Overview (The Solar System)
Originally, Cosmology was a branch of philosophy devoted to understanding the nature of reality and the origin and structure of everything that exists. With the growth of Astrophysics during the nineteenth and twentieth centuries, cosmology rapidly became a major area of research in astronomy and physics, and its focus narrowed to the origin and evolution of energy and matter in the universe as a whole. Cosmology today is concerned with the large-scale structure of the universe, including the distribution of billions of galaxies and galaxy clusters throughout space and time. Cosmologists use physical laws to derive mathematical models of the early universe to within 10-43 second of its beginning. They also extrapolate physical processes into the distant future to predict the future of the universe and its contents. Nevertheless, modern cosmology still retains some philosophical qualities.
Modern cosmology has its basis in Albert Einstein’s general theory of relativity, which he published in 1915. In 1922, the Russian mathematical physicist Alexander Alexandrovich Friedmann derived two types of solutions to the field equations of general relativity in which the universe initially expands with time. In one type (called “open”), the universe continues to expand forever. In the other type (called “closed”), the universe expands to some maximum size, after which it contracts. In 1927, the Belgian priest and cosmologist Abbé...
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Methods of Study (The Solar System)
Cosmology is studied both theoretically and observationally, the two complementing each other. New observations need to be interpreted by theories, and theories need to be confirmed by further observations. Cosmological observations are now made over the entire electromagnetic spectrum, from high-energy, short-wavelength gamma rays, through X rays, ultraviolet, visible light, infrared, microwaves, to long-wavelength radio waves. Not all electromagnetic radiation penetrates Earth’s atmosphere, so parts of the Electromagnetic spectrum must be observed from satellites above Earth orbit, above the atmosphere.
The speed at which all forms of electromagnetic radiation travel through a vacuum is exceedingly fast but finite, being very close to 300,000 kilometers per second. Therefore, looking out to greater distances means looking further back in time. When astronomers look at Earth’s moon, at a distance of about 400,000 kilometers, they see it as it was about 1.3 seconds earlier. When one observes the Sun, at a distance of about 150 million kilometers, it appears as it was 8 minutes and 20 seconds earlier. The nearest star system outside our solar system, the Alpha Centauri system, is at a distance of 4.3 light-years, meaning that we see that system as it was 4.3 years ago. Distant galaxies are billions of light-years away, so we see them as they were billions of years ago. In this manner it is possible to observe the early...
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Context (The Solar System)
The value of cosmology lies in understanding the structure and organization of the universe, where it came from, and how it will develop in the future. Cosmology gives us a perspective on our place in the universe. At the same time, cosmology provides a way to test the laws of physics on a grand universal scale.
Two of the major unsolved questions in cosmology involve the nature of dark matter and dark energy. There are numerous situations in astronomy in which a study of the dynamics of a system implies gravitational forces that far exceed what the observed mass can account for. The deficit in observed mass was originally called “missing mass.” However, the dynamical mass calculations seem reliable, so astronomers now generally use the term “dark matter,” since the mass really is not missing, it is just not observable in any part of the electromagnetic spectrum. Dark matter probably includes nonluminous ordinary matter that has not been observed yet, such as small conglomerates of non-radiating matter, black dwarfs, and black holes. However, indications are that most dark matter is much more exotic—completely unknown forms of matter that do not interact with ordinary matter except gravitationally. Possible candidates include a class of particles called WIMPs (weakly interacting massive particles) and cosmic strings (long, thin, massive lines of unbroken symmetry left over from the early universe in which the strong, weak,...
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Further Reading (The Solar System)
Bartusiak, Marcia. Thursday’s Universe. New York: Times Books, 1986. A thorough survey of major twentieth century breakthroughs and theories in astrophysics. Discusses the development of major cosmological principles and the people behind these ideas. Big bang cosmology is described clearly from very early stages of the universe to the distant future universe.
Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. New York: Addison-Wesley, 2008. A well-written college-level textbook for introductory astronomy courses. Two chapters provide a thorough discussion of cosmology.
Fraknoi, Andrew, David Morrison, and Sidney Wolff. Voyages to the Stars and Galaxies. Belmont, Calif.: Brooks/Cole-Thomson Learning, 2006. A well-written, thorough college textbook for introductory astronomy courses. Several chapters contain material concerning cosmology.
Freedman, Roger A., and William J. Kaufmann III. Universe. 8th ed. New York: W. H. Freeman, 2008. College-level introductory astronomy textbook. Two chapters deal with cosmology.
Guth, Alan H., and Paul J. Steinhardt. “The Inflationary Universe.” Scientific American 250 (May, 1984): 116-129. This general review article is an excellent presentation of big bang cosmology with the inclusion of inflation, in which the very early universe briefly undergoes extremely rapid expansion.
Hawking, Stephen W. A...
