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COSMOLOGY. During the fifteenth century, the cosmological systems of the Epicurean atomists, Plato, and the Stoics were known from antiquity, but the cosmology that was taught in universities throughout Europe was that of Aristotle, as augmented by Ptolemy. By the beginning of the eighteenth century a new cosmology, associated with the names of Copernicus, Kepler, Galileo, Descartes, and Newton, had almost completely replaced the earlier consensus. The present article considers the cosmologies of these main figures and reviews changes in historians' understanding of the causes of the scientific revolution.


Aristotle's cosmos was finite, spherical, and full. Its outer boundary was a sphere carrying the fixed stars. Its center was the Earth, and the sphere carrying the Moon divided the cosmos into a terrestrial portion and a celestial portion. The region beneath the Moon consisted of four elements, each endowed with the tendency to return to its natural place by a motion along a radius of the cosmos. The element Earth tended to seek the center; water moved naturally to a sphere surrounding the central globe of Earth; air sought a sphere concentric to water, and fire, which in its pure form was quite transparent, would naturally move to the region above the air and beneath the Moon. The general structure of the world reflected its elementary constitution, with most earth covered by water and both inner elements covered by air. Only the sphere of fire was not directly observable, although it was a theoretical necessity. Mixing and transmutation created complex combinations of elements, such as people, plants, and animals. Changes in the proportions of the four elements explained terrestrial change, especially growth and decay.

By contrast, the heavens consisted of a single element, ether, which was already in its natural place, and moved naturally in a circle, at constant speed, around the central earth. Deprived of the opportunity for transmutation or mixing of elements, the heavens were incapable of physical change. The order of the heavenly bodies was determined partly by observation and partly by convention. Eclipses and occultations made it clear that the Moon was the closest heavenly body and the fixed stars were the most distant. Mars, Jupiter, and Saturn could be ordered according to their periods of return, with the longest being the farthest away. However, the periods of return for the remaining planets and the Sun were not distinguishable. The locations of the five known planets were divided by the zone occupied by the Sun, and, beyond the Moon, an ordering of Mercury, followed by Venus, followed by the sun became conventional.

The heavens consisted of nested concentric shells. A single heavenly body was confined within and carried by each shell. Physically, the heavenly bodies were believed to be denser regions in the ether. During the fifteenth and sixteenth centuries, followers of Averroes (Ibn Rushd) and Ptolemy violently disagreed over the inner structure of these shells.

In the Almagest Ptolemy had introduced a system of moving circles carrying other circles to explain the details of planetary motion. In the Planetary Hypotheses he introduced a corresponding set of physical models, which Arabic commentators presented as sets of hollow orbs carrying smaller spheres within them. These, in turn, carried individual planets. Ptolemaic astronomers assumed that the orb clusters for different planets fitted perfectly inside one another, and were thereby able to calculate the distances of planets, including the Sun, and their relative sizes. But most importantly, Ptolemy's mathematical apparatus allowed the calculation of planetary positions with an accuracy sufficient, for example, to predict eclipses of the Sun and Moon, and approximate conjunctions and other planetary alignments important in astrology. These models were presented in Georg Peurbach's Theoricae novae planetarum (c. 1474), which rapidly became a standard text. Averroists objected to the eccentric circles and epicycles used by their rivals on the grounds that they were not strictly centered on the Earth. They proposed that planets were carried by a series of nested orbs, exactly concentric to the Earth, but, as late as the 1530s, attempts to construct predictive models failed. Copernicus was exposed to both viewpoints during his education.


Motivated by a desire to establish an absolute order for the planets, Copernicus moved the center of the cosmos to the Sun (On the Revolutions of the Heavenly Spheres, 1543). In other respects, his cosmology was conservative. He continued to assume that the planets were carried by orbs and that the sphere of fixed stars was the boundary of a finite universe, although his shift of center created large and inexplicable gaps between orbs, and especially between the outermost planet, Saturn, and the fixed stars. These gaps were later explained by Kepler using the geometrical construction introduced in the Mysterium Cosmographicum (1596). The immediate reaction, led by astronomers at the Lutheran University of Wittenberg, was to adapt Copernicus's new models to an Earth-centered system and to reject his cosmology on physical and scriptural grounds.

To remove Aristotle's cosmology, it was necessary to undermine his account of the construction of the heavens. Two major factors began this process: the revival of Stoic physics and precise observations of comets. Aristotle had taught that comets, which appeared and vanished at irregular intervals, must be long-lasting fires in the region below the Moon, because there could be no change in the heavens. In 1572 a nova suggested that change did occur in the heavens. Attempts to measure comets' distances placed them in the heavens. At the same time, the revival of Stoic physics suggested that the heavens might be filled by a continuous fluid rather than Aristotle's solid spheres. Tycho Brahe in Denmark and Michael Maestlin in Germany both measured precise distances for a comet that appeared in 1577. Both concluded that the comet had moved through a series of Aristotle's Earth-centered spheres and that any spheres must be centered on the Sun. Maestlin became a Copernican, later teaching his ideas to Johannes Kepler. But Brahe was unable to accept the motion of the Earth and developed a new cosmology in which the Earth remained the center, the Moon and Sun circled the Earth, and the remaining planets circled the Sun. To avoid the overlap his system created between the orbs of Mars and the Sun, Brahe adopted fluid heavens in which celestial spheres were no more than geometrical boundaries.

