Word: two
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Dates: during 1990-1999
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This required abandoning the idea that there is a universal quantity called time that all clocks measure. Instead, everyone would have his own personal time. The clocks of two people would agree if they were at rest with respect to each other but not if they were moving. This has been confirmed by a number of experiments, including one in which an extremely accurate timepiece was flown around the world and then compared with one that had stayed in place. If you wanted to live longer, you could keep flying to the east so the speed of the plane added...
...should appear the same to all freely moving observers was the foundation of the theory of relativity, so called because it implies that only relative motion is important. Its beauty and simplicity were convincing to many scientists and philosophers. But there remained a lot of opposition. Einstein had overthrown two of the Absolutes (with a capital A) of 19th century science: Absolute Rest as represented by the ether, and Absolute or Universal Time that all clocks would measure. Did this imply, people asked, that there were no absolute moral standards, that everything was relative...
This unease continued through the 1920s and '30s. When Einstein was awarded the Nobel Prize in 1921, the citation was for important--but by Einstein's standards comparatively minor--work also carried out in 1905. There was no mention of relativity, which was considered too controversial. I still get two or three letters a week telling me Einstein was wrong. Nevertheless, the theory of relativity is now completely accepted by the scientific community, and its predictions have been verified in countless applications...
Among the consequences of this law is that if the nucleus of a uranium atom fissions (splits) into two nuclei with slightly less total mass, a tremendous amount of energy is released. In 1939, with World War II looming, a group of scientists who realized the implications of this persuaded Einstein to overcome his pacifist scruples and write a letter to President Roosevelt urging the U.S. to start a program of nuclear research. This led to the Manhattan Project and the atom bomb that exploded over Hiroshima in 1945. Some people blame the atom bomb on Einstein because he discovered...
...dependent universe wasn't taken seriously until observations were made in the 1920s with the 100-in. telescope on Mount Wilson. These revealed that the farther other galaxies are from us, the faster they are moving away. In other words, the universe is expanding and the distance between any two galaxies is steadily increasing with time. Einstein later called the cosmological constant the greatest mistake of his life...