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Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of") is the study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scholarly and scientific study of the origin, large-scale structures and dynamics, and ultimate fate of the universe, as well as the scientific laws that govern these realities.
The term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, and in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis.
Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation and eschatology.
Physical cosmology is studied by scientists, such as astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, and philosophers of space and time. Because of this shared scope with philosophy, theories in physical cosmology may include both scientific and non-scientific propositions, and may depend upon assumptions that can not be tested. Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual celestial objects. Modern physical cosmology is dominated by the Big Bang theory, which attempts to bring together observational astronomy and particle physics; more specifically, a standard parameterization of the Big Bang with dark matter and dark energy, known as the Lambda-CDM model.
Name | Author and date | Classification | Remarks |
---|---|---|---|
Hindu cosmology | Rigveda (c. 1700–1100 BC) | Cyclical or oscillating, Infinite in time | One cycle of existence is around 311 trillion years and the life of one universe around 8 billion years. This Universal cycle is preceded by an infinite number of universes and to be followed by another infinite number of universes. Includes an infinite number of universes at one given time. |
Jain cosmology | Jain Agamas (written around 500 AD as per the teachings of Mahavira 599–527 BC) | Cyclical or oscillating, eternal and finite | Jain cosmology considers the loka, or universe, as an uncreated entity, existing since infinity, the shape of the universe as similar to a man standing with legs apart and arm resting on his waist. This Universe, according to Jainism, is broad at the top, narrow at the middle and once again becomes broad at the bottom. |
Babylonian cosmology | Babylonian literature (c. 3000 BC) | Flat earth floating in infinite "waters of chaos" | The Earth and the Heavens form a unit within infinite "waters of chaos"; the earth is flat and circular, and a solid dome (the "firmament") keeps out the outer "chaos"-ocean. |
Eleatic cosmology | Parmenides (c. 515 BC) | Finite and spherical in extent | The Universe is unchanging, uniform, perfect, necessary, timeless, and neither generated nor perishable. Void is impossible. Plurality and change are products of epistemic ignorance derived from sense experience. Temporal and spatial limits are arbitrary and relative to the Parmenidean whole. |
Biblical cosmology | Genesis creation narrative | Earth floating in infinite "waters of chaos" | The Earth and the Heavens form a unit within infinite "waters of chaos"; the "firmament" keeps out the outer "chaos"-ocean. |
Atomist universe | Anaxagoras (500–428 BC) & later Epicurus | Infinite in extent | The universe contains only two things: an infinite number of tiny seeds (atoms) and the void of infinite extent. All atoms are made of the same substance, but differ in size and shape. Objects are formed from atom aggregations and decay back into atoms. Incorporates Leucippus' principle of causality: "nothing happens at random; everything happens out of reason and necessity". The universe was not ruled by gods. |
Pythagorean universe | Philolaus (d. 390 BC) | Existence of a "Central Fire" at the center of the Universe. | At the center of the Universe is a central fire, around which the Earth, Sun, Moon and planets revolve uniformly. The Sun revolves around the central fire once a year, the stars are immobile. The earth in its motion maintains the same hidden face towards the central fire, hence it is never seen. First known non-geocentric model of the Universe. |
De Mundo | Pseudo-Aristotle (d. 250 BC or between 350 and 200 BC) | The Universe then is a system made up of heaven and earth and the elements which are contained in them. | There are "five elements, situated in spheres in five regions, the less being in each case surrounded by the greater — namely, earth surrounded by water, water by air, air by fire, and fire by ether — make up the whole Universe." |
Stoic universe | Stoics (300 BC – 200 AD) | Island universe | The cosmos is finite and surrounded by an infinite void. It is in a state of flux, and pulsates in size and undergoes periodic upheavals and conflagrations. |
Aristotelian universe | Aristotle (384–322 BC) | Geocentric, static, steady state, finite extent, infinite time | Spherical earth is surrounded by concentric celestial spheres. Universe exists unchanged throughout eternity. Contains a fifth element, called aether, that was added to the four classical elements. |
Aristarchean universe | Aristarchus (circa 280 BC) | Heliocentric | Earth rotates daily on its axis and revolves annually about the sun in a circular orbit. Sphere of fixed stars is centered about the sun. |
