The Active Materials Project aims to investigate the significance of active materials for our understanding of the material basis of life. Active materials include self-propelled nanoparticles, motor proteins and microtubules, and colloidal suspensions of cells and bacteria. Such materials display many of the bulk properties associated with larger-scale living systems: they are far-from-equilibrium systems that are often described in agential, goal-oriented terms; they engage in emergent, collective behaviours such as flocking and swarming; and they exhibit distinctive properties and behaviours across a range of different spatial and temporal scales.
AMP2 Summer School & Workshop (Georgetown University, July 2018)
The AMP 2018 Summer School & Workshop focused on the following three general themes.
Models, Boundaries, and Scale
What techniques and strategies are required in order to model and understand active matter systems? Reductionist strategies for understanding bulk behavior of inactive materials often fail, and materials scientists have developed a variety of multiscale techniques, such as homogenization, that treat materials as having different structures and features at different scales. These techniques aim to integrate the characteristic, dominant features of the materials at different scales. This contrasts with the reductionist view, according to which all characteristics of materials stem entirely from the characteristics at the most fundamental scale. To what extent are such techniques importable to the active materials case? Can multiscale techniques be applied to active materials, or do new techniques need to be developed? In either case, how are these techniques justified?
One apparent difference between inactive materials and active materials involves the role of boundaries. Modeling of bulk behavior in inactive materials plays down the role of boundaries or constraints. But in active materials, boundaries seem to play a constitutive role. Are these boundaries self-generated, and if so, how? In the inactive case, the lack of boundaries enable correlated behavior on extremely large scales, while in the active case, the extent of correlated behavior if much more limited extent. How do these constraints affect our understanding of the long-range correlated behavior characteristic of active materials?
As well as considering questions concerning how active materials are best modelled, we will consider basic questions concerning the distinguishing features of active materials. What are the defining characteristics of active matter? What makes material active rather than inactive? Active materials can be found on many scales, and the individual entities which make up those materials vary vastly, from nanoparticles to entire organisms. What minimal complexity is required to generate activity in such systems?
In investigating such questions, nanoscale systems provide a particularly useful model for understanding both the characteristic behaviors and scale-dependent constraints on active materials. Nanomaterials are characterized by novel material behaviors that arise due to scale-dependent physical and chemical properties. In many of these materials, bulk behavior tends to disappear or get overtaken by behaviors characteristic of surfaces or boundaries. What is the relationship between these sorts of boundary behaviors and the boundary behaviors that characterize and constitute active-material behaviors? What is the role of structure in explaining behaviors in active matter systems? Is structure presupposed or derived in explanations of the behavior of active materials? How does structure itself vary across multiple scales?
The Bigger Picture: The Broader Significance of Research on Active Matter
The final general theme concerns the relationship between work on active matter and more general philosophical questions concerning modeling and explanation. Active matter research offers a potentially very fruitful set of case studies for understanding scientific reasoning and explanation more generally. Since research on active matter typically occurs at the intersection of different branches of science, it presents us with a rich basis for exploring questions concerning the integration of theories, data, models and explanations in science. It also raises questions concerning the scope and significance of the techniques developed to deal with these inter-theoretic domains: Can insights gained from the modeling of active matter be applied to other areas of science – in particular, other areas that deal with collective, emergent phenomena in other kinds of systems?
Finally, how does research on active materials impact the way we think about other long-standing philosophical problems, such as the origin and nature of agential, goal-directed behavior? Research on active matter suggests a variety of questions concerning agential behavior, both in individuals and in groups. How should we characterise agency in these cases, and in what ways might this inform our understanding of other forms of agency? How does material agency relate to the kinds of autonomous behavior that are regarded as characteristic of living and cognitive systems? Do these all involve agents of the same sort, or do they stand in different relationships to one another?
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