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...
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....
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.
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...
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.
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...
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...
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...
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...
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...
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.
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...
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.
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.
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)...
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...
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...
