IES Seminar - Prof Shijun Liao - Ultra-chaos: statistics instability and crisis of reproducibility


Hudson Beare Lecture Theatre 2


Thursday, September 21, 2023 - 13:00 to 14:00

We are pleased to announce our next speaker, Professor Shijun Liao, from Shanghai Jiaotong University, China, on Thursday 21st September 1pm-2pm to present his work on "Ultra-chaos: statistics instability and crisis of reproducibility". 

The talk will take place in the Hudson Beare Lecture Theatre 2. We will also use the video link below through MS Teams (link below) for those who prefer to join online. 

Abstract: Chaos theory is widely regarded as the third greatest scientific revolution in physics in 20th century, comparable to Einstein’s theory of relativity and the quantum mechanics.  It is widely believed that, although trajectories of a chaotic system are unstable due to “butterfly-effect”, its statistics should be stable and thus its results should be reproducible in the meaning of statistics.  Note that reproducibility is the cornerstone of modern science.  Unfortunately, more and more experiments have been reported to be not reproducible, which leads to the so-called “crisis of reproducibility”.  By means of a new strategy of numerical technique, namely the “clean numerical simulation” (CNS), we found that there exist the so-called “ultra-chaos” whose statistics are unstable to small disturbances, corresponding to statistics instability.  Since random tiny disturbances are unavoidable, in practice any experimental and/or numerical results of an ultra-chaotic system cannot be repeated even in the meaning of statistics.  Therefore, even if all artificial disturbances are excluded, the crisis of reproducibility still cannot be avoided in practice.  Ultra-chaos as a new concept reveals the incompleteness of the modern paradigm of scientific researches, which is based on the reproducibility of experiments.  In this talk, we briefly introduce the basic ideas of the “clean numerical simulation” (CNS), describe the definition of ultra-chaos, give a few examples of ultra-chaos, and suggest some conjectures and open questions, including the so-called “modified fourth Clay millennium problem”.                           

Bio: Prof. Liao gained his PhD in 1992 from Shanghai Jiaotong University, China.  Thereafter he worked as a teaching staff there, became a professor in 1995 and the Chunsheng Chair professor in 2001.  He is now the head of State Key Laboratory of Ocean Engineering.

Prof. Liao works in nonlinear mechanics, ocean engineering and applied mathematics.  He is the founder of the “homotopy analysis method” (HAM), an analytic approximation method for highly nonlinear problems.  Unlike other methods, the HAM can provide a simple way to guarantee convergence of solution series.  Today, the HAM has been widely accepted and used by researchers all over the world.  Besides, Prof. Liao proposed a new strategy to gain reliable results of chaotic systems, called the “Clean Numerical Simulation” (CNS).  Using the CNS, he attacked a famous problem, i.e. the periodic orbits of three-body problem that can be traced back to Newton in 1687, and proposed an effective approach and roadmap to numerically gain planar periodic orbits with arbitrary masses by means of machine learning.  The CNS has been successfully applied to some turbulent flows now.      

Prof.-Dr. Liao has published two books and more than 200 journal articles.  His books and publications have been cited 20163 times in scholar-google.  He was awarded “Shanghai Peony Award in Natural Science”, “National Award in Natural Science” and “Shanghai Scientific Elite”.  He was listed among “the Highly Cited Researcher” in 2014, 2015 and 2016.


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