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Cosmology (Encyclopedia of Science)
Cosmology is the study of the origin, evolution, and structure of the universe. This science grew out of mythology, religion, and simple observations and is now grounded in mathematical theories, technological advances, and space exploration.
Ancient astronomers in Babylon, China, Greece, Italy, India, and Egypt made observations without the assistance of sophisticated instruments. One of their first quests was to determine Earth's place in the universe. In A.D. 100, Alexandrian astronomer Ptolemy suggested that everything in the solar system revolved around Earth. His theory, known as the Ptolemaic system (or geocentric theory), was readily accepted (especially by the Christian Church) and remained largely unchallenged for 1,300 years.
A Sun-centered solar system
In the early 1500s, Polish astronomer Nicolaus Copernicus (1473543) rose to challenge the Ptolemaic system. Copernicus countered that the Sun was at the center of the solar system with Earth and the other planets in orbit around it. This sun-centered theory, called the Copernican system (or heliocentric theory), was soon supported with proof by Danish astronomer Tycho Brahe (1546601) and German astronomer Johannes Kepler (1571630). This proof consisted of careful calculations of the positions of the planets. In the early 1600s, Kepler developed the laws of planetary motion, showing...
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Cosmology (Encyclopedia of Science and Religion)
Many, perhaps all, early cosmologies or descriptions of the structure of the world were anthropocentric (focused on the role and fate of human beings) and they envisioned a universe subject to whims of gods. As such, cosmology and religion were closely intertwined.
From the ancient Greeks through the Middle Ages, over some two millennia, the geocentric cosmology or worldview of Aristotle (38422 B.C.E.) dominated much of the Western intellectual world. Circular and unalterable heavens rotated around the Earth, which was motionless in the center of the one and only world. Created during roughly the same period and in the same regions of the world, Aristotelian philosophy and Biblical accounts of cosmology and cosmogony are, not surprisingly, congruent in some respects. Aristotle's teleological explanations assumed that the world was fulfilling a purpose formed by a superhuman mind; Christian philosophy also is inherently meaningful and purposive.
During the Middle Ages, Aristotelian cosmology was subordinated to religious concerns. In the sixteenth century Nicolaus Copernicus (1473543) displaced the Earth, though not the solar system, from the center of the universe, and increasingly from the center of God's attention as well. In the seventeenth century Galileo Galilei (1564642) destroyed Aristotelian cosmology. The subsequent mechanical cosmology of Isaac Newton (1642727), though initially requiring God's intervention to keep the planets circling the sun, eventually replaced God completely with the universal law of gravity.
Early in the twentieth century, the American astronomer Harlow Shapley (1885972) showed that the solar system is not at the center of our galaxy, but off to the side, and that our galaxy is many times larger than previously contemplated. A few years later, Edwin Hubble (1889953) showed that our galaxy is but one of many island universes, and that the acentric universe is expanding. Each new cosmological discovery displaced humankind farther from the center of the universe and seemed to render humans less significant in an increasingly immense universe.
A contemporary resurgence of dialogue between scientific cosmology and religious thought late in the twentieth century involved yet another version of the traditional design argument for God. The Anthropic Principle noted that values of the fundamental constants of nature (the speed of light, Planck's constant, etc.) and the fundamental physical laws are "fine-tuned" to precisely what is needed for the evolution of life. As with earlier cosmologically based arguments for the existence of God, the Anthropic Principle has proven highly vulnerable to theory-change in science. The inflationary Big Bang cosmological model now explains much fine-tuning without recourse to God.
The history of the relationship between cosmology and religion, particularly in Western thought, has been enlivened by changes in cosmological understanding and beliefs. As the Earth has been increasingly displaced from the center of the universe and observed phenomena have been increasingly brought under the rule of natural physical laws, humankind's relationship with and understanding of God has required revisions.
See also ANTHROPIC PRINCIPLE; BIBLICAL COSMOLOGY; BIG BANG THEORY; BIG CRUNCH THEORY; FEMINIST COSMOLOGY; GALILEO GALILEI; GEOCENTRISM
Danielson, Dennis Richard. The Book of the Cosmos: Imagining the Universe from Heraclitus to Hawking. Cambridge, Mass.: Perseus, 2000.
Gribbin, John. Companion to the Cosmos. London: Weidenfeld & Nicolson, 1996.
Hetherington, Norriss S. Encyclopedia of Cosmology: Historical, Philosophical, and Scientific Foundations of Modern Cosmology. New York and London: Garland, 1993
North, John. The Norton History of Astronomy and Cosmology. New York and London: Norton, 1995.
Cosmology (World of Earth Science)
Cosmology is the study of the origin, structure and evolution of the universe.
