Are black holes about information?

Information theory is increasingly invoked by physicists concerned with fundamental physics, including black hole physics. But to what extent is the application of information theory in those contexts legitimate? Using the case of black hole thermodynamics and Bekenstein's celebrated argument for the entropy of black holes, I will argue that information-theoretic notions are problematic in the present case. Bekenstein's original argument, as suggestive as it may appear, thus fails. This example is particularly pertinent to the theme of the present collection because the Bekenstein-Hawking formula for black hole entropy is widely accepted as 'empirical data' in notoriously empirically deprived quantum gravity, even though the laws of black hole thermodynamics have so far evaded empirical confirmation.Comment: 20 pages; forthcoming in Richard Dawid, Radin Dardashti, and Karim Th\'ebault (eds.), Epistemology of Fundamental Physics, Cambridge University Press; minor changes and additions of reference

The (A)temporal Emergence of Spacetime

This paper examines two cosmological models of quantum gravity (from string theory and loop quantum gravity) to investigate the foundational and conceptual issues arising from quantum treatments of the big bang. While the classical singularity is erased, the quantum evolution that replaces it may not correspond to classical spacetime: it may instead be a non-spatiotemporal region, which somehow transitions to a spatiotemporal state. The different kinds of transition involved are partially characterized, the concept of a physical transition without time is investigated, and the problem of empirical incoherence for regions without spacetime is discussed.Comment: Forthcoming in Philosophy of Science; 13 page

Decentralization Estimators for Instrumental Variable Quantile Regression Models

The instrumental variable quantile regression (IVQR) model (Chernozhukov and Hansen, 2005) is a popular tool for estimating causal quantile effects with endogenous covariates. However, estimation is complicated by the non-smoothness and non-convexity of the IVQR GMM objective function. This paper shows that the IVQR estimation problem can be decomposed into a set of conventional quantile regression sub-problems which are convex and can be solved efficiently. This reformulation leads to new identification results and to fast, easy to implement, and tuning-free estimators that do not require the availability of high-level "black box" optimization routines

Omitted variable bias of Lasso-based inference methods: A finite sample analysis

We study the finite sample behavior of Lasso-based inference methods such as post double Lasso and debiased Lasso. We show that these methods can exhibit substantial omitted variable biases (OVBs) due to Lasso not selecting relevant controls. This phenomenon can occur even when the coefficients are sparse and the sample size is large and larger than the number of controls. Therefore, relying on the existing asymptotic inference theory can be problematic in empirical applications. We compare the Lasso-based inference methods to modern high-dimensional OLS-based methods and provide practical guidance

The fate of presentism in modern physics

There has been a recent spate of essays defending presentism, the view in the metaphysics of time according to which all and only present events or entities exist. What is particularly striking about this resurgence is that it takes place on the background of the significant pressure exerted on the position by the relativity of simultaneity asserted in special relativity, and yet in several cases invokes modern physics for support. I classify the presentist arguments into a two by two matrix depending on whether they take a compatibilist or incompatibilist stance with respect to both special relativity in particular and modern physics in general. I then review and evaluate what I take to be some of the most forceful and intriguing presentist arguments turning on modern physics. Although nothing of what I will say eventuates its categorical demise, I hope to show that whatever presentism remains compatible with empirical facts and our best physics is metaphysically repugnant.Comment: 23 pages, 4 figure

A quantum-information-theoretic complement to a general-relativistic implementation of a beyond-Turing computer

There exists a growing literature on the so-called physical Church-Turing thesis in a relativistic spacetime setting. The physical Church-Turing thesis is the conjecture that no computing device that is physically realizable (even in principle) can exceed the computational barriers of a Turing machine. By suggesting a concrete implementation of a beyond-Turing computer in a spacetime setting, Istv\'an N\'emeti and Gyula D\'avid (2006) have shown how an appreciation of the physical Church-Turing thesis necessitates the confluence of mathematical, computational, physical, and indeed cosmological ideas. In this essay, I will honour Istv\'an's seventieth birthday, as well as his longstanding interest in, and his seminal contributions to, this field going back to as early as 1987 by modestly proposing how the concrete implementation in N\'emeti and D\'avid (2006) might be complemented by a quantum-information-theoretic communication protocol between the computing device and the logician who sets the beyond-Turing computer a task such as determining the consistency of Zermelo-Fraenkel set theory. This suggests that even the foundations of quantum theory and, ultimately, quantum gravity may play an important role in determining the validity of the physical Church-Turing thesis.Comment: 27 pages, 5 figures. Forthcoming in Synthese. Matches published versio

