Asimina Arvanitaki (Perimeter Institute for Theoretical Physics, Canada)
Title: Particle Physics Beyond Colliders.
Abstract: Recently there have been several proposals of low-energy precision experiments that can search for new particles, new forces, and the Dark Matter of the Universe in a way that is complementary to collider searches. In this talk, I will present some examples involving ranging from atomic clocks, to astrophysical black holes accessible to LIGO.
Abhay Ashtekar (The Pennsylvania State University, USA)
Title: Loop Quantum Gravity: basics and some recent advances.
Abstract: In this talk I will first provide a broad overview of Loop Quantum Gravity, emphasizing the interplay between gravity, geometry and the quantum that lies at its foundation. This approach has resolved some of the fundamental issues that had been posed already in the 1970s, such as the quantum nature of geometry, singularity resolution and the consequent physics beyond Einstein, and formulation and resolution of physical questions in absence of a classical spacetime geometry. In contrast to, say, string theory where the focus has shifted to application of techniques from classical gravity to other areas of physics, we will see that, in loop loop quantum gravity, the focus continues to be on questions rooted in quantum gravity, proper. In the second part of the talk, I will discuss a few recent advances to illustrate that the approach has matured sufficiently to commence the creation of 2-way bridges between fundamental theory and observations.
Lisa Barsotti (MIT Kavli Institute - LIGO Laboratory, USA)
Title: The future of ground-based gravitational-wave detection: instruments and science.
Abstract: The era of gravitational-wave astrophysics started in 2015 with the first-ever detection of gravitational waves from a binary black hole system by the Laser Interferometer Gravitational-wave Observatory (LIGO). Since then, the network of ground-based gravitational-wave detectors has evolved to include the Virgo detector, with both LIGO and Virgo progressively improving their sensitivity. This global network of detectors has, as of this writing, observed more than 10 events. However, even when they reach their design sensitivity, the current instruments will only able to detect signals from a very small portion of the Universe. What would happen if we could improve their sensitivity by an order of magnitude, or more, and extend their astrophysical reach to the very edge of the Universe? In this talk I will describe the world-wide effort targeted at building more sensitive gravitational-wave detectors, and the main science targets of this next-generation network.
Katerina Chatziioannou (Flatiron Institute, New York, USA)
Title: Multimessenger astrophysics with gravitational waves.
Abstract: Less than two years ago, GW170817 brought the beginning of the era of multimessenger astrophysics with gravitational waves. In this talk I will give an overview of the unique opportunities, as well as the unique challenges, of multimessenger astrophysics. I will discuss the novel insights GW170817 has given us with an emphasis on results made possible thanks to the multimessenger nature of the signals we received. Finally, I will discuss recent results from the third observing run of the advanced detectors as well as future prospects as the network of gravitational wave detectors improves in sensitivity and expands in number.
Heino Falcke (Radboud Universiteit, Nijmegen, The Netherlands)
Title: Imaging the event horizon in the Galactic center and M87.
Abstract: When illuminated by ambient light, the event horizon of black holes will cast a dark shadow. For the supermassive black holes in the Galactic center and in M87, this shadow is detectable with the “Event Horizon Telescope” (EHT), a global mm-wave very long baseline interferometry experiment. The Galactic Center hosts a compact radio source, Sgr A*, with a mass of only 4 Million solar masses, determined precisely from stellar orbits. This gives a robust prediction for a shadow size, allowing detailed tests of general relativity there. However, the imaging is challenging due to rapid source variability and image blurring in the interstellar medium. Imaging of M87 is not affected by these effects, but the black hole mass is more uncertain. With advanced computer simulations the appearance of the sources and their shadows can be modelled and predicted in detail. A first global campaign of the EHT was successfully conducted in 2017 and the data is currently being analysed and we discuss here the first results.
Andrea Ghez (University of California, Los Angeles, USA)
Title: Our Galactic Center: A Unique Laboratory for the Physics & Astrophysicsof Black Holes.
