www.internationalschoolhistory.net

S6 History – 4hr Optional Theme – 6.B Culture and Society before 1945 Einstein and Modern Physics

Biography Albert Einstein (14 March 1879 – 18 April 1955) was a German-born theoretical physicist who developed the general theory of relativity, one of the two pillars of modern physics. He received the 1921 Nobel Prize in Physics. He was visiting the United States when Adolf Hitler came to power in 1933 and did not go back to Germany. He settled in the U.S., becoming an American citizen in 1940. On the eve of World War II, he endorsed a letter to President Roosevelt alerting him to the potential development of the atom bomb and recommending that the U.S. begin similar research. This eventually led to what would become the Manhattan Project. Later, with the British philosopher Bertrand Russell, Einstein signed the Russell–Einstein Manifesto, which highlighted the danger of nuclear weapons. Einstein was affiliated with the Institute for Advanced Study in Princeton, until his death in 1955. His great intellectual achievements and originality have made the word "Einstein" synonymous with genius. Ideas At the end of the 19th century it was widely generally accepted that all the important laws of physics had been discovered and that, henceforth, research would be concerned with clearing up minor problems and particularly with improvements of method and measurement. However, around 1900 serious doubts arose about the completeness of the classical theories. Einstein began by asking simple imaginative questions like: ‘what would the world look like if I rode on a beam of light?’ or ‘What is time?’ Newton, in the Principia (1686), had given an unambiguous answer: "Absolute, true and mathematical time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration." This definition is basic to all classical physics. Einstein had the genius to question it, and found that it was incorrect. According to Einstein’s theory of relativity, each "observer" necessarily makes use of his own scale of time. Furthermore, for two observers in relative motion, their time-scales will differ. This induces a related effect on distance. Both space and time become relative concepts, fundamentally dependent on the observer. Each observer generates his own space-time framework or coordinate system. All observers have equal validity, there being no absolute frame of reference. Motion is relative, but only relative to other observers. What is absolute is stated in Einstein's first relativity postulate: "The basic laws of physics are identical for two observers who have a constant relative velocity with respect to each other." To say that Einstein's radical theory of relativity revolutionized science is no exaggeration. Although Einstein made many other important contributions to science, the theory of relativity alone represents one of the greatest intellectual achievements of all time. Modern Physics In the 19th century, experimenters began to detect unexpected forms of radiation: Wilhelm Röntgen caused a sensation with his discovery of X-rays in 1895; in 1896 Henri Becquerel discovered that certain kinds of matter emit radiation on their own accord. In 1897, J. J. Thomson discovered the electron, and new radioactive elements found by Marie and Pierre Curie raised questions about the supposedly indestructible atom and the nature of matter. Marie and Pierre coined the term "radioactivity" to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel's forms of radiation with electrons and the element helium. Rutherford identified and named two types of radioactivity and in 1911 interpreted experimental evidence as showing that the atom consists of a dense, positively charged nucleus surrounded by negatively charged electrons. Studies of radiation and radioactive decay continued to be a preeminent focus for physical and chemical research through the 1930s, when the discovery of nuclear fission opened the way to the practical exploitation of what came to be called "atomic" energy. Activity Watch Jacob Bronowski’s short but brilliant documentary about Einstein on the International School History website. With the help of diagram explain the theory of relativity to a scientifically illiterate history teacher. 220114