MACHINE LEARNING

# Active Matter

I first caught wind of Active Matter through the work of one of my favorite researchers, Tamas Vicsek, whose intellectual bling includes a fractal bearing his name.

My understanding of this sprawling sub-domain of physics is that we can study the activity of individuals agents and systems as though studying something like hydrodynamics, kinematics, and non-equilbrium statistical phsyics. Crowds become streams. Flocks become rivers. Networks of agents become oceans.

It is this vision of Active Matter that I’ll be discussing in this post, and on my site in general, but make not mistake of it, this field is awesome and sprawling, and worthy of a more extensive tour than I will ever be able to give.

## Collective Motion

What governs the shape of a moving crowd leaving a moving theater? We know there’s not a central choreographer, and I don’t think we’d go so far as to say we have a genetic predisposition to filing out of a theater, so why is it we can identify patterns in crowd dynamics?

The interesting behavior outlined in Vicsek et al’s paper **Novel Type
of Phase Transition in a System of Self-Driven Particles** is a phase
transition as agents fall into sync. Just as there is a specific moment,
a phase transition, from gas to liquid, there is a point of inflection
in system. There are a lot of assumptions in the model though, including
particles that maintain a constant absolute velocity, with an update to
the average direction of neighbors in each time step. How are neighbors
calculated (the range of perception)? Does doubt play a role? Such
questions are not addressed in this article, nor are they immediately
relevant, but I ask them to hightlight the distance between the
assumptions of this model and real, biological system Such questions are
not addressed in this article, nor are they immediately relevant, but I
ask them to hightlight the distance between the assumptions of this
model and real, biological system Such questions are not addressed in
this article, nor are they immediately relevant, but I ask them to
hightlight the distance between the assumptions of this model and real,
biological systems.