Abstract: The proximity of our Galaxy's center presents a unique opportunity to study a galactic nucleus with orders of magnitude higher spatial resolution than can be brought to bear on any other galaxy. After more than a decade of diffraction-limited imaging on large ground-based telescopes, the case for a supermassive black hole at the Galactic center has gone from a possibility to a certainty, thanks to measurements of individual stellar orbits. The rapidity with which these stars move on small-scale orbits indicates a source of tremendous gravity and provides the best evidence that supermassive black holes, which confront and challenge our knowledge of fundamental physics, do exist in the Universe. This work was made possible through the use of speckle imaging techniques, which corrects for the blurring effects of the earth's atmosphere in post-processing and allowed the first diffraction-limited images to be produced with these large ground-based telescopes.
Further progress in high-angular resolution imaging techniques on large, ground- based telescopes has resulted the more sophisticated technology of adaptive optics, which corrects for these effects in real time. This has increased the power of imaging by an order of magnitude and permitted spectroscopic study at high resolution on these telescopes for the first time. With adaptive optics, high resolution studies of the Galactic center have shown that what happens near a supermassive back hole is quite different than what theoretical models have predicted, which changes many of our notions on how galaxies form and evolve over time. By continuing to push on the cutting-edge of high-resolution technology, we have been able to capture the orbital motions of stars with sufficient precision to test Einstein’s General theory of Relativity in a regime that has never been probed before.
Gabriela González (Louisiana State University, USA)
Title: Einstein, agujeros negros y ondas gravitacionales.
Abstract: Hace más de 100 años, Einstein predijo que el espacio-tiempo era dinámico, y había “ondas gravitacionales” que viajaban a la velocidad de la luz. El 14 de setiembre del 2015, los dos observatorios de LIGO en EEUU detectaron por primera vez una señal debida a ondas gravitacionales viajando a través de la Tierra, creadas hace unos 1,300 millones de años por el abrazo final de dos agujeros negros que habían estado bailando el tango. Desde entonces, hemos detectado varias señales más, incluyendo una con fuegos artificiales originadas por la colisión de dos estrellas de neutrones, ayudándonos a entender el origen de metales pesados (y preciosos). Voy a describir la larga e increíble historia de este descubrimiento, y el futuro de este nuevo campo de la astronomía.
Edward K. Porter, (Laboratory of Astroparticles and Cosmology, Paris, France)
Title: The detection of compact binary mergers using the Advanced LIGO andAdvanced Virgo detectors
Abstract: In September 2015, the Advanced LIGO and Advanced Virgo detectors began a series of science runs in the quest to discover gravitational waves. On the 14th of September 2015 the first detection of gravitational waves from the merger of a binary black hole was made. A further leap forward was made on the 17th of August 2017 with the detection of a binary neutron star merger, and the beginning of a new era of multi-messenger astronomy. In this talk, I will review the detections made as of the end of the second science run and highlight the implications of these detections in the fields of fundamental physics, astronomy and cosmology. I will also provide an update on the progress of the third science run, which began on April 1st 2019.
Abstract: The past few years have seen a lot of mathematical progress in general relativity. Some of the highlights include stability of black holes, stability of the Kerr Cauchy horizon, and the instability of the anti de-Sitter spacetime. There have also been various results concerning the structure of (null, spacelike and asymptotically self-similar) singularities. I will survey some of these results in the talk. In particular, I will explain how they provide insights on the nature of singularities in general relativity and the cosmic censorship conjectures.
Shiraz Minwalla (Tata Institute of Fundamental Research, India)
Title: Black Hole dynamics at large D.
Abstract: We demonstrate that black hole dynamics simplifies - without trivializing - in the limit in which the number of spacetime dimensions D in which the black holes live is taken to infinity. In the strict large D limit and under certain conditions we show the equations that govern black hole dynamics reduce to the equations describing the dynamics of a non gravitational membrane propagating in an unperturbed spacetime (e.g. flat space). We explore the possibility of using 1/D as an effective expansion parameter for studying black hole dynamics in a finite number of dimensions.