Today, Johannes Kepler is credited with discovering the three laws of planetary motion that bear his name, but his innovations were not generally accepted until Isaac Newton showed that they followed from his own theory. Kepler introduced the modern concept of an orbit, located the cause of planetary motion in the Sun, and replaced the circles of traditional astronomy with ellipses, but he continued to regard the fixed stars as the boundary of a finite universe. Like Tycho, he adopted a theory that made the substance of the heavens a fluid. The unprecedented accuracy of his astronomical tables advertised the importance of his insights after his death in 1630.

Galileo Galilei, by contrast, preserved many features of traditional cosmology. He never adopted Kepler's ellipses and denied that comets were celestial objects. However, his telescopic discoveries offered a host of new observational evidence supporting Copernicus. Jupiter's moons showed that the Averroists were wrong in demanding a single center of rotation for the cosmos. Sunspots and the observation of terrestrial features on the Moon showed that the heavens were not changeless and suggested that a single physics should embrace both heavens and Earth. The cycle of phases displayed by Venus showed that it, at least, circled the Sun. It was possible to accommodate all of these innovations in a modified Aristotelian scheme (as postulated by Du Chevreul in 1623), but the motions of comets and their implications for the substance of the heavens were unaccounted for. In the climate created by the Catholic Church's condemnation of Copernicanism in 1616 and 1633, Tycho Brahe's system became the most attractive option to anyone wishing to reconcile religious orthodoxy, traditional physics, and new astronomical discoveries. Jesuits exported it to China, and it was taught in Northern European universities into the eighteenth century.

Galileo's later work helped revive the ancient theory that matter was composed of atoms, a viewpoint that was being developed by Beeckman, Gassendi, and Descartes. The latter delayed publishing an atomistic cosmology because of Galileo's condemnation. In Le Monde, finished in 1633, but not published until 1664, Descartes described a cosmos filled by vortices of atoms. Stars naturally formed at the center of each vortex, while matter falling onto their surface caused sunspots. A large enough quantity of infalling material formed a crust over the entire star, which then became free of its vortex and wandered through the heavens, appearing as a comet. When finally captured by another vortex, the comet became a planet. Descartes therefore explained many new discoveries in a single scheme that was inherently heliocentric, although the sun was now just one among many vortex centers scattered throughout space.

Newton's synthesis (1689) provided a detailed mathematical physics that unified the heavens and the Earth. The planets were now held in place not by vortices, but by universal gravitation. Comets were divided into returning and nonreturning, and the reappearance of Halley's comet in 1758 was a highly visible success. With the general acceptance of Newton's system, cosmology assumed a form that persisted until the early twentieth century. As with Descartes, the Sun was identified as a star. The planets with their attendant satellites were bound to the Sun, but were not unique; other stars were assumed to be the centers of other planetary systems. Comets were definitely celestial, although only the determination of the numerical value of Newton's Universal Gravitational Constant allowed the recognition of their diminutive mass in comparison to planets or stars. Newton's First Law required that inertial motion continue indefinitely and implied a universe that was infinite in space.


The changes in cosmology just described have often been taken as the centerpiece of an event known as the scientific revolution, usually described as the replacement of Aristotle's scientific system with modern mathematical physics, based on experimental evidence. But recent historiography has tended to emphasize continuity with earlier achievements. It is now clear that the modern conception of experiment developed over a long period, with important changes beginning in the sixteenth century with the work of astronomers and early mathematical physicists. Kepler's unification of physics and mathematical astronomy became an important precedent, although it was more important with hindsight, after the development of new mathematical techniques for doing physics by Descartes, Newton, and their contemporaries. The work of Boyle and other members of the early Royal Society, as well as members of similar institutions in France and Italy, also contributed, although the modern conception of experiment did not emerge until the power of the new mathematical methods had been reconciled with the empiricism advocated by Bacon, a process that continued from Newton's career through the development of mathematical physics in France during the Enlightenment. Galileo's use of experiment resembles the earlier, rather than the later, concept. He was clearly not the originator of the experimental method, and modern research also demonstrates that his ideas on physics and scientific method in general were transformations of existing ideas rather than complete novelties.

Recent historians also give a more equal role to noncanonical sciences such as alchemy and astrology in the development of modern science. Alchemy clearly contributed to the replacement of Aristotle's theory of the terrestrial elements. Astrology remained important as the main motive for the study of astronomy and cosmology because of applications including medical diagnosis and treatment, weather prediction, and political planning. Although most practitioners followed the great Lutheran reformer and educator Philipp Melanchthon in believing that the heavens predisposed rather than compelled terrestrial events, casting horoscopes was a professional skill prized by the patrons of Tycho Brahe, Kepler, and Galileo. Alchemy was gradually transformed, first into the phlogiston theories of Stahl and his contemporaries, and then into the modern discipline of chemistry at the hands of Lavoisier. The disappearance of astrology lacks a generally agreed explanation. In England, at least, its public suppression may have had less to do with the development of the new science and new scientific societies after the Civil War than with the fact that its supporters were on the losing side after the Restoration of Charles II.

The supposed warfare between science and religion is now recognized to be largely a fiction of late-nineteenth-century historiography. Both Catholic and Protestant churches were active in supporting and sometimes opposing the new science. During the sixteenth century, for example, followers of Melanchthon arranged for the publication of Copernicus's work and actively spread his ideas, although, initially, they accepted his mathematical astronomy and rejected his cosmology. The trial of Galileo in 1633 cannot be attributed solely to his defense of Sun-centered cosmology. Other factors may include the dynamics of patronage (Galileo's patron Ciampoli offended the pope; other supporters had died) and internal church politics (the potential rebellion of a Spanish faction over the pope's handling of the Counter-Reformation). The condemnation of Copernicanism, and especially the outbreak of the Thirty Years' War in 1618, created new difficulties, but the Jesuit order of the Catholic Church remained at the forefront of scientific research. Kepler and Newton both saw their religious beliefs as integral to, rather than separable from, their scientific work.

