Information about discussion groups



Philosophy of string theory

Testing Theories



Emergence & correspondence

  • Philosophy of string theory

Group facilitator: Keizo Matsubara

Basic information

In this group we will discuss philosophical questions about string theory.

Here are three topics that we will address:

  1. The Landscape of string theory: How should one think about the so-called Landscape in string theory; where string theory allows for a number of different effective theories? Does this lead to an untestable theory without any sharp predictions that we should not take seriously as science or is there a different way of thinking about the situation?
  2. Dualities: How should dualities in string theories best be interpreted and understood? Why do most physicists not think of dualities as examples of underdetermination? What impact does dualities have for questions about ontology?
  3. Spacetime in string theory: (The dualities mentioned above are of relevance to address some aspects of this topic.) Is string theory background independent? How does general relativity appear as a classical limit of string theory? What should we make of claims that spacetime has extra dimensions than the one we are used to? Could it be the case that in a more fundamental description of string/M-theory, spatiotemporal concepts are not used and if that is the case how can we understand the emergence of space and time from such a picture?

The basic plan is to discuss 1) on Monday 2) on Tuesday and 3) on Thursday. However, based on how the discussion goes we might want to continue some discussion from earlier days and thus discuss some topic to a lesser degree.

The intention is to focus on conceptual and philosophical questions that can be addressed without going to far into formal and technical aspects of the theory. Hence, attending the group does not require much previous knowledge about string theory.

Lecturers attending meetings

In addition to the participants lecturers will also attend the meeting. Nick Huggett will be present on the Monday meeting and Djordje Minic will attend the meeting on Thursday.

Reading list

Some texts may contain technicalities that could be difficult to follow. I urge you to not be discouraged and concentrate on the conceptual and philosophical issues.

The papers can all be found on PhilPapers or ArXiv.  If for some reason you have difficulty accessing the papers please send me an e-mail.

You should read the texts below before coming to the meeting. I have for each day indicated first one main text that should be read carefully and then two texts that should be at least skimmed through or read in a cursory fashion, this means do not worry about all technical details but try to get the main ideas in the texts. Of course if you have time to read the cursory reading texts more carefully that is even better.


Main text: (This main text is pretty short and for this day I suggest you spend a little extra time on the cursory reading material.)

Steven Weinstein (2006), “Anthropic reasoning and Typicality in multiverse cosmology and string theory”. Class.Quant.Grav. 23: 4231-4236. (arXiv:hep-th/0508006)

Cursory reading:

Smolin (2007), “Scientific alternatives to the anthropic principle”, (In Carr (ed.) Universe or Multiverse? CUP(2007).)(arXiv: hep-th/0407213)

Susskind (2007), “The anthropic landscape of string theory”, (In Carr (ed.) Universe or Multiverse? CUP(2007).)(arXiv: hep-th/0302219)


Main text:

Keizo Matsubara (2013), “Realism, Underdetermination and String Theory Dualities”, Synthese 190(3):471-489.

Cursory reading:

Dean Rickles (2011), “A Philosopher Looks at String Dualities” SHPMP, 42:54-67.

Dean Rickles (forthcoming), “Dual theories: `Same but Different’ or `Different but Same’?” SHPMP.


Main text:

Nick Huggett (forthcoming), “Target Space ≠ Space ”, SHPMP.

Cursory reading:

Dean Rickles (2013), “AdS/CFT duality and the emergence of spacetime”, SHPMP 44:312-320.

Nick Teh (2013), “Holography and Emergence”, SHPMP 44:300-311.

Suggested further reading for those who are extra interested

You are not at all expected to have read the texts below they are just some suggestions for further reading. The texts included below are all books. In addition to the books below there are of course a large number of articles and other books the list below is just a small selection.

I do not write full reference information for the texts, it should be sufficiently easy to find them based on the information given.