Paolo Pani (Università di Roma "La Sapienza", Italy)
Title: The unbearable lightness of spacetime: testing the nature of dark compact objects.
Abstract: Strong gravity just entered the precision era. Gravitational-wave and electromagnetic measurements of very compact objects allow us to probe into outstanding foundational issues, from he nature of dark matter, to the fate of spacetime singularities and the loss of unitarity in Hawking evaporation. According to General Relativity and Standard Model physics, all massive, dark and compact objects are black holes. Any observation suggesting otherwise would be evidence for new physics. We overview the viability of exotic compact objects, their peculiar signatures, and their observational status, including the experimental evidence for black holes with current and future experiments.
Rafael Porto (DESY, Germany)
Title: Progress in analytic methods for the two-body problem in gravity.
Abstract: Abstract: I review the status of the binary inspiral problem in the framework of the Post-Newtonian (PN) approximation in general relativity. The conservative dynamics has been recently talked to fourth order in the PN expansion by different methods: Arnowitt-Deser-Misner (ADM) Hamiltonian, Fokker action, and Effective Field Theory (EFT) approaches. In addition to ultraviolet (UV) divergences because of the point-particle approximation, infrared (IR) singularities arise due to subtleties in the separation between near and far zones at 4PN order. In this talk I will concentrate on how these are naturally handled within the EFT formalism, emphasizing the contrast with the other methodologies. I will illustrate how the gravitational binding energy at 4PN order includes a contribution from the 'tail effect' which resembles the celebrated factor of 5/6 and Bethe logarithm in the Lamb shift. I conclude with the challenges ahead and future probes of 'new physics' using gravitational wave precision data.
Eva M. Silverstein (Stanford University, USA)
Title: Accelerated expansion in cosmology: problems and progress.
Abstract: The accelerated expansion of the universe offers new observational handles on high energy physics and demands a more complete framework for quantum gravity. After summarizing the basic observations and theoretical implications, I will overview some recent developments. A combination of analytic and numerical general relativistic calculations have extended the range of initial conditions consistent with early universe inflation. In string theory, metastable accelerated expansion plausibly results from an interplay of highly structured energy sources. The resulting geometry contains horizons, which play a key role in seeding structure, while raising basic conceptual questions. The anti-de Sitter/conformal field theory duality, which formulates quantum gravity in terms of quantum field theory, does not directly apply. We show how it can be upgraded in a way that preserves some essential features, leading to a statistical interpretation of the Gibbons-Hawking de Sitter horizon entropy in terms of an entanglement entropy in the dual description. Moving from thought experiments back to empirical ones, we describe a variety of new calculations of primordial non-Gaussianity by various groups, including effects of the tails of the non-Gaussian distribution which can enhance primordial black hole formation over a range of mass scales.
Stephen Taylor (California Institute of Technology, United States of America)
Timothy Pennucci (Eötvös Loránd University, Hungary)
Title: Pulsar Timing Arrays: The next frontier of gravitational wave astronomy.
Abstract: Gravitational-wave detectors are yielding a bounty of observations, and revolutionising our understanding of stellar-mass black holes. But what about the supermassive black holes that lurk at the heart of massive galaxies? These titans form binaries over cosmic time as a byproduct of hierarchical galaxy growth, emanating gravitational waves in the nanohertz sensitivity band of networks of Milky Way millisecond pulsars. Pulsar-timing arrays (PTAs) like the North American Nanohertz Observatory for Gravitational waves (NANOGrav), the European Pulsar Timing Array (EPTA), the Parkes Pulsar Timing Array (PPTA) and the fusion of these efforts into the International Pulsar Timing Array (IPTA), are poised to chart this new frontier of gravitational wave discovery within the next several years. With this new window onto the warped Universe, PTAs will bring a sea-change in our understanding of supermassive binary black-hole demographics and dynamical interactions.Combined with electromagnetic signatures of binary AGN in upcoming time-domain synoptic surveys, PTAs will extend the arena of multi-messenger astronomy to the most massive black holes in the Universe. Additionally, pulsar-timing arrays are currently placing compelling constraints on modified gravity theories, cosmic strings, and ultralight scalar-field dark matter. I will review the current status of PTA searches, and present some milestones on the road to the exciting next decade and beyond of PTA discovery.
