Iām happy to share the new
@noumenal_labs preprint, āDynamic Markov blanket detection for macroscopic physics discovery,ā by Jeff Beck and me
arxiv.org/abs/2502.21217:
Hereās a thread!
This paper resolves a key outstanding issue in the literature on the free energy principle (FEP), namely, to develop a principled approach to the detection of dynamic Markov blankets. The FEP has been proposed as a generalized modeling method capable of mathematically describing arbitrary objects that persist in random dynamical systems; that is, a mathematical theory of āeveryā āthing.ā' The FEP starts with a mathematical definition of a āthingā or āobjectā: any object that we can sensibly label as such must be separated from its environment by a boundary. Under the FEP, this boundary is formalized as a Markov blanket that establishes conditional independence between that object and its environment.
Nearly all work on the free energy principle has been devoted to explicating the dynamics of information flow in the presence of a Markov blanket, and so the existence of a Markov blanket is usually assumed. Garnering significantly less interest is the question of how to discover Markov blankets in the first place in a data-driven manner.
Accordingly, in this preprint, we leverage the free energy principle (FEP), and the associated constructs of Markov blankets and ontological potentials, to develop a Bayesian approach to the identification of objects, object types, and the macroscopic, object-type-specific rules that govern their behavior. This is accomplished by reframing the problem of object identification and classification and the problem of macroscopic physics discovery as Markov blanket discovery. More specifically, we develop a class of macroscopic generative models that use two types of latent variables: (1) macroscopic latent variables that coarse-grain microscopic dynamics in a manner consistent with the imposition of Markov blanket structure, and (2) latent assignment variables that label microscopic elements or observations in terms of their role in a macroscopic object, its boundary, or the environment.
Crucially, these latent assignment variables are also allowed to evolve over time, in a manner consistent with Markov blanket structure. As such, this algorithm allows us to identify not only the static Markov blankets that have concerned the literature to date, but also ā and most importantly ā to detect and classify the dynamic, time dependent, wandering blankets that have caused controversy in the literature since the turn of the 2020s. This allows us to model the exchange of matter and energy between an organism and its environment, but at the cost of massively expanding the set of Markov blankets that we need to consider. We handle this additional complexity by applying the automatic Occamās razor effect of Bayesian inference to select the best partition.
In developing this algorithm, we provide an empirical, definitive conclusion to the debates about whether objects like flames and living creatures, which undergo material turnover, have Markov blankets. We demonstrate that they do, providing simulations that identify the Markov blankets of Newtonās cradle, a burning fuse, a Lorenz attractor, and an artificial lifeform generated by Particle Lenia.
We also make philosophical and theoretical contributions to the free energy principle. We offer a new, deflationary take on the free energy principle, focusing on the role of the modeler. In the extant literature on the free energy principle, the role of surprise minimization is treated tautologically, not empirically: the idea is that āthings minimize surpriseā. Our treatment focuses more on the pragmatics of empirical modelling, where the role of surprise is better summarized as ālabeling something as an object of a specific type minimizes my surprise.ā