The origins of cosmology predate the human written record. The earliest civilizations constructed elaborate myths and folk tales to explain the wanderings of the Sun, Moon, and stars through the heavens. Ancient Egyptians tied their religious beliefs to celestial objects and Ancient Greek and Roman philosophers debated the composition and shape of the Earth and the Cosmos. For more than 13 centuries, until the Scientific Revolution of the sixteenth and seventeenth centuries, the Greek astronomer Ptolemy's model of an Earth-centered Cosmos composed of concentric crystalline spheres dominated the Western intellectual tradition.
Polish astronomer Nicolaus Copernicus' (1473543) reassertion of the once discarded heliocentric (Sun-centered) theory sparked a revival of cosmological thought and work among the astronomers of the time. The advances in empiricism during the early part of the Scientific Revolution, embraced and embodied in the careful observations of Danish astronomer Tycho Brahe (1546601), found full expression in the mathematical genius of the German astronomer Johannes Kepler (1571630) whose laws of planetary motion swept away the need for the errant but practically useful Ptolemaic models. Finally, the patient observations of the Italian astronomer and physicist Galileo, in particular his observations of moons circling Jupiter and of the phases of Venus, empirically laid to rest cosmologies that placed Earth at the center of the Cosmos.
English physicist and mathematician Sir Isaac Newton's (1642727), important Philosophiae Naturalis Principia Mathematica (Mathematical principles of natural philosophy) quantified the laws of motion and gravity and thereby enabled cosmologists to envision a clockwork-like universe governed by knowable and testable natural laws. Within a century of Newton's Principia, the rise of concept of a mechanistic universe led to the quantification of celestial dynamics, that, in turn, led to a dramatic increase in the observation, cataloging, and quantification of celestial phenomena. In accordance with the development of natural theology, scientists and philosophers debated conflicting cosmologies that argued the existence and need for a supernatural God who acted as "prime mover" and guiding force behind a clockwork universe. In particular, French mathematician Pierre Simon de Laplace (1749827) argued for a completely deterministic universe, without a need for the intervention of God. Most importantly to the development of modern cosmology, Laplace asserted explanations for celestial phenomena as the inevitable result of time and statistical probability.
By the dawn of the twentieth century, advances in mathematics allowed the development of increasingly sophisticated cosmological models. Many advances in mathematics pointed toward a universe not necessarily limited to three dimensions and not necessarily absolute in time. These intriguing ideas found expression in the intricacies of relativity and theory that, for the first time, allowed cosmologists a theoretical framework upon which they could attempt to explain the innermost workings and structure of the universe both on the scale of the subatomic world and on the grandest of galactic scales.
As direct consequence of German-American physicist Albert Einstein's (1879955) relativity theory, cosmologists advanced the concept that space-time was a creation of the universe itself. This insight set the stage for the development of modern cosmological theory and provided insight into the evolutionary stages of stars (e.g., neutron stars, pulsars, black holes, etc.) that carried with it an understanding of nucleosythesis (the formation of elements) that forever linked the physical composition of matter on Earth to the lives of the stars.
Twentieth-century progress in cosmology has been marked by corresponding and mutually beneficial advances in technology and theory. American astronomer Edwin Hubble's (1889953) discovery that the universe is expanding, Arno A. Penzias and Robert W. Wilson's observation of cosmic background radiation, and the detection of the elementary particles that populated the very early universe all proved important confirmations of the Big Bang theory. The Big Bang theory asserts that all matter and energy in the universe, and the four dimensions of time and space were created from the primordial explosion of a singularity of enormous density, temperature, and pressure.
During the 1940s Russian-born American cosmologist and nuclear physicist George Gamow (1904968) developed the modern version of the big bang model based upon earlier concepts advanced by Russian physicist Alexander (Aleksandr Aleksandrovich) Friedmann (also spelled as Fridman, 1888925) and Belgian astrophysicist and cosmologist Abbé Georges Lemaître (1894966). Big bang based models replaced static models of the universe that described a homogeneous universe that was the same in all directions (when averaged over a large span of space) and at all times. Big bang and static cosmological models competed with each other for scientific and philosophical favor. Although many astrophysicists rejected the steady state model because it would violate the law of mass-energy conservation, the model had many eloquent and capable defenders. Moreover, the steady model was interpreted by many to be more compatible with many philosophical, social and religious concepts centered on the concept of an unchanging universe. The discovery of quasars and of a permeating cosmic background radiation eventually tilted the cosmological argument in favor of big bang-based models.
Technology continues to expand the frontiers of cosmology. The Hubble Space Telescope has revealed gas clouds in the cosmic voids and beautiful images of fledgling galaxies formed when the universe was less than a billion years old. Analysis of these pictures and advances in the understanding of the fundamental constituents of nature continue to keep cosmology a dynamic discipline of physics and the ultimate fusion of human scientific knowledge and philosophy.
See also Cosmic microwave background radiation; Stellar life cycle