On this page you can find links to video of all the lectures given in the summer school we ran, June 19-24 2016, in Lake Geneva, Wisconsin. You can watch them all, in the order they were presented, following the syllabus virtually, if you like: the links in the following schedule will take you to the titles and abstracts, and links to the lectures. (Sorry, meals not provided!) Or you can just scroll down to find lectures that interest you.
|2.00-4.00||breakout groups||breakout groups||breakout groups||free||round table
|4.30-5.50||Rovelli||participant talks||Minic||free||groups 2.30-4.30|
Do we need to quantize gravity, as it is tacitly assumed in much of fundamental physics? Even though the standard lore falls short of justifying an affirmative answer, the fact that matter is not classical requires our going beyond general relativity. Though conclusive in this respect, this fact offers no guidance as to the direction in which a quantum theory of gravity must be sought. Despite its being unobserved to date, Hawking radiation and black hole thermodynamics is widely considered our firmest hint, weak though it may be. As the theoretical derivation of Hawking radiation and black hole thermodynamics relies on a semi-classical mélange of physical principles, it raises the question of whether we need the unified blend of a full quantum theory of gravity at all, particularly given that the latter is generally expected to reject at least some of the principles of the former. Although this issue is not settled, it seems as if the difficulties in articulating a semi-classical theory can only be overcome in full quantum gravity.
This will lead us to the second part of my talk, in which I will sketch some of the philosophical and foundational problems that come up in quantum gravity and that will be addressed in various lectures and discussions throughout the week. The vantage and focal point for many of these issues will be the apparent disappearance of spacetime in full quantum theories of gravity.
As for readings, some of the things I will discuss in the two parts are covered in the following papers (maybe the third in particular might serve as preparation):
- Nick Huggett and Craig Callender (2001). Why quantize gravity (or any other field for that matter)?. Philosophy of Science 68: S382-S394.
- Christian Wüthrich (2005). To quantize or not to quantize: fact and folklore in quantum gravity. Philosophy of Science 72: 777-788.
- Nick Huggett and Christian Wüthrich (2013). Emergent spacetime and empirical (in)coherence. Studies in the History and Philosophy of Modern Physics 44: 276-285.
- Mon AM2: Ismael, “Seeing Space”
I take it for granted that we have immediate awareness of the visible and tangible reality of space. But it is more subtle than one might think to say exactly what that means and the constraints that it places on physics. The first talk will look at what the visible and tangible reality of space amounts to. I will look at the role that space plays in our experience, and the connection between space and objectivity, at how the mind stabilizes a conception of an external, spatially organized world out of regularities in experience. I will talk about how the brain coordinates visual, tactual and sensorimotor information and stabilizes a conception of space as the common arena of both perception and action.
There is no required reading, but if you want to have a peek at Mach, Space and Geometry, or Rick Grush, “Self, World and Space: The Meaning and Mechanisms of Ego- and Allocentric Spatial Representation”, you will be welcome to.
- Mon PM: Rovelli, “Space & Time (or not?) in Loop Quantum Gravity”
Background reading: https://arxiv.org/abs/gr-qc/9903045
- Tue AM1:Rovelli, “Is Time’s Arrow Perspectival?”
Background reading: https://arxiv.org/abs/1505.01125
- Tue AM2: Ismael, “Time perception, predictive processing, and what all of this has to do with physics”
(video coming soon)
In the second talk, I’ll talk about the perception of time and introduce some newer and more speculative ideas relating perception and action. Then I will raise questions about the implications that all of this holds for what it means to accommodate our experience of space and time in a world that is not ultimately spatial. I’ll close with some remarks about empirical coherence and whether we really need local beables.
Again, there is no required reading. The talk will be self-contained, but you would be welcome to look at Rick Grush, “Internal models and the construction of time: generalizing from state estimation to trajectory estimation to address temporal features of perception, including temporal illusions”, and Clark “Whatever next? Predictive brains, situated agents, and the future of cognitive science”. If you haven’t read Maudlin’s “Completeness, Supervenience, and Ontology”, http://iopscience.iop.org/article/10.1088/1751-8113/40/12/S16, you should do so in any case.
