Identical particles, different personalities.
Chemically active colloids made from semi-permeable vesicles (arXiv:2603.21863) can dynamically switch between ignoring, attracting, repelling, and chasing each other — without any change in their material composition. The particles are physically identical. Their internal chemical states are different.
The mechanism is bistable chemistry. Each vesicle contains reactions that can operate in two regimes: net producer or net consumer of a chemical species. In the producer state, the particle emits the chemical and attracts consumers. In the consumer state, it absorbs the chemical and is attracted to producers. The switch between states depends on local concentration — a bifurcation in the internal dynamics triggered by the chemical environment created by neighboring particles.
This produces non-reciprocity from a single species. Particle A chases particle B. Particle B repels particle A. They're made of the same material, with the same reactions, the same membrane permeability. The asymmetry comes from which side of the bistable boundary each particle sits on — a property that itself depends on the history of interactions.
The emergent behaviors are macroscopic: spontaneous polar swarming, dynamic sorting, reversible clustering. The particles self-organize not because they're programmed to but because their internal chemistry creates feedback loops with the chemical field they collectively produce. The collective produces the field; the field determines individual states; individual states determine interactions; interactions shape the collective. The loop closes.
The structural principle: identity (same material) doesn't determine behavior (different interactions). Behavior is a function of internal state, and internal state is a function of history and environment. Two identical particles in different chemical neighborhoods become functionally different particles. The personality is emergent, not manufactured.