Ptolemaic model | Ptolemy (2nd century AD) | Geocentric (based on Aristotelian universe) | Universe orbits around a stationary Earth. Planets move in circular epicycles, each having a center that moved in a larger circular orbit (called an eccentric or a deferent) around a center-point near Earth. The use of equants added another level of complexity and allowed astronomers to predict the positions of the planets. The most successful universe model of all time, using the criterion of longevity. Almagest (the Great System). |
Aryabhatan model | Aryabhata (499) | Geocentric or Heliocentric | The Earth rotates and the planets move in elliptical orbits around either the Earth or Sun; uncertain whether the model is geocentric or heliocentric due to planetary orbits given with respect to both the Earth and Sun. |
Medieval universe | Medieval philosophers (500–1200) | Finite in time | A universe that is finite in time and has a beginning is proposed by the Christian philosopher John Philoponus, who argues against the ancient Greek notion of an infinite past. Logical arguments supporting a finite universe are developed by the early Muslim philosopher Alkindus, the Jewish philosopher Saadia Gaon, and the Muslim theologian Algazel. |
Multiversal cosmology | Fakhr al-Din al-Razi (1149–1209) | Multiverse, multiple worlds and universes | There exists an infinite outer space beyond the known world, and God has the power to fill the vacuum with an infinite number of universes. |
Maragha models | Maragha school (1259–1528) | Geocentric | Various modifications to Ptolemaic model and Aristotelian universe, including rejection of equant and eccentrics at Maragheh observatory, and introduction of Tusi-couple by Al-Tusi. Alternative models later proposed, including the first accurate lunar model by Ibn al-Shatir, a model rejecting stationary Earth in favour of Earth's rotation by Ali Kuşçu, and planetary model incorporating "circular inertia" by Al-Birjandi. |
Nilakanthan model | Nilakantha Somayaji (1444–1544) | Geocentric and heliocentric | A universe in which the planets orbit the Sun, which orbits the Earth; similar to the later Tychonic system |
Copernican universe | Nicolaus Copernicus (1473–1543) | Heliocentric with circular planetary orbits | First described in De revolutionibus orbium coelestium. |
Tychonic system | Tycho Brahe (1546–1601) | Geocentric and Heliocentric | A universe in which the planets orbit the Sun and the Sun orbits the Earth, similar to the earlier Nilakanthan model. |
Bruno's cosmology | Giordano Bruno (1548–1600) | Infinite extent, infinite time, homogeneous, isotropic, non-hierarchical | Rejects the idea of a hierarchical universe. Earth and Sun have no special properties in comparison with the other heavenly bodies. The void between the stars is filled with aether, and matter is composed of the same four elements (water, earth, fire, and air), and is atomistic, animistic and intelligent. |
Keplerian | Johannes Kepler (1571–1630) | Heliocentric with elliptical planetary orbits | Kepler's discoveries, marrying mathematics and physics, provided the foundation for our present conception of the Solar system, but distant stars were still seen as objects in a thin, fixed celestial sphere. |
Static Newtonian | Isaac Newton (1642–1727) | Static (evolving), steady state, infinite | Every particle in the universe attracts every other particle. Matter on the large scale is uniformly distributed. Gravitationally balanced but unstable. |
Cartesian Vortex universe | René Descartes, 17th century | Static (evolving), steady state, infinite | System of huge swirling whirlpools of aethereal or fine matter produces what we would call gravitational effects. But his vacuum was not empty; all space was filled with matter. |
Hierarchical universe | Immanuel Kant, Johann Lambert, 18th century | Static (evolving), steady state, infinite | Matter is clustered on ever larger scales of hierarchy. Matter is endlessly recycled. |
Einstein Universe with a cosmological constant | Albert Einstein, 1917 | Static (nominally). Bounded (finite) | "Matter without motion". Contains uniformly distributed matter. Uniformly curved spherical space; based on Riemann's hypersphere. Curvature is set equal to Λ. In effect Λ is equivalent to a repulsive force which counteracts gravity. Unstable. |
De Sitter universe | Willem de Sitter, 1917 |
Expanding flat space.
Steady state. Λ > 0 |
"Motion without matter." Only apparently static. Based on Einstein's general relativity. Space expands with constant acceleration. Scale factor increases exponentially (constant inflation). |
MacMillan universe | William Duncan MacMillan 1920s | Static and steady state | New matter is created from radiation; starlight perpetually recycled into new matter particles. |
Friedmann universe, spherical space | Alexander Friedmann 1922 | Spherical expanding space.
k= +1 ; no Λ |
Positive curvature. Curvature constant k = +1
Expands then recollapses. Spatially closed (finite). |
Friedmann universe, hyperbolic space | Alexander Friedmann, 1924 |
Hyperbolic expanding space.
