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Guy Consolmagno (Specola Vaticana)17/06/2024, 09:00
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Dominique Lambert (University of Namur)17/06/2024, 09:40
The aim of the talk is to explain, with some historical details, where the concept of Lemaître’s Primeval Atom Hypothesis (1931) came from. We will confront this Hypothesis with his studies (1933-1940) on the initial singularity (and the way to avoid it) and also on the Cosmological Constant, as well as on the Cosmic Rays. We will show how all these intuitions and studies are supported by...
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Claus Kiefer (U)17/06/2024, 10:20
In 1933, Georges Lemaître published a solution of Einstein's equation describing spherically symmetric dust clouds. This is nowadays often called the Lemaître-Tolman-Bondi (LTB) solution and used, in particular, to describing the gravitational collapse of a dust cloud. In my talk, I shall discuss the quantization of this model. A full theory of quantum gravity is not yet available, but...
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Alexander Kamenshchik17/06/2024, 11:30
We discuss the problem of singularity crossing in isotropic and anisotropic universes. We study the conditions on the disappearance of singularities in quantum cosmology and the behaviour of quantum particles in the vicinity of singularities. Some and attempts to develop general approach to the connection between the field reparametrization and the elimination of singularities will be...
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Raphael Bousso (University of California, Berkeley)17/06/2024, 12:10
Our search for a quantum theory of gravity is aided by a unique and perplexing feature of the classical theory: General Relativity already “knows” about its own quantum states (the entropy of a black hole), and about those of all matter (via the covariant entropy bound). The results we are able to extract from classical gravity are inherently nonperturbative and increasingly sophisticated....
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Theodore Jacobson (University of Maryland)17/06/2024, 15:00
Gibbons and Hawking's gravitational partition function remains enigmatic, despite nearly 50 years and much evidence that it indeed counts quantum states. I will discuss steps toward a better understanding of the topology of the paths, the (initially Lorentzian) contour of integration, the counted states, and why a semiclassical treatment can capture that count.
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Renate Loll (Radboud University Nijmegen)17/06/2024, 15:40
Where may genuinely new insights on the origin of our universe still come from today? Is there an unexplored part of theory space not beset by countless ambiguities, free parameters or ad-hoc assumptions? I will argue that this place is full, nonperturbative quantum gravity based on the gravitational path integral. It requires geometry beyond Riemann, but sticks with the fundamental tenets of...
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Prof. Roberto Casadio (Bologna University)17/06/2024, 16:50
It is often assumed that quantum gravity belongs at the Planck scale, but a possibly much larger size for the ground state emerges in the (non-perturbative) quantisation of the Oppenheimer-Snyder model of dust collapse that naturally hints at Bekenstein’s area law. The effective geometry for such quantum black holes can then be obtained which describe integrable singularities without inner horizons.
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17/06/2024, 17:30
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Michael Turner (University of Chicago)18/06/2024, 09:00
LCDM is the most expansive and most successful cosmological paradigm yet. It is supported by a wealth of precision data and observations, with many successes to its credit. However, it is incomplete: what is the nature of dark energy and the identity of the dark matter particle?; absence of a first principles model for inflation with supporting evidence, and firm ideas about the...
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Joseph Silk (Paris, Inst. Astrophys. and Johns Hopkins U. and Oxford U.)18/06/2024, 09:40
Remarkable progress has been made in precision cosmology since the pioneering choices laid out a century ago by Lemaitre, yet we are currently at a turning point. Experiments have become so large and expensive that we need to prioritize where to go next for compelling and guaranteed science return that is significantly beyond current limits in cosmology. The lunar surface allows a unique way...
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Licia Verde18/06/2024, 10:50
The Hubble-Lemaitre parameter not only relates redshifts to distances in the nearby Universe, it is also a key parameter of the standard cosmological model. H0 affects several physical processes, different cosmic epochs and multiple observables. There are more than a dozen ways to measure H0, which with few exceptions, yield values that gather around two "camps" which do not agree with each...
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Wendy Freedman (University of Chicago)18/06/2024, 11:30
I will describe new results from a major JWST program to improve measurements of the Hubble constant. The 10 times greater sensitivity and 4 times higher resolution of JWST in the near-infrared provide a powerful means of addressing challenges in previous measurements of the extragalactic distance scale. Distances to a sample of Type Ia supernova hosts have been measured using three...
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Patrick Brady18/06/2024, 12:10
Brady will describe the current state of ground-based, gravitational-wave astronomy and the prospects for the future. He will present highlights from LIGO-Virgo-KAGRA observations with an emphasis on their cosmological implications. Gravitational waves from black-hole-binary mergers are now being detected about twice per week and astronomers are eagerly awaiting the next multi-messenger event....
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Adam Riess (John Hopkins University)18/06/2024, 15:00
We present high-definition observations with the James Webb Space Telescope of Cepheid variables used to calibrate the luminosity of Type Ia Supernovae and the Hubble constant. The superior resolution of JWST negates crowding noise, the largest source of variance in the NIR Cepheid Period-Luminosity relations (Leavitt laws) measured with HST. Together with the use of two-epochs to constrain...
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Daniel Sudarsky (Universidad Nacional Autonoma de Mexico)18/06/2024, 15:40
We will discuss aspects of the gravity/quantum interphase and the type approaches that can be adopted in its exploration. In so doing we will be forced to consider conceptual difficulties in quantum theory which reveal a fundamental difficulty that must be faced in that pursuit. We will present a path designed to overcome them, and explore some of its implications for cosmology, including the...
