# The Second Annual Bristol-MCMP Workshop on Foundations of Physics: Problems in Classical and Quantum Statistical Mechanics (27 January 2018)

Statistical mechanics plays a central in almost every field of physics: solid state, fluid mechanics, cosmology, astrophysics, the study of black holes, every major program of quantum gravity, low temperature physics, the Standard Model, experimental error analysis, and on and on. Its conceptual and foundational problems---among them, the role and interpretation of probabilities, the nature of entropy and the Second Law, the root of irreversibility, its relation to thermodynamics---are as deep and unresolved as those of any other field of physics as well. All of these are active and central areas of research in contemporary work on the foundations of physics. Indeed, in recent decades the scope of statistical mechanics has grown to encompass fundamental work in such diverse fields as economics and formal epistemology as well. This workshop will address problems pertaining to a wide spectrum of such issues with an emphasis on technical work, with the aim both of examining the problems in their own right and of investigating whether approaches and techniques from some areas can be of use in others.

## Speakers

- Dr. Karim Thébault (University of Bristol/MCMP)
- Dr. Sean Gryb (Bristol)
- Patricia Palacios (LMU/MCMP)
- Dr. Erik Curiel (LMU/MCMP)
- Dr. Neil Dewar (LMU/MCMP)
- Prof. Roman Frigg (LSE/MCMP)

## Program

Time | Event |
---|---|

09:30 - 10:00 | Registration, Coffee & Pastries |

10:00 - 10:50 | Karim Thébault: Epistemic Humility and Maximum Entropy Reasoning in Quantum and Classical Statistical Physics |

10:50 - 11:10 | Coffee |

11:10 - 12:00 | Neil Dewar: Supervenience and Definition |

12:00 - 13:30 | Lunch |

13:30 - 14:20 | Patricia Palacios: On the Universality of Hawking Radiation |

14:20 - 14:40 | Coffee |

14:40 - 15:30 | Erik Curiel: Irreversibility Associated with the Second Law in Thermodynamics and in Statistical Mechanics |

15:30 - 16:20 | Sean Gryb: Epistemic Humility in the Context of Quantum Cosmology |

16:20 - 16:50 | Coffee & Snacks |

16:50 - 17:40 | Roman Frigg: Can Somebody Please Say What Gibbsian Statistical Mechanics Says? |

19:15 | Conference Dinner (Osterwaldgarten) |

## Abstracts

### Erik Curiel: Irreversibility Associated with the Second Law in Thermodynamics and in Statistical Mechanics

In so far as one holds that thermodynamics can be reduced to statistical mechanics, one faces the problem of what exactly in the one theory can be reduced to what exactly in the other, and how. I focus on how irreversibility in thermodynamics may be reduced to that in statistical mechanics. I consider two different two of irreversibility (almost never clearly distinguished in the literature), that associated with the Minus-First Law and that with the Second Law. I argue that the reduction of the first kind is successful in both the Boltzmannian and the Gibbsian frameworks, but in interestingly different ways. I then argue that the reduction of the second fails in both frameworks, for entirely different reasons. In particular, I argue that the irreversibility associated with the thermodynamical Second Law has nothing to do with temporal asymmetry, but rather with an asymmetry in the types of cyclic engines one may in principle construct and the asymmetric way in which heat and work enter into the constraints. In statistical mechanics, on the other hand, the irreversibility does have centrally to do with temporal asymmetry. I conclude with a few remarks about the light this may shed on the questions surrounding the relations of the Second Law to the arrow of time.top

### Neil Dewar: Supervenience and Definition

Philosophers have spent a lot of time thinking about "supervenience": a relation whereby one set of facts suffices to fix another set of facts. Model theorists have spent a lot of time thinking about "implicit definition": a relation whereby part of the structure of a model suffices to fix the rest of the structure. I'll look at the relationships between these two notions and their application to reduction in statistical physics, and use it as a chance to reflect more generally on the relationship between logic and philosophy of science.top

### Roman Frigg: Can Somebody Please Say What Gibbsian Statistical Mechanics Says?

Among working physicists, Gibbsian statistical mechanics (GSM) is the most widely used version of statistical mechanics. Yet a closer look at GSM reveals that it is unclear what the theory actually says and how it bears on experimental practice. The root cause of the difficulties is the status of the Averaging Principle, the proposition that what we observe in an experiment is the ensemble average of a phase function. We review different stances toward this principle, ranging from unconditional acceptance to blatant rejection. We find all of them wanting and suggest that the problem finds an elegant solution if one adds a Boltzmannian definition of equilibrium to GSM, which results in what we call the 'Gibbsmannian approach'.top

### Sean Gryb: Epistemic Humility in the Context of Quantum Cosmology

Epistemic humility dictates that conditions placed upon the state ofsome system should involve the minimum possible assumption of information that we do not have. I argue that such a principle can serve as a particularly powerful methodological tool for constraining and interpreting cosmological physics. The utility of this principle is illustrated in the context of a unitary quantum model of the universe, where it leads to restrictive and physically interesting constraints on the model parameters. I then comment on how epistemic humility could shed light on other conventional problems that modern inflationary theory purports to address.top

### Patrica Palacios: On the Universality of Hawking Radiation

Unruh and Schützhold (2005) suggested that the Hawking effect in black holes should be understood as a universal phenomenon based upon generic insensitivity of the characteristic thermal flux to modified dispersion relations. From that, they infer that the trans-Planckian problem is irrelevant to the Hawking effect in a way that validates the many different approaches to derive the Hawking radiation. Nonetheless, some questions remain open. For instance: Is the alleged universality of Hawking radiation of the same kind as the universality that characterizes phase transitions in condensed matter systems? Are the mathematical methods used to derive the universality of the Hawking radiation analogous to the methods used to infer the universality of critical phenomena? In this contribution, we address these questions by comparing the methods used by Unruh and Schützhold with the Wilsonian approach to renormalization. (Based on joint work with Karim Thébault and Sean Gryb.)

top

### Karim Thébault: Epistemic Humility and Maximum Entropy Reasoning in Quantum and Classical Statistical Physics

If one considers statistical mechanics as a form of statistical inference rather than as a physical theory, it is found that the usual computational rules, starting with the determination of the partition function, are an immediate consequence of the "maximum-entropy principle" (Jaynes 1957). To what extent can maximum entropy reasoning be extended from classical to quantum physics? In particular, to what extent can we use maximum entropy reasoning to constrain the form of the wavefunction in the context of a psi-epistemic interpretation? In this talk I will argue that although any general attempt to constraint the wavefunction via appeal to maximum-entropy reasoning is misguided, a related "principle of epistemic humility" offers an attractive strategy for side stepping the cosmological measurement problem.top

## Fees

No conference fee. The conference dinner is on a Dutch-treat basis.

## Registration

Please send notice to attend to erik.curiel@lmu.de. Please say whether you plan to attend the conference dinner or not.

## Venue

Main University Building

Prof.-Huber-Platz 2

D-80539 München

Room V002

## LMU Roomfinder

If you need help finding the venue or a particalur room, you might consider using the LMU's roomfinder, a mobile web app that lets you display all of the 22.000 rooms at the 83 locations of the LMU in Munich.