k= -1 ; no Λ |
Negative curvature. Said to be infinite (but ambiguous). Unbounded. Expands forever. |
Dirac large numbers hypothesis | Paul Dirac 1930s | Expanding | Demands a large variation in G, which decreases with time. Gravity weakens as universe evolves. |
Friedmann zero-curvature | Einstein and De Sitter, 1932 | Expanding flat space
k= 0 ; Λ = 0 Critical density |
Curvature constant k = 0. Said to be infinite (but ambiguous). "Unbounded cosmos of limited extent". Expands forever. "Simplest" of all known universes. Named after but not considered by Friedmann. Has a deceleration term q =½, which means that its expansion rate slows down. |
The original Big Bang (Friedmann-Lemaître) | Georges Lemaître 1927–29 | Expansion
Λ > 0 Λ > |Gravity| |
Λ is positive and has a magnitude greater than gravity. Universe has initial high-density state ("primeval atom"). Followed by a two-stage expansion. Λ is used to destabilize the universe. (Lemaître is considered the father of the big bang model.) |
Oscillating universe (Friedmann-Einstein) | Favored by Friedmann, 1920s | Expanding and contracting in cycles | Time is endless and beginningless; thus avoids the beginning-of-time paradox. Perpetual cycles of big bang followed by big crunch. (Einstein's first choice after he rejected his 1917 model.) |
Eddington universe | Arthur Eddington 1930 | First static then expands | Static Einstein 1917 universe with its instability disturbed into expansion mode; with relentless matter dilution becomes a De Sitter universe. Λ dominates gravity. |
Milne universe of kinematic relativity |
Edward Milne, 1933, 1935;
William H. McCrea, 1930s |
Kinematic expansion without space expansion | Rejects general relativity and the expanding space paradigm. Gravity not included as initial assumption. Obeys cosmological principle and special relativity; consists of a finite spherical cloud of particles (or galaxies) that expands within an infinite and otherwise empty flat space. It has a center and a cosmic edge (surface of the particle cloud) that expands at light speed. Explanation of gravity was elaborate and unconvincing. |
Friedmann–Lemaître–Robertson–Walker class of models | Howard Robertson, Arthur Walker, 1935 | Uniformly expanding | Class of universes that are homogeneous and isotropic. Spacetime separates into uniformly curved space and cosmic time common to all co-moving observers. The formulation system is now known as the FLRW or Robertson–Walker metrics of cosmic time and curved space. |
Steady-state expanding | Hermann Bondi, Thomas Gold, 1948 | Expanding, steady state, infinite | Matter creation rate maintains constant density. Continuous creation out of nothing from nowhere. Exponential expansion. Deceleration term q = -1. |
Steady-state expanding | Fred Hoyle 1948 | Expanding, steady state; but unstable | Matter creation rate maintains constant density. But since matter creation rate must be exactly balanced with the space expansion rate the system is unstable. |
Ambiplasma | Hannes Alfvén 1965 Oskar Klein | Cellular universe, expanding by means of matter–antimatter annihilation | Based on the concept of plasma cosmology. The universe is viewed as "meta-galaxies" divided by double layers and thus a bubble-like nature. Other universes are formed from other bubbles. Ongoing cosmic matter-antimatter annihilations keep the bubbles separated and moving apart preventing them from interacting. |
Brans–Dicke theory | Carl H. Brans, Robert H. Dicke | Expanding | Based on Mach's principle. G varies with time as universe expands. "But nobody is quite sure what Mach's principle actually means." |
Cosmic inflation | Alan Guth 1980 | Big Bang modified to solve horizon and flatness problems | Based on the concept of hot inflation. The universe is viewed as a multiple quantum flux—hence its bubble-like nature. Other universes are formed from other bubbles. Ongoing cosmic expansion kept the bubbles separated and moving apart. |
Eternal inflation (a multiple universe model) | Andreï Linde, 1983 | Big Bang with cosmic inflation | Multiverse based on the concept of cold inflation, in which inflationary events occur at random each with independent initial conditions; some expand into bubble universes supposedly like our entire cosmos. Bubbles nucleate in a spacetime foam. |
Cyclic model | Paul Steinhardt; Neil Turok 2002 | Expanding and contracting in cycles; M-theory. | Two parallel orbifold planes or M-branes collide periodically in a higher-dimensional space. With quintessence or dark energy. |
Cyclic model | Lauris Baum; Paul Frampton 2007 | Solution of Tolman's entropy problem | Phantom dark energy fragments universe into large number of disconnected patches. Our patch contracts containing only dark energy with zero entropy. |
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