The importance of new career paths and new scientific institutions has qualified earlier accounts of the scientific revolution. Copernicus was a lowly member of the Catholic hierarchy, who, until almost the end of his life, pursued his research essentially in private. His earliest supporters were university teachers, like Melanchthon's followers at Wittenberg and Maestlin at Tübingen. But his most important successors were courtiers whose research was supported by patronage. Tycho Brahe was financed by the king of Denmark, and later the Holy Roman emperor, who also supported his successor Kepler. Galileo moved from a university post to the court of the Medici in Florence, where he did his most important work. The first scientific societies appeared during the seventeenth century and provided new avenues of scientific communication, including published proceedings and journals, and new forms of support for scientists. In later life, Newton dominated the Royal Society of London. But the acceptance of Newton's system in Germany, and especially in France, followed the adoption of the new science as an intellectual fashion by the upper classes throughout Europe. This process depended upon the ascendancy of another social forum, the salon, where, for the first time since antiquity, women made major contributions to science.

The scientific revolution was not the work of a few great men, nor the result of changes that occurred only in the mathematical sciences, or in sciences that still exist today. It was not the result of the sudden appearance of the modern conception of experiment, nor did it come about because of any early separation between science and religion. There are profound differences between the content, method, and structure of the sciences from the origin to the close of the early modern period, but these changes are now regarded as the result of a complex combination of intellectual, theological, social, and institutional causes.

See also Alchemy ; Aristotelianism ; Astrology ; Bacon, Francis ; Boyle, Robert ; Brahe, Tycho ; Charles II (England) ; Copernicus, Nicolaus ; Descartes, René ; Enlightenment ; Galileo Galilei ; Gassendi, Pierre ; Kepler, Johannes ; Lavoisier, Antoine ; Medici Family ; Melanchthon, Philipp ; Newton, Isaac ; Scientific Revolution ; Stoicism ; Thirty Years' War (16181648)


Primary Sources

Aiton, E. J. "Peurbach's Theoricae Novae Planetarum :A Translation with Commentary." Osiris, 2nd series, 3 (1987): 544.

Brahe, Tycho. De Mundi Eetherei Recentioribus Phaenomenis. Uraniborg, 1588. Tycho's book on comets and his new cosmic scheme.

Chevreul, Jacques du. Sphaera. Paris, 1623. Contains an Aristotelian cosmic scheme that accommodates all Galileo's telescopic discoveries. (See also Ariew, below.)

Copernicus, Nicolaus. On the Revolutions of the Heavenly Spheres. Translated by A. M. Duncan. New York, 1976. Translation of De Revolutionibus Orbium Coelestium (1543).

Galilei, Galileo. Dialogue Concerning the Two Chief World Systems, Ptolemaic & Copernican. Translated by Stillman Drake. Berkeley, 1967. English translation of Dialogo sopra i due massimi sistemi del mondo, Tolemaico e Copernicano (1632), the work for which Galileo was condemned.

Goldstein, Bernard R. "The Arabic Version of Ptolemy's Planetary Hypotheses." Transactions of the American Philosophical Society 57 (1967), Part 4. Presents Ptolemy's physical models.

Descartes, René. The World and Other Writings. Translated by Stephen Gaukroger. Cambridge, U.K., 1998. English versions of Le monde de Mr Descartes; ou, Le traite de la lumiere. Paris, 1664.

Ptolemy's Almagest. Translated by G. J. Toomer. New York, 1984. Ptolemy's main work on mathematical astronomy. (See also Goldstein, above.)

Secondary Sources

Aiton, E. J. The Vortex Theory of Planetary Motions. London, 1972. Cartesian cosmology.

Ariew, Roger. Descartes and the Last Scholastics. Ithaca, N.Y, 1999. Presents Descartes in the context of Aristotelian responses to the new philosophy and science, including the work of Du Chevreul.

Barker, Peter, and Roger Ariew, eds. Revolution and Continuity: Essays in the History and Philosophy of Early Modern Science. Washington, D.C., 1991. Appraises the alleged discontinuity between medieval and modern science.

Biagioli, Mario. Galileo Courtier: The Practice of Science in the Culture of Absolutism. Chicago, 1993.

Dear, Peter. Revolutionizing the Sciences: European Knowledge and its Ambitions, 15001700. Princeton, 2001. Sound introduction that balances the contributions of canonical and noncanonical sciences.

Densmore, Dana. Newton's Principia: The Central Argument. Santa Fe, N.M., 1995. Translation, with notes, and expanded proofs of key mathematical arguments in Principia Mathematica (1687).

Osler, Margaret J., ed. Rethinking the Scientific Revolution. Cambridge, U.K., 2000. New historiography for early modern science.

Sutton, Geoffrey V. Science for a Polite Society: Gender, Culture, and the Demonstration of Enlightenment. Boulder, Colo., 1995. The social framework of Cartesian and Enlightenment science.

Westman, Robert S. "The Astronomer's Role in the Sixteenth Century: A Preliminary Survey." History of Science 18 (1980): 105147. Classic study of the transition from university support to patronage support in early modern science.

Peter Barker

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Cosmology is the study of the origin and evolution of the universe. In the last half of the twentieth century, astronomers made enormous progress in understanding cosmology. The discovery that the universe apparently began at a specific point in time and has continued to evolve ever since is one of the most revolutionary discoveries in science.

