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Nobel Prizes 2021

Handling complexity: On 2021 Nobel Prize in Physics

The Physics Nobel winners have developed tools to get a handle on complex systems

October 08, 2021 12:02 am | Updated 12:17 pm IST

Bringing to a close speculation about the winner of the Physics Nobel prize this year, the Nobel committee decided to award a trio of researchers . One half went to Syukuro Manabe of Princeton University, U.S., and Klaus Hasselmann of the Max Planck Institute for Meteorology, Hamburg, Germany, for their work in climate science. In the long line of researchers who estimated the warming of the atmosphere due to gases in it, Syukuro Manabe’s modelling, in collaboration with others — and over decades — is a classic work that showed, even in the 1960s, that the atmosphere would undergo another 2.3° C warming with the doubling of carbon dioxide content. Klaus Hasselmann identified a way of treating the random noise-like variations of the weather, devising a method to generate useful “signals” on the scale of the climate. Of interest was the way these models could show the effect of human activities on the climate. The other half of the prize, to Giorgio Parisi from the Sapienza University of Rome, Italy, is for developing a method to sensibly study complex condensed matter systems called “spin glasses” — an outstanding feat in both mathematical and physical innovation. The idea to break what is called “replica symmetry”, seen in a spin glass, in a consistent manner, which was his contribution, led to a method to study one of the simplest models of a genuinely complex system. His work has helped solve problems in mathematics, biology and neuroscience; for instance, how memory is stored in networks of nerve cells.

What ties together the seemingly disparate works — the climate science work by Syukuro and Hasselmann on the one hand and theoretical condensed matter physics work by Parisi on the other — is that both describe complex physical systems. Physics is often thought of as a science of simple systems, and it is mostly celebrated and sometimes chided for this. Even rocket science, which inspires awe for its grandeur and accuracy, is mostly the study of so-called simple systems. Complexity arises when there are many, many interacting pieces in the system, with each moving in an independent way. The deceptively easy-looking problem of water rushing out of a tap is notoriously difficult to understand as to when it makes a transition from simple streamlined flow to a complex turbulent flow. The Nobel winners this year have handled such complex systems and developed tools to get meaningful, quantitative results out of them. Notable in this is the climate scientists’ work, which makes it obvious where science stands on the issue of global warming and estimates the human fingerprint on climate change. With the COP26 summit drawing close, the Nobel committee’s decision only underscores the need to take this into account.

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