Reinventing Gravity : A Physicist Goes Beyond Einstein, by Moffat, John W.
- ISBN: 9780061170881 | 0061170887
- Cover: Hardcover
- Copyright: 1/1/2008
|Introduction: A New Gravity Theory||p. ix|
|Prologue: The Elusive Planet Vulcan, a Parable||p. 1|
|Discovering and Reinventing Gravity||p. 7|
|The Greeks to Newton||p. 9|
|The Standard Model of Gravity||p. 49|
|The Beginnings of Modern Cosmology||p. 51|
|Dark Matter||p. 69|
|Conventional Black Holes||p. 78|
|Updating the Standard Model||p. 89|
|Inflation and Variable Speed of Light (VSL)||p. 91|
|New Cosmological Data||p. 110|
|Searching for a New Gravity Theory||p. 125|
|Strings and Quantum Gravity||p. 127|
|Other Alternative Gravity Theories||p. 143|
|Modified Gravity (MOG)||p. 153|
|Envisioning and Testing the MOG Universe||p. 171|
|The Pioneer Anomaly||p. 173|
|MOG as a Predictive Theory||p. 181|
|Cosmology without Dark Matter||p. 193|
|Do Black Holes Exist in Nature?||p. 200|
|Dark Energy and the Accelerating Universe||p. 205|
|The Eternal Universe||p. 212|
|Table of Contents provided by Ingram. All Rights Reserved.|
A Physicist Goes Beyond Einstein
The Greeks to Newton
Is there any phenomenon in physics as obvious as the force of gravity? Gravity keeps the planets in their orbits around the sun and holds stars together in galaxies. It prevents us from floating off the Earth, makes acorns and apples fall down from trees, and brings arrows, balls, and bullets to the ground in a curved path.
Yet gravity is so embedded in our environment that many thousands of years passed before humans even perceived gravity and gave it a name. In fact, the everyday evidence of gravity is extremely difficult to "see" when one lives on one planet, without traveling to another for comparison. The little prince in Saint-Exupéry's tale would have formed a vastly different idea of gravity from living only on his small asteroid. To early human beings, just as to most of us today, the behavior of falling objects is a practical experience taken for granted rather than an example of a universal force. Because the Earth is large and we only experience gravity from the effects of Earth, and not some other object, we tend to think of gravity as "down," without realizing that gravity is a property of bodies in general. In contrast, electromagnetism is a much more obvious force. We see it in lightning and magnets and feel it in static electricity. But it took many centuries to discover gravity, and some promising ideas along the way turned out to be completely wrong. It wasn't until the late seventeenth century that Isaac Newton recognized that the same force of attraction or "togetherness" that ruled on the Earth also bound objects in the heavens. The paradigm shift that Newton wrought was in understanding gravity as a universal force.
The story of the discovery of gravity is also the story of astronomy, especially the evolving ideas about the solar system. Western science originated with the Greeks, whose model of an Earth-centered universe dominated scientific thought for almost 2,000 years. The Greek mind was abstract, fond of ideals and patterns, and slipped easily into Christianity's Earth- and human-centered theology. It took many centuries for thinkers such as Copernicus, Kepler, Galileo, and Newton to break with the enmeshed Platonic and Christian views of the universe, to turn astronomy and physics into sciences, and to develop the idea of gravity.
Greek astronomy and gravity
Plato's most famous student was Aristotle (384-322 bc), whose system of thought formed the basis of Western science and medicine until the Renaissance. For Aristotle, four elements composed matter: Earth, Water, Air, and Fire. Earth, as the basest and heaviest of the elements, was at the center of the universe. Although Aristotle did not use the Greek equivalent of the word "gravity," he believed that people and objects did not fall off the Earth because they were held by the "heaviness" of Earth.
Plato had taught that nature's most perfect shapes were the circle, in two dimensions, and the sphere in three. Aristotle's cosmology in turn relied heavily on circles and spheres. Around Aristotle's Earth, several "crystalline spheres" revolved. First were the Earth-related spheres of Water, Air, and Fire. Spheres farther out contained the heavenly bodies that appeared to move around the Earth: the moon, sun, and the five planets known to the Greeks (Mercury, Venus, Mars, Jupiter, and Saturn). Beyond these was the sphere of the "fixed stars," while the final sphere was the dwelling place of God, the Prime Mover of all the spheres. This cosmology needed spheres for the heavenly bodies to move on because Aristotle believed that objects could move only when in contact with another moving object. The spheres were "crystalline" rather than translucent or opaque because the fixed stars had to be visible to observers on Earth through the other rotating spheres.
The ancient Greeks knew that the Earth was a sphere, but most astronomers pictured it as a static object, immovable at the center of the universe. This view stemmed from "common sense": In our everyday experience, barring earthquakes, we do not sense any motion of the Earth. Also, if the Earth moved through the heavens, the Greeks argued, we would observe stellar parallax. Parallax can easily be demonstrated by holding a finger up in front of one's face and closing first one eye and then the other; the finger appears to be moving from side to side relative to objects in the background. Similarly, if the Earth moved through the heavens, then the stars nearest to Earth in the stellar sphere would move relative to those more distant. Since this did not happen, Aristotle concluded that the Earth stayed still at the center of the universe.
Aristotle and his contemporaries did not conceive of the vast distances that actually separate objects in the universe, and believed that the "fixed stars" were thousands of times closer to Earth than they are. In fact, we can detect parallax in the nearer stars today, as the Earth moves around the sun, and more dramatically as the solar system moves around the Milky Way galaxy. Powerful telescopes take photographs of the same stars at different points in the Earth's or solar system's orbit, and differences in the stars' positions relative to background stars can be seen when comparing those photographs.
One prominent Greek astronomer, Aristarchus of Samos (310-230 bc), did propose a heliocentric universe. He had figured out that the sun was a great deal larger than the Earth, and it made more sense to him that a smaller object would orbit a larger one. Aristarchus concluded that the universe was much larger than most people believed, that the sun was at its center, and that neither the sun nor the sphere of fixed stars moved. Aristarchus correctly placed the moon in orbit around the Earth, and all the planets, including Earth, orbiting the sun. He also concluded that we do not observe parallax because the stars are almost infinitely far away from the sun.
But Aristarchus was clearly ahead of his time. Most mathematicians and astronomers in ancient Greece considered the geocentric model of the universe to be a far simpler and more logical explanation of the movements of planets than the heliocentric universe of Aristarchus. Aristarchus was actually charged with impiety for removing the Earth and human beings from the center of the universe.Reinventing Gravity
A Physicist Goes Beyond Einstein. Copyright © by John Moffat. Reprinted by permission of HarperCollins Publishers, Inc. All rights reserved. Available now wherever books are sold.
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