Emergence and Emergent Concepts

Chemistry is particularly concerned with emergent properties. These are properties that only occur when multiple constituent objects come together in a particular way or arrangement, but that are also not reducible to those constituents. For example: we canot say that a single water molecule is liquid or frozen - a cluster of such molecules that interact in a specific way is required to make such an attribution sensible. As chemistry never studies single atoms or molecules, but rather their interaction, the notion of emergence is useful to chemistry. It can help draw clearer distinctions, but can also be of use as a didactical tool in conveying chemical ideas outside of science.

A first step of this project studies an array of emergent chemical properties. The result of this was that some of these properties emerge gradually with an increasing number of particles, whereas others appear "suddenly" at discrete points. For instance, hexameres of six water molecules exhibit "gear-like" rotation that is absent in clusters of five molecules - a first step on the way to liquidity. Some properties only occur at "magical numbers" of particles - for example, football-like structures of carbon atoms, so called fullerenes, can only be formed of 60, 120, 180 and so forth atoms. Studying these turning points is a promising venue for chemical research.

A second step is to investigate the philosophical consequences of these observations. The question here is how we form concepts describing these emergent properties. It seems that gradually emerging properties allow us a certain liberty in forming our concept that is absent in other cases. There are various strategies of using this "wiggle room". One interesting strategy that is popular in science can be seen in the way we address phase transitions, which occur gradually. According to our theoretical description, these only appear at the limit of infinitely many particles. This seemingly unusual way of addressing the gradual emergence may be seen as a kind of "safety mechanism". However, it still allows us to attribute freezing or thawing to a finite number of particles "speaking loosely".

This project is a cooperation with Tim Neudecker, professor of theoretical chemistry at the University of Bremen.

Literature:

Sieroka, N., T. Lossau and T. Neudecker (2024). Emergent Properties in Chemistry - Relating Molecular Properties to Bulk Behavior. Chemistry: A European Journal 30 (25): e202303868.
Hsieh, Chieh-Min et al. (2022): Can a Finite Chain of Hydrogen Cyanide Molecules Model a Crystal? ChemPhysChem 23(23), e202200414.