Lattice Models of Bacterial Turbulence

生物体的协调行为确实令人着迷。无论是观看几何图案的简单乐趣，还是观察从混乱中出现的秩序的更深层次的，几乎是哲学的满足感，鱼群和鸟群或昆虫的集体运动，大卫阿滕伯勒爵士如此成功地推广，对公众和科学家都有同样的吸引力。对这种行为如何产生的研究改变了我们对动物行为、生物群体生物学和社会互动的理解。令人惊讶的是，这些现象对统计和软物质物理学产生了强烈的影响，刺激了现在所谓的活性物质领域的发展。在试图提炼这种集体行为的哪些方面可以归因于物理相互作用的过程中，出现了非平衡物理学的一个新方向，即试图理解粒子从环境中提取能量并将其转化为自我推进所形成的物质的独特状态。在这个提议中，我们专注于游泳细菌的稀溶液-游泳微生物的原型模型。这样的解决方案往往表现出独特的动力学状态，被称为“细菌湍流”。在非常低的密度下，细菌悬浮液看起来没有特征和无序，而在更高但仍然足够低的密度下，集体运动在系统的尺度上开始。我们提出了一个高风险，高收益的研究计划，将建立一类新的晶格模型描述集体运动的微观自推进粒子悬浮在流体中。与其他非平衡晶格模型类似，我们的模型足够简单，可以详细研究集体运动的确切性质。如果成功，该模型将获得类似于凝聚态物理学中的伊辛模型的地位，并将成为一类新的活性物质系统原型，最终丰富了我们对非平衡物理学和自然界中迷人的集体现象的理解。

There is something truly fascinating about coordinated behaviour of living organisms. Be it the simple pleasure of watching geometrical patterns or a deeper, almost philosophical, satisfaction of observing order appear from chaos, collective motion in schools of fish and flocks of birds or insects, so successfully popularised by Sir David Attenborough, appeals equally to the general public and scientists alike. Studies of how this behaviour comes about transformed our understanding of animal behaviour, biology of groups of organisms, and social interactions. Surprisingly, such phenomena have had a strong impact on statistical and soft matter physics by stimulating the development of what is now called the field of active matter. In the attempt to distill what aspects of such collective behaviour can be attributed to physical interactions, there emerged a new direction in non-equilibrium physics that seeks to understand the unique states of matter formed by particles that extract energy from their environment and transform it into self-propulsion.In this proposal we focus on dilute solutions of swimming bacteria - an archetypal model for swimming microorganisms. Such solutions often exhibit a unique dynamical state, known as "bacterial turbulence". At very low densities, bacterial suspensions appear featureless and disordered, while at higher, yet still sufficiently low densities, collective motion sets in on the scale of the system. We propose a high-risk, high-gain research programme that will establish a novel class of lattice models describing collective motion in microscopic self-propelled particles suspended in a fluid. Similar in spirit to other non-equilibrium lattice models, our model is simple enough to allow for detailed studies into the exact nature of collective motion.If successful, the model will gain the status similar to, say, the Ising model in condensed matter physics, and will establish itself as a new archetypal class of active matter systems, ultimately enriching our understanding of non-equilibrium physics and fascinating collective phenomena in nature.