Cosmology

The Hubble Ultra-Deep Field. Every speck of light in this image is an entire galaxy. This is just a small region of a Universe which could contain as many as 200 billion galaxies.

Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order. ^[1] Modern cosmology is dominated by the Big Bang theory, which brings together observational astronomy and particle physics.^[2]

Though the word cosmology is recent (first used in 1730 in Christian Wolff's Cosmologia Generalis), the study of the universe has a long history involving science, philosophy, esotericism, metaphysics, and religion. Related studies include cosmogony, which focuses on the origin of the Universe, and cosmography, which maps the features of the Universe. Cosmology is also connected to astronomy. However, they are contrasted in that while the former is concerned with the Universe in its entirety, the latter deals with individual celestial objects.

Disciplines

In recent times, physics and astrophysics have played a central role in shaping the understanding of the universe through scientific observation and experiment. What is known as physical cosmology shaped through both mathematics and observation the analysis of the whole universe. It is generally understood to begin with the Big Bang combined with cosmic inflation – an expansion of space from which the universe is thought to have emerged ~13.7±0.2×10⁹ (roughly 13.5-13.9 billion) years ago.^[3]

Physical cosmologists propose that the history of the universe has been governed entirely by physical laws. Such theories of an impersonal universe governed by physical laws were first proposed by Roger Bacon.^{[citation needed]} Between the domains of religion and science, stands the philosophical perspective of metaphysical cosmology. This ancient field of study seeks to draw intuitive conclusions about the nature of the universe, man, a supernatural creator and/or their relationships based on the extension of some set of presumed facts borrowed from spiritual experience and/or observation.

Metaphysical cosmology has also been described as the placing of man in the universe in relationship to all other entities. This is exampled by the observation made by Marcus Aurelius of a man's place in that relationship: "He who does not know what the world is does not know where he is, and he who does not know for what purpose the world exists, does not know who he is, nor what the world is."^[4]

Cosmology is often an important aspect of the creation myths of religions that seek to explain the existence and nature of reality. In some cases, views about the creation (cosmogony) and destruction (eschatology) of the universe play a central role in shaping a framework of religious cosmology for understanding humanity's role in the universe.

A more contemporary distinction between religion and philosophy, esoteric cosmology is distinguished from religion in its less tradition-bound construction and reliance on modern "intellectual understanding" rather than faith, and from philosophy in its emphasis on spirituality as a formative concept.

Historical cosmologies

Further information: Timeline of cosmology

Name	Author and date	Classification	Remarks
Babylonian cosmology	Babylonian literature (1900-1200 BC)	Plurality of heavens and earths	The Earth and Heavens are a "spatial whole, even one of round shape," revolving around the "cult-place of the deity"[clarification needed] rather than the Earth,[5] and there is a plurality of heavens and earths.[6]
Brahmanda (Hindu Cosmology)	Hindu Rigveda (1700–1100 BC)	Cyclical or oscillating, Infinite in time	The universe sustains for around 311,040,000,000,000 years, or 100 Years of Brahma. There is a smaller period of unmanifestation in around 4 billion years, that is, one Day of Brahma. The universe cycles between expansion and total collapse. After one cycle of the life of Brahma another universe follows for infinity, each of which exists for a time period of 311 trillion 40 billion years. It also speaks of an infinite number of universes at one given point of time. The Universe expanded from a concentrated form, a point called a Bindu. The universe, as a living entity, is bound to the perpetual cycle of birth, death, and rebirth.
Atomist universe	Anaxagoras (500-428 BC) & later Epicurus	Infinite in extent	The universe contains only two things: an infinite number of tiny seeds, or 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. This is the first known non-geocentric model of the Universe.[7]
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, as it pulsates in size and periodically passes through 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 (later known as quintessence), 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 (based on Aristotelian universe)	Ptolemy (2nd century AD)	Geocentric	Universe orbits about 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 the 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, possibly around either the Earth or the Sun. It is uncertain whether the model is geocentric or heliocentric due to planetary orbits given with respect to both the Earth and the Sun.
Abrahamic 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 & 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 and the Sun orbits the Earth, similar to the later Tychonic system.
Copernican universe	Nicolaus Copernicus (1543)	Heliocentric	First clearly described heliocentric model, 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.
Static Newtonian	Sir 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	A system of huge swirling whirlpools of aethereal or fine matter produces what we would call gravitational effects. His vacuum was not empty. All space was filled with matter that swirled around in large and small vortices.
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 being 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 (radius of universe) increases exponentially, i.e. constant inflation.
MacMillan universe	William Duncan MacMillan 1920s	Static & steady state	New matter is created from radiation. Starlight is perpetually recycled into new matter particles.
Friedmann universe of 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 of 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, a.k.a. the Einstein-DeSitter universe	Einstein & DeSitter 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. a.k.a. Friedmann-Lemaître Model	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 to be the father of the big bang model.)
Oscillating universe (a.k.a. Friedmann-Einstein; was latter's 1st choice after rejecting his own 1917 model)	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.
Eddington	Arthur Eddington 1930	First Static then Expands	Static Einstein 1917 universe with its instability disturbed into expansion mode; with relentless matter dilution becomes a DeSitter universe. Λ dominates gravity.
Milne universe of kinematic relativity	Edward Milne, 1933, 1935; William H. McCrea, 1930s	Kinematic expansion with NO space expansion	Rejects general relativity and the expanding space paradigm. Gravity not included as initial assumption. Obeys cosmological principle & rules of special relativity. The Milne expanding universe consists of a finite spherical cloud of particles (or galaxies) that expands WITHIN flat space which is infinite and otherwise empty. It has a center and a cosmic edge (the surface of the particle cloud) which expands at light speed. His explanation of gravity was elaborate and unconvincing. For instance, his universe has an infinite number of particles, hence infinite mass, within a finite cosmic volume.
Friedmann-Lemaître-Robertson-Walker class of models	Howard Robertson, Arthur Walker, 1935	Uniformly expanding	Class of universes that are homogenous and isotropic. Spacetime separates into uniformly curved space and cosmic time common to all comoving observers. The formulation system is now known as the FLRW or Robertson-Walker metrics of cosmic time and curved space.
Steady-state expanding (Bondi & Gold)	Herman 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 (Hoyle)	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 —hence its 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	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."[citation needed]
Cosmic inflation	Alan Guth 1980	Big Bang with modification to solve horizon problem and flatness problem.	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 preventing them from interacting.
Eternal Inflation (a multiple universe model)	Andreï Linde 1983	Big Bang with cosmic inflation	A 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.

