Statistical physicist Prof. Leihan Tang joins Westlake University as a full-time chair professor of the Center for Interdisciplinary Studies of the School of Science. He will also establish and lead the statistical physics and complex systems lab.
Tang was elected as a fellow of the American Physical Society.
"My work is to translate our curiosity about the real world into equations," Tang said.
What are complex systems?
Complex systems are composed of many components that act collectively with inherence and evolution over time.
Tang takes a bottle of water out of the fridge. "For example, water can exist as a gas, liquid and solid. What happens to the structure of water when the temperature changes? What occurs in that process?"
To answer these questions, one must look at the water molecules as a whole. When the temperature rises or drops, how do the water molecules interact with one another? This is known as a collective action.
In our day-to-day lives, collective actions tend to be complex and hard to predict.
The bottle of water is now covered in a layer of water drops. Inside the bottle, water molecules jump up and down in erratic trajectories. Over a century ago, Austrian physicist Ludwig Boltzmann discovered that heat transference wasn't one-directional. Rather, hot molecules moved faster than cold ones, which made them more likely to collide into cold molecules. Thus, it was more likely for heat to pass from hot objects to cold ones.
Introducing probability into physics gave rise to statistical physics. Scientists specializing in statistical physics don't study molecules; rather, they use statistics to decipher their collective actions. This is Tang's specialty.
Tang started his academic journey in spatial physics at the University of Science and Technology. Looking back, he was only scratching the surface. "Unlike math, one needs a deep understanding and knowledge of natural phenomena to study physics well," he said. "With math, you can rely on the logic." He noted that, on the path of physics, it is impossible to engage in deep contemplation and ask good questions without conducting experiments and interacting with real systems.
Tang went to Carnegie Mellon University in 1981 through the China-U.S. Physics Examination and Application program organized by the Nobel laureate Prof. Tsung-Dao Lee. In the U.S., he studied statistics under Prof. Bob Griffiths, a leading scholar known for being meticulous. "That was when I started studying complex systems in-depth using certain models," he said. "I began to contemplate combining mathematic theories with actual physics systems."
Complex systems are everywhere. From cell movements to the universe, from flocks of birds to the motion of hurricanes, from the ups and downs of real estate prices to political campaigns, we find ourselves in endless complex systems. Even human bodies are the result of evolution, another complex system.
The combination of math and physics makes statistical physics a natural interdisciplinary subject. Tang doesn't have specific research interests; his interests grow as he learns and collaborates with individuals in other disciplines.
Life sciences and complex systems
Tang spent eight years working as a postdoctoral researcher after he graduated from Carnegie Mellon University in 1987. He briefly served as a lecturer at the Blackett Laboratory, Imperial College London, before joining Hong Kong Baptist University in 1997 as an associate professor, ascending to the rank of full professor in 2005.
Over time, Tang turned his focus to life itself. He led his team to work with experimental scientists in life sciences to develop a series of quantitative tools and models in statistical physics. By studying the collective behavior of a large number of microscopic individuals, he revealed the veil of complex systems and provided a unique perspective for life science research.
So far, he has made several original discoveries in microbial metabolism, protein aggregate formation and wetting, cell population movement, and physiological processes related to puberty.
You might have experienced this: When walking into a pitch-dark room, at first you can't see a thing. A few minutes later, your eyes adapt to the environment, and gradually you regain some visibility.
In 2019, Tang and his student Shouwen Wang co-authored a paper in which they established a model to describe the mechanism behind this phenomenon: how a group of adaptive cells achieve collective oscillation by adapting different frequencies.
Imagine a theater with a full audience, where each person represents a cell. When the show concludes, the audience starts to applaud. At first, they aren't in sync, but after a while the applause tends to reach congruence. Such rhythm is especially strong when the crowd demands an encore.
Scientific research might start small—from the collective behavior of cells to organs, and further on to complex organisms. Research that crosses the border of micro and macro brings us closer to the nature of life.
In the era of AI
In the 21st century, we are surrounded by complex systems, including urbanization, global warming, sustainable development, AI, and translational medicine. While opinions differ as to which most defines this century, it's fair to say that biology, complex systems and AI have propelled the scientists of our time to the forefront of interdisciplinary research.
The launch of AlphaFold provides an example of how interdisciplinary research has exploded.
Scientists have accumulated massive standard data on protein structures, which provided the foundation for AlphaFold. The development of genomics, proteomics, and metabolomics gathered further data which provided the foundation for the interdisciplinary research of physics, biology and AI with the help of AI predicted data.
This is what inspired Tang. In an internal meeting, he pulled out a sketch and tried to find the bursting point for complex system research. There were three circles in the sketch. One represented the School of Life Sciences, where researchers excel at researching every aspect of organisms. The second stood for the School of Science, where researchers are adept at establishing models with mathematical tools. The third was the School of Engineering, where researchers push the limits of AI.
Tang has unlimited expectations of what the three could achieve.
He started to pay attention to Westlake University last summer. At the beginning of 2024, Tang visited Westlake and concluded: "There's a group of smart and idealistic people at Westlake – that makes it a good place to do research. I can't say that I am learning something new every day, but there's a chance to make that happen at Westlake."
