# Albert Einstein

## Albert Einstein (1879-1955)

Figure 27 Albert Einstein

Albert Einstein was born in Ulm, Germany on 14 March 1879. The following year he and his family moved to Munich where he had a successful, though not brilliant, school career. In 1896 Einstein renounced his German citizenship and started to study for a high-school teaching diploma at the prestigious Eidgenössische Technische Hochschule (ETH) in Zurich, Switzerland. Amongst his fellow students at ETH was Mileva Marie, who became his first wife. Einstein graduated in 1900 and in December of that year submitted his first paper to a scientific journal. However, he failed to get any of the university positions that he applied for, and after some temporary school teaching he became, in 1902, a technical expert (third-class) at the patent office in Bern. He continued to pursue his interest in physics while at the patent office, and worked on a doctoral thesis during his spare time.

1905 was an extraordinary year in Einstein's life and in the progress of science. During that year he produced four of his most important papers. In the first he explained Brownian motion - the apparently random motion exhibited by pollen grains and other small particles when they are suspended in a fluid. According to Einstein, the motion is a result of the incessant bombardment of the suspended particles by molecules of the fluid. The quantitative success of this explanation established beyond reasonable doubt the existence of molecules, which until then had been questioned by many physicists. In his second 1905 paper, Einstein formulated a theory of the photoelectric effect - the liberation of electrons from a metal exposed to electromagnetic radiation. His explanation was one of the earliest applications of quantum physics and was an important step in the development of that subject. It was mainly for this piece of work that Einstein was awarded the Nobel Prize for Physics in 1921. His third and fourth 1905 papers concerned the special theory of relativity. He laid out the foundations of the subject in the third paper and in the fourth he provided a brief but eloquent justification of his famous equation E = mc2, which uses c, the speed of light in a vacuum, to relate the mass m of a body to its total energy content E.

Figure 28 Einstein's 1905 paper On the Electrodynamics of Moving Bodies. This was his first paper on special relativity.

Although these brilliantly original papers eventually established Einstein as a physicist of the first rank, three more years were to elapse before he obtained his first academic post. During that time he worked on a variety of topics and did pioneering work on the quantum physics of solids. In 1909 he was finally appointed to a lecturing post at the University of Bern, in 1911 he became a professor at the University of Prague and in 1912 he returned to Zurich, as Professor of Theoretical Physics at ETH. By this time his attention was focused on the search for a general theory of relativity that would extend his earlier work on the special theory. The principle of equivalence which he formulated in 1907 had convinced Einstein that a general theory of relativity would also be a new theory of gravity, and it was from the gravitational point of view that the problem of general relativity was attacked. In 1914 Einstein moved to Berlin, the main centre of scientific research in the German-speaking world, to take up a research professorship that would free him from teaching duties. He and his wife separated soon after the move, and were eventually divorced. Einstein continued to work on general relativity and in 1916 produced the first systematic treatment of the subject in a long paper entitled Die Grundlage der allgemeinen Relativätstheorie ('The foundations of general relativity theory'). The creation of general relativity was one of the greatest intellectual achievements of the twentieth century: it led on to the study of black holes and the prediction of gravitational waves, and it provided a firm basis for future investigations in cosmology - the study of the Universe as a whole. Observations carried out in 1919, during a total eclipse of the Sun, confirmed one of the key predictions of general relativity: the gravitational deflection of starlight passing close to the edge of the Sun. This quantitative success of Einstein's theory was widely reported, and did more than any other event to make Einstein into an instantly recognised icon of scientific genius.

Figure 29 The article from the Times of 7 November 1919. Copyright Times Newspapers Limited, 1919.

Soon after completing the general theory, Einstein turned his attention to the quantum theory of electromagnetic radiation and postulated the existence of stimulated emission - the process that now underpins the operation of lasers. However, in 1917 he became seriously ill. He was nursed back to health by his cousin Elsa, whom he married in 1919. His second marriage seems to have been reasonably happy, but he was not, by his own admission, a good husband.

By the early 1920s Einstein's best scientific work was done: he wrote in 1921 'Discovery in the grand manner is for young people… and hence for me is a thing of the past'. He was nonetheless extremely influential in the physics community and he did much to prepare the ground for many later developments. He travelled a lot, and became increasingly active in social and political causes, particularly in support of Zionism. (Many years later he was offered the presidency of Israel, which he declined.) In 1932, Einstein and his wife left Germany for good, mainly in response to growing anti-Semitism, and moved to the USA where Einstein settled as a professor at the Institute for Advanced Study in Princeton, New Jersey. Einstein eventually became an American citizen, though he also retained the Swiss citizenship he had held since his twenties. Although Einstein was a believer in peace and harmony, and eventually argued for a world government, he also recognised the dangers of Nazism and the potential power of atomic science. As a result, in 1939, he was persuaded to co-sign a letter to the American President, Franklin D. Roosevelt, warning of the possibility of atomic weapons. This is widely thought to have had a decisive effect in prompting the US government to undertake the development of the atomic bomb, though Einstein himself played no part in the project.

Although Einstein had been deeply involved in the birth of quantum physics, he became increasingly dissatisfied with the way the subject developed after the mid-1920s. He did not believe that it gave a truly fundamental account of natural phenomena. His last major contribution to the field was the development of Bose-Einstein statistics in 1925. However, his name is also recalled in the Einstein-Podolsky-Rosen experiment, a 'thought experiment' proposed in 1935 in an attempt to show that quantum physics was seriously flawed. The attempt was unconvincing, but it did emphasise the gulf that separated quantum physics from the classical physics that preceded it. The other project of Einstein's later years that continues to be remembered is his search for a unified field theory that would bring together gravity and electromagnetism. He continued to work on this up to the time of his death, often with great ingenuity, but little of that work is regarded as being of enduring value. He died in Princeton in 1955.

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