The ArgumentEinstein's mass-energy relationship was not confirmed experimentally until 1933 when Bainbridge showed that the Cockcroft-Walton experiment afforded a test of it. Earlier, however, it had been used constantly in the analysis of nuclear reactions, as can be seen in those involved in the determination of the mass of the neutron. Chadwick in 1932 was convinced that the neutron mass was about 1.0067 amu (atomic mass units), indicating that the neutron was a proton-electron compound, since that figure was less (...) than the sum of the proton and electron masses. Chadwick's value was challenged in 1933 by Lawrence, who proposed a much lower value of 1.0006 amu, and by Curie and Joliot, who proposed a much higher value of 1.011 amu.Much controversy ensued; eventually, Chadwick and Goldhaber showed in 1934 that the neutron mass was about 1.0080 amu, greater than the sum of the proton and electron masses, proving that the neutron was a new elementary particle (which could decay spontaneously), and providing conclusive experimental support for excluding electrons from the nucleus. These results remained unchanged with further refinements in the last decimal place, the entire pursuit of which provided still further vindication of Einstein's massenergy relationship. (shrink)

Kernphysiker in einer neuen Welt: Die Emigranten der dreißiger Jahre in Amerika. - Unter der großen Anzahl derjenigen, die durch Nationalsozialismus zur Emigration gezwungen wurden und zwischen 1933 und 1941 in die Vereinigten Staaten von Amerika einwanderten, befanden sich auch mehr als hundert Physiker, und unter ihnen einige der genialsten Kernphysiker der Welt. Die Physik in Amerika hatte damals den Status einer voll ausgereiften Wissenschaft erreicht, und so kam es zu einem bedeutsamen und facettenreichen Zusammenwirken zwischen den emigrierten und den (...) einheimischen Kernphysikern, zumal sie die verschiedenen Forschungsgebiete vertraten, die sich durch die Entdeckungen und Erfindungen des Jahres 1932 (Neutron, Deuterium, Positron, Cockcroft-Walton-Beschleuniger, Zyklotron) aufgetan hatten. Von besonderer Bedeutung Für die Konsolidierung und Entwicklung der gesamten Kernphysik war dabei die Veröffentlichung von drei Artikeln in den Reviews of Modern Physics von 1936 und 1937, bekannt als die „Bethe-Bibel”︁. Nach der Entdeckung der Kernspaltung von 1938 und dem Ausbruch des Krieges 1939 in Europa wirkte die Befürchtung, daß Hitler eine Atomwaffe erhalten könnte, als mächtige, Emigranten und Nicht-Emigranten gleichermaßen erfassende einigende Kraft unter den Atomphysikern in Amerika, und die meisten von ihnen stellten ihre Fähigkeiten in den Dienst der US-Regierung und arbeiteten am Manhatten-Projekt und an anderen militärischen Forschungsvorhaben mit. Bei Kriegsende waren die in den dreißiger Jahren emigrierten Kernphysiker wie so viele Flüchtlinge vor ihnen Amerikaner geworden, und keiner von ihnen kehrte in sein Geburtsland zurück.Among the large number of refugees from Nazism and Fascism entering the United States between 1933 and 1941 were more than 100 physicists, including some of the most gifted nuclear physicists in the world. By that time physics in America had come of age, and a remarkable and multifaceted symbiosis occurred between the émigré and native-born nuclear physicists as they pursued the many avenues of research opened up by the discoveries and inventions of 1932 (neutron, deuterium, positron, Cockcroft-Walton accelerator, cyclotron). Of particular importance for the consolidation and development of the entire field of nuclear physics was the publication in 1936–37 of the three articles in the Revieus of Modern Physics known as the „Bethe Bible”︁. With the discovery of nuclear fission in 1938 and the outbreak of war in Europe in 1939, the fear that a nuclear weapon might fall into Hitler's hands served as a powerful unifying force among nuclear physicists in Amerika, émigrés and non-émigrés alike, and most placed their talents in the service of the United States Government working on the Manhattan Project and other wartime research. By the end of the war, like so many refugees before them, the émigré nuclear physicists of the 1930s had become Americans, and not one of them returned to the country of his birth. (shrink)

This book discusses both the philosophy of mathematics and of mathematics education. The first part is a critique of existing approaches and a new philosophy of mathematics. Chapters include: (1) "A Critique of Absolutist Philosophies of Mathematics," (2) "The Philosophy of Mathematics Reconceptualized," (3) "Social Constructivism as a Philosophy of Mathematics," (4) "Social Constructivism and Subjective Knowledge," and (5) "The Parallels of Social Constructivism." The second part of the book explores the philosophy of mathematics education and shows that many aspects (...) of mathematics education rest on underlying, usually implicit, philosophical assumptions. Making these assumptions explicit puts a critical tool into the hands of teachers and researchers. Chapters in this section are: (6) "Aims and Ideologies of Mathematics Education," (7) "Groups with Utilitarian Ideologies," (8) "Groups with Purist Ideologies," (9) "The Social Change Ideology of the Public Educators," (10) "Critical Review of Cockcroft and the National Curriculum," (11) "Hierarchy in Mathematics, Learning, Ability and Society," (12) "Mathematics, Values and Equal Opportunities," and (13) "Investigation, Problem Solving and Pedagogy." Each chapter contains notes. (Contains 654 references.) (MKR). (shrink)