On this page you can find links to video of all the lectures given in the summer school that we ran June 26-July 1 2022, in Morzine, France. You can watch them all in the order they were presented, following the program virtually, if you like: the links in the following schedule will take you to the titles and abstracts, and links to the lectures. Or you can just scroll down to find lectures that interest you.
On Sunday, 26 June 2022, we will start the summer institute with the poster session + welcome reception from 18:30 to 20:00, when we will be going to dinner.
|MON, 27 June||TUE, 28 June||WED, 29 June||THU, 30 June||FRI, 1 July|
|09:00-10:30||Wallace 1||Sakellariadou 1||Wallace 2||Smeenk 2||Rapporteur session (10:00-12:00)|
|10:30-11:00||Coffee break||Coffee break||Coffee break||Coffee break|
|11:00-12:30||Wüthrich||Smeenk 1||Crowther 2||Sakellariadou 2|
|14:00-15:30||Working groups||Working groups||Hike, free time||Working groups||Departure|
|16:00-16:30||Coffee break||Coffee break||Coffee break|
Abstracts of Lectures (alphabetical)
Karen Crowther (University of Oslo)
Principles play various roles in theory construction and assessment in QG, and different approaches to QG utilise different principles in different ways. In the first part of the talk I introduce the idea of principles in QG, and in the second part of the talk, I explore the possible role of the holographic principle in the development of QG.
Lecture 2: Four Attitudes Towards Singularities in Search for a Theory of QG (slides same as for first lecture, YouTube video)
This lecture explores four different attitudes that we might have towards singularities in the search for a theory of QG. It uses examples from the physics literature to show how these different attitudes towards various singularities can lead to different scenarios for the new theory. The lecture also discusses the more general issue of finding and evaluating constraints upon any new theory of QG.
Nick Huggett (University of Illinois Chicago)
The characteristic – Planck – energy scale of quantum gravity is utterly beyond current technology, making experimental access to the relevant physics apparently impossible. Nevertheless, low energy experiments linking gravity and the quantum have been undertaken: the Page and Geilker quantum Cavendish experiment, and the Colella-Overhauser-Werner neutron interferometry experiment, for instance. However, neither probes states in which gravity remains in a coherent quantum superposition, unlike — it is claimed — recent proposals that have created considerable interest among physicists. In essence, if two initially unentangled subsystems interacting solely via gravity become entangled, then a simple theorem of quantum mechanics shows that gravity cannot be a classical subsystem. There are formidable challenges to creating such a system, but remarkably, tabletop technology into the gravitational fields of very small bodies has advanced to the point that such an experiment might be feasible in the next several years. In this talk I will explain the proposal and what it aims to show, highlighting the important ways in which its interpretation is theory-laden. (Drawn from joint work with Niels Linnemann and Mike Schneider.)
- Huggett, Nick, Niels Linnemann, and Mike Schneider. “Quantum gravity in a laboratory?.” arXiv preprint: 2205.09013 (2022).
Mairi Sakellariadou (King’s College London)
After presenting the standard cosmological model based on General Relativity, I will highlight some open questions and discuss the inflationary paradigm from a critical point of view. I will argue that we need a theory of quantum gravity and that cosmology is the ideal test bed for a quantum theory of spacetime geometry. I will then briefly review different approaches to quantum gravity and discuss possible tests through cosmological/astrophysical implications. I will end with some criticisms, open questions, debates on quantum gravity proposals and phenomenological cosmological models.
Chris Smeenk (Western University Canada)
There is a sharp divide between different ways of approaching a theory of the origins of the universe. One approach aims to select an initial state in some sense, rather than treating initial conditions as merely contingent facts. This ‘selection’ takes several forms, ranging from constraints needed to account for thermodynamic asymmetries (versions of the ‘Past Hypothesis’), to new theoretical principles that select a specific state (such as the no boundary proposal, or the more recent CPT symmetric universe), to (more controversially) anthropic selection from an ensemble. The opposing approach aims to minimize the impact of the initial state, by showing that dynamics with appropriate features will generate an output state with desirable features for suitably ‘generic’ initial conditions. The aim of the first lecture is to provide an overview of the more philosophical aspects of these debates, and develop an argument current versions of ‘dynamical’ theories are not self-sufficient: they require substantive constraints on the initial states, and hence require some appeal to selection.
Inflationary cosmology proposes that the universe passed through a transient phase of exponential expansion in the early universe, leading to several characteristic features in the post-inflationary state. Inflation has been the dominant account of this phase of the universe’s history for nearly four decades, based on its phenomenological success. It remains a ‘paradigm’ in that a wide range of inflationary models are compatible with observations, but there is no single canonical model. After briefly reviewing standard lore regarding inflation, I will focus on two foundational questions regarding inflation. First, how should we characterize inflation’s success in matching observations of the early universe, and to what extent does this support the theory? Second, how does inflation relate to theories of quantum gravity? More specifically, to what extent does inflation require assumptions about the pre-inflationary state or ‘trans-Planckian’ modes, and can inflationary models be consistently treated as low-energy effective field theories?
