The young aspiring mathematician took notes with impeccable care. He knew his German friend would also appreciate it. He didn't know it yet, but that classmate sitting next to him in geometry class would eventually become one of the most brilliant minds of the 20th century: Albert Einstein. Sherlock Holmes had John Watson, Don Quixote had Sancho Panza, and Einstein always had Marcel Grossmann by his side, the faithful companion who not only shared his notes but also became a key figure in the development of a theory that would change our understanding of the universe. "Those notes were my salvation," Einstein explained.

The Universe is expanding, and it's doing so ever faster, although astronomers don't quite know why. To find out, a team of cosmologists from the University of Toulouse III - Paul Sabatier and the University of Geneva have put the current model of the Universe predicted by Einstein's own theories to the test. The results, published in the magazine Nature Communications, indicate that the theory of general relativity, which the German physicist developed more than a hundred years ago, may be insufficient to accurately describe the evolution of the universe. "We have enough evidence to believe that Einstein's theory is not definitive," says Isaac Tutusaus, a Catalan cosmologist at the University of Toulouse III - Paul Sabatier and co-author of the study.

The dining room of the Hotel Métropole in Brussels gave off the usual aroma of morning coffee. The most brilliant minds of the early 20th century gathered around the tables, deep in intense and profound conversations, commenting on and refuting the presentations given the day before during the final session of the Fifth Solvay Conference. This series of meetings between eminent scientists was initiated by the Belgian chemist Ernest Solvay and, since 1911, was dedicated to delving into the most complex problems of physics and chemistry.