The History of the Universe: In the Beginning

The universe began in what astronomers dubbed the "Big Bang"an initial event, after which the universe began to expand. Current estimates place the Big Bang at about 13 to 15 × 109 years ago. During the first seconds after the Big Bang, the universe was extremely hot and dense. The physics needed to understand the universe in these early stages is very speculative because it is impossible to recreate these conditions in an experiment today to check the predictions of the theory. Before 10-44 seconds after the Big Bang, the four fundamental forces of naturegravity, the electromagnetic force, and the strong and weak nuclear forceswere unified into a single force. At 10-44 seconds, gravity separated from the others; at 10-34 seconds, the strong force became separated; and at 10-11 seconds, the weak force separated from the electromagnetic force.

During this period the universe began a sudden burst of exponential expansionfaster than the speed of light. This expansion is called "inflation" and explains why the universe we observe is so uniform. Temperatures were so hot (1027 K) before inflation that the familiar particles that make up atoms today (protons and neutrons ) were not stablethe universe was a hot soup of quarks (particles that are hypothesized to make up baryons), leptons (electrons and neutrinos), photons, and other exotic particles.

The History of the Universe: Formation of the Elements, Stars, and Galaxies, and the Cosmic Microwave Background

As the universe expanded after inflation it continued to cool. For the first three minutes conditions everywhere were similar to those at the center of stars today, and fusion of protons into deuterium, helium, and lithium took place. Most of the helium we see today in stars is believed to have been produced during these early minutes. The universe was an extremely opaque plasma, and photons dominated the mass density and dynamical evolution of the universe. When the universe cooled sufficiently to allow the free electrons to recombine with the hydrogen and helium nuclei, suddenly the opacity dropped, and the photons were free to stream through space unimpeded. These photons are seen today as the cosmic microwave background, a bath of light that is seen in all directions today. The experimental detection of the cosmic microwave background was one of the great triumphs of the Big Bang theory. Recombination and the subsequent production of the cosmic microwave background occurred about 180,000 years after the Big Bang.

At this point the matter distribution of the universe was still fairly uniform, with only small density fluctuations from place to place. As the universe expanded, the slightly overdense regions began to collapse. Sheets and filaments in the gas formed, which drained into dense clumps where star formation began. Eventually, these protogalactic fragments merged and galaxies and quasars formed. The universe began to look like it does today.

The Future of the Universe: Einstein's Biggest Blunder or Most Amazing Prediction?

Cosmologists predict the future of the universe as well as study its past. Whether the universe will expand forever or eventually slow down, turn around, and recollapse depends on how fast the galaxies are moving apart today and how much gravity there is to counter the expansionquantities that in principle can be measured.

German-born American physicist Albert Einstein (1879-1955) described the modern theory of gravity, general relativity. He used the idea that space could be curved to reformulate English physicist and mathematician Isaac Newton's (1642-1727) theory of gravity. In general relativity, the mass of an object curves the space around it, and parallel lines no longer go on forever without intersecting. In many textbooks the curvature of space is represented by a sphere or a saddle shapebut in reality, space is three-dimensional, and the "curvature" is not in a particular direction. Einstein wrote down what are called "field equations" that described how the curvature of space can be calculated from mass and energy. When he solved the equations he realized that even if the universe is infinite, isotropic (the same in all directions), and homogeneous (the same density everywhere), it would not be static. Depending on the geometry, it would expand or contract. American astronomer Edwin P. Hubble (1889-1953) had not yet discovered that the universe expands, so in 1917 Einstein added a "parameter" lambda, called the cosmological constant, to the field equations. Later, when Hubble showed that the universe is expanding, and that there was no need to add a cosmological constant to the field equations, Einstein called the cosmological constant "the biggest blunder of my life."

Were Einstein alive to day, he would be amazed to learn about recent observations that suggest that the cosmological constant is not zero and that the expansion is accelerating. In this case, the curvature of space is not so easily related to the dynamical evolution of the universe. At the beginning of the twenty-first century, theorists had not come up with a theory for the origin of a non-zero lambda that has testable predictions. Certainly, more observations are called for to confirm or refute this result.

Nonetheless, the conditions in the universe in the distant future can be described, given the physics that is understood today. If the universe is closed, then the Hubble expansion will eventually stop, and the universe will then collapse. If the density of the universe is, for the sake of argument, about twice the critical density for closing the universe, then the expansion stops about 50 billion years after the Big Bang. At about 85 billion years after the Big Bang, the density of the universe will again be about what it is today. At this point, the nearby galaxies will appear to move toward us, more distant galaxies will be standing still, and the very distant galaxies will be moving away. Eventually, the galaxies will all touch, and the universe will continue to contract and heat. Soon the stars will be cooler than the universe as a whole, so radiation will not be able to flow out of them, and they will explode. As a result, 100 billion years after the Big Bang will come the big crunch. At this point the universe may become a black holeor it may bounce, and cycle again.

If the universe is open or flat, the Hubble expansion goes on forever. Physical processes that take such a long time that they are irrelevant in today's universe will eventually have time to occur. After 1 trillion (1012) years, star formation will have used up all the available gas, and no new stars will form. Stellar remnants such as white dwarfs, neutron stars , and black holes will remain. After 1018 years, galaxies will evaporatetheir stars will disperse into space. After 1040 years, protons and neutrons will decay into positrons and electrons. After that, only black holes will exist. The black holes will eventually evaporate by Hawking radiation. At 10100 years after the Big Bang, all of the black holes, even the supermassive ones in quasars, will be gone. The universe will be very black and cold indeed.