Francesca Vidotto (Western University Canada)
To select the principles guiding the construction of a quantum theory of gravity, we need to select what we consider the fundamental aspect of respectively the quantum theory and the spacetime one. I focus on discreteness as the core aspect of the quantum theory, and on the identification of spacetime as a dynamical (gauge) field in general relativity. These principles lead to loop quantum gravity. By highlighting these principles, we can clarify questions such as spacetime emergence and the disappearance of Newtonian time in quantum gravity. I give a brief overview of the theory, discussing the covariant formulation of the theory. This gives transition amplitudes that provides a tool for concrete physical computation. I mention the principal applications such as the graviton propagator or the black-hole transition into a white hole. The application to cosmology is the main topic of a separate lecture.
Lecture 2: The Path to Quantum Cosmology (cancelled)
In the history of the development of quantum gravity, quantum cosmology has represented at first a simplified framework to study the quantization. Cosmological symmetries allow to reduce the infinite degrees of freedom of general relativity to a few, that can be quantized. Loop quantum cosmology is a successful example of how this has led to both a better understanding of the theory and, most importantly, to several observational predictions. Vice versa, in this lecture I discuss the path to extract cosmological predictions starting from the full covariant loop quantum gravity dynamics. I focus on the general way to understand singularity resolution in the theory, and the current effort to compute primordial quantum fluctuations. These research directions are made possible by the strong conceptual backup provided by the principles discussed in the first lecture, probing once more the role philosophical stances play in the theory construction.
David Wallace (University of Pittsburgh)
I will give a conceptually-focussed presentation of `low-energy quantum gravity’ (LEQG), the effective quantum field theory obtained from general relativity and which provides a well-defined theory of quantum gravity at energies well below the Planck scale. I will emphasize the extent to which some such theory is required by the abundant observational evidence in astrophysics and cosmology for situations which require a simultaneous treatment of quantum-mechanical and gravitational effects, contra the often-heard claim that all observed phenomena can be accounted for either by classical gravity or by non-gravitational quantum mechanics, and I will explain how a treatment of the theory as fluctuations on a classical background emerges as an approximation to the underlying theory rather than being put in by hand. I will briefly discuss the search for a Planck-scale quantum-gravity theory from the perspective of LEQG and/or give an introduction to the Cosmological Constant problem as it arises within LEQG.
- D.Wallace, “Quantum gravity at low energies”, https://arxiv.org/abs/2112.12235
I distinguish between two versions of the black hole information-loss paradox. The first arises from apparent failure of unitarity on the spacetime of a completely evaporating black hole, which appears to be non-globally-hyperbolic; this is the most commonly discussed version of the paradox in the foundational and semipopular literature, and the case for calling it `paradoxical’ is less than compelling. But the second arises from a clash between a fully-statistical-mechanical interpretation of black hole evaporation and the quantum-field-theoretic description used in derivations of the Hawking effect. This version of the paradox arises long before a black hole completely evaporates, seems to be the version that has played a central role in quantum gravity, and is genuinely paradoxical.
- D. Wallace, “Why black hole information loss is paradoxical”, https://arxiv.org/abs/1710.03783.
- D. Harlow, “Jerusalem lectures on black holes and quantum information”, https://arxiv.org/abs/1409.1231.
- S. Mathur, “The black hole information loss paradox: a pedagogical introduction”, https://arxiv.org/abs/0909.1038.
- G. Belot, J. Earman and L. Ruetsche, “The Hawking information loss paradox: the anatomy of controversy”, https://www.journals.uchicago.edu/doi/10.1093/bjps/50.2.189.
Christian Wüthrich (University of Geneva)
Our best theoretical framework for understanding black holes suggests that black hole emit Hawking radiation. The trouble with this hypothesis is that the predicted Hawking radiation of astrophysical black holes is way too tiny to be detectable against the fluctuations of the cosmic microwave background radiation. In this context, so-called ‘analogue experiments’ involving for example ‘dumb holes’ in fluids and Bose-Einstein condensates have recently been promoted as means of confirming the existence of Hawking radiation in real black holes. The proposal of analogue gravity has led to a lively debate in philosophy of science about the possibility of actually confirming hypotheses on inaccessible target systems such as astrophysical black holes. I will review this debate and comment on some of the most recent developments.
- K. Crowther, N. Linnemann, C. Wüthrich. What we cannot learn from analogue experiments. Synthese 198 (2021): S3701-S3726. https://link.springer.com/article/10.1007/s11229-019-02190-0.
- R. Dardashti, K.P.Y. Thébault, E. Winsberg. Confirmation via analogue simulation: what dumb holes could tell us about gravity. British Journal for the Philosophy of Science 68 (2017): 55-89. https://www.journals.uchicago.edu/doi/abs/10.1093/bjps/axv010.
- P.W. Evans and K.P.Y. Thébault. On the limits of experimental knowledge. Philosophical Transactions of the Royal Society A378 (2020): 2177. https://royalsocietypublishing.org/doi/epdf/10.1098/rsta.2019.0235.