Abstract

We know well that ice is a crystal where molecules are arranged in a regular pattern, while water is a liquid where molecules have a disordered arrangement. Also, water flows, while ice is a solid. There is a natural physical theory that links the crystalline order of ice to its solid properties. However, this theory fails for materials like window glass, which manage to be physically solid, without crystalline order. Some modern theories aim to explain this by the concept of “amorphous order”—they say that glass is an ordered material, but the order is not apparent to our eye. Other theories argue that the relevant order can only be seen if one looks at the system in space-time, instead of regular space. This remains a controversial area of science, despite the fact that glassy materials have been used by humans for thousands of years.

I use these examples to discuss some unusual types of Order in physical theories, and how this can be quantified.

About the Speaker: Dr Robert Jack is an interdisciplinary Lecturer with a joint appointment between the Dept of Chemistry and DAMTP . His research uses the theory of statistical mechanics to understand the behaviour of complex systems including biomolecules, glassy liquids, and soft matter. In particular, he is interested in co-operative dynamics: for example, how do molecules move in crowded environments? What are the co-operative mechanisms for colloidal self-assembly, and the folding of biomolecules?