Standard physics textbooks in string theory are:

Becker, Becker & Schwarz, String theory and M-theory  (More up to date)

Green, Schwarz &Witten, Superstring theory 2 volumes

Polchinski, String theory 2 volumes

Zwiebach, A first course in string theory (Easiest to start with)

History of string theory

Rickles, A Brief History of String Theory

Philosophy of string theory

Dawid, String Theory and the Scientific Method

  • Testing Theories

Group Facilitator: Radin Dardashti

Theories of quantum gravity have the problem of being theories most relevant at the Planck scale.  Approximately 15 orders of magnitude beyond what the Large Hadron Collider in CERN, the biggest experiment ever built, can currently reach.

So testing these theories directly seems unrealistic in the foreseeable future and it needs to be replaced, if that is possible, with indirect ways of theory assessment.

In this group we will discuss proposed alternative methods of theory assessment. The focus will be on the use of analogue models to test empirically inaccessible target systems. The most famous example of these being the fluid dynamical analogue models of black hole Hawking radiation. What can we learn from these analogue models? Can we use the evidence in one system to confirm the other? If yes, under what conditions? If no, what is the epistemic gain of analogue simulation? These and other questions will be considered. If time allows, we will also discuss the viability of some methods of theory assessment, which completely lack empirical data. Options would be Dirac’s account (and later McAllister’s) on beauty in science or Dawid’s non-empirical theory assessment based on limitations on scientific underdetermination.

Here is the list of literature:

– Barceló, Carlos, Stefano Liberati, and Matt Visser (2005). “Analogue Gravity”. In: Living Rev. Rel 8.12.

– Unruh, W.G. (2014). “Has Hawking Radiation Been Measured?” In: Foundations of Physics 44.5, pp. 532–545.

– Dawid, Richard (2015) Modelling Scientific Confirmation. [Preprint]

– Dirac, Paul A. M. (1940). “The Relation Between Mathematics and Physics.” In: Proceedings of the Royal Society of Edinburgh 59, pp. 122– 129.

– McAllister, James W. (1990). “Dirac and the Aesthetic Evaluation of Theories”. In: Methodology and Science 23, p. 87.

You of course do not have to read all of them in detail, especially the Barcelo et al paper (150 pages). But it would be useful to have a look, so you know about the topics you would like to discuss in more detail.

  • Metaphysics

Group facilitator: Baptiste Le Bihan

Topic: Many approaches to quantum gravity suggest a radical ontological move by claiming that time and/or spacetime are not fundamentally real. The aim of these discussions will be two-fold: first, to understand the metaphysical implications of a non-spatio-temporal world (meetings 1 and 2), in focusing in particular on the existence of time (meeting 1) and the existence of spacetime (meeting 2), and second to understand the metaphysical nature of the connection between a fundamental non-spatio-temporal world and the phenomenal spatio-temporal world (meeting 3). Are approaches to quantum gravity compatible with the reality of time? With the reality of spacetime? And what does it take for such entities to be real? Many researchers suggest that the fundamental realm is very different from the phenomenal macroscopic world, in their structures (loop quantum gravity, causal set theory) or in their numbers of physical dimensions (string theory). Should we construe the two realms as being connected by a robust ontological relation of emergence like a relation of causation or a relation of grounding, or should we construe this relation as a mere way of speaking?

So the plan is this:

Meeting 1: Discussions on the disappearance of time, with Jill North (using text 1).

Meeting 2: Discussions on the emergence of spacetime in the context of wave function realism, with Alyssa Ney (using text 2).

Meeting 3: Discussions on the emergence of spacetime in the context of approaches to quantum gravity, with Christian Wüthrich (using text 3).

Required readings:

– Text 1: Carlo Rovelli (2011). “Forget Time”. Foundations of Physics 41 (9):1475-1490.

– Text 2: Alyssa Ney (2015). “Fundamental Physical Ontologies and the Constraint of Empirical Coherence: A Defense of Wave Function Realism”. Synthese 192 (10):3105-3124.

– Text 3: Nick Huggett & Christian Wüthrich (2013). “Emergent Spacetime and Empirical Coherence”. Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 44 (3):276-285.

