The years between 1900 and 1949 were a time of extremes that included two world wars, a revolution in Russia, and the Depression in the United States. Scientific revolutions brought exciting new knowledge but also called into question the most basic concepts. New technologies and materials provided more deadly instruments of war but also lengthened lives and eased the demands on raw human muscle power. Exploration in this period echoed these extremes. Since many of the easier targets had already been reached, explorers headed for the poles, ventured deep beneath the ocean's surface, and high into the atmosphere.
Scientists also explored new frontiers, introducing new concepts while at the same time upsetting much of the perceived order by which the natural world worked. Revolutions in physics drew an entirely new picture of the most basic elements of physical reality. Our knowledge of the age, extent, and history of the universe, and Earth's place in it, shifted radically. The concept of evolution, introduced in the nineteenth century and developed in the twentieth, had profound implications for the nature and meaning of human life. Culturally and intellectually, these were exhilarating but deeply unsettling times.
Science provided so many answers during this period that scientists enjoyed increased prestige, especially after the creation of the first atomic weapon that effectively ended World War II. In a world that was growing increasingly secular, science offered a source of understanding and meaning; science took on questions that were once the province of religion, such as human origins, the creation of the universe, and the nature of consciousness and behavior. Scientific growth is visible in the founding of research institutes and the growth of professional scientific associations.
Looking Back to the Nineteenth Century
The rapid pace of invention that accelerated in the twentieth century began in the nineteenth. New machines and new capabilities in communication and transportation brought large-scale social changes. Many of the inventions of the nineteenth century followed advances in the understanding of electricity, thermodynamics, and the chemical properties of materials. These advances were part of a science that expressed itself by classifying and rationalizing the world around us, so as to better understand and utilize its complexities.
In addition to studying physical phenomena, scientists explored and classified the living world. This study of living things led to the emergence of the concept of evolution, in which natural variations in animals lead, through natural selection, to changes that tailor animals to specific habitats. It's no surprise that in this time when people's daily lives were changing as a result of new technologies and gadgets, the idea of change itself, and the idea of progress toward a future that humans can shape, became central to Western experience.
Scientific Revolutions and Developments
In 1900 scientists had identified only one sub-atomic particle (the electron). Over the next 50 years, physicists identified the other two major sub-atomic particles (protons and neutrons) and developed a surprising picture of the atom, based on the idea that the amount of energy an atomic particle can have is limited to certain discrete values, or quanta. Quantum mechanics, developed independently by Erwin Schrödinger and Werner Heisenberg, plus a series of developments from Albert Einstein, including general and special relativity and the equivalence between mass and energy, utterly transformed not only physics but astronomy and chemistry, explaining atomic structure, the properties of chemical elements, and the process of nuclear fusion that fuels the stars. Furthermore, exotic concepts from quantum physics and relativity (such as the dual wave-particle nature of light) called into question such everyday concepts as space, time, and reality, and the Heisenberg uncertainty principle suggested that there are inherent limits to our measurements of physical properties.
Physics was deeply affected by World War II. The Manhattan Project, an American effort that developed the first atomic bomb, did much to bring physics and physicists dramatically to the forefront of public consciousness. The use of atomic bombs over the Japanese cities of Hiroshima and Nagasaki hastened the end of World War II and set the stage for an arms race in the second half of the twentieth century. The peaceful development of nuclear power held great promise toward the end of the first half of the twentieth century (although later developments had mixed results).
Astronomers during this period resolved an important debate about spiral nebulae, determining that these were separate, distant "island universes" or galaxies. This shifted the Milky Way from being the only such system in the universe to being only one among many. Edwin Hubble discovered that other galaxies are receding from us, with speeds proportional to their distances. This was the first evidence for an expanding universe, in which galaxies rush away from each other as the result of the birth of the universe in an initial Big Bang.
Closer to home, scientists also studied the planets of the solar system. Percival Lowell's observations of Mars convinced him that he had seen evidence of life on the red planet. Although his perception of canals on the Martian surface later proved to be mistaken, his work contributed to a great interest in Martian and other extraterrestrial life. This interest is evident in the science fiction of the times, including the novels of Edgar Rice Burroughs and the novel War of the Worlds by H. G. Wells. When a radio script based on this novel was presented on the air in 1938, large numbers of people mistook the broadcast for a news report, and panic followed, illustrating the growing power of the media as well as the hold other worlds had on the popular imagination.
Atomic and quantum physics provided tools that chemists used to explain the chemical properties of the elements and how these relate to their places on the periodic table, continuing and refining the work done in the nineteenth century to organize and rationalize this science. Chemists developed new materials—for example, silicones—later widely used as lubricants and water repellents, and built on previous discoveries related to radioactivity. In 1927, for example, Hermann Müller demonstrated that genetic mutations are simply chemical changes that can be induced by radioactivity.