The questions asked by cosmologists are some of the most simple and yet most profound questions intelligent creatures can ask. What is the origin of this beautiful and complex universe we live in, and what is its ultimate fate? Amazing progress was made over the last hundred years in cosmology, but clearly many important parts of the story are yet to be discovered.

see also Age of the Universe (volume 2); Einstein, Albert (volume 2); Galaxies (volume 2); Hubble Constant (volume 2); Hubble, Edwin P. (volume 2); Shapley, Harlow (volume 2); What is Space? (volume 2).

Jill Bechtold


Guth, Alan H., and Alan P. Lightman. The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Reading, MA: Addison-Wesley Publishing, 1998.

Hogan, Craig J., and Martin Rees. The Little Book of the Big Bang: A Cosmic Primer. New York: Copernicus Books, 1998.

Livio, Mario, and Allan Sandage. The Accelerating Universe: Infinite Expansion, the Cosmological Constant, and the Beauty of the Cosmos. New York: John Wiley & Sons, 2000.

Rees, Martin J. Just Six Numbers: The Deep Forces that Shape the Universe. New York:Basic Books, 2001.

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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 (14731543) 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 (15461601) and German astronomer Johannes Kepler (15711630). This proof consisted of careful calculations of the positions of the planets. In the early 1600s, Kepler developed the laws of planetary motion, showing that the planets follow an ellipse, or an oval-shaped path, around the Sun. He also pointed out that the universe was bigger than previously thought, although he still had no idea of its truly massive size.

The first astronomer to use a telescope to study the skies was Italian Galileo Galilei (15641642). His observations, beginning in 1609, supported the Copernican system. In the late 1600s, English physicist Isaac Newton (16421727) introduced the theories of gravity and mass, explaining how they are both responsible for the planets' motion around the Sun.

Over the next few centuries, astronomers and scientists continued to make additions to people's knowledge of the universe. These included the discoveries of nebulae (interstellar clouds) and asteroids (small, rocky chunks of matter) and the development of spectroscopy (the process of breaking down light into its component parts).

Modern cosmology

During the first two decades of the twentieth century, physicists and astronomers looked beyond our solar system and our Milky Way galaxy, forming ideas about the very nature of the universe. In 1916, German-born American physicist Albert Einstein (18791955) developed the general theory of relativity, which states that the speed of light is a constant and that the curvature of space and the passage of time are linked to gravity. A few years later, Dutch astronomer Willem de Sitter (18721934) used Einstein's theory to suggest that the universe began as a single point and has continued to expand.

Words to Know

Asteroid: Relatively small, rocky chunk of matter that orbits the Sun.

Copernican system: Theory proposing that the Sun is at the center of the solar system and all planets, including Earth, revolve around it.

Gravity: Force of attraction between objects, the strength of which depends on the mass of each object and the distance between them.

Light-year: Distance light travels in one solar year, roughly 5.9 trillion miles (9.5 trillion kilometers).

Mass: Measure of the total amount of matter in an object.

Nebula: Cloud of interstellar gas and dust.

Ptolemaic system: Theory proposing that Earth is at the center of the solar system and the Sun, the Moon, and all the planets revolve around it.

Radiation: Energy in the form of waves or particles.

Spectroscopy: Process of separating the light of an object (generally, a star) into its component colors so that the various elements present within that object can be identified.

Speed of light: Speed at which light travels in a vacuum: 186,282 miles (299,728 kilometers) per second.

In the 1920s, American astronomer Edwin Hubble (18891953) encountered observable proof that other galaxies exist in the universe besides our Milky Way. In 1929, he discovered that all matter in the universe was moving away from all other matter, proving de Sitter's theory that the universe was expanding.

Creation of the universe

Astronomers have long been interested in the question of how the universe was created. The two most popular theories are the big bang theory and the steady-state theory. Belgian astrophysicist Georges-Henri Lemaître (18941966) proposed the big bang theory in 1927. He suggested that the universe came into being 10 to 15 billion years ago with a big explosion. Almost immediately, gravity came into being, followed by atoms, stars, and galaxies. Our solar system formed 4.5 billion years ago from a cloud of dust and gas.

In contrast, the steady-state theory claims that all matter in the universe has been created continuously, a little at a time at a constant rate, from the beginning of time. The theory, first elaborated in 1948 by Austrian-American astronomer Thomas Gold, also states that the universe is structurally the same all over and has been forever. In other words, the universe is infinite, unchanging, and will last forever.

Astronomers quickly abandoned the steady-state theory when microwave radiation (energy in the form of waves or particles) filling space throughout the universe was discovered in 1964. The existence of this radiationcalled cosmic microwave backgroundhad been predicted by supporters of the big bang theory. In April 1992, NASA (National Aeronautics and Space Administration) announced that its Cosmic Background Explorer (COBE) satellite had detected temperature fluctuations in the cosmic microwave background. These fluctuations indicated that gravitational disturbances existed in the early universe, which allowed matter to clump together to form large stellar bodies such as galaxies and planets. This evidence all but proves that a big bang is responsible for the expansion of the universe.

Continued discoveries

At the end of the twentieth century, astronomers continued to revise their notion of the size of the universe. They repeatedly found that it is larger than they thought. In 1991, astronomers making maps of the universe discovered great "sheets" of galaxies in clusters and super-clusters filling areas hundreds of millions of light-years in diameter. They are separated by huge empty spaces of darkness, up to 400 million light-years across. And in early 1996, the Hubble Space Telescope photographed at least 1,500 new galaxies in various stages of formation.

