Professor James Peebles - A Second Laureate of the Georges Lemaître International Prize Honored by the Nobel Prize in Physics

The Nobel Prize in Physics 2019 has been awarded to three scientists "for contributions to our understanding of the evolution of the universe and Earth's place in the cosmos" among which, besides Professors Michel Mayor (Université de Geneva) and Didier Queloz (Université de Geneva and Cambridge University), we are pleased to welcome Professor James (aka Jim) Peebles from Princeton University (USA), "for theoretical discoveries in physical cosmology" (see ).

At UCLouvain especially, but also more widely in Belgium, this announcement was indeed welcomed with real happiness because it honors a great cosmologist of the twentieth century. This decision was also received with a certain dose of pride because Jim Peebles is the first winner, in the spring of 1995, of the prestigious Georges Lemaître International Prize awarded since that date every two years by UCLouvain. In addition, in 1996 Jim Peebles was also a Doctor Honoris Causa of the Faculty of Sciences of UCLouvain. These recognitions were granted for his many foundational scientific contributions to modern physical cosmology, which are now recognized by the Nobel Prize in Physics. Jim Peebles is also as a great defender in North America of the scientific legacy of Georges Lemaître in modern physical cosmology. Jim Peebles visited in 2014 the Georges Lemaître archives at UCLouvain.

With Professor Kip Thorne (California Institute of Technology, USA), recipient of the Nobel Prize in Physics in October 2017 and winner of the International Georges Lemaître Prize in October 2016, Jim Peebles is the second laureate of the Georges Lemaître Prize to be honored next with the award of the Nobel Prize in Physics. A double distinction that certainly is also in the spotlight of the Georges Lemaître International Prize, now awarded by the Louvain Foundation of UCLouvain.

Continuing directly in the path traced by Georges Lemaître, over the past fifty years Jim Peebles' original and profound contributions to physical cosmology have led to the transformation of this broad field of fundamental research from a state of conceptualization and theoretical speculation to that of a science in its own right based directly on the active observation of the universe and totally subject to the intellectual rigor and critical approach of scientific experimental methodology. The theoretical paradigm developed by Jim Peebles since the 1960s is an essential contribution to the contemporary conceptual framework for understanding the universe and its evolution since its inception.

The Big Bang theory describes the universe since its very first moments. Since "This unique moment, which had no yesterday" [Georges Lemaître], when the Universe was extremely dense and hot, there are nearly 14 billion years. Since then the Universe has been constantly expanding and cooling, becoming ever larger and colder. Barely 400,000 years after the Big Bang, the universe became transparent, and the light was able to spread freely to reach every corner, including our detectors on Earth, and penetrate all the space offered by the Universe. Today, this cosmological fossil radiation, or Cosmic Microwave Background (CMB) is omnipresent all around us and, encoded in its rich distinctive properties, it is a precious messenger for many of the secrets of the Universe. With the theoretical tools and calculations he has developed, Jim Peebles has succeeded in interpreting these early fossil traces of the genesis of the universe and in discovering new physical processes of importance for his understanding today.

And so in a totally unexpected way, over the last decades Jim Peebles' work has revealed to us a Universe of which only 5% of the matter and energy that participates in its gravitational expansion is known to us. This 5% is the material that specifically composes the stars, the planets, all that can be found on Earth, and finally ourselves. The remainder, 95% of its content, is still totally unknown, and is designated, if nothing better, as being dark matter and dark energy (see again ).

As Jim Peebles says in his interview with the Nobel Committee ( ), his scientific adventure is certainly comparable to that of an explorer of the Universe which, in its cosmological peregrinations, discovers secrets - worthy of a Georges Lemaître Prize and the Nobel Prize of Physics - and mysteries concerning our Universe. These mysteries are indeed those of dark matter and dark energy, whose indisputable existence is today one of the major challenges for modern physics of the 21st century. And how does Jim Peebles dream of solving this cosmological and astrophysical enigma that he himself actively contributed to being unveiled by Mother Nature?:

"One of the wonderful things about this exploration is that of course we do not know what we will see. And it is true here. I hope that we will be surprised by what is the nature of the dark matter. It might be something that has already been considered seriously. If so, the demonstration will be a detection, perhaps in the laboratory. There are remarkably sensitive experiments now hoping to detect the interaction of dark matter with ordinary matter. It might be because of its annihilation that releases energy that can be detected as radiation. But my romantic dream - I guess I'm in love with these things - my romantic dream is that we will be surprised yet once again. I'm hoping that will be the case. "



Published on November 19, 2019