Physics Interest Group

Meeting time: Friday afternoons (about every other week—see the calendar below), 1:30–3:00 pm Central time 
Meeting place: online via Zoom

The physics interest group (PIG) reads and discusses works of mutual interest in the history and philosophy of physics. We select readings for a variety of reasons: to keep up on the most exciting developments in the field, to help participants scrutinize literature relevant to their research projects (faculty or graduate student research), to provide feedback on works in progress being written by participants (graduate students, faculty, and Center visitors), to revisit classic articles in the literature, and sometimes just to have fun discussing a topic related to physics. For more information please contact Jos Uffink ( or Samuel Fletcher (

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Fall 2021

Please join our mailing list for the zoom invitation or email

The remainder of the PIG meetings this term turn to a close reading of David Wallace’s arguments concerning probability in his 2012 classic, The Emergent Multiverse. Supplemental readings highlight recent developments in this area. These readings are organized as a part of the NSF grant, “Quantum Probabilities Beyond Quantum Measurement,” led by Ben Feintzeig, Sam Fletcher, and Jeremy Steeger.

  • October 8: Selections from Chapter 3, “Chaos, Branching, and Decoherence.”
    Sections 3.1–3.5 (pp. 64–81) and Sections 3.8–3.10 (pp. 87–99; 29 pages total).
    Technical difficulty rating: **
    This chapter summarizes Wallace’s work popularizing the use of decoherence (roughly, the “washing-out” of states corresponding to incompatible properties into the environment) to justify the emergence of classical physics in EQM. Decoherence yields a branching structure, and this structure is the backbone of his arguments concerning probability.
    As an optional supplement, we suggest Josh Rosaler’s (2016) “Interpretation neutrality in the classical domain of quantum theory” (Studies in History and Philosophy of Modern Physics, 53, pp. 54–72). Rosaler argues that branching structure recovers classical physics on several approaches to measurement.
  • October 22: Selections from Chapter 4, “The Probability Puzzle.”
    Sections 4.1–4.4 (pp. 113–122) and Sections 4.8–4.13 (pp. 132–156; 33 pages total).
    Technical difficulty rating: *
    This chapter sketches Wallace’s decision-theoretic derivation of Born-rule probabilities from symmetries in the space of quantum states (a.k.a. the Deutsch-Wallace theorem). He also argues that no single-world theory can support such a derivation.
    As an optional supplement, we suggest Jeremy Steeger’s (2021) “One world is (probably) just as good as many” (on the PhilSci Archive), which argues contra Wallace that Bohmian mechanics can support a Deutsch-Wallace-style derivation.
  • November 5: Selections from Chapter 5, “Symmetry, Rationality, and the Born Rule.”
    Sections 5.1–5.7 (pp. 157–182, 25 pages total).
    Technical difficulty rating: ***
    This chapter contains a rigorous statement of the Deutsch-Wallace theorem. Wallace controversially defends four axioms of rationality that derive the Born rule, but that are specific to the Everettian’s context.
    As an optional supplement, we suggest section 5.8, which argues against alternative rationality principles.
  • November 19: Selections from Chapter 6, “Everettian Statistical Inference.”
    Sections 6.1–6.8 (pp. 199–224; 25 pages total).
    Technical difficulty rating: *
    In this chapter, Wallace generalizes his derivation of the Born rule to cases where the state, the dynamics, or the truth of quantum theory is unknown.
    As an optional supplement, we suggest section 6.10; here, Wallace situates his approach to the Born rule within the EQM literature up to 2012.
  • December 3: Selections from Sebens and Carroll, “Self-locating uncertainty and the origin of probability in Everettian quantum mechanics.”
    Sections 1, 3–4, 6, A, and B (pp. 26–39, 39–54, 60–68; 26 pages total)
    Technical difficulty rating: *
    Sebens and Carroll give a new epistemic argument for Everettian probability values that requires only a single principle of rationality. They couple this argument with an interesting critique of several of Wallace’s rationality principles.
    As an optional supplement, we suggest McQueen and Vaidman’s (2019) “In defence of the self-location uncertainty account of probability in the many-worlds interpretation” (Studies in History and Philosophy of Modern Physics, 66, pp. 14–23), which gives an interesting critique of Sebens and Caroll’s argument.

Previous PIG topics