Einstein, Albert (1879-1955)

      He was one of the greatest figures in physics. Apart from his creation of the special and general theory of relativity, he made he made great contributions to statistical mechanics and to the quantum theory, specially the quantum theory of radiation.

      Einstein was born on March 14, 1879, at Ulm, Germany. The family moved soon, however, to Munich, where his father started a small factory, and the boy began his schooling there while the school instruction with its pedantic methods bored him, his uncle on his father’s side aroused his interest in mathematics, and this had a lasting influence. After the family moved to Italy Einstein continued his schooling in Aarau, Switz. In 1896 he entered the Swiss Federal Polytechnic School in Zurich to be trained as a teacher in physics and mathematics. He did not find the instruction very inspiring and occupied himself mostly with the reading of the works of Ludwig Boltzman, James Clerk Maxwell, Hermann Helmholtz, Heinrich Hertz and Gustav Kirchhoff. In 1900 he received his diploma and acquired Swiss citizenship. (He received a PH.D. degree in 1905 from the University of Zurich.) he searched in vain for an academic position and finally took a post with the patent office in Berne,

 where his main duty was the preliminary examination of patent application. His job left him with ample time to contemplate the fundamental problems in physics. The year 1905 saw the appearance of four Einstein’s important papers. Each contained a great discovery in physics: the creation of the special theory of relativity; the establishment of the mass energy equivalence; the creation of the theory of Brownian motion; the foundation of the photon theory of light. In a symbolic fashion these papers chartered the three main directions in physics to which Einstein contributed the most: the theory of relativity, statistical mechanics and quantum theory of radiation.

       In 1909 Einstein became professor at the University of Zurich; in 1910 he joined the German university in Prague (then part of the Austrian-Hungarian empire), returning in 1912 to Zurich as a professor at the Swiss Federal Polytechnic School. Finally, in 1913 he became a professor at the University of Berlin, the director of the Kaiser Wilhelm institute, and a member of Prussian Academy of Science. During this time Einstein came to the conclusion that the correct generalization of the special theory must also furnish a theory of gravitation. His efforts were finally successful, and after several preliminary versions he published in 1916 his great paper on general theory of relativity. Beside this he contributed to the problems on statistical mechanics.

       As his fame mounted he became, much against his will, an important public figure. He was appointed to the Intellectual Cooperation organization of the League of the Nations (1922), and his interest at social problems, his fame and his lucid way of speaking resulted in his appearing many times in public either to draw attention in social problems or to discuss the recent theories of physics. He traveled widely in Europe, the United States and Asia. His visit to United States in 1921 was for the purpose of supporting the Zionist movement.

       In 1922 he received the 1921s Nobel Prize in physics “for the photoelectric law and his domain of theoretical physics.” the photoelectric was contained in 1905 paper on the photon.

       Beginning with the 1920s Einstein’s approach to the unsolved problems of physics became increasingly divergent from the main development in physics. In 1926 Erwin Schrodinger, on one hand (wave mechanics), and Wern Heisnberg, Max Born and Pascual Jordan, on the other hand (matrix mechanics), development the quantum theory of material system.

        Through the theory was eminently successful, the probabilistic interpretation connected with it made Einstein believe the theory was provisional nature. This belief was only strengthened by the fact that the methods of the general theory and that of the new quantum theory were quite different. As well shall see, the general theory succeeded

      In geometrizing the laws of physics in the sense of the physics (at least as far as the laws of gravitation were concerned) were but geometrical propositions concerning the geometry of space-time. Einstein felt that the proper development of physics should lie in the reduction of the other laws of physics as well geometrical propositions. Unified field theories. The name arose because the aim was to demonstrate that boat the gravitational field and the electromagnetic field stem from the geometrical properties of space-time unifying thereby in a sense the fields. For the rest of his life Einstein’s main interest in physics was in that direction. However, he also contributed to the problem of the probabilistic interpretation of quantum theory, by drawing attention critically to the difficulties inherent in it.

