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| 4. Science |
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(See 1911)| Science and technology became increasingly international but major developments were concentrated in Europe and the U.S. Throughout the interwar years, physics remained the center of most scientific activity, illuminating a universe that lacked any absolute reality. In 1919 Ernest Rutherford (1871–1937) showed that the atom could be split. By 1944 seven subatomic particles had been identified. Although few nonscientists understood the revolution in physics, the implications of the new theories and discoveries, as presented by newspapers and popular writers, were disturbing to millions of men and women in the 1920s and 1930s. | 1 |
| The major benchmarks in scientific inquiry follow. | 2 |
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| a. Mathematics, Physics, Astronomy |
| 1915 |
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| Einstein announced his general theory of relativity, which explained the advance of Mercury's perihelion and predicted the subsequently observed bending of light rays near the sun. | 3 |
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| 1918 |
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| Harlow Shapley (1885–1972), from an extensive study of the distribution of globular clusters and cepheid variable stars, increased the estimated size of our galaxy about ten times. He envisioned the galaxy as a flattened lens-shaped system of stars in which the solar system occupied a position far from the center. | 4 |
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| 1919 |
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| Rutherford found that the collision of alpha particles with nitrogen atoms resulted in the disintegration of the nitrogen and the production of hydrogen nuclei (protons) and an isotope of oxygen. He was the first person to achieve artificial transmutation of an element. | 5 |
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| 1919 |
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| Arthur S. Eddington (1882–1944) and others, by studying data obtained during a total solar eclipse, verified Einstein's prediction of the bending of light rays by the gravitational field of large masses. | 6 |
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| 1919–29 |
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| Edwin P. Hubble (1889–1953) detected cepheid variable stars in the Andromeda Nebula, a discovery that allowed him to determine the distances between galaxies. | 7 |
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| 1924 |
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| Louis-Victor de Broglie (1892–1987) determined from theoretical considerations that the electron, which had been considered a particle, should behave as a wave under certain circumstances. Experimental confirmation was obtained in 1927 by Clinton Davisson (1881–1958) and Lester H. Germer (1896–1971). | 8 |
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| 1925 |
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| Wolfgang Pauli (1900–1958) announced the exclusion principle (in any atom no two electrons have identical sets of quantum numbers). This principle was an important aid in determining the electron structure of the heavier elements. | 9 |
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| 1925–26 |
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| Werner Karl Heisenberg (1901–76) and Erwin Schrödinger (1887–1961) independently, and in different ways, laid the theoretical foundations of the new quantum mechanics, which, though violating classical notions of causality, successfully predicts the behavior of atomic particles. | 10 |
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| 1927 |
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| George Lemaître (1894–1966), in order to explain the red shift in the spectra from distant galaxies, introduced the concept of the expanding universe. Eddington pursued research in this subject from 1930. | 11 |
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| 1928 |
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| Paul A. Dirac (1902–84), by combining quantum mechanics and relativity theory, devised a relativistic theory of the electron. | 12 |
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