Cosmology (from the Greek κόσμος, kosmos "world" and -λογία, -logia "study of") is a branch of astronomy concerned with the studies of the origin and evolution of the universe, from the Big Bang to today and on into the future. It is the scientific study of the origin, evolution, and eventual fate of the universe. Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, and its ultimate fate, as well as the laws of science that govern these areas.
The Ancient Greek language includes the forms of Greek used in Ancient Greece and the ancient world from around the 9th century BCE to the 6th century CE. It is often roughly divided into the Archaic period, Classical period, and Hellenistic period. It is antedated in the second millennium BCE by Mycenaean Greek and succeeded by Medieval Greek.
Astronomy is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry to try and explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets. Relevant phenomena include supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, astronomy studies everything that originates outside Earth's atmosphere. Cosmology is a branch of astronomy. It studies the Universe as a whole.
The Universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire Universe is unknown, it is possible to measure the size of the observable universe, which is currently estimated to be 93 billion light-years in diameter. In various multiverse hypotheses, a universe is one of many causally disconnected constituent parts of a larger multiverse, which itself comprises all of space and time and its contents.
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.
Thomas Blount (1618–1679) was an English antiquarian and lexicographer.
German philosophy, here taken to mean either (1) philosophy in the German language or (2) philosophy by Germans, has been extremely diverse, and central to both the analytic and continental traditions in philosophy for centuries, from Gottfried Wilhelm Leibniz through Immanuel Kant, Georg Wilhelm Friedrich Hegel, Arthur Schopenhauer, Karl Marx, Friedrich Nietzsche, Martin Heidegger and Ludwig Wittgenstein to contemporary philosophers. Søren Kierkegaard is frequently included in surveys of German philosophy due to his extensive engagement with German thinkers.
Christian Wolff was a German philosopher. Wolff was the most eminent German philosopher between Leibniz and Kant. His main achievement was a complete oeuvre on