Blas Cabrera, the great Spanish physicist friend of Einstein

90 years ago, Albert Einstein and Blas Cabrera walked through Madrid. The first needs no introduction, but the second remains unknown to most of his compatriots. However, Blas Cabrera y Felipe (Lanzarote, 1878 - Mexico, 1945) is one of the fathers of Spanish physics, as well as a benchmark in the field of magnetism. Characters such as Ramón y Cajal, Marie Curie, Niels Bohr and Erwin Schrödinger crossed paths in his life.

“Car ride with the Kocherthalers. I wrote a response to Cabrera's speech at the Academy. In the afternoon, a meeting at the Academy with the king as president. Afterwards, tea with an aristocratic lady”. This is how Albert Einstein described in his laconic diary how March 4, 1923 passed during his visit to Madrid, where he spent eleven days between his conferences in Barcelona and Zaragoza.

The Kocherthalers were a family of German bankers, friends of Einstein, and Blas Cabrera, the physicist who acted as host during his stay in the capital and who, indeed, that day extolled the figure of the genius of relativity in a presentation at the Academy of Sciences , under the watchful eye of King Alfonso XIII.

The precision with which the Spanish physicist exposed the German's work made Einstein respond: "Your words have reached the depths of my heart because they demonstrate the conscious and affectionate way in which you have studied my life's work, echoing the phrase of the poet: We want to receive less praise, and, instead, that it be read to us with application.

Cabrera also had tea that afternoon at the home of the Marquises of Villavieja, a social event attended, among other personalities, by Gregorio Marañón and his wife; Ortega y Gasset, Ramiro de Maeztu and Gomez de la Serna. During the evening Einstein played the violin, and together with the musician Fernández Bordas offered a brief concert to the select audience.

The next day, the host was with the German physicist during a meeting at the Mathematical Society, although it is unknown if he also accompanied him to visit Santiago Ramón y Cajal, "a wonderful old man, seriously ill", according to the genius noted in his diary. .

Cabrera, unknown to the majority of the public, "is the most relevant Spanish physicist of the first third of the 20th century," the historian of science José Manuel Sánchez Ron points out to SINC, "and he was fully incorporated into the international scientific community in his field : the magnetism".

"At the institutional level -continues the expert-, the Board for the Extension of Studies appointed him director of the Physical Research Laboratory in 1911, a center that contributed notably to the development of physics and chemistry in Spain and to its international recognition".

That laboratory was a center of scientific excellence. Cabrera, in addition to directing it, was in charge, together with the researcher Arturo Duperier, of one of its four sections: Electromagnetism. The other three were Chemistry coordinated by Enrique Moles, Spectrometry and Spectrography led by Miguel Catalán and Metrology led by Julio Palacios.

The quality of the work of Cabrera's team, which published around 150 investigations, was recognized by the leading experts in magnetism of the time. One of the most relevant studies was the measurement of the magnetic moments of rare earth ions –15 elements from the lanthanide group, together with yttrium and scandium–.

His basic research has allowed the development of medical magnetic resonance imaging.

His theoretical interpretation of this work led to the advent of quantum mechanics in 1925. The detailed experiments were carried out by Cabrera and Duperier, but the theory was developed by John Hasbrouck van Vleck de Van Vieck of Harvard University.

Van Vleck, Nobel Prize in Physics in 1977, spoke of Cabrera in this way: "In the history of paramagnetism he will be remembered as the physicist who did the right experiment at the right time." In the Nobel book on the Theory of electrical and magnetic susceptibilities, Cabrera's name appears more frequently than that of any other researcher.

"It is difficult to publicize the figure of a character whose work is difficult for the general public to understand," Jacinto Quevedo Sarmiento, former director of the Elder Museum of Science and Technology in Las Palmas de Gran Canaria, told SINC, where a few years ago he organized the Albert & Blas - Einstein and Cabrera exhibition.

“Perhaps one of the best ways to introduce your work is to remember that your research in basic sciences, together with the contributions of your colleagues, served as the basis for the development of the device with which we do magnetic resonance imaging, something that everyone in the world understands that it helps to take care of our health”, comments Quevedo, who considers his countryman the “most universal Canarian scientist”.

Blas Cabrera y Felipe was born on May 20, 1878 in Arrecife, Lanzarote. Three years later the family moved to Tenerife. In La Laguna he went to school and high school, where he met the love of his life, María Sánchez Real, whom he would marry in 1906.

Cajal convinced him to leave Law

Years before, in 1894, he had moved to Madrid to study Law, like his father. But Ramón y Cajal must have seen something in him to convince him –perhaps during some social gathering at the Café Suizo– to leave literature and go over to science.

