Madan Rao likes to build his work bottom-up, brick by brick. Begin with the least complicated situation and slowly build on it, adding bells and whistles slowly to the basic model. All physicists are trained to do that. First in one dimension, then two, then three. Ignore air resistance for the moment. Imagine that the cow is a sphere.-Madan Rao-National Centre for Biological Sciences, Bengaluru-Using equations and concepts of physics to figure out what makes life tick-Such techniques can be used to understand genetics evolution , spread of diseases, climate, industrial processes, society and terrorism.Rao is not a conventional physicist. In other words, he does not research the physical world. He does not seek to understand what atoms are made of, how the universe is evolving, or how matter gets the properties that we see.Yet he is a physicist at heart. His tools are from physics, and he does not know much else at a deep level.Rao is a professor at the National Centre for Biological Sciences (NCBS) in Bengaluru. Using equations and concepts of physics, he is trying to figure out what makes life tick. How does a cell membrane go about its complicated set of tasks every day? How do mitochondria — which generates energy — develop in a cell? How does chromatin — a complex of genetic material and protein — get its organisation? His lab at the NCBS is a room full of papers, books and one computer. He does not need any other equipment.At a basic level, biology is chemistry and physics. At an even more basic level, chemistry itself is all physics. So Rao is trying to accomplish what all physicists do, to build theories from bottom up. Instead of building models of inanimate matter, he is building models of life step by step.Probing biology at such a deep level has its applications. Understanding membranes is a way to figure out how bacteria and viruses get into the cell, or how to get drugs across the membrane into the cell. Understanding anything about life has an impact on human health. That is not all.Rao’s expertise is in statistical physics, the science of aggregate behaviour.Physicists have developed this science to understand how a bunch of atoms and molecules behave, even if we cannot keep track of what individual molecules do.Part of statistical physics is an old but still useful subject, and it deals with properties of large systems that are at peace with their surroundings: for example, a glass of water that is still and has cooled to the surrounding temperature.The other part of statistical physics, about matter that is in flux, is a rapidlyevolving subject with a staggering variety of applications. This branch is called non-equilibrium statistical mechanics.The actual technical definition is complicated. In a nutshell, put rather simplistically, it is the study of the collective behaviour of systems that are in ferment.Since almost everything in nature is in ferment, non-equilibrium statistical physics is one of the most widely-studied subjects at the moment. It has become a useful tool to understand genetics, evolution, spread of diseases, climate, industrial processes, the stock market, society and terrorism, among others.About 20 years ago, Rao met Jitu Mayor, now the director of NCBS. Rao was building a theoretical model of the cell membrane, an artificial membrane of sorts, and Mayor was researching real living membranes.Rao was interested in knowing how well the artificial membrane resembles the actual membrane. The two scientists started collaborating, leading to a series of research papers.Cell membranes are astonishingly complex structures that make life possible. They are not passive boundaries between the living cell and the non-living environment.They are the chief negotiators between the living and the non-living, regulating the flow of molecules into and out of the cell. Bacteria and viruses have to fool the cell membrane to get in. Understanding the cell membrane deeply can give scientists ideas about outsmarting bacteria and viruses. And more.Rao has built a theoretical framework for biologists like Mayor to understand how a cell membrane works. His core ideas are about how the membrane uses energy to become active, and regulate all its functions. When Rao began work on this two decades ago, a theoretical membrane — from which scientists can also develop artificial membranes — was a passive structure. Now, with increased understanding, an artificial membrane that he constructs is no longer a passive entity. It is rich in detail, vibrant with activity.NCBS is part of a cluster of biology institutions that does research on a wide variety of life science problems. This gives Rao the opportunity to interact closely with biologists, and look for areas where they need help. A project that he is beginning now is with S Ramaswamy, professor at the Institute of Stem Cell Biology and Regenerative Medicine.Ramaswamy is interested in understanding how proteins do their jobs in the body. He is especially interested in how proteins, after they are made in the cell, acquire bells and whistles that are critical to their function. It is often the difference between health and disease. These additions are sugar molecules that fine-tune the protein function to a high level of precision. It is hard for biologists to model how the addition of sugar molecules controls protein function in the body. There are far too many things going on at the same time.Statistical physics was partly developed to deal with how order emerges from disorder. For specialists in the field, the whole world is a stage.