Cosmology (fromAncient Greekκόσμος (cosmos) 'the universe, the world' andλογία (logia) 'study of') is a branch ofphysics andmetaphysics dealing with thenature of theuniverse, thecosmos. The termcosmology was first used in English in 1656 inThomas Blount'sGlossographia,^[2] and in 1731 taken up in Latin byGerman philosopherChristian Wolff inCosmologia Generalis.^[3]Religious or mythological cosmology is a body of beliefs based onmythological,religious, andesoteric literature and traditions ofcreation myths andeschatology. In the science ofastronomy, cosmology is concerned with the study of thechronology of the universe.

Physical cosmology is the study of theobservable universe's origin, its large-scale structures and dynamics, and theultimate fate of the universe, including thelaws of science that govern these areas.^[4] It is investigated by scientists, includingastronomers andphysicists, as well asphilosophers, such asmetaphysicians,philosophers of physics, andphilosophers of space and time. Because of this shared scope withphilosophy,theories in physical cosmology may include bothscientific and non-scientific propositions and may depend upon assumptions that cannot betested. Physical cosmology is a sub-branch of astronomy that is concerned with the universe as a whole. Modern physical cosmology is dominated by theBig Bang Theory which attempts to bring togetherobservational astronomy andparticle physics;^[5][6] more specifically, a standard parameterization of the Big Bang withdark matter anddark energy, known as theLambda-CDM model.

Theoretical astrophysicistDavid N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of thespeed of light.^[7]

Physics andastrophysics have played central roles in shaping our understanding of the universe through scientific observation and experiment.Physical cosmology was shaped through both mathematics and observation in an analysis of the whole universe. The universe is generally understood to have begun with theBig Bang, followed almost instantaneously bycosmic inflation, anexpansion of space from which the universe is thought to have emerged13.799 ± 0.021billion years ago.^[8]Cosmogony studies the origin of the universe, andcosmography maps the features of the universe.

InDiderot'sEncyclopédie, cosmology is broken down into uranology (the science of the heavens), aerology (the science of the air), geology (the science of the continents), and hydrology (the science of waters).^[9]

Metaphysical cosmology has also been described as the placing of humans in the universe in relationship to all other entities. This is exemplified byMarcus Aurelius's observation that 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."^[10]

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 a large scale. In its earliest form, it was what is now known as "celestial mechanics," the study of theheavens. Greek philosophersAristarchus of Samos,Aristotle, andPtolemy proposed different cosmological theories. ThegeocentricPtolemaic system was the prevailing theory until the 16th century whenNicolaus Copernicus, and subsequentlyJohannes Kepler andGalileo Galilei, proposed aheliocentric system. This is one of the most famous examples ofepistemological rupture in physical cosmology.

Isaac Newton'sPrincipia Mathematica, published in 1687, was the first description of thelaw of universal gravitation. It provided a physical mechanism forKepler's laws and also 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 theCopernican principle—that the bodies on Earth obey the samephysical laws as all celestial bodies. This was a crucial philosophical advance in physical cosmology.

Modern scientific cosmology is widely considered to have begun in 1917 withAlbert Einstein's publication of his final modification ofgeneral relativity in the paper "Cosmological Considerations of the General Theory of Relativity"^[11] (although this paper was not widely available outside of Germany until the end ofWorld War I). General relativity promptedcosmogonists such asWillem de Sitter,Karl Schwarzschild, andArthur Eddington to explore its astronomical ramifications, which enhanced the ability ofastronomers to study very distant objects. Physicists began changing the assumption that the universe was static and unchanging. In 1922,Alexander Friedmann introduced the idea of an expanding universe that contained moving matter.

In parallel to this dynamic approach to cosmology, one long-standing debate about the structure of the cosmos was coming to a climax – theGreat Debate (1917 to 1922) – with early cosmologists such asHeber Curtis andErnst Öpik determining that somenebulae seen in telescopes were separate galaxies far distant from our own.^[12] While Heber Curtis argued for the idea that spiral nebulae were star systems in their own right as island universes, Mount Wilson astronomerHarlow Shapley championed the model of a cosmos made up of theMilky Waystar system only. This difference of ideas came to a climax with the organization of theGreat Debate on 26 April 1920 at the meeting of the U.S.National Academy of Sciences inWashington, D.C. The debate was resolved whenEdwin Hubble detectedCepheid Variables in theAndromeda Galaxy in 1923 and 1924.^[13][14] Their distance established spiral nebulae well beyond the edge of the Milky Way.

Subsequent modelling of the universe explored the possibility that thecosmological constant, introduced by Einstein in his 1917 paper, may result in anexpanding universe, depending on its value. Thus theBig Bang model was proposed by theBelgian priestGeorges Lemaître in 1927^[15] which was subsequently corroborated byEdwin Hubble's discovery of theredshift in 1929^[16] and later by the discovery of thecosmic microwave background radiation byArno Penzias andRobert Woodrow Wilson in 1964.^[17] These findings were a first step to rule out some of manyalternative cosmologies.

