Particles and the Universe, Facts On File

[sanraj]

Library of Congress Cataloging | English | ISBN-9780596529680 | Jun-2007 | PDF | 5.85 MB | 177 pages | RAR Compressed - 2.29 MB | No Password

Introduction
AS A STUDENT forced to flee Cambridge University during an epidemic in 1665–66, Isaac Newton—later knighted, becoming Sir Isaac—found a lot of time to do experiments. He put this time to good use, discovering the basis for many of the laws of physics he would go on to publish a few decades later. Newton’s equations accurately described acceleration and motion, and his universal law of gravitation explained in a concise and mathematical way gravity on Earth as well as in the solar system. The physics of Newton dominated physics for more than 200 years. In Newton’s viewpoint, forces caused changes in motion, which could be precisely determined and calculated, and concepts such as space and time were absolute, the same for everyone. Physicists continued to accept this point of view until, in the 20th century, exceptions began to appear. With improved instruments and more imaginative theories, people began to probe objects and events that were not encountered in everyday life—tiny particles inside an atom,
immense objects such as the entire universe, and small or large objects moving at exceptionally fast speeds. Laws described by Newton failed to hold true in many cases. New laws, and occasionally entirely new concepts, were needed. The new laws reduce to the old laws in familiar situations but increase their scope and accuracy. Particles and the Universe documents the phenomena in which Newton’s physics failed and explains “modern” physics that formed the basis for a new set of laws. One thing that did not change was the scientific method—observations lead to theories, which must be tested for accuracy. Each chapter of Particles and the Universe delves into the observations, theories, and tests of a particular topic:

1.nuclear physics
2.quantum mechanics
3.particle physics
4.relativity

cosmology, the study of the universe Nuclear physics investigates the properties and behavior of the central portion, or nucleus, of the atom. This branch of physics has had perhaps the biggest impact on the world in the 20th century because it evolved into knowledge that helped build the most destructive weapons people have ever known. The atomic bombs that ended World War II in 1945, and the weapons race that followed, changed the course of history. But applications of nuclear physics have also provided enormous energy for peaceful purposes, generating about 16 percent of the world’s electricity. The strange behavior of tiny particles such as the components of an atom required physicists to revise their theories, as well as the way that those theories are understood and applied. Quantum mechanics supplies the equations to describe the motion and properties of particles, but its measurements have peculiar features. Properties of objects tend to have a discrete nature—their values increase by specific amounts, like the integers (. . .–2, –1, 0, 1, 2,. . .) rather than being continuous, like the real number line, in which the value can be any number. Calculations in quantum mechanics also introduce an amount of uncertainty that can never disappear. Physicists dealt with uncertainty before quantum mechanics, but it was due to a lack of knowledge, not due to the nature of physics itself, as it is in the newer theory. To probe the nature of matter even further, physicists have built gigantic accelerators capable of hurling particles down a pathway at nearly the speed of light. Crashes between high-speed particles have enough energy to tear them apart or to create entirely new particles, and hundreds of different particles exist. Particle physics is the branch of physics devoted to classifying these particles, identifying their properties, and explaining the forces they exert on each other as they interact. Extremely fast speeds, such as those achieved by particle accelerators, were another phenomenon requiring a
fresh perspective in physics. A few decades before huge accelerators were built, Albert Einstein, one of the greatest physicists of all time, concerned himself with the laws of physics as they would appear to observers in motion. Einstein believed physics should be the same for all observers, and his special theory of relativity, published in 1905, generated strange but accurate predictions of slowly moving clocks and shrinking lengths. The general theory of relativity, proposed a decade later, involved gravitation and had its own astonishing consequences, such as the discovery of objects in space so dense that not even light can escape them. Einstein’s theories have survived every test so far. The special and general theories of relativity are also important tools in the study of the universe. These theories help astronomers understand the observations made with telescopes and other instruments, which reveal a host of spectacular objects and events. One of the most fascinating phenomena is the expansion of
the universe itself, a prediction of the general theory of relativity even Einstein refused to believe at first. All chapters include a description of the profound changes caused by the new discoveries, along with applications such as earth-shattering weapons, machines to image the activity of a human brain, and precise satellite navigation systems. The rise of 20th-century physics altered the landscape of science, producing new ideas and theories that dramatically advanced scientific knowledge in previously unexplored realms of the universe.

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