March 4, 2025 | Shumaila Firoz, Asian College of Journalism
There is a comforting illusion that the world is built upon order. Despite this perception of organization, there is substantial disorder in the physical world that often goes unnoticed. The study of disordered systems even won the 2021 Nobel Prize in Physics, awarded to Giorgio Parisi "for the discovery of the interplay of disorder and fluctuations in physical systems from atomic to planetary scales".
Pinaki Chaudhuri, a faculty at The Institute of Mathematical Sciences (IMSc), Chennai recently presented a popular talk on disordered systems at Science at the Sabha 2025. He shed light on the pervasiveness of disorder in the natural world from materials that are hard to classify to complex systems like crowds and natural disasters. Blending scientific rigour and accessibility, he spoke about the unusual properties and complex behaviour of disordered systems, leaving a deep appreciation of such phenomena.
Pinaki Chaudhuri from IMSc Chennai spoke about disordered systems across scales, from molecular arrangements in disordered materials to biological and natural phenomena. (Photo: IMSc Media)Rebel materials
Nature has many examples of structured arrangements, such as crystalline materials with an ordered arrangement of atoms or molecules. Disordered materials like glass defy this regular structure, existing in a state that is unlike a typical solid. Glass holds its shape, does not flow at room temperature and breaks into smaller fragments when struck. In contrast to crystalline solids, glass has a random arrangement of molecules. Such materials called amorphous solids seem to exist between solid and liquid states, refusing to classify neatly. What makes materials with such a random arrangement have solid-like properties remains a mystery.
The packing of underlying components to fill up space shapes the properties of such materials. In disordered materials, these components can settle into different arrangements even from the same starting conditions. Researchers use computer models to study how these components interact with each other to give rise to various packing arrangements having different energy states.
Disordered solids come in various forms and size-scales. They range from metallic glasses with high endurance strength where atoms are disordered at less than a nanometer scale, to granular solids like sand, where particles are visible to the naked eye. Based on the size-scale of their components, they can occur as hard or soft amorphous solids.
Flow and failure
Disordered solids have unique properties that are different from traditional rigid materials. Examples of soft disordered solids are a pile of grains, sand castles, ketchup, toothpaste and tar. These maintain their shape until an external force causes them to flow. This transition occurs at the yield stress, which describes the minimum force required to make a material flow like a liquid. A pile of grains behaves like a solid when stable, but can flow like a liquid with a slight disturbance. Toothpaste remains in the tube until you squeeze it, when it flows onto your toothbrush.
The mechanical properties of disordered systems are a balance between flow and failure. Disordered systems are characterized by unpredictable behaviour as they have many components that interact with each other in complex ways. This is an important challenge while working with materials as it is difficult to predict when they may fail in response to varying pressure, temperature and stress. Avalanches and landslides are other examples of disordered solids breaking, which can have devastating human consequences. Researchers are interested in understanding how and where fracture starts, which can be used to predict and prevent failure. This can be used to design better materials and structures and predict catastrophic events.
Traffic snarls to tumour cells
Another property of disordered systems is jamming, for example, the sudden clogging of a funnel when rice grains stop flowing abruptly after having smoothly passed through it. This phenomenon, a quick transition from a flowing state to a rigid one, occurs due to the tight packing of components in a constrained space. Other contexts in which jamming is relevant are traffic snarls, stampedes, transport of macromolecules within cells, the spread of tumour cells, etc. This has implications for materials science, urban planning, health care and even disaster management.
An unconventional view of the world
Disordered systems help us recognize that the world is not as neatly structured as our school textbooks might suggest, but is rather complex. From the organization of natural structures to the traffic systems that we navigate daily, disorder is everywhere, shaping the way materials, organisms, and even human societies function. As research progresses, our understanding of these disordered systems may reveal new insights into some of nature’s most complex and unpredictable behaviours, and even social organization.
It is a field that refuses to fit into conventional categories, much like the materials and systems it seeks to understand.
Edited by Bharti Dharapuram
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Pinaki's talk is available to watch online on the Matscience YouTube channel.
Shumaila Firoz can be contacted at shumailafiroz4668 [at] gmail [dot] com.
