SMRI Seminar: Peletier -- Loschmidt’s Paradox, thermodynamics, and a broken cookie

Loschmidt’s Paradox, thermodynamics, and a broken cookie Mark Peletier, Eindhoven
University of Technology 

Thursday 3rd September 2026 1 pm - 2 pm SMRI Seminar Room (Macleay Building A12 Room
301) 

Abstract: Loschmidt's Paradox is the following question: How it is possible that we
observe irreversible, dissipative behaviour in our daily lives, while the microscopic
equations of matter are reversible in time? We grow older, not younger; heat flows from
hot to cold, not the other way around; and a broken cookie can not be unbroken.  How is
this compatible with the observation that the equations for microscopic matter - quantum
mechanics - are reversible in time? 

This connects to the question of `thermodynamic consistency', which is an important
topic among thermodynamicists: is a given evolution equation `consistent with
thermodynamics'? A current conjecture among a group of thermodynamicists is that such
`thermodynamic consistency' should be understood as `the equation can be written in
GENERIC form', where GENERIC is a mathematically precisely defined class of evolution
equations.  

A central element of this GENERIC structure is how it implements the irreversibility,
the dissipative behaviour that is at the heart of Loschmidt's Paradox.  In fact it
implements this in a quite restrictive manner, and a natural question is: can this
structure be derived from more microscopic systems, such as quantum mechanics or
classical Newtonian mechanics? Are the thermodynamicists justified in assuming that
`consistent thermodynamic evolution equations' should be of this form? 

In this talk I will discuss these issues, and report on some recent insights that we
obtained with Alex Mielke and Johannes Zimmer.