Nobel Prize in Physics: why a prize for theorists of complex systems | Conicet researchers explain the reasons for today’s award

Researchers Thanks Manabe, Klaus Hasselmann and Giorgio Parisi were announced as the winners Nobel Prize in Physics 2021. As reported by the Swedish Academy of Sciences, they received the highest honor in the field for “their innovative contributions to our understanding complex physical systems“. More specifically, their work related to mathematical modeling, a fundamental tool for understanding climate change, global warming and the role of human actions. On December 8, during the ceremony in Stockholm, will receive $ 1.1 million, the equivalent of SEK 10 million.

Contrary to what happened on Monday with the Nobel Prize in medicine, this time the The prize was shared. Half went to Giorgio Parisi (Italian, Sapienza University of Rome), recognized for the discovery of “hidden patterns in complex and disordered materials”, keys to understanding the theory of complex systems. From his work, it has been possible to describe many different materials and phenomena, ranging from atomic scale to planetary scale. The remaining half was divided between Thanks Manabe (Japanese, Princeton University) and Klaus Hasselmann (German Max Planck Institute for Meteorology), distinguished for their contributions to the creation of climate models. While the first demonstrated how increasing greenhouse gas emissions caused temperatures to rise, the second designed a model that relates weather and climate to explain why we can continue. to trust climatic instruments even though the weather is chaotic. and editable.

The complexity of complex systems

“It’s difficult to synthesize, but I will try: in a word, the physics of complex systems is the physics of noise. It constitutes one of the great advances in physics over the past 60 years, insofar as it has caused a revolution and brought the discipline closer to many applications “, he underlines. Pablo Mininni, doctor of UBA and principal researcher of Conicet at the Institute of Physics of Buenos Aires. Today, physics is applied in a wide range of fields: from life sciences, neuroscience and stock modeling, to climate change. “We are used to thinking that the nature around us is in balance, but many systems are not and walk on the border between order and disorder.. Although the atmospheric system seems balanced to us, it actually receives energy from the sun all the time, which is converted into motion, winds and storms, and dissipated into heat, ”continues Mininni.

The main characteristic of complex systems, in this sense, is their variability and his fluctuations. Parisi was one of the referents who made the most contributions ranging from particle physics to others related to cosmological scales. One of the most famous in the scientific field is its research related to the so-called “Spin glasses”. “A magnet is made up of a group of particles that line up in the direction of the magnetic field that you see. It forms a system in which matter can be totally in a disorderly, ordered state, or in the midst of order and disorder, ”says the physicist.

With this same criterion, Parisi approached a more well-known phenomenon: turbulence, the disordered movement of a fluid, which one notices while stirring the coffee in a cup, as well as, which is perceived while traveling by plane and passing a situation of apparent balance and calm to the experimentation of shaking. “The great advantage of this type of theory is that it allows us to recognize what part of the noise we see constitutes the dynamics of the system. Led to climate change, it makes it possible to discern those phenomena which are not part of the natural variability of the climate but which have a link with human action“, precise.

Human responsibility in climate change

“The Nobel Prize is a huge recognition, it makes me very happy that climate change is recognized as a problem in all areas. Manabe and Hasselmann laid the foundation for everything we know today about the climate system and made it possible to justify responsibility for human activity“, dice Anna sorensson, PhD from UBA and Conicet researcher at Sea and Atmosphere Research Center.

In turn, Japanese and German scientists have carried out surveys to explain how carbon dioxide increases temperature. “Manabe worked in the 1960s and created the first physical model of energy balance. For decades, he was a pioneer in estimating that if CO2 doubled, the global temperature could rise by 2 ° C. Today, the estimate varies between 1.5 ° C and 4.5 ° C, so it was quite correct within that range, ”explains Sorensson. Its virtue was to design a model almost 60 years ago, very simple compared to the tools used today, but sufficiently calibrated to describe the current and future climate variability scenario.

And then he continues with the reference of the other distinguished researcher: “Hasselmann was the first to define traces left by climatic forces in the atmosphere. He characterized the traces left, for example, by solar radiation and carbon dioxide. They are what, in short, allow us to attribute changes to specific causes and to affirm the implications of human actions on climate change ”. Likewise, he built simplified models oriented towards ocean variability problems. The oceans have a very long “memory”, so if their circulation is affected, the system is able to “remember” it for several centuries. Generally, the contributions of both have served to justify that the main cause of climate change is human activity.

Following the presentation of the Nobel Prize in Medicine on Monday and in Physics on Tuesday, this week’s program continues with the presentation of the Nobel Prize in Chemistry on Wednesday, the Nobel Prize in Literature on Thursday, the Nobel Peace Prize on Friday and the Nobel Prize economy Monday.

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