[Reminder, starting in a few minutes !] 23/06/2022 – Jean-Jacques Szczeciniarz: Elements of Penrose’s Conform Cyclic Cosmology

The question I would like to enter upon with you is the question of the coherence and  of the significance of the Cosmology according to R. Penrose. The basic question he poses is the issue of how our universe happened to come about with a Big Bang that was extraordinary special-yet special in what appears to have been a very particuliar way where, with regard to gravity, its entropy was enormlously low in comparaison with what it might have been, but the entropy was close to maximum in every other respect. The issue has to do with  the origin of the Second Law and with the evident fact that the entropy of our universe seems to be vastly increasing, despite the fact that the very early universe and the very remote future appear to be umconfortably similar to one another.  In order to clear up these  mysteries Roger Penrose proposes a new scheme, that is a new scenario : the conformal cyclic cosmology (CCC) theory of which I will give elements of the construction.  

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[Zoom link updated !] 23/06/2022 – Jean-Jacques Szczeciniarz: Elements of Penrose’s Conform Cyclic Cosmology

The question I would like to enter upon with you is the question of the coherence and  of the significance of the Cosmology according to R. Penrose. The basic question he poses is the issue of how our universe happened to come about with a Big Bang that was extraordinary special-yet special in what appears to have been a very particuliar way where, with regard to gravity, its entropy was enormlously low in comparaison with what it might have been, but the entropy was close to maximum in every other respect. The issue has to do with  the origin of the Second Law and with the evident fact that the entropy of our universe seems to be vastly increasing, despite the fact that the very early universe and the very remote future appear to be umconfortably similar to one another.  In order to clear up these  mysteries Roger Penrose proposes a new scheme, that is a new scenario : the conformal cyclic cosmology (CCC) theory of which I will give elements of the construction.  

23/06/2022 – Jean-Jacques Szczeciniarz: Elements of Penrose’s Conform Cyclic Cosmology

The question I would like to enter upon with you is the question of the coherence and  of the significance of the Cosmology according to R. Penrose. The basic question he poses is the issue of how our universe happened to come about with a Big Bang that was extraordinary special-yet special in what appears to have been a very particuliar way where, with regard to gravity, its entropy was enormlously low in comparaison with what it might have been, but the entropy was close to maximum in every other respect. The issue has to do with  the origin of the Second Law and with the evident fact that the entropy of our universe seems to be vastly increasing, despite the fact that the very early universe and the very remote future appear to be umconfortably similar to one another.  In order to clear up these  mysteries Roger Penrose proposes a new scheme, that is a new scenario : the conformal cyclic cosmology (CCC) theory of which I will give elements of the construction.  

19/05/2022 – Niels Martens : Philosophy of Dark Matter

This presentation will start with a brief overview of the recent literature on the philosophy of dark matter, which has been steadily growing over the past two decades. We then focus on the question of what the dark matter research programme and its main alternative, modifications of gravity, can teach us about the distinction between (dark) matter and modified gravity/spacetime. Interesting in this regard is a small recent trend of hybrid dark matter/ modified gravity theories. We provide a conceptual analysis of a popular hybrid theory, Berezhiani & Khoury’s superfluid ‘dark matter’ theory. We investigate the senses in which the single novel entity postulated by such theories can be both dark matter and modified gravity, which leads to three groups of possible ontological interpretations of hybrid theories. We conclude that hybrid theories push back against the Democritean-Newtonian tradition of assuming a strict conceptual dichotomy between (dark) matter and spacetime/gravity, thereby opening up theory space.

21/04/2022 – Gilles Cohen-Tannoudji and Jean-Pierre Gazeau : From Lemaître’s primitive atom to the Higgs boson, the challenge of a scientific cosmogony may be about to be met.

In his 1946 book The Primitive Atom Hypothesis - Essay on Cosmogony (currently being republished), Georges Lemaître, Catholic priest and eminent scientist considered as the father of modern cosmology, challenges a scientific cosmogony that stands out from pre-scientific, mythological or theological cosmogonies. Is this challenge about to be met thanks to recent advances in observational astrophysics and the epistemology of quantum physics? That's what we think and what we try to convince you of.

24/03/2022 – Lydia Patton: Theories and Parameters in Testing Frameworks for General Relativity

Modeling methods in gravitational wave astronomy (GWA) are, understandably, geared toward detection and confirmation. Focus on GWA as a platform for testing reveals the need for a broader framework of analysis, showing how the background theory can be investigated. The paper begins with the problem of testing general relativity (GR) through astronomy, especially the role of parameters in theory testing.  The paper concludes with an analysis of recent testing methods. Yunes and Pretorius caution that a fundamental bias may be present due to the assumption of the correctness of general relativity built in to the methods, and propose  parametrized post-Einsteinian (PPE) framework for testing 'generic' deviations from GR’s predictions.  Mukherjee, Wandelt, and Silk propose another approach using the BAO scale to measure possible differences between EM and GW luminosity distance. In both cases, the use of parameters in the context of physics-informed modeling is analyzed as a basic method.

03/02/2022 – Emily Thomas: From Unreal to Real Time: British Metaphysics 1870s-1920s

Around the turn of the twentieth century, British metaphysics of time saw two major changes. First, from the 1870s to 1900s, philosophers became convinced time was unreal. Philosophers en masse denied the reality of time, from F. H. Bradley to J. M. E. McTaggart. Second, from the 1890s onwards, philosophers began to embrace time, developing newfangled theories. The early theories of Victoria Welby, F. C. S. Schiller, Bertrand Russell, and Samuel Alexander, conceived time to be static. The later theories of C. D. Broad, Arthur Eddington, Susan Stebbing, R. G. Collingwood, and many others, conceived time to be dynamic. This broad-brush, big ideas paper asks, Why did these two changes occur? It explores the role of biological evolution, the spatialisation of time, and temporal psychology; and asks how the ongoing debates between static and dynamic theories got started.

25/11/2021 – Claus Beisbart: How can cosmological simulations shown to be credible? Perspectives from the literature on validation and verification

How credible are simulation results, in particular in cosmology where data is sparse? The last decade has seen intensified attempts to clarify the evaluation of simulations quite generally. In particular, researchers from disciplines such as fluid dynamics and engineering distinguish between validation and verification and try to make both methods more rigorous. But does their approach make sense in cosmology? The aim of this talk is to compare current practice in cosmology with the demands of simulation assessment in engineering. I argue that these demands define something like an ideal benchmark, which is difficult to attain though in cosmology.