"Collective behaviour is ubiquitous in nature: from crystallization through to animal swarming. Such phenomena are ubiquitous in colloids– 0.1-1micron particles suspended in liquids by Brownian motion – and are responsible for their amazing ability to ‘self assemble’. The self assembly of colloids is now an established route to new materials, e.g. photonic crystals. Recently, active colloidal particles capable of self propulsion have been synthesized. Their collective behaviour is completely unknown. The researcher proposes a research programme into collective phenomena in active suspensions. While synthetic active colloids have only recently been synthesized, ‘natural active colloids’ have existed for billions of years – motile bacteria. Therefore the candidate proposes to investigate both natural motile particles (bacteria) as well as synthetic ones. The bacterial results should have significant biological relevance, although the primary goal is to generate new, fundamental physics insights, which will lead to ‘design principles’ for a completely new type of self-assembled structures based on active colloids. We will use a new method, ‘differential dynamic microscopy’ (DDM), which uses everyday laboratory apparatus (a microscope and a camera) to generate comprehensive dynamical information on the collective motion of suspended particles (in the form of the so-called ‘intermediate scattering function’). Compared to single-particle tracking, the standard tool in active colloids and bacterial motility research to date, DDM yields much better averages and is orders of magnitude quicker to perform. The researcher and co-workers have demonstrated recently the use of DDM for the high-throughput characterisation of the motility of dilute populations of bacteria. A second goal of the proposed work is to develop DDM into a versatile tool for studying active particles of all kinds, at a range of concentrations."