Mark Van Raamsdonk (University of British Columbia, Canada)
Title: Gravitational physics from quantum information constraints.
Abstract: In this talk, I will review some of the remarkable connections between gravitational physics and the physics of entanglement in conformal field theories. I will describe how the structure of entanglement in a conformal field theory can be captured by the geometry of an asymptotically AdS spacetime, and how constraints on entanglement imply (at least to second order in perturbation theory around AdS) that this spacetime must satisfy Einstein’s equations. Further quantum information theoretic constraints suggest new results in classical gravity, including a family of positive energy theorems for gravitational subsystems.
Abstract: Over the past 20 years cosmology has made the transition to a precision science: the standard cosmological model has been established and its parameters are now measured with unprecedented precision. This model successfully describes observations from widely different epochs of the Universe, from primordial nucleosynthesis all the way to the present day. However, there is a big difference between modelling and understanding. The next decade will see the era of large surveys; a large coordinated effort of the scientific community in the field is on-going to map the cosmos producing an exponentially growing amount of data. I will discuss expectations, challenges, hopes, and even possible surprises from these surveys.
Abstract: The "analogue spacetime" programme uses various physical analogues (typically condensed matter analogues) to simulate kinematic aspects of general relativity --- that is, curved spacetimes up to and including horizons, and free quantum fields defined thereupon, but not the dynamical Einstein equations. From a theoretical perspective this is enough to simulate Hawking radiation, (which is a purely kinematic effect), but not Bekenstein entropy, (which is an intrinsically dynamic effect depending on the Einstein equations.) A number of experiments have now been carried out (surface waves on water, photons in nonlinear optics, phonons in Bose-Einstein condensates) that probe various aspects of the (analogue) Hawking radiation process. I will give abroad overview of the experiments performed to ate, salient points of the underlying theory, and discuss what we can and cannot learn from this analogue Hawking radiation effect.
William Joseph Weber (University of Trento, Italy)
Title: From LISA Pathfinder to LISA: preparing for gravitational wave observation from space.
Abstract: LISA, the Laser Interferometer Space Antenna, has been selected by ESA to be the Cosmic Vision L3 "large" mission. It promises to open the field of gravitational wave observation in the band from tens of microHertz to near 1 Hz, a low frequency window that is only accessible from space, rich in sources from both inside our galaxy and out to cosmological distances. LISA is slated for an early 2030s launch and is currently in the phase A of development, building off the success of the “Einstein geodesic explorer” mission LISA Pathfinder. In this talk we present the science that LISA can do, the measurement science heritage from LISA Pathfinder demonstrator mission's interferometric measurement of the relative acceleration between two free-falling test masses, and the unique experimental challenges presented by the full 3 spacecraft LISA observatory.
Clifford M. Will (University of Florida, Gainesville, USA)
Title: Stars askew in the heavens: the centenary of Eddington's eclipse expeditions.
Abstract: One hundred years ago this May, Arthur Stanley Eddington and colleagues measured the bending of starlight by the Sun. The announcement of the results made Einstein an overnight international celebrity and set the stage for a century of putting his theory to the test of experiment. The story of gravity’s effect on light is one of the most fascinating in all of science. It dates back to the 18th century, and its chapters feature great scientific achievements as well as racist propaganda. The saga continues to the present, with gravitational lenses, event horizon imaging and even movie Oscars! We present a scientific and historical overview of this story, concluding with a visit to the Sundy Farm on the island of Principe, exactly 100 years after Eddington’s day in the (eclipsed) Sun.