On November 7, 1915, the London newspaper The Times made headlines as follows: “Revolution in the
science. A new theory of the universe. Newton’s ideas, surpassed ”. A few days later, The New York Times claimed that Albert Einstein had achieved “one of the greatest successes – if not the greatest – in the history of human thought.” It had all started eight years earlier, in 1907. Einstein, sitting at his desk in the Bern Patent Office (Switzerland) as a second-class technical expert, reflected on the implications of the special theory of relativity , which he had formulated in 1905 and from which the famous formula E = mc2 is derived. He wanted to answer the question that had haunted him since he was sixteen: what would the world look like riding on a ray of light? Suddenly, an idea came to mind: “If a person falls freely, he does not feel his own weight.”
He later told his old friend Michele Angelo Besso, who also worked at the Patent Office, that it had been the happiest thought of his life. Einstein had come across the so-called equivalence principle: locked in a closet, there is no way to distinguish whether we are on a planet or are being carried through space at constant acceleration. That is, gravity and acceleration are interchangeable. He had just found the key to building a relativistic theory incorporating gravitation, the future general theory of relativity.
But like any good story, this one has a mystery. From 1907 to 1911, the German physicist was silent. We do not know if he worked on the problem during those years, in which he published scientific articles on other topics. In 1911 he moved from Switzerland to Prague to teach at the city’s German university. It was here that he took the first steps towards his revolutionary hypothesis.
The first thing was to formally develop the principle of equivalence. I would then show that light from a very massive object undergoes a redshift. How did this happen? He had no idea, since he lacked the mathematical knowledge to do so; I just knew it had to happen. In the same way, when moving through a gravitational field, a light ray would experience this phenomenon: since the energy of the beam is reduced when passing through said field and the speed of light is invariable , what decreases is its frequency. Or what is the same, the wavelength increases and its color shifts to the red side of the spectrum.
It was his first run into mathematics. Special relativity had not required very complex equations, but if he wanted to include gravity he needed a powerful device that he knew little about: the tensor calculus. Luckily, he had friends who could help him. One of them was a man twenty years older than him and to whom history has done little justice: Georg Alexander Pick.
They both liked to play the violin, and they used to walk around Prague talking about math. Pick also knew the work of two Italians, Gregorio Ricci and Tullio Levi-Civita, who suited him perfectly to Einstein’s theory . It is possible that he recommended reading his articles, but if he did, he ignored him. Such forgetfulness would delay his work for several years.
The third step was to discover that massive objects not only attract other bodies, but also light. It was not a new idea, since Newton’s physics already predicted it. In fact, the German astronomer Johann Georg von Soldner conjectured in 1801 that, if light consisted of small particles, a ray that passed the surface of the Sun would be deflected 0.84 arc seconds. Einstein’s calculations yielded other values, which he would later fix exactly.
Shortly after arriving in the Czech capital, our man received an offer from the Zurich Polytechnic Institute to teach. He didn’t think twice, for he disliked the pretentious and servile attitude of the people in Prague. But before leaving, he came to a revolutionary conclusion: the space around a massive body is non-Euclidean.
Einstein didn’t know much about this. After months of unsuccessful calculations, he wrote to Marcel Grossmann, an old friend: “Grossmann, you must help me or I will go crazy!” And so it was: they worked together on developing a first draft of the equations. But there was still a long way to go. In 1913, Max Planck, father of quantum theory, and fellow physicist Walther Hermann Nernst convinced Einstein to accept a teaching position in Berlin without a teaching load . Thus, the adolescent who denied his German citizenship returned as an adult to the country’s capital.
Something that worried the father of relativity a lot was getting experimental confirmation. This time he was helped by an enthusiast of his theory, Erwin Finlay-Freundlich, an astronomer he knew from his time in Prague. Einstein was sure the light was buckling as he passed a massive body, and he urged him to test it. The first thing Finlay-Freundlich did was to see if the passage of starlight next to Jupiter produced that effect: nothing.
Then he realized that the smallest celestial object with which the deviation could be measured was the Sun, but it was impossible to see stars by day. At the end of 1912, one of the two realized that there was a unique moment that would allow it to do so: they had to organize an expedition to make observations during the next total solar eclipse, which would occur on August 21, 1914. April 6 of that year, Einstein settled in Berlin, and on July 2 he was appointed a member of the Prussian Academy of Sciences . In this way, he was able to get involved in the preparations for the mission.
On July 19, Finlay-Freundlich left for Crimea accompanied by two technicians. But they did not even manage to mount the telescope: on August 1 World War I broke out and the Russians arrested the three members of the team, who they took for spies . Fortunately, the Germans had captured several Russian officers and the Academy lobbied to exchange them for the scientists. Einstein, instead of being happy to have his friend back, got angry with him.
In 1914, general relativity was far from being a complete theory. Einstein outlined each of his blind spots in a race of trial and error. He faced two major problems: one, that his equations could be used for a rotating system; and two, to give an exact account of the advance of the perihelion of Mercury (see box on the next page). In addition, he had to correctly calculate the deflection of the light. On November 4, 1915, he presented a new version of his equations at the Prussian Academy of Sciences, although he acknowledged that he had not made great strides since his first attempts with Grossmann.
On the 11th he took a wrong step and started again. A week later he made new changes and, to his surprise, discovered what was the ratio of the 43 arcseconds advance per century of Mercury’s orbit that Newtonian mechanics did not explain. In addition, he obtained the exact figure for the deflection of light: 1.75 arc seconds. Einstein continued to work feverishly: on November 25 the final field equations were before his eyes . It was the happiest moment of his life, according to him.
