PhD Position (M/F) – Physics of Collective Motion

Job Description

Thesis Subject

**Objective**

The aim of this PhD project is to understand the collective dynamics of large animal groups through the statistical analysis of their shape fluctuations. The project will combine field experiments, data analysis, and modelling.

**Background and positioning**

In systems as diverse as microorganism colonies and fish schools, we understand how the emergence of orientational order can produce coherent collective motion without centralised control. Yet, when observing a fish school, the most immediately perceptible structure is not the orientation of individual fish, but the group itself: a cohesive phase whose shape fluctuates continuously while remaining capable of responding collectively to localised perturbations.

Paradoxically, the shape dynamics of animal groups remain far less well understood than the interactions among their individual members. Numerical models reproduce some of the visual features of animal crowds, but the mechanisms governing their morphological fluctuations and their response to external perturbations remain largely unknown.

This PhD project proposes to approach fish schools as cohesive active phases with fluctuating interfaces. We will draw on a field dataset collected through observations of schools ranging in size from several hundred to several million individuals. Several aggregation sites that can be observed at fixed dates and locations have already been identified.

**Three research areas**

**Area 1 —** Expand our dataset through new field observation campaigns in natural environments.

**Area 2 —** Understand the statistical properties of spontaneous shape fluctuations in the three main collective states observed in fish: swarming, milling, and schooling. Based on quantitative measurements, we will develop a hydrodynamic description of fish schools viewed as cohesive active phases. In particular, we will seek to establish an analogue of Laplace's law linking the local geometry of the interface to the group's effective mechanical properties. This approach will allow us to investigate the universality of the behaviours observed across species and collective regimes.

**Area 3 —** Study the response of fish schools to predator attacks in order to identify the mechanisms governing information propagation in these systems.

**Candidate profile**

Candidates should have a strong background in statistical physics and computational physics. Excellent data-analysis skills are essential, as is a high level of proficiency in English for effective collaborative work.

Your Work Environment

The project will be carried out at the Physics Laboratory of ENS de Lyon, on the Monod campus. It is part of a research programme on collective dynamics initiated over six years ago, in which the team now holds a leading international position. Over the past twenty years, Denis Bartolo has supervised twenty PhD students, whose work has consistently led to at least one publication in a leading international journal.

The Physics Laboratory of ENS de Lyon provides a stimulating scientific environment spanning a broad range of fundamental physics. The PhD project will investigate the dynamics of fish schools by combining field measurements, data analysis and modelling. It will include field campaigns devoted to collecting video data, followed by their analysis using state-of-the-art computing servers capable of running large-scale parallel simulations.

The successful candidate will work closely with two postdoctoral researchers, who will share their technical expertise and enthusiasm for the physics of collective motion. ENS de Lyon also offers a friendly and supportive working environment, conducive to research training and providing opportunities to gain initial teaching experience.

Constraints and risks

No specific risks

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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