In the late 1990s, while studying a certain group of supernovas, astronomers discovered that older objects in the group were receding at a speed similar to younger objects. In a "closed" universe, the expansion of the universe should slow down as it ages. Older supernovas should be receding more rapidly than younger ones. This is the theory that astronomers used to put forth: that at some future point the universe would stop expanding and then close back in on itself, an inverted big bang. However, with this recent finding, astronomers tend to believe that the universe is "open," meaning that the universe will continue its outward expansion for billions of years until everything simply burns out.


Creationism is a theory about the origin of the universe and all life in it. Creationism holds that Earth is perhaps less than 10,000 years old, that its physical features (mountains, oceans, etc.) were created as a result of sudden calamities, and that all life on the planet was miraculously created as it exists today. It is based on the account of creation given in the Old Testament of the Bible.

Because Creationism is not based on any presently held scientific principles, members of the scientific community dismiss it as a possible theory on how the universe was created. However, people who strongly believe in Creationism feel that it should be taught as a part of science education. The heated debate between the two sides continues.

[See also Big bang theory; Dark matter; Doppler effect; Galaxy; Redshift; Relativity, theory of ]

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cosmology, area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe.

Modern Cosmological Theories

Present models of the universe hold two fundamental premises: the cosmological principle and the dominant role of gravitation. Derived by Hubble, the cosmological principle holds that if a large enough sample of galaxies is considered, the universe looks the same from all positions and in all directions in space. The second point of agreement is that gravitation (or an antigravitation force, called dark energy) is the most important force in shaping the universe. According to Einstein's general theory of relativity, which is a geometric interpretation of gravitation, matter produces gravitational effects by actually distorting the space about it; the curvature of space is described by a form of non-Euclidean geometry. A number of cosmological theories satisfy both the cosmological principle and general relativity. The two main theories are the big-bang hypothesis and the steady-state hypothesis, with many variations on each basic approach.

The Steady-State Theory

According to the steady-state theory, now of historical interest only, the universe expands, but new matter is continuously created at all points in space left by the receding galaxies. The theory implies that the universe has always expanded, with no beginning or end, at a uniform rate and that it always will expand and maintain a constant density.

The Big-Bang Theory

According to big-bang theories, at the beginning of time, all of the matter and energy in the universe was concentrated in a very dense state, from which it "exploded," with the resulting expansion continuing until the present. This "big bang" is dated between 10 and 20 billion years ago, most likely c.13.75 billion years ago. In this initial state, the universe was very hot and contained a thermal soup of quarks, electrons, photons, and other elementary particles. The temperature rapidly decreased, falling from 1013 degrees Kelvin after the first microsecond to about one billion degrees after three minutes. As the universe cooled, the quarks condensed into protons and neutrons, the building blocks of atomic nuclei. Some of these were converted into helium nuclei by fusion; the relative abundance of hydrogen and helium is used as a test of the theory. After many millions of years the expanding universe, at first a very hot gas, thinned and cooled enough to condense into individual galaxies and then stars.

Several spectacular discoveries since 1950 have shed new light on the problem. Optical and radio astronomy complemented each other in the discovery of the quasars and the radio galaxies. It is believed that the energy reaching us now from some of these objects was emitted not long after the creation of the universe. Further evidence for the big-bang theory was the discovery in 1965 that a cosmic background noise is received from every part of the sky. This background radiation has the same intensity and distribution of frequencies in all directions and is not associated with any individual celestial object. It has a blackbody temperature of 2.7°K (-270°C) and is interpreted as the electromagnetic remnant of the primordial fireball, stretched to long wavelengths by the expansion of the universe. More recently, the analysis of radiation from distant celestial objects detected by artificial satellites and orbiting observatories has given additional evidence for the big-bang theory.

Development of Modern Cosmology

The earliest pre-Ptolemaic theories assumed that the earth was the center of the universe (see Ptolemaic system). With the acceptance of the heliocentric, or sun-centered, theory (see Copernican system), the nature and extent of the solar system began to be realized. The Milky Way, a vast collection of stars separated by enormous distances, came to be called a galaxy and was thought to constitute the entire universe with the sun at or near its center. By studying the distribution of globular star clusters the American astronomer Harlow Shapley was able to give the first reliable indication of the size of the galaxy and the position of the sun within it. Modern estimates show it to have a diameter of about 100,000 light-years with the sun toward the edge of the disk, about 28,000 light-years from the center.

During the first two decades of the 20th cent. astronomers came to realize that some of the faint hazy patches in the sky, called nebulae, are not within our own galaxy, but are separate galaxies at great distances from the Milky Way. Willem de Sitter of Leyden suggested that the universe began as a single point and expands without end. After studying the red shift (see Doppler effect) in the spectral lines of the distant galaxies, the American astronomers Edwin Hubble and M. L. Humason concluded that the universe is expanding, with the galaxies appearing to fly away from each other at great speeds. According to Hubble's law, the expansion of the universe is approximately uniform. The greater the distance between any two galaxies, the greater their relative speed of separation.

At the end of the 20th cent. the study of very distant supernovas led to the belief that the cosmic expansion was accelerating. To explain this cosmologists postulated a repulsive force, dark energy, that counteracts gravity and pushes galaxies apart. It also appears that the universe has been expanding at different rates over its cosmic history. This led to a variation of the big-bang theory in which, under the influence of gravity, the expansion slowed initially and then, under the influence of dark energy, suddenly accelerated. It is estimated that this "cosmic jerk" occurred five billion years ago, about the time the solar system was formed. This theory postulates a flat, expanding universe with a composition of c.70% dark energy, c.30% dark matter, and c.0.5% bright stars.