Table notes: the term "static" simply means not expanding and not contracting. Symbol G represents Newton's gravitational constant; Λ (Lambda) is the cosmological constant.

Physical cosmology

Main article: Physical cosmology

Physical cosmology is the branch of physics and astrophysics that deals with the study of the physical origins and evolution of the Universe. It also includes the study of the nature of the Universe on its very largest scales. In its earliest form it was what is now known as celestial mechanics, the study of the heavens. The Greek philosophers Aristarchus of Samos, Aristotle and Ptolemy proposed different cosmological theories. In particular, the geocentric Ptolemaic system was the accepted theory to explain the motion of the heavens until Nicolaus Copernicus, and subsequently Johannes Kepler and Galileo Galilei proposed a heliocentric system in the 16th century. This is known as one of the most famous examples of epistemological rupture in physical cosmology.

With Isaac Newton and the 1687 publication of Principia Mathematica, the problem of the motion of the heavens was finally solved. Newton provided a physical mechanism for Kepler's laws and his law of universal gravitation allowed the anomalies in previous systems, caused by gravitational interaction between the planets, to be resolved. A fundamental difference between Newton's cosmology and those preceding it was the Copernican principle that the bodies on earth obey the same physical laws as all the celestial bodies. This was a crucial philosophical advance in physical cosmology.

Modern scientific cosmology is usually considered to have begun in 1917 with Albert Einstein's publication of his final modification of general relativity in the paper "Cosmological Considerations of the General Theory of Relativity," (although this paper was not widely available outside of Germany until the end of World War I). General relativity prompted cosmogonists such as Willem de Sitter, Karl Schwarzschild and Arthur Eddington to explore the astronomical consequences of the theory, which enhanced the growing ability of astronomers to study very distant objects. Prior to this (and for some time afterwards), physicists assumed that the Universe was static and unchanging.

In parallel to this dynamic approach to cosmology, one long-standing debate about the structure of the cosmos was coming to a climax. Mount Wilson astronomer Harlow Shapley championed the model of a cosmos made up of the Milky Way star system only ; while Heber D. Curtis argued for the idea that spiral nebulae were star systems in their own right - island universes. This difference of ideas came to a climax with the organization of the Great Debate at the meeting of the (US) National Academy of Sciences in Washington on 26 April 1920. The resolution of this debate came with the detection of novae in the Andromeda galaxy by Edwin Hubble in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way and has galaxies of their own.