      During the late 1920s the political situation in Germany deteriorated more and more. When Einstein left Berlin in 1932 for a visit to California he was already aware that Adolf Hitler and the Nazi party would soon be

 in power. Einstein returned to Europe, though not to Germany, resigned from his positions in Berlin and prepared for his emigration to the United States. During the winter of 1933 he joined the Institute for Advanced Study in Princeton, N. J., and settled there for the rest of his life. He became a U. S. citizen in 1940. At the Institute Einstein continued his work on general relativity, the unified field theories and the critical discussion of the interpretation of quantum theory. He also co-operated with charitable and social organizations to help the large numbers of refugees who were arriving in the United States from Nazi Germany.

      In 1939 it became known that two German physicists, Otto Hahn (q. v.) and Lise Meitner, had had discovered the fission of uranium. Enrico Fermi (q. v.), an Italian physicist who at that time had arrived in the United States, became aware of the fact that if the fission could be made into a self-perpetrating chain reaction, enormous quantity of energy could be released. Fermi and the Hungarian physicist Leo Szilard, realizing the important military implications, decided to point this out the U. S. government. Szilard and Eugene Wigner, another Hungarian physicist, asked Einstein, whom they had known in Berlin, to appeal directly to president Franklin D. Roosevelt, pointing out if Germany succeeded in developing a bomb based on these principles. Einstein’s famous letter to president Roosevelt resulted in the Manhattan project and in the development of the atom bomb.

      In 1945 Einstein retired from his position at the institute but continued to work there until his death in Princeton on April 18, 1955.

Scientific contributions—Einstein, like Isaac Newton, at his death left a physics vastly changed by his own contributions. As pointed out previously his main achievements lay in the theory of relativity, statistical theory and the photon theory of light. In addition to these discoveries he left to the world of physics a new viewpoint: the aim of geometrization of physics.

      The theory of special relativity arose from the attempt to reconcile the laws of the mathematics with the laws of electromagnetic field. Einstein realized that this can only be accomplished if we analyze carefully the methods observers would use to correlate their time and space measurements while moving with a constant velocity relative to each other. In this way he was able to specify general conditions which theories must satisfy to be deemed laws of nature, and he also showed how mechanics should be modified so that this might be accomplished.

      From purely theoretical side the special theory thus furnishes a powerful guiding principle in our search for the laws of nature. Moreover, it shows that our simple concepts of space and time, upon which the laws Newtonian mechanics were based, require profound modifications. This entailed that the length of a meter rod and the duration of a second on a clock depend on the state of the motion of the observer with respect to the instruments. For an observer a moving meter rod will look shorter and the seconds on a moving clock will look longer. For ordinary velocities this change is completely negligible; however, if we approach speeds which are comparable to the speed of light this becomes of great import. The practical significance of these results was immense. The conclusions of this beautiful theory not only furnished us with a deeper understanding but also supplied us with part of the laws which describe the behavior of fast elementary particles now so widely used in physical research. Moreover, it was one of the results of special theory that mass and energy are equivalent in the sense that if m units of mass could be made to disappear, mc² units of energy would be liberated, c being the speed of light. In this way the masses of nuclei furnish the large amounts of energy supplied by nuclear reactions. Nature herself makes the use of nuclear reactions, and they provide the main energy source in stars.