Emergent spacetime and empirical (in)coherence

Numerous approaches to a quantum theory of gravity posit fundamental ontologies that exclude spacetime, either partially or wholly. This situation raises deep questions about how such theories could relate to the empirical realm, since arguably only entities localized in spacetime can ever be observed. Are such entities even possible in a theory without fundamental spacetime? How might they be derived, formally speaking? Moreover, since by assumption the fundamental entities can't be smaller than the derived (since relative size is a spatiotemporal notion) and so can't 'compose' them in any ordinary sense, would a formal derivation actually show the physical reality of localized entities? We address these questions via a survey of a range of theories of quantum gravity, and generally sketch how they may be answered positively.Comment: 18 pages, 1 figure, accepted for publication in Studies in History and Philosophy of Modern Physic

Recherche de l'expression de la lamine A et de la progérine chez des patients avec un syndrome myélodysplasique/syndrome myéloprolifératif avec thrombocytose

Les syndromes myélodysplasiques (SMD) et myéloprolifératifs (SMP) sont des maladies qui touchent les cellules souches de la moelle hématopoïétique. Les symptômes varient selon le sous-type de SMD ou SMP allant de l'anémie à la polyglobulie, de la leucopénie à la leucocytose et de la thrombopénie à la thrombocytose. Ces syndromes se développent à la suite de mutations acquises qui provoquent des anomalies des cellules souches. En outre, plusieurs études ont mis en évidence des anomalies de processus épigénétiques comme l'hyperméthylation de l'ADN et la déacéthylation des histones. La maladie de Hutchinson-Gilford ou progéria est provoquée par une mutation sur le gène de la lamine A (protéine de l'enveloppe nucléaire) qui a pour conséquence l'augmentation de l'utilisation d'un site de splicing normalement peu utilisé ce qui engendre une protéine anormale, la progérine. Cette protéine a pour effet de modifier les processus épigénétiques. Une étude récente sur des patients souffrant de progéria a révélé la présence d'une thrombocytose chez tous les patients. Le but du présent travail a été d'étudier l'expression de la lamine A et de la progérine chez les patients souffrant de SMD ou SMP avec une thrombocytose suivis par le Service d'hématologie du CHUV. Nous avons sélectionné parmi les patients souffrant de SMD ou SMP ceux avec une thrombocytose supérieure à 400 G/l au moment du diagnostic. Nous avons ensuite effectué une PCR pour détecter la lamine A et la mutation de la lamine A que l'on trouve dans la progéria. Sur les 33 patients sélectionnés, nous avons pu analyser les échantillons de 18 d'entre eux. Le matériel était issu de cellules mononucléées ou de granulocytes. Les résultats démontrent la présence de la lamine A et l'absence de la mutation trouvée dans la progéria chez 16 patients. Cependant, chez 2 patients, la PCR laisse suspecter la présence de progérine en plus de celle de la lamine A. D'autres investigations seront nécessaires pour confirmer cette dernière observation. S'il s'avère que la progérine est effectivement présente chez ces deux patients, il faudrait étendre l'analyse à d'autres patients avec une hémopathie maligne. Plusieurs publications rapportent l'absence de lamine A dans les cellules hématopoïétiques. Cependant, le présent travail démontre clairement que les cellules mononucléées du sang ou de la moelle osseuse de certains patients avec SMP/SMD expriment la lamine A. Nous n'avons toutefois pas étudié si la lamine A et, éventuellement la progérine, sont exprimées par les cellules hématopoïétiques normales. En conclusion, ce travail a révélé qu'il serait très intéressant d'étudier le rôle potentiel des lamines nucléaires et en particulier de la lamine A et de la progérine dans l'hématopoïèse et le développement des SMD/SMP et d'autres hémopathies malignes. Il a donc ouvert la voie pour de futurs projets de recherche

When the actual world is not even possible

Approaches to quantum gravity often involve the disappearance of space and time at the fundamental level. The metaphysical consequences of this disappearance are profound, as is illustrated with David Lewis's analysis of modality. As Lewis's possible worlds are unified by the spatiotemporal relations among their parts, the non-fundamentality of spacetime---if borne out---suggests a serious problem for his analysis: his pluriverse, for all its ontological abundance, does not contain our world. Although the mere existence---as opposed to the fundamentality---of spacetime must be recovered from the fundamental structure in order to guarantee the empirical coherence of the non-spatiotemporal fundamental theory, it does not suffice to salvage Lewis's theory of modality from the charge of rendering our actual world impossible