of very different possible worlds. In this talk I will be concerned with the question of whether dualites reflect some deep aspect of reality, or whether they are simply a formal device that aids computations in difficult contexts (functioning in much the same way as a change of variables). This links quite natural

Radin Dardashti (MCMP/LMU) comments on Richard Dawid's "String Theory and Scientific Realism" at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013).

Richard Dawid (Vienna) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "String Theory and Scientific Realism". Abstract: T-duality, which is an important feature of string theory, implies that the string scale constitutes a minimal length scale: within the conceptual framework of the theory, no higher energy scale can provide new information. This in turn may be taken to suggest that, if ST is valid at its own characteristic scale, no new theories which become empirically distinguishable from string theory at higher energy scales should be expected to be found. The problem with this final theory claim hinges on the fact that it seems to beg the question by presupposing the conceptual framwork the finality of which it aims to establish. In the talk I aim at understanding significance an limitations of string theorys final theory claim based on the distinction between local and global limitations to scientific underdetermination. It will be argued that the final

Karen Crowther (Sydney) comments on Daniele Oriti's "Dissappearance and Emergence of Space and Time in Quantum Gravity" at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013).

Daniele Oriti (Potsdam) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Disappearance and Emergence of Space and Time in Quantum Gravity". Abstract: We recall the hints for the disappearance of continuum space and time at microsopic scales, coming from classical and semi-classical gravitational physics. These include arguments for discreteness or for a fundamental non-locality, in a quantum theory of gravity. We compare how these ideas are realized in specific quantum gravity approaches, and focus in particular on the group field theory formalism, itself strictly related to other approaches, in particular loop quantum gravity. Next, we consider the emergence of continuum space and time from the collective behaviour of discrete, pre-geometric and non-spatio-temporal atoms of quantum space. After discussing the notion of emergence, with Bose condensates as one paradigmatic examples, and some specific cenceptual difficulties with the notion of emergent spacetime,

Karim Thébault (MCMP/LMU) gives a talk at the MCMP Workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Time Remains". Abstract: Even classically, it is not entirely clear how one should understand the implications of general covariance for the role of time in physical theory. On one popular view, the essential lesson is that change is relational in a strong sense, such that all that it is for a physical degree of freedom to change is for it to vary with regard to a second physical degree of freedom. This implies that there is no unique parameterziation of time slices, and also that there is no unique temporal ordering of states. At a quantum level this approach to general relativity is generally understood lead to a universe eternally frozen in an energy eigenstate. Here we will start from a different interpretation of the classical theory, and in doing so show one may avoid this acute "problem of time" in quantum gravity. Under our view, duration is still regarded as relative, but tempor

J. Brian Pitts (Cambridge) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Real Change Happens in Hamiltonian General Relativity; Just Ask the Lagrangian (about Time-like Killing Vectors, First-Class Constraints and Observables)". Abstract: In Hamiltonian GR, change has seemed absent. Attention to the gauge generator G facilitates a neglected calculation: a first-class constraint generates a bad physical change in electromagnetism and GR, spoiling the constraints, Gauss's law or the momentum and Hamiltonian constraints in the (physically relevant) velocities. Only as a team G do first-calss constraints generate a gauge transformation. To find change, insist on Hamiltonian-Lagrangian equivalence. Change is ineliminable time dependence; in vaccum GR it is the absence of a time-like Killing vector field. Neglecting spatial dependence, invariantly something depends on time via Hamilton's equations iff there is no time-like Killing vector. According to Bergmann, rea

Dennis Lehmkuhl (Wuppertal) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Einstein's approach to Quantum Gravity". Abstract: It is common knowledge that despite being a pioneer of the early quantum theory, Einstein opposed the probabilistic interpretation of the new quantum mechanics of 1925 / 1926, and he would have opposed any approach of a quantization of gravity relying on this interpretation. What is less well-known is that Einstein had an alternative approach that bears some similarities to more recent ideas to general relativize quantum mechancis rather than quantizing general relativity. Einstein identified discreteness in nature with quantum theory: the existence of photons, the quantisation of electric charge, etc. Roughly speaking, his idea was that these quantum features of reality could be derived from a generally covariant field theory of gravitation and electromagnetism by finding overdetermined partial differential equations which allow for so

Robert Helling (LMU) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "The "Shut up and Calculate" Approach to Quantum Gravity". Abstract: Quantum mechanics would have never been developed requiring to first understand all foundational issues. Rahter, it was approached in a pragmatic way summarized as shut up and calculate. For quantum gravity we already understand a number of its properties even if it is still unclear what form the final theory will have and how it solves its conceptual conundrums. The often repeated claim that quantum gravity lacks empirical data is - taken without qualification - not true. Rather, the requirement to reduce to known theories relativity in the appropiate limits togehter with our expericence of everyday physics rule out most creative proposals for a theory of quantum gravity. We want to pursue the effective-filed-theory line-of-thought neglecting conceptual expectations. The effective field theory approach still leaves room for a

Claus Kiefer (Cologne) gives a talk at the MCMP workshop "Quantum Gravity in Perspective" (31 May-1 June, 2013) titled "Quantum Geometrodynamics: whence, whither?". Abstract: Quantum geometrodynamics is canonical quantum gravity with the three-metric as the configuration variable. Its central equation is the Wheeler-DeWitt equation. Here I give an overview of the status of this approach. The issues discussed include the problem of time, the relation to the convariant theory, the semiclassical approximation as well as applicatoins to black holes and cosmology. I conclude that quantum geometrodynamics is still a viable approach and provides insights into both the conceptual and technical aspects of quantum gravity.