Since around 1990, several dramatic advances inobservational cosmology have transformed cosmology from a largely speculative science into a predictive science with precise agreement between theory and observation. These advances include observations of the microwave background from theCOBE,^[18]WMAP^[19] andPlanck satellites,^[20] large new galaxyredshift surveys including2dfGRS^[21] andSDSS,^[22] and observations of distantsupernovae andgravitational lensing. These observations matched the predictions of thecosmic inflation theory, a modifiedBig Bang theory, and the specific version known as theLambda-CDM model. This has led many to refer to modern times as the "golden age of cosmology".^[23]

In 2014, the BICEP2 collaboration claimed that they had detected the imprint ofgravitational waves in thecosmic microwave background. However, this result was later found to be spurious: the supposed evidence of gravitational waves was in fact due to interstellar dust.^[24][25]

On 1 December 2014, at thePlanck 2014 meeting inFerrara,Italy, astronomers reported that theuniverse is13.8 billion years old and composed of 4.9%atomic matter, 26.6%dark matter and 68.5%dark energy.^[26]

Religious or mythological cosmology is a body of beliefs based onmythological,religious, andesoteric literature and traditions ofcreation andeschatology. Creation myths are found in most religions, and are typically split into five different classifications, based on a system created byMircea Eliade and his colleague Charles Long.

• Types of Creation Myths based on similar motifs:
  • Creationex nihilo in which the creation is through the thought, word, dream or bodily secretions of a divine being.
  • Earth diver creation in which a diver, usually a bird or amphibian sent by a creator, plunges to the seabed through aprimordial ocean to bring up sand or mud which develops into a terrestrial world.
  • Emergence myths in which progenitors pass through a series of worlds and metamorphoses until reaching the present world.
  • Creation by the dismemberment of a primordial being.
  • Creation by the splitting or ordering of a primordial unity such as the cracking of acosmic egg or a bringing order fromchaos.^[27]

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 found in religion.^[28] Some questions about the Universe are beyond the scope of scientific inquiry but may still be interrogated through appeals to other philosophical approaches likedialectics. Some questions that are included in extra-scientific endeavors may include:^[29][30]

• What is the origin of the universe? What is its first cause (if any)? Is its existence necessary? (seemonism,pantheism,emanationism andcreationism)
• What are the ultimate material components of the universe? (seemechanism,dynamism,hylomorphism,atomism)
• What is the ultimate reason (if any) for the existence of the universe? Does the cosmos have a purpose? (seeteleology)
• Does the existence of consciousness have a role in the existence of reality? How do we know what we know about the totality of the cosmos? Does cosmological reasoning reveal metaphysical truths? (seeepistemology)

Charles Kahn, a historian of philosophy, attributed the origins of ancient Greek cosmology toAnaximander.^[31]

Table notes: the term "static" simply means not expanding and not contracting. SymbolG represents Newton'sgravitational constant; Λ (Lambda) is thecosmological constant.

• Bragg, Melvyn (2023)."The Universe's Shape".bbc.co.uk. BBC. Retrieved23 May 2023.Melvyn Bragg discusses shape, size and topology of the universe and examines theories about its expansion. If it is already infinite, how can it be getting any bigger? And is there really only one?
• "Cosmic Journey: A History of Scientific Cosmology".history.aip.org. American Institute of Physics. 2023. Retrieved23 May 2023.The history of cosmology is a grand story of discovery, from ancient Greek astronomy to -space telescopes.
• Dodelson, Scott; Schmidt, Fabian (2020).Modern Cosmology 2nd Edition. Academic Press.ISBN 978-0128159484. Download full text:Dodelson, Scott; Schmidt, Fabian (2020)."Scott Dodelson - Fabian Schmidt - Modern Cosmology (2021) PDF"(PDF).scribd.com. Academic Press. Retrieved23 May 2023.
• Charles Kahn. 1994.Anaximander and the Origins of Greek Cosmology. Indianapolis: Hackett.
• "Genesis, Search for Origins. End of mission wrap up".genesismission.jpl.nasa.gov. NASA, Jet Propulsion Laboratory, California Institute of Technology. Retrieved23 May 2023.About 4.6 billion years ago, the solar nebula transformed into the present solar system. In order to chemically model the processes which drove that transformation, we would, ideally, like to have a sample of that original nebula to use as a baseline from which we can track changes.
• Leonard, Scott A; McClure, Michael (2004).Myth and Knowing. McGraw-Hill.ISBN 978-0-7674-1957-4.
• Lyth, David (12 December 1993). "Introduction to Cosmology".arXiv:astro-ph/9312022.These notes form an introduction to cosmology with special emphasis on large scale structure, the cmb anisotropy and inflation. Lectures given at the Summer School in High Energy Physics and Cosmology, ICTP (Trieste) 1993.) 60 pages, plus 5 Figures.
• "NASA/IPAC Extragalactic Database (NED)".ned.ipac.caltech.edu. NASA. 2023. Retrieved23 May 2023.April 2023 Release Highlights Database Updates
  • "NASA/IPAC Extragalactic Database (NED)".ned.ipac.caltech.edu. NASA. 2020. Retrieved23 May 2023.NED-D: A Master List of Redshift-Independent Extragalactic Distances
• Sophia Centre. The Sophia Centre for the Study of Cosmology in Culture, University of Wales Trinity Saint David.