- Tue PM: Participant talks
(video coming soon)
John Dougherty (UCSD): Shiftlessness of the higher orders
Faced with isomorphic models of some physical theory, philosophers generally divide into two camps. Shifty philosophers (to use Belot’s terminology) argue that these models can or must be taken to represent different physical states of affairs. Shiftless philosophers argue that isomorphic models never represent distinct states of affairs. Physicists, for their part, distinguish between kinds of isomorphism: some correspond to physical differences, while others are redundancies of description. Belot and others have argued that shiftless philosophers can account for neither our intuitive judgements about modality nor physicists’ distinction between physical transformations and those that are “mere gauge”. I offer a shiftless view that avoids these objections. It does so by attending not just to isomorphisms between models, but also to isomorphisms between isomorphisms—2-isomorphisms, in the language of higher category theory. In addition to retaining the motivations for shiftlessness, this view naturally resolves a number of puzzles in gauge field theories concerning determinism, locality, and non-perturbative effects in quantization.
Michael Miller (Pittsburgh): The significance of perturbative finiteness
Abstract: A central purported theoretical virtue of string theory is that it is perturbatively finite in the sense that individual orders of perturbation theory yield finite values. Whether or not the perturbative finiteness of string theory has been conclusively demonstrated is the subject of some recent debate. My aim in this talk is to appraise the significance of perturbative finiteness for the philosophical project of interpreting a theory whose structure is characterized perturbatively. To this end, I will review some aspects of the ultraviolet problem in quantum field theory and draw a comparison to the situation in string theory.
Karen Crowther (Geneva): Coming to terms with the breakdown of spacetime (video unavailable)
Sebastián Murgueitio (Notre Dame): On the PBR theorem
The Pusey-Barret-Rudolph theorem (PBR) has set strong constraints on the so called “psi-epistemic” models of quantum mechanics, models according to which the quantum state contains information about the physical state but it is not itself part of the ontology. “Psi-epistemic” models are to be contrasted with “psi-ontic” models, according to which the quantum state is part of the ontology of quantum mechanics. In this talk, I will do two main things. First, I will show that the distinction between “psi-epistemic” and “psi-ontic” models, as usually presented in the literature, is problematic. The main problem stems from the fact that the usual distinction appeals to philosophical dense concepts, such as “direct correspondence” and “direct representation”, that are not defined in a rigorous way. Second, I will discuss in detail “the independence assumption” (one of the main assumptions by PBR) according to which the ontic state of systems independently prepared are themselves independent. By building on an argument by Leifer, I will explain why the main argument in favor of the assumption is not well supported.
- Wed AM1: Belot, “Background-Independence”
Intuitively, a physical theory is background-independent if the structure required to make sense of its equations is itself subject to dynamical evolution, rather than being imposed ab initio. Many people take one of the great lessons of general relativity to be that we should be looking for background-independent theories. But what precisely does that mean? Reflection on examples suggests that background-independence is a graded notion that depends on interpretative as well as formal considerations. I will defend the claim that a theory is fully background-independent relative to an interpretation if each physical possibility corresponds to a distinct spacetime geometry and it falls short of full background-independence to the extent that this condition fails.
- Wed AM2: Ney, “Functionalizing Space in Quantum Mechanics”
Functionalism, with an eye to functionalizing spacetime. I will talk about how this has recently been discussed in the context of wave function realism.
I thought as background readings, perhaps: Albert 1999, “Elementary Quantum Metaphysics”, and a paper of mine at the minor revision stage, Finding the World in the Wave Function (but should probably instead be called finding space in the wave function). http://philpapers.org/rec/NEYFTW
- Wed PM1: Minic, “String Theory – an overview”
Abstract: In these two lectures, the three main phases of string theory are reviewed.
In the first lecture we start with a historical overview, and then talk briefly about the
pioneering period of string theory, and then, move on to the foundations of perturbative
string theory in terms of the Polyakov path integral and the technology of conformal
field theory. We also mention the initial attempts at a non-perterturbative formulation as
well as the role of T-duality and soliton-like configurations.
