Introduction
3
But active matter is not necessarily dispersed in the form of particles. The notion of
intrinsic orientation comes from the physics of condensed matter, which engaged with
directed interactions in solids and fluids long before studies of active matter came
on the scene. Moreover, most scientists active in these studies have been nurtured on
problems in the physics of condensed matter. The orientation of magnetic or electric
dipoles is a major factor determining the structure of crystalline solids – but solids,
with their solidity, are not properly qualified to be active, unless dispersed. Liquids
are more akin to active matter, and of all liquids, most kindred are partially ordered
liquids, liquid crystals, combining various degrees of orientation with fluidity. This
is the source of another research direction, active liquid crystals, which added the
attribute of activity to the intrinsic properties of oriented liquids. The resulting
models may involve assemblies of orientable particles but are largely “wet”, and
involve continuum rather than discrete description.
From here, the direct route for further expansion goes to soft matter, flexible
solids and colloids endowed with some kind of activity. This area is most relevant for
biology, as tissues, cells, and their components have a similar texture and consistency.
Moreover, activity is their innate feature: they are machines consisting of machines,
and themselves parts of greater machines, which are already beyond the realm of
mere matter, even soft and active.
Living matter, driven by the complex interplay of genes and proteins, is far more
complicated than models of active matter can afford. Specific molecular interactions
are of most concern to biologists and biochemists, but it is gradually understood that
factors of a general nature, common to active and living matter, play a substantial role
in cellular and developmental processes. Finally, advanced biomorphic technology
creates soft robots and artificial swimmers imitating, still on a basic level, soft natural
machines. All of this will come out in our narrative.
3
But active matter is not necessarily dispersed in the form of particles. The notion of
intrinsic orientation comes from the physics of condensed matter, which engaged with
directed interactions in solids and fluids long before studies of active matter came
on the scene. Moreover, most scientists active in these studies have been nurtured on
problems in the physics of condensed matter. The orientation of magnetic or electric
dipoles is a major factor determining the structure of crystalline solids – but solids,
with their solidity, are not properly qualified to be active, unless dispersed. Liquids
are more akin to active matter, and of all liquids, most kindred are partially ordered
liquids, liquid crystals, combining various degrees of orientation with fluidity. This
is the source of another research direction, active liquid crystals, which added the
attribute of activity to the intrinsic properties of oriented liquids. The resulting
models may involve assemblies of orientable particles but are largely “wet”, and
involve continuum rather than discrete description.
From here, the direct route for further expansion goes to soft matter, flexible
solids and colloids endowed with some kind of activity. This area is most relevant for
biology, as tissues, cells, and their components have a similar texture and consistency.
Moreover, activity is their innate feature: they are machines consisting of machines,
and themselves parts of greater machines, which are already beyond the realm of
mere matter, even soft and active.
Living matter, driven by the complex interplay of genes and proteins, is far more
complicated than models of active matter can afford. Specific molecular interactions
are of most concern to biologists and biochemists, but it is gradually understood that
factors of a general nature, common to active and living matter, play a substantial role
in cellular and developmental processes. Finally, advanced biomorphic technology
creates soft robots and artificial swimmers imitating, still on a basic level, soft natural
machines. All of this will come out in our narrative.