A number of questions must be answered, however, before cosmologists can establish a single, comprehensive theory. The expansion rate and age of the universe must be established. The nature and density of the missing mass, the dark matter and dark energy that is far more abundant than ordinary, visible matter, must be identified. The total mass of the universe must be determined to establish whether it is sufficient to support an equilibrium condition—a state in which the universe will neither collapse of its own weight nor expand into diminishing infinity. Such an equilibrium is called "omega equals one," where omega is the ratio between the actual density of the universe and the critical density required to support equilibrium. If omega is greater than one, the universe would have too much mass and its gravity would cause a cosmic collapse. If omega is less than one, the low-density universe would expand forever. Today the most widely accepted picture of the universe is an omega-equals-one system of hundreds of billions of galaxies, many of them clustered in groups of hundreds or thousands, spread over a volume with a diameter of at least 10 billion light-years and all receding from each other, with the speeds of the most widely separated galaxies approaching the speed of light. On a more detailed level there is great diversity of opinion, and cosmology remains a highly speculative and controversial science.


See D. W. Sciama, Modern Cosmology and the Dark Matter Problem (1993); J. D. Barrow, The Origin of the Universe (1994); P. Coles and F. Lucchin, Cosmology: The Origin and Evolution of Cosmic Structure (1995); M. S. Longair, Our Evolving Universe (1996); B. Green, The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory (2000); S. Hawking, The Universe in a Nutshell (2001); R. P. Kirshner, The Extravagant Universe: Exploding Stars, Dark Energy, and Accelerating Cosmos (2002); S. Singh, Big Bang: The Origin of the Universe (2005).

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Cosmology (Gk., kosmos + logos). Reflection on, and account of the world/universe as a meaningful whole, as embodying or expressing an order or underlying structure that makes sense: cosmogony is concerned with the coming into being of the cosmos, and cosmography with the description of its extent.

It is rare for religions to give a single cosmology or cosmogony purporting to be a description of the origin of the universe, in the way in which a scientific cosmology might aim to give a critically realistic account of the origin and nature of the universe. Religious cosmologies give accounts of origin and nature, but principally in order to display the cosmos as an arena of opportunity; and for that reason, a religion may offer, or make use of, many cosmogonies without making much attempt to reconcile the contradictions between them. It is this aesthetic and spiritual relaxation which allows religions to address cosmological issues from the point of view of accountability and responsibility (as at the present time over issues of ecology), not as competitors with a scientific account: thus the Vancouver Assembly of the World Council of Churches (see ECUMENISM) decided ‘to engage member churches in a conciliar process of mutual commitment (covenant) to justice, peace and the integrity of creation (subsequently known as JPIC)’; while this (especially the word ‘covenant’) depends on a particular understanding of creation, and thus of cosmogony, it has moved far beyond concerns about identifying the ‘correct’ account of the cosmos and its origins.


Tanach (Jewish scripture) contains at least six different types of creation narrative, all of which are integrated to the overriding cult of Yahweh. The controlling accounts are those in Genesis: God created everything that exists in six days and rested on the seventh (1–2. 4). A second, more anthropocentric account (Genesis 2. 4–24), although differing in detail, also emphasizes that God is the origin of everything. The world is created solely in obedience to the divine will.


Christians inherited the Jewish cosmology, but virtually from the outset (as early as Paul's letters) they associated Christ with the activity of the Father in creation. Furthermore, creation now has its end and purpose in him. Not surprisingly, therefore, Christian interest in cosmology and creation has seen them as a matter, not of technique, but of relationship—i.e. the relation of dependence which the created order has on its creator, not just for its origin, but for its sustenance. Thus God is the cause, not simply of things coming to be, but also of their being. The prevailing cosmography for millennia was one of a ‘three-decker’ universe (heaven above, earth in the middle, and hell below), but its ‘correction’ by modern cosmologies has not affected the more fundamental point of the earlier (or of any) religious cosmology which mapped the universe as an arena of opportunity. For that reason, a three-decker universe may well persist indefinitely in liturgy.


The Qurʾān strongly affirms God as creator and disposer of all that is. By a simple word, kun (‘Be’), he commands and it is (2. 117, 6. 73). God is al-Khāliq (the Creator, from khalaqa, ‘he created’), and has the power and authority to bring about all things as he disposes (qadar, Allāh). Everything that he has created is a sign (ayā), not only of God for those who have eyes to see, but also that God has power to continue his creative act in relation to humans by bringing them from the grave for judgement (e.g. 50. 6–11). The creation of a first man and first woman, and of the earth and seven heavens in two days, and of the cosmos in six, is described in such a way that, given the nature of the Qurʾān, any apparent conflict with other accounts (e.g. in the natural sciences) would have to be resolved in favour of the Qurʾān.


Vedic religion displays a clear sense of an ordered universe in which ṛta prevails. There are many different accounts of how the universe came into being, some implying agency, others emanation from a pre-existing state in which there is neither beginning nor end. Thus Śaṅkara understood the emanation as a progress from the subtle to the gross constituents of the world. But earlier than that, there had developed a sense of an unending process like a wave, with elements rising up into organized appearance, but then lapsing into a corresponding trough during ‘the sleep of Brahmā’, a period of dissolution (pralaya). It was thus possible that the cosmos arose from infinite space and consciousness, a belief expressed through Aditi. In truth, Indian religion accepted that the origin of the cosmos could not be known, but that the conditions of ordered life could be extremely well known. Cosmology lays out the terms for achieving that understanding—cosmology, again, as the arena of opportunity—while remaining agnostic about detail.