Subsequent modeling of the universe explored the possibility that the cosmological constant introduced by Einstein in his 1917 paper may result in an expanding universe, depending on its value. Thus the big bang model was proposed by the Belgian priest Georges Lemaître in 1927 which was subsequently corroborated by Edwin Hubble's discovery of the red shift in 1929 and later by the discovery of the cosmic microwave background radiation by Arno Penzias and Robert Woodrow Wilson in 1964. These findings were a first step to rule out some of many alternative physical cosmologies.

Recent observations made by the COBE and WMAP satellites observing this background radiation have effectively, in many scientists' eyes, transformed cosmology from a highly speculative science into a predictive science, as these observations matched predictions made by a theory called Cosmic inflation, which is a modification of the standard big bang model. This has led many to refer to modern times as the "Golden age of cosmology."^[8]

Metaphysical cosmology

Main article: Cosmology (metaphysics)

In philosophy and metaphysics, cosmology deals with the world as the totality of space, time and all phenomena. Historically, it has had quite a broad scope, and in many cases was founded in religion. The ancient Greeks did not draw a distinction between this use and their model for the cosmos. However, in modern use it addresses questions about the Universe which are beyond the scope of science. It is distinguished from religious cosmology in that it approaches these questions using philosophical methods (e.g. dialectics). Modern metaphysical cosmology tries to address questions such as:

• What is the origin of the Universe? What is its first cause? Is its existence necessary? (see monism, pantheism, emanationism and creationism)
• What are the ultimate material components of the Universe? (see mechanism, dynamism, hylomorphism, atomism)
• What is the ultimate reason for the existence of the Universe? Does the cosmos have a purpose? (see teleology)
• Does the existence of consciousness have a purpose? How do we know what we know about the totality of the cosmos? Does cosmological reasoning reveal metaphysical truths?

See also

Astronomy portal

• Absolute time and space
• Astrology
• Astronomy
• List of astrophysicists
• Non-standard cosmology
• Taiji
• Tao

Notes

1. ^ http://www.newscientist.com/article/dn9988-instant-expert-cosmology.html
2. ^ http://oxforddictionaries.com/definition/cosmology
3. ^ Spergel; Verde; Peiris; Komatsu; Nolta; Bennett; Halpern; Hinshaw et al. (2003). "First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations". arXiv:astro-ph/0302209 [astro-ph]. 
4. ^ "The thoughts of Marcus Aurelius Antonius viii. 52". http://www.gutenberg.org/files/15877/15877-h/15877-h.htm#viii._52. 
5. ^ Norriss S. Hetherington (1993), Cosmology: historical, literary, philosophical, religious, and scientific perspectives, Taylor & Francis, p. 46, ISBN 0815309341 
6. ^ Norriss S. Hetherington (1993), Cosmology: historical, literary, philosophical, religious, and scientific perspectives, Taylor & Francis, p. 44, ISBN 0815309341 
7. ^ Boyer, C. A History of Mathematics. Wiley, p. 54.
8. ^ Alan Guth is reported to have made this very claim in an Edge Foundation interview EDGE

References

• Cronin, Vincent, The View from Planet Earth: Man Looks at the Cosmos, New York: William Morrow & Company, Inc., 1981, ISBN 0-688-00642-6
• Jean-Marc Rouvière, Brèves méditations sur la création du monde, L'Harmattan, Paris 2006.
• Roos, Matts Introduction to Cosmology. John Wiley & Sons, Ltd, Chichester: 2003.
• Hawley, John F. & Katerine A. Holcomb Foundations of Modern Cosmology. Oxford University Press, Oxford: 1998.
• Hetherington, Norriss S. Cosmology: Historical, Literary, Philosophical, Religious, and Scientific Perspectives. Garland Publishing, New York: 1993.
• Long, Barry. The Origins of Man and the Universe ISBN 0-9508050-6-8
• Martinus Thomsen's The Third Testament is about the explanation of life, everything inside it and the reason (or origin) of it.
• Arthur Koestler's The Sleepwalkers (1959) provides a scholarly study of the history of cosmology from the Chaldeans to Kepler.
• Schechner, Sara J. Comets, Popular Culture, and the Birth of Modern Cosmology. Princeton, New Jersey: Princeton University Press. 1997.
• Weinberg, Steven. 1992. Dreams of a Final Theory (Pantheon Books, NY) ISBN 0-679-41923-3

External links

• Cosmic Journey: A History of Scientific Cosmology from the American Institute of Physics
• Project Cosmology A schematic for the cosmos (3D, interactive unification of scientific schematics)
• Introduction to Cosmology David Lyth's lectures from the ICTP Summer School in High Energy Physics and Cosmology
• The Sophia Centre The Sophia Centre for the Study of Cosmology in Culture, University of Wales Trinity Saint David
• the Genesis cosmic chemistry module