He did so, and in 1898, the year that gave name to a whole generation of writers, Cabrera graduated in Physical-Mathematical Sciences at the Central University of Madrid, now Complutense. In 1901 he obtained his Ph.D. in Physical Sciences from the same university and he was appointed professor four years later.

Einstein and Marie Curie sponsor their entry into the Solvay Conference

Undoubtedly, one of the most significant years in Cabrera's career is 1928, when he was appointed member of the Scientific Committee of the VI Solvay Conference, the triennial meeting that brought together the most brilliant minds of the time: Schrödinger, Planck, Dirac, Lorentz. , Rutherford, Heisenberg, Born… His candidacy was proposed by his friend Albert Einstein and by none other than Marie Curie. This conference was held in 1930, whose main theme was the specialty of the Spanish physicist: magnetism. In the official photo he appears sitting next to Bohr.

The fame and work of the director of the Madrid laboratory reached the United States. The Rockefeller Foundation decided to subsidize the creation of a new, even more modern National Institute of Physics and Chemistry with $420,000. The building, baptized with the name of his benefactor, was inaugurated in February 1932 and today is occupied by the Rocasolano Institute of Chemistry-Physics of the CSIC.

There, the experimental work to determine the atomic magnetic moments of the rare earths was continued. Moles, Duperier – already a world authority on cosmic radiation – and even his own son, Nicolás Cabrera, also collaborated in these measures.

In 1933 he was appointed secretary of the Paris-based International Committee for Weights and Measures. That same year he participated in the VII Solvay Conference, dedicated on that occasion to the structure of the atomic nucleus. He also participated in the creation of the Santander International Summer University –now the Menéndez Pelayo International University–, a center of which he was appointed rector the following year.

Unfortunately, at this Cantabrian university, he was surprised by the event that would cut short his brilliant career: the Spanish Civil War. After an incident with fascist students, he was forced to organize a group of 130 people to try to return to Madrid, first sailing by boat to the French border to avoid the national front.

With the Civil War, he left Spain to continue doing science

“We undertook that unfortunate trip,” Cabrera told Ortega in a letter, “in which, apart from the inconvenience of the passage to France after the fall of Irún, nothing happened until San Juan de Luz, where the entourage dissolved and the expedition was reduced to less than a hundred”.

But the environment in the Spanish capital was not conducive to science, and at the end of 1936 Cabrera left Spain for good and settled in Paris, where he continued his work in the International Committee of Weights and Measures. It is then that he again participates in the organization of the VIII Solvay Conference on elementary particles and their interactions, although in the end it is suspended as a result of the Second World War.

He was one of the founding members of the Spanish Society of Physics and Chemistry, and the Annals of this institution served as a platform to publish his first works. His experiments on electromagnetism at the Physical Research Laboratory were making him a world expert on the subject, but he felt the need to improve himself abroad.

In March of that year, another of his prestigious friends, Erwin Schrödinger –known for his contributions to quantum mechanics and his famous 'cat'–, sent Cabrera a letter in Spanish in these terms: “And what's up, how pass it vs.? What will become of the magnificent institute of him? Is there any hope of going back there? I guess these are the same questions that you ask yourself daily without being able to answer them. All this is a terrible misfortune."

Schrödinger, who had also been forced to leave Germany a few years earlier due to the rise of the Nazi Party, even went so far as to propose that Cabrera flee to South America: “I thought if, adding our two well-known names in the world – at least in the world of physics – we offered to transplant European physics to a remote place, in Peru, for example”.

Morally sunk in his exile 

In the end it would not be the Andean country where the Spanish physicist would go, but to Mexico. The impossibility of returning to Spain and the pressure from the Franco regime to make him leave the International Committee of Weights and Measures left him "morally devastated", as his son would remember years later. In 1941 Cabrera moved from Paris to the Aztec capital, where he was welcomed with open arms by the Autonomous University of Mexico.

There, in exile, he would spend the last days of his life. Cabrera died on August 1, 1945 due to Parkinson's disease, without his wishes to return to his homeland and rejoin his long-awaited National Institute of Physics and Chemistry fulfilled. "As in other cases, it was a tragedy, another victim of the Civil War," laments Sánchez Ron.

In any case, the legacy of his experiments and his words, such as those he addressed to Einstein during his visit to Madrid, remains: "I hope that at the end of your life, which will also be that of my generation, scientific Spain, which today As soon as you find it in embryo, it has reached the place that it has the inexcusable duty to occupy. So at least we think those for whom optimism is a motor virtue of progress.

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