      Already in 1907 Einstein came to the conclusion that the electromagnetic field must be influenced by gravitational field. During his research he developed his famous principle of equivalence which later became the corner stone of the general theory of relativity. This principle states that an accelerated observer will see a physical process taking place the same way as if he were not accelerated, but a gravitational field would be present which would produce the same acceleration as that of the observer. In this way the linking of gravitational fields and accelerated observers took place. This principle had great consequences. The geometrical interpretation of the special theory, as processed originally by Hermann Minkowski, suggested that a possible development of the special theory would lie in the admission of accelerated observers. However, at the outset it was not certain that this could be accomplished. Einstein realized that this would be successful only if the theory also embraced the phenomenon of gravitation. He slowly developed his general theory of the relativity. The intellectual beauty of the theory is very great. In it the laws of the physics are the laws of geometry in four dimensions, and these laws in term are determined by the distribution of matter and energy in the Universe. on the practical side the theory accounted for the anomalous behaviors in the motion of the planet mercury, and it predicted two new phenomena- the bending of light rays in the gravitational fields and the change of frequency of light in gravitational fields. Both effects were later observed. The general theory of relativity gave a new impetus to cosmology, the theory which deals with the properties of the universe in the large. Einstein inaugurated this development with the paper in 1917 demonstrating the possibility of a spatially finite though unbounded universe within the general theory. Later many other possibilities were investigated by others. Einstein proposed several generalizations to his general theory. Each attacked from a new angle the possibility of deriving both the gravitational and the electromagnetic fields from the geometrical properties of space-time. None of these attempts met with complete success, through most of them contain mathematical results of great elegance.

      We turn now to Einstein’s statistical theories and his work on nature of light. Roughly speaking, there were two phases in his contribution. In the beginning he dealt with the classic problems of statistical mechanics while later he attacked problems in which quantum theory and statistical mechanics were merged. In general Einstein considered the principles of statistical mechanics as having the most secure foundations in a changing physics. This is the reason that Einstein was able to drive several laws of quantum theory (before quantum theory as a theory had merged) by investigating what these (tentative) laws must be in order to satisfy the condition of thermal equilibrium. For this reason we will discuss here his contributed to quantum theory as well. Einstein’s first papers (1902) dealt with the general foundations of statistical mechanics he immediately applied them to an important problem. It was known for a long time that small particles, bodies visible through a microscope only, undergo a violent agitation if suspended in liquids. This “Brownian motion” Einstein explained as due to the thermal motion of the molecules in the liquid which bounce against the suspended particle. Einstein showed that with this assumption he could explain quantitatively the motion of the small particles (1905). This theoretical explanation of the Brownian motion was the first visible proof of the molecular constitution of matter.

      At the same time he also applied his interest the investigation of the nature of the light (1905) by investigating the thermal properties of light with a low radiation density. He observed that for low intensities the thermal properties of light are of such a nature as if light were composed of independent quanta of energy. This argument suggested to Einstein that there should be experiments where this discrete nature of light would reveal itself directly. These phenomena, the photoelectric effect, photo ionization and photoluminescence, were actually known and the experimental results yielded beautifully to this interpretation. At the same time he demonstrated (1907)that if we assume that under certain conditions the energy of a system can take discrete values only, we can satisfactorily explain the specific heat of solid elements thus remove one of the great stumbling blokes oh 19^th century statistical mechanics. Following this, he showed (1917) that the processes of emotion and absorption of light must be governed by new laws if light is to have this new discrete property. These new laws were the first known laws of quantum theory of matter derived before the advent of quantum theory. (Some of the quantum laws of radiation, of course, had already been discovered by Max Planck [q.v] in 1900.)

      Einstein’s last great contribution to statistical mechanics was the development of the quantum theory of a monatomic gas, following the idea of Sir Jagadis Chunder Bose, an Indian physicist (1924-25). These two papers stimulated Schrödinger to develop his wave mechanics which marked the coming of age of quantum theory.

Personality. –Einstein’s personality was as impressive as his scientific work. He believed in a world of simplicity and harmony which can only be created if people act according to principles founded on experience and consciously clear thinking. His character as revealed through his actions was of noble simplicity. He was full of benevolence, integrity and humour. Except for his humour his traits were impersonal and wholly of as unsentimental nature. Notwithstanding the aloofness inherent in such an attitude, he had a passionate and active interest in social justice and responsibility.

      In science he maintained that though the world can be understood in terms of reason the criteria for the acceptance of a theory are, in the last analysis, aesthetical.

      He once summed up his general outlook toward the world by saying: raffiniert ist der Herrgott, aber boshaft ist nicht (“God is subtle but he is not malicious”).

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