Suggested reading to go further:

On the connection between metaphysics and philosophy of physics:

– Steven French & Kerry McKenzie (2012). “Thinking Outside the Toolbox: Towards a More Productive Engagement Between Metaphysics and Philosophy of Physics”. European Journal of Analytic Philosophy 8 (1):42-59.

Interesting philosophical views about spacetime:

– Jonathan Schaffer (2009). “Spacetime the One Substance”. Philosophical Studies 145 (1):131-148.

– L. A. Paul (2002). “Logical Parts”. Noûs 36 (4):578–596.

A classical argument against the reality of time:

– J. Ellis McTaggart (1908). “The Unreality of Time”. Mind 17 (68):457-474.

Reading advices:

I know that the required readings are quite a lot. So here are a few advices to ease the preparation:

– For the paper “Forget Time”, we will focus on the philosophical ideas, so feel free to ignore mathematical equations if you are not a specialist of mathematics. The idea with this paper is to ascertain whether we should abandon the whole notion of time, or only certain properties usually ascribed to time.

– The two other papers focus on the problem of empirical coherence and the possible emergence of a 3D or 4D space from a more fundamental higher-dimensional space, the first (Ney, 2015) in the framework of philosophy of quantum mechanics, the second (Huggett & Wüthrich, 2013) in the framework of approaches to quantum gravity. I suggest to focus our discussions on the ontological consequences of various solutions to the problem of empirical coherence during the last two meetings.

– If it is too much work, focus on two of the three texts (but it’s important to read at least one time the three texts).

– There is no need to understand everything in the papers.

– The other suggested readings are there to guide you if you want to invest more time in the preparation, in particular if you are unfamiliar with metaphysics.

– I want the group to be a space where you can discuss your own ideas (related to the topic of time and space in contemporary physics) with other students. So although I will be there to put some context at the beginning of each discussion, and although we’ll have an invited speaker specialist of various topics for each meeting, it’s up to you what exactly you want to discuss. I suggest, therefore, that you think of a little discussion/question related to the topic, that you would like to discuss at each session.

  • Singularities

Group facilitator: Juliusz Doboszewski

(1) Practicalities

We will have three meetings, on Monday, Tuesday and Thursday. At the end of the summer institute there will be a short (few minutes long) summary of what happened during the reading groups; ideally some of you will do so.

The general idea is to cover some general features of singularities on Monday, and discuss two types of real-life phenomena which involve singularities, and are in a natural way related to questions raised in the search for the theory of quantum gravity – Big Bang and black holes – on Tuesday and Thursday. See the description.

Most likely some of the invited speakers will be joining us on Tuesday and Thursday; I will confirm that soon.

(2) Short description


Singularities are among main reasons to be dissatisfied with classical general relativity as a description of space and time; they are also a focus of many discussions in the philosophy of physics and technical work in classical and quantum gravity. This reading group is intended to be something like a Singularities 101. First session will cover a brief introduction to classical general relativity and various characterizations of singularities (including differences between artificial holes in spacetime and physical singularities, and relations between singularities and other unpleasant features of spacetime). During the second session we will discuss the Big Bang singularity and its fate in loop quantum cosmology (i.e. the ‘quantum bounce’ scenario). Finally, we will discuss the classical and semi-classical descriptions of black holes, focusing on the “no hair” theorems and the significance of the Bekenstein-Hawking entropy.

(3) Reading materials.

It would be great if you would find some time to familiarize yourself with the texts marked as basic. Papers described as bonus are, well, bonus. Basics for first two days are (I hope) rather accessible, the third day is a bit more brutal. I know, I’m sorry, don’t be afraid: hopefully after first two days it will seem less brutal.

If there is any particular topic or paper that you would like to discuss in details, feel free to let me know, and we will see what can be done.

