Scientific Discoveries

Even before World War I, new ideas and scientific discoveries were challenging long-held ideas about the nature of the world and even of people. Like the war, science helped feed a sense of uncertainty that flowed through Western culture.

Curie Experiments with Radioactivity

The ancient Greeks were the first to propose that all matter is composed of tiny, indivisible atoms. Over the centuries, most scientists came to accept this idea. But discoveries made in the early 1900s showed that the atom was more complex than anyone suspected.

The Polish-born French scientist Marie Curie and others experimented with an atomic process called radioactivity. They found that the atoms of certain elements, such as radium and uranium, spontaneously release charged particles. As scientists studied radioactivity further, they discovered that it can change atoms of one element into atoms of another. Such findings proved that atoms are not solid and indivisible.

Einstein Proposes the Theory of Relativity

In 1905 and 1916, the German-born physicist Albert Einstein introduced his theories of relativity. Einstein argued that measurements of space and time are not absolute but are determined by many factors, including the relative position of the observer. Einstein's ideas raised questions about Newtonian science, which compared the universe to a machine operating according to absolute laws.

Photo of an older man with uncombed hair and a mustache, writing an equation on a chalkboard.

Albert Einstein received the 1921 Nobel Prize in Physics and is well known for his mass-energy formula. Einstein fled Germany and became an American citizen in 1940.

In the postwar years, many scientists came to accept the theories of relativity. To the general public, however, Einstein's ideas were difficult to understand. They seemed to further reinforce the unsettling sense of a universe whirling beyond the understanding of human reason.

In 1934, building on Curie's and Einstein's theories, Italian physicist Enrico Fermi and other scientists around the world discovered atomic fission, or the splitting of the nuclei of atoms in two. This splitting produces a huge burst of energy. In the 1940s, Fermi (now an American), along with fellow American physicists J. Robert Oppenheimer and Edward Teller, would use this discovery to create the devastating atomic bomb.

Fleming Discovers Penicillin

In 1928, the Scottish scientist Alexander Fleming made a different type of scientific discovery. One day, he picked up a discarded laboratory dish that he had used to grow bacteria. The dish had grown some mold, which had killed the bacteria. Fleming called this nontoxic mold “penicillin.” Fleming's penicillin was the first antibiotic, or medicine used to kill micro-organisms such as bacteria. Later scientists developed a wide range of antibiotics.

Freud Analyzes the Mind

The Austrian physician Sigmund Freud (froyd) also challenged faith in reason. He suggested that the subconscious mind drives much of human behavior. Freud said that learned social values such as morality and reason help people to repress, or check, powerful urges. But an individual feels constant tension between repressed drives and social training. This tension, argued Freud, may cause psychological or physical illness.

Freud pioneered psychoanalysis, a method of studying how the mind works and treating mental disorders. Although many of his theories have been discredited, Freud's ideas have had an extraordinary impact far beyond medicine. They strongly influenced the art and literature of the postwar West.

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Table of Contents

World History Topic 1 Origins of Civilization (Prehistory–300 B.C.) Topic 2 The Ancient Middle East and Egypt (3200 B.C.–500 B.C.) Topic 3 Ancient India and China (2600 B.C.–A.D. 550) Topic 4 The Americas (Prehistory–A.D. 1570) Topic 5 Ancient Greece (1750 B.C.–133 B.C.) Topic 6 Ancient Rome and the Origins of Christianity (509 B.C.-A.D. 476) Topic 7 Medieval Christian Europe (330–1450) Topic 8 The Muslim World and Africa (730 B.C.-A.D. 1500) Topic 9 Civilizations of Asia (500–1650) Topic 10 The Renaissance and Reformation (1300–1650) Topic 11 New Global Connections (1415–1796) Topic 12 Absolutism and Revolution Topic 13 The Industrial Revolution Topic 14 Nationalism and the Spread of Democracy (1790–1914) Topic 15 The Age of Imperialism (1800–1914) Topic 16 World War I and the Russian Revolution (1914–1924) Topic 17 The World Between the Wars (1910–1939) Topic 18 World War II (1930–1945) Topic 19 The Cold War Era (1945–1991) Topic 20 New Nations Emerge (1945–Present) Topic 21 The World Today (1980-Present) United States Constitution Primary Sources 21st Century Skills Atlas Glossary Index Acknowledgments