Müller's work was part of the major biological effort of this time period, understanding the mechanisms behind natural selection. The rediscovery of Gregor Mendel's laws of heredity in 1900 helped biologists begin to understand the genetic foundations of natural selection. Biologists also explored the role of chromosomes in heredity and advanced their understanding of other areas such as the ways that cells and hormones work.
Biology had a very direct impact on people's lives, as indicated by the Scopes trial in Tennessee in 1925 and the use of eugenics as a rationale for efforts to eliminate "undesirables," such as Germany's 1933 Eugenic Sterilization Law. Genetics was also applied to agriculture, with the introduction of hybrids and the improvement of animal stocks. Developments in agriculture, including dam-building and irrigation that allowed dry lands to be cultivated, resulted in shifts in occupation and population, as fewer farmers were able to feed more people.
Science also sought to bring a rational, systematic approach to the mysteries of the mind. Ivan Pavlov, B. F. Skinner, and other scientists studied behavior in animals, and some of their discoveries were applied to the developing schools of psychology attempting to explain human behavior. In addition to psychoanalysis, shock therapies, such as electroshock therapy and surgical lobotomy, were developed to treat mental illness.
New Capabilities and Conveniences
Scientists' ability to identify causes and solve problems was especially evident in public health during this period. Life-saving developments include the chlorination of drinking water to kill disease-causing micro-organisms, the discovery of the specific agents that cause infectious diseases such as yellow fever, whooping cough, measles, and scarlet fever, the realization that some diseases are caused by a vitamin deficiency and can be treated by vitamins, the development of the first antibiotics, the development of diagnostic tests such as the Pap test, and the fluoridation of water to prevent tooth decay.
New machines eased some of the burdens of maintaining a household. Women's lives began to change as a result of electric appliances such as refrigerators and electric irons; the first microwave was patented in 1945. New materials found a variety of uses and also made life easier. Bakelite, the first synthetic plastic, was patented in 1907. Advances in the understanding of polymers, an effort that began in the 1920s, led to increased use of plastics after World War II. In the 1930s nylon became the first successful synthetic fiber product, introducing clothing that was easier to maintain and less dependent on natural sources such as silk.
The first powered flight at the beginning of the century heralded an era of rapid developments in transportation. Passenger travel in dirigibles ended due to the potential for disaster, demonstrated in the Hindenburg explosion in 1936. The patenting of the jet engine in 1930, however, helped make airplanes increasingly important for carrying passengers and goods, as aviation progressed from its adventurous early days marked by the daring flights of Charles Lindbergh, Amelia Earhart, and others. Aviation was in its infancy in World War I, but by World War II air power played an important role, making possible the fire-bombing of cities and providing a way to deliver the first atomic bombs.
Humanity looked to the skies in other ways as well, with the first liquid-fueled rocket, launched by Robert Goddard in 1926. Although one of the earliest applications of rocketry was warfare, the German V-2 rockets, used against England during the war, were later the basis for early experiments in space-going rockets developed in the United States.
Everyday life was overwhelmingly affected by the automobile, which became much more widely used due to Henry Ford's development of the Model T, the first car to be mass-produced on an assembly line. Relatively cheap and easily available, it launched a series of changes that transformed modern life, making the United States in particular a much more mobile country, with cities and lifestyles increasingly built around the personal car.
Mass Production and Mass Communication
Mass production and mass communication had their beginnings in assembly lines like Ford's and the introduction of radio, television, and movies. From the first regular radio broadcasts in Pittsburgh in 1920, to the first regular TV broadcasts by the BBC, to the earliest regularly scheduled U.S. TV in 1941, mass media became increasingly available in the home. Popular mass culture began to develop in this age when more and more people were exposed to the same news and entertainment content and the same consumer goods. Advances in transportation combined with these developments to make the world seem a smaller place, well on its way to the global culture of the close of the century.
The Legacy of Science: 1900-1949
Building on the science and technology of this period, and funded by post-war affluence, science introduced a dizzying array of new technologies that have wrought radical social changes. While many new technologies (for example, nuclear power and the creation of artificial materials such as plastics) were originally greeted enthusiastically, during the second half of the century the negative side of a highly technical culture became more evident, and science was both castigated as the cause of these ills and hailed as the means for dealing with increasing population, dwindling natural resources, and pollution. The physical sciences were prominent in the immediate post-war period, as the space race followed up on the rocketry work of World War II. The biological sciences attained more prominence later in the century as advances in genetics, diagnostic and surgical procedures, and drug therapies improved the length and quality of life. Mass media, combined with computing and satellite technologies, continued to develop far beyond their beginnings in the first half of the century. As the twenty-first century begins, the networked world we now know grows and changes daily.