Monday, 20.07


Erik Curiel, Peter Bokulich, Singularities and black holes:


John Manchak, Global spacetime structure, in Batterman (ed) Oxford Handbook of Philosophy of Physics [systematic overview of various global features of spacetime, many of which are relevant for questions concerning singularities]

Robert Geroch, Singularities, in: Carmeli, Fickler, Witten “Relativity” [1970 conference proceedings] [appendix D includes an accessible overview of the proofs of singularity theorems]

Tuesday, 21.07


– Ashtekar, Singularity resolution in loop quantum cosmology: A brief overview [what the title promises]


– Abhay Ashtekar, Alejandro Corichi, Parampreet Singh, Robustness of key features of loop quantum cosmology [more technical paper, if you’re brave enough]

Thursday, 23.07


– Claus Kiefer, Quantum Gravity, 2nd ed., chapter 7.1 [introduction to the laws of black hole mechanics, Hawking radiation and Bekenstein-Hawking entropy]

– Piotr T. Chruściel, Joao Lopes Costa, Markus Heusler, Stationary Black Holes: Uniqueness and Beyond [we will mostly be interested in section 5 – examples of violation of the no hair conjecture]


– Visser et al, Small, dark, and heavy: But is it a black hole?

  • Emergence & correspondence

Group facilitator: Karen Crowther

There will be three sessions (Monday, Tuesday and Thursday) for two hours each, and that these sessions are meant to be an intensive reading group rather than lectures (there will be lectures during the Institute, too, but these are separate).

So, since I have not yet met all of you in person, let me introduce myself! My name is Karen, and I will be starting as a postdoc at the University of Geneva in September (having recently finished as a postdoc at the University of Pittsburgh). I wrote my PhD thesis on the Emergence of Spacetime in Quantum Gravity, and I have also written a book on the subject, which is still with the publishers at this stage. My book is more introductory and philosophical than the one that Huggett and Wuthrich are working on, and it deals with the framework of effective field theory, condensed matter approaches to QG, discrete approaches to QG, and LQG. I would be more than happy to email you the manuscript if you would like it, please ask.

Here is my initial proposal for the reading group:


Loop Quantum Gravity

1. Wüthrich, C. Lehmkuhl, D. (Ed.) Raiders of the Lost Spacetime. Towards a Theory of Spacetime Theories, Birkhäuser, Forthcoming


Physical Salience

2. Huggett, N. & Wüthrich, C. Emergent spacetime and empirical (in)coherence. Studies in History and Philosophy of Modern Physics, 2013, 44, 276-285


Other approaches

3. Oriti, D. Disappearance and emergence of space and time in quantum gravity. Studies in History and Philosophy of Modern Physics, 2014, 46, 186-199

I am hoping that Chris Wuthrich will join in the discussion on Monday, and also Nick Huggett on Tuesday.

Papers 1 and 3 are quite long, but I know that some of you are already postdocs, and that several have strong physics backgrounds, so I chose these papers because they are clear on the physics and get into actual examples. But I welcome your feedback—if you have suggestions for other papers that you would like to discuss with the group, please let me know! We could change paper 3, or include it in the Tuesday session, since it is similar to paper 2. We could also discuss certain sections of other papers, if you have questions about a particular issue in another paper, or are working on something related to the topic and would like to get feedback from the rest of the group.

Other suggestions/supplementary readings:

The “classic” papers on the topic are by Butterfield and Isham. I am guessing at least some of you have read these already… they are very long and dense! But these have strongly influenced all further work, in particular Wuthrich (in paper 1) uses the Butterfield/Isham account of emergence (note that Oriti in paper 3 uses a different account of emergence, which comes from later papers by Butterfield). If there are sections that you want to discuss from these, please say so.

Spacetime and the Philosophical Challenge of Quantum Gravity:

On the Emergence of Time in Quantum Gravity:

I am also working on a paper on correspondence in QG, a draft of which I attach. I would be happy to discuss this, too, and to get your feedback. It is short and more philosophical, so it might be fun to get into for something different.

OK! So please let me know if you have any suggestions. Also, please read papers 1-3 and highlight some questions and discussion points before the Summer Institute begins.