There was a greater confidence in cosmography. Vertically, the world was understood to be made up of seven continents (dvipas), ranged in circles with intervening oceans around the central point of Mount Meru. Vertically, if one takes a cross-section of the Brahmāṇḍa, one finds a series of layers. At the top are the lokas of the gods and high attainers; next are the planets, sky, and earth; then the underworlds, and finally the twenty-eight narakas or hells. See also CARDINAL DIRECTIONS.

Jainism and Buddhism

The Indian scepticism about the work of the gods or God in creating this cosmos was taken to a further extreme in both Jainism and Buddhism. The Jains inherited the triloka (see LOKA), and envisaged it as something like an hour-glass, squeezed in at the middle. Above (Urdhvaloka) are a series of heavens of increasing brightness, at the top of which is ‘the slightly curved place’ (Iśatpragbhara) where dwell the liberated and disembodied souls. In the middle is the Madhyaloka, which includes the continent inhabited by humans. Below is the Adholoka, a series of increasingly terrible hells—from which release is eventually certain, though the intervening time may be unimaginably long.

Buddhism inherited the same basic cosmography, but adapted it greatly. It envisages a series of levels, all of which are open to the process of reappearance: at the summit are the four realms of purely mental rebirth, (arūpaavacara); below them are the realms of pure form (rūpa-avacara), where the gods dwell in sixteen heavens, five of which are known as ‘pure abodes’ (suddhāvāsa), the remaining eleven of which arise out of the jhānas (meditational states). Lower still are the sense-desire heavens, including those of the Tāvatiṃsa gods (the thirty-three Vedic gods, the chief of whom, Indra, known as Sakka, has become a protector of Buddhism) and of the Tusita gods (where bodhisattvas spend their penultimate birth, and in which Maitreya now dwells). The world is simply a process, passing through cycles (kappa) of immense length.

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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' (14731543) 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 (15461601), found full expression in the mathematical genius of the German astronomer Johannes Kepler (15711630) 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 (16421727), 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 (17491827) 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 (18791955) 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 (18891953) 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 (19041968) 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, 18881925) and Belgian astrophysicist and cosmologist Abbé Georges Lemaître (18941966). 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

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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 (384322 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 (14731543) 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 (15641642) destroyed Aristotelian cosmology. The subsequent mechanical cosmology of Isaac Newton (16421727), 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 (18851972) 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 (18891953) 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.

norriss hetherington

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100. Cosmology

See also 25. ASTRONOMY ; 318. PLANETS ; 387. SUN .

a 19th-century theory about cosmic evolution, developed from contemporary science, that regards the cosmos as self-existent and self-acting. cosmist , n.
1. a theory about the origin and the evolution of the universe.
2. the branch of astrophysics that studies the origin and evolution of specific astronomical systems and the universe as a whole.
3. cosmology. cosmogonist , n. cosmogonic , adj.
1. the branch of astronomy that maps and describes the main features of the universe.
2. a description or representation of the main features of the universe. cosmographer , n. cosmographic , cosmographical, adj.
1. the branch of astronomy that studies the overall structure of the physical universe.
2. the branch of philosophy that studies the origin, structure, and evolution of the universe, especially such characteristics as space, time, causality, and freedom. cosmologic, cosmological , adj. cosmologist , n.
the concept that the universe and God are identical; pantheism. cosmotheist , n.
the concept of the cosmos as alive.
the belief concerning the creation by a transcendant God of the universe, matter, and living organisms out of nothing. creationist , n.
1. the concept that the earth is the center of the universe.
2. Astronomy. the measurements or observations that are relative to the center of the earth. geocentric , adj.
1. the concept that the sun is the center of the universe.
2. Astronomy. the measurements or observations that are relative to the center of the sun. Also heliocentricity. heliocentric , adj.
the theory that the totality of existence comprises only the physical universe in time and space. pancosmic , adj.
a Gnostic theory that considered Satans to be the controlling will of the universe.
the philosophical theory of Herbert Spencer that cosmic evolution is cyclic, controlled by mechanical forces which tend toward equilibrium and relative complexity until a peak is reached, after which dissolution occurs, the universe reverts to a simple state, and the cycle begins again. Spencerian , n., adj.
the belief that purpose and design control the development of the universe and are apparent through natural phenomena. teleologist , n. teleology , n.
the science of the universe. universologist , n.

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cosmology The study of the origin and evolution of the universe. The current big bang cosmology derives the observable universe from a singular event 15–20 billion years ago. Previous hypotheses include the steady-state theory, in which the expansion of the universe was due to the continuous creation of matter. The most celebrated of earlier world views was the Ptolemaic system, in which the Earth was the centre of the universe; this was superseded by the Copernican revolution, which displaced the Earth from its central position.

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cosmology Branch of scientific study that brings together astronomy, mathematics and physics in an effort to understand the make-up and evolution of the universe. Once considered the province of theologians and philosophers, it is now an all-embracing science, which has made great strides in the 20th century. The discovery by Edwin Hubble in the 1920s that galaxies are receding from each other promoted the Big Bang theory. Associated with this is the oscillating Universe theory. The other main theory is the steady-state theory.

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cos·mol·o·gy / käzˈmäləjē/ • n. (pl. -gies) the science of the origin and development of the universe. ∎  an account or theory of the origin of the universe. DERIVATIVES: cos·mo·log·i·cal / ˌkäzməˈläjikəl/ adj. cos·mol·o·gist / -jist/ n.

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This entry includes two subentries:

Cosmology and Astronomy

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