Statistical and Biological Physics
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It has been exactly 20 years since the first physical studies which attempted to connect macroscopic collective behaviours in biological active matter systems to phase transitions and nonequilibrium physics. During the years, it has become clear that the precise knowledge of the interaction among the constituents is the key for understanding the emergence of order. In recent years, Boltzmann equations for propelled particles have been developed in order to connect the microscopic dynamics of the individual constituents to the meso- or macroscopic behaviour of the system. However due to the lack of quantitative experimental data, all models relied on very crude assumption of the interaction – most times simple digital interaction were assumed: collisions below 90 degrees align, above they are unaffected by the collision. more

Active matter is a fascinating new field in soft matter physics aiming to understand how macroscopic properties of interacting active particles emerge from properties of the constituent particles as well as their interactions. To this end, kinetic theory has been successfully applied to connect the physics at the microscopic scale with the corresponding macroscopic description; it was able to predict the emergent patterns and collective dynamics for interacting propelled particle systems. One central finding is that the degree of alignment of colliding active particles competes with the strength of randomness of the individual’s persistent random walks. This randomness arises from the inherent active fluctuations of each particle, i.e. the non-thermal and local input and dissipation of energy. more