,
Erik Winfree
Creative Commons Attribution 4.0 International license
Universality is one of the defining hallmarks of a useful neural network model: it means that the model is expressive enough, in principle, to learn arbitrary target behavior rather than being limited to a narrow class. Inspired by rigorous formal analogies between stochastic neural networks and lattice models in which molecules occupy discrete sites, contribute species-dependent interaction energies with neighbors, and rearrange according to the Boltzmann distribution, we ask whether interactions can be programmed to yield arbitrary spatial distributions. At the level of fine-grained spatial arrangements of species, universality fails: arbitrary spatial microstate distributions cannot be represented, as shown by a counting argument and explicit construction of unrepresentable distributions. Yet, for a natural observable - spatial patterns of molecular labels - universality can be achieved. We show that a grand-canonical lattice model of anisotropic molecules is universal for arbitrary label distributions, and a similar model with isotropic molecules is also universal given a simple symmetry-breaking boundary condition. Our results suggest that equilibrium systems of multivalent molecules undergoing stochastic rearrangement governed by local pairwise interactions can act similarly to probabilistic neural networks: with sufficient microstate detail in hidden dimensions, they can be universal in a meaningful macrostate observable.
@InProceedings{chalk_et_al:LIPIcs.DNA.32.11,
author = {Chalk, Cameron and Winfree, Erik},
title = {{Universal Spatial Distribution Approximation in Equilibrium Lattice Models with Local Pairwise Interactions}},
booktitle = {32nd International Conference on DNA Computing and Molecular Programming (DNA 32)},
pages = {11:1--11:24},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-444-4},
ISSN = {1868-8969},
year = {2026},
volume = {387},
editor = {Scalise, Dominic and Schweller, Robert},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DNA.32.11},
URN = {urn:nbn:de:0030-drops-267812},
doi = {10.4230/LIPIcs.DNA.32.11},
annote = {Keywords: universality, molecular programming, neural networks, self-assembly}
}