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Roger Penrose (Mathematical Institute, Oxford)18/06/2024, 16:50
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18/06/2024, 17:30
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Misao Sasaki19/06/2024, 09:00
Thanks to the rapid progress in gravitational wave astronomy/cosmology, primordial black holes (PBHs) have become one of the hot topics in cosmology. It has made projections of detecting signatures of PBHs feasible. In parallel, it has become clear that there exist a number of ways to produce PBHs from inflation. In this talk, I'll review the PBH formation from inflation and the associated...
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Andrei Linde19/06/2024, 09:40
I will briefly describe the basic principles of inflationary theory, and then I will discuss a set of simple inflationary models, such as Starobinsky model, Higgs inflation and alpha-attractors, which can describe all presently existing inflation-related observational data using no more than one or two parameters. Generalized versions of these models may also describe dark energy and...
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Gia Dvali19/06/2024, 10:50
We discuss implications of an universal phenomenon of ``memory burden", which implies that information carried by a system tends to stabilize it. The effect is maximally prominent in objects of high microstate degeneracy. We discuss implications of this effect for black holes and for de Sitter cosmology. The memory burden effect leads to a slow-down of black hole decay, the latest by the time...
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Hiroshi Oguri19/06/2024, 11:30
Recently, it has become increasingly clear that there are constraints on the low-energy effective theories of quantum gravity that cannot be captured by the standard Wilsonian paradigm. For gravitational theories in asymptotically anti-de Sitter spacetimes, we can formulate such constraints and aim to prove or falsify them using the AdS/CFT correspondence. I will review recent progress in this...
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Cumrun Vafa (Harvard University)19/06/2024, 12:10
Motivated by principles of quantum gravity learned from string theory, we contemplate on the fate of our universe. In particular we explain why the dark energy is expected to decay and with it the Universe will undergo a transition to a new state, which is expected to take place not too far in the future.
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Thomas Hertog (KULeuven)19/06/2024, 15:00
Georges Lemaître saw in the quantum birth of the universe also an epistemic horizon, a notion he somewhat poetically expressed in his primeval atom hypothesis. In this he differed from both Einstein and Eddington, and from present-day proponents of the multiverse. I present a novel holographic version of the Hartle-Hawking no-boundary proposal for the origin of the universe and I argue that...
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William Unruh (University of British Columbia)19/06/2024, 15:40
Is there a quantum to classical transition in physics somewhere between the microscopic to macroscopic? What is microscopic and macroscopic? Assuming we model macroscopid as the mass of size of the system, and using techniques I suggested in the early 80's, it is now known that the Ligo mirrors (40Kg, .5 m in size) center of mass motion is quantum. This talks will take us through simple model...
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Maria Sakellariadou19/06/2024, 16:50
I will first review how gravitational waves (transients or searches for a gravitational-wave background) are used to constrain particle physics models beyond the Standard Model, early Universe cosmological scenario, or dark matter candidates. I will then discuss the angular power spectrum of gravitational-wave transient sources as a probe of the large-scale structure.
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19/06/2024, 17:30
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20/06/2024, 06:15
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Edward Witten (Department of Physics-Princeton University-Unknown)21/06/2024, 09:00
I consider the algebra of observables along the worldline of an observer as a background independent algebra in the context of quantum gravity or cosmology.
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Gabriele Veneziano21/06/2024, 09:40
The equations of classical (i.e. tree-level) string cosmology in $(d+1)$-dimensional spacetimes with $d$ abelian isometries are well known to be invariant under an O(d,d;R) group of transformations acting on the metric, dilaton and antisymmetric-tensor fields. This symmetry has recently allowed for an all-order classification of higher-derivative ($\alpha ‘$) corrections by Hohm and Zwiebach....
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Michele Cicoli (Università di Bologna)21/06/2024, 10:50
I will discuss recent progress in constructing models of inflation and dark energy from string theory which are theoretically robust, can fit current data and can lead to observable predictions. I will mention 3 possibilities for the inflaton field: a Kaehler modulus, an axion and a brane modulus. I will also argue that axions are the best candidates to drive dark energy.
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Thibault Damour (nstitut des Hautes Etudes Scientifiques)21/06/2024, 11:30
Gravitational wave signals from coalescing binary black holes are detected, and analyzed, by using large banks of template waveforms. The construction of these templates makes an essential use of the analytical knowledge of the motion and radiation of gravitationally interacting binary systems. A new angle of attack on gravitational dynamics consists of considering (classical or quantum)...
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Eric Poisson (University of Guelph)21/06/2024, 12:10
One of the most exciting prospects of gravitational-wave astronomy is to measure the tidal deformability of neutron stars and convert these measurements into constraints on the equation of state of nuclear matter at very high densities. I describe the ongoing effort by many researchers to model the tidal interactions between compact bodies in binary inspirals, which involves the strong...
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Lajos Diosi (Wigner Research Centre for Physics)21/06/2024, 15:00
Unified theory of space-time with quantized matter and the physics of quantum measurement were considered unrelated for long time, studied by two separate research communities. Quantum cosmologists have always been part of main stream physics, using heavy artillery of mathematics. Quantum measurement problem solvers, with the speaker among them, used light weapons and sometimes whimsical...
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Michele Cicoli (Università di Bologna)21/06/2024, 15:40
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21/06/2024, 21:00
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Seminario di Albano Laziale
Piazza S. Paolo, 5, 00041 Albano Lazialehttps://maps.app.goo.gl/bxmSJh7SbSmqgisdA
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