1) E. Witten, Physics Today 68 (2015) 38; Physics Today, April 1996, page 24;
Physics Today,, May 1997, page 28
2) J. Polchinski, arXiv:1412.5704
- Wed 7-8pm: Participant Talks
(video coming soon)
Lopez Armengol, F.G.; Romero, G.E. (Instituto Argentino de Radioastronomía): Some philosophical issues in the causal set approach to quantum gravity
Causal sets provide a fundamental description of the emergence of spacetime from discrete entities endowed only with simple relational properties. A characteristic feature of this approach is that it provides a natural explanation for the cosmological constant. In this work we discuss the philosophical (in particular ontological) implications of this feature.
Niels Linnemann (Geneva): Avoiding (some) semi-classical traps on the road to quantum gravity: how not to establish non-renormalizability (joint work with Juliusz Doboszewski)
One of the central questions which have to be addressed at the beginning of the search for a theory of quantum gravity is the choice of theoretical framework: Perturbative non-renormalizability of the Einstein-Hilbert action of general relativity is usually taken as a decisive argument against the viability of standard QFT. There are however multiple examples of theories which are perturbatively non-renormalizable, but renormalizable in a more general sense. A natural question, then, is whether there could be a “no go” result, establishing non-renormalizability of GR in this more general sense. Shomer and Banks’ entropy argument claims to be exactly that. In this talk, we critically assess their argument, which we take to light-heartedly use extrapolations from the currently known classical (or semi-classical) regime to a regime about which we can only surely know through a theory of quantum gravity. The main point we want to make is that candidates for a theory of quantum gravity in which dimensionality of spacetime is a dynamical, scale-dependent variable — among them some which render GR as renormalizable in a more general sense — stand in direct conflict with the validity of the Bekenstein-Hawking formula at higher energies.
Jeremy Steeger (Notre Dame): Sheaves, generalized probability, and the hierarchy of quantum contextuality
We show the conceptual links between two promising research programs on quantum contextuality: one using sheaf theory (Abramsky and Brandenburger 2011), and the other using generalized probability spaces (Gudder 1984; Feintzeig 2015). We demonstrate that a sheaf-theoretic hierarchy tracking strengths of obstructions to classical distributions on deterministic hidden variables is recovered as specifications of the ease of construction of a Dutch book from a generalized probability distribution on such variables.
- Thur AM1: Matsubara, “Dualities and spacetime in string theory: Conceptual and philosophical issues”
In this lecture I will take a look at dualities from a philosophical point of view and address conceptual and interpretational issues. I will especially address questions about what consequences dualities may have for how we should think about spacetime in string theory and other questions about ontology.
To follow the lecture I do not think it is required to prepare by reading anything in advance. However, if you want to be extra prepared you may take a look at the following two articles. If you want to be even more prepared see further reading suggestions for Monday and Thursday of the discussion group “Philosophy of string theory”.
Keizo Matsubara (2013), “Realism, Underdetermination and String Theory Dualities”, Synthese 190(3):471-489.
Nick Huggett (2015), “Target ≠ Space ”, SHPMP.
- Thur AM2: Minic, “Modular Space-Time and Metastring Theory”
Abstract: In these two lectures, the three main phases of string theory are reviewed.
In the second lecture we discuss the period of dualities, including the topics of D-branes, M-theory and AdS/CFT duality with applications. We also address the question of string vacua with applications to cosmology and particle physics. In the concluding part of this lecture we discuss the recent work on metastring theory and modular space-time.
- Thur AM1: Ney, “A Primer On Emergentism”
Talk of the emergence of spacetime is thrown around, but are we talking actually about emergence in the sense it has been of interest to philosophers of mind and science.
Reading: Brian McLaughlin, The Rise and Fall of British Emergentism
- Fri AM2: Belot, “Ten Weird Things about de Sitter Spacetime”
De Sitter spacetime stands to Minkowski spacetime as the sphere stands to the Euclidean plane—in a sense, it is the second most natural spacetime geometry. De Sitter first presented it to Einstein as a counter-example to Einstein’s claim about the physics of the positive Lambda sector of general relativity. It is the gift that keeps on giving. Some topics: time and simultaneity in de Sitter spacetime; topology of de Sitter spacetime and its relatives; the cosmological no hair conjecture; energy/mass in asymptotically de Sitter spacetimes; the indiscernibility of cosmic topology; Boltzmann brains in an exponentially expanding universe. Suggested background reading (because the history is fascinating, but we won’t have time to discuss it in detail): Michel Janssen’s notes on the Einstein-de Sitter controversy.