# Mathematical physics that proved that the future of the universe is well defined | Science

The Spanish philosopher José Ortega y Gasset affirmed: “To be surprised, to be surprised … is to begin to understand.” The same idea pushed from girl to Yvonne Choquet-Bruhat to want to “unravel some of the secrets of the strange universe in which we live, and the role that human beings play in it,” as expressed in their autobiography. The French scientist, who turned 96 on December 29, has always hoped that physics and mathematics could help us carry out this effort. His contributions, fundamentally framed in the field of general relativity, have made him a leading figure in the area of mathematical physics of the twentieth century.

Yvonne Choquet-Bruhat – the surname “Choquet” acquired in his second marriage to Gustave Choquet – was born in Lille (France) in a cultured family. His father, Georges Bruhat (1887-1945), was a professor of physics at the University of Lillle, and his mother, Berthe Hubert (1892-1972), professor of art, literature and philosophy in several French high schools. From an early age, Choquet-Bruhat showed great talent for physics and mathematics. At eighteen he won a silver medal of the “General Concours”, a nationwide competition in which the best students in the country were rewarded. In 1943 he began his Mathematics studies at the Superior Normal School of Sévres, on the outskirts of Paris, where he graduated three years later.

It was then that he began his research activity at the prestigious French National Center for Scientific Research (CNRS), under the advice of the renowned mathematical physicist André Lichnerowicz. He completed his thesis on the so-called initial value problem (or Cauchy problem) in the context of general relativity, in which the existence of solutions for the equations proposed by Albert Einstein is studied, when they meet certain starting conditions. In the cosmological framework, the question would determine whether the future of the universe is well defined when we only have its information in a “specific time”, which is known as the initial data of the problem.

Choquet-Bruhat managed to prove, by studying complex differential equations and geometric techniques, that if it is based on an initial fact that meets certain plausible physical restrictions, there is only one possible future for the universe

Among other merits, it is worth noting that she was the first woman chosen to be part of the French Academy of Sciences

** Coffee and theorems** It is a section dedicated to mathematics and the environment in which they are created, coordinated by the Institute of Mathematical Sciences (ICMAT), in which researchers and members of the center describe the latest advances in this discipline, share meeting points between mathematics and other social and cultural expressions and remember those who marked their development and knew how to transform coffee into theorems. The name evokes the definition of the Hungarian mathematician Alfred Rényi: “A mathematician is a machine that transforms coffee into theorems.”

Editing and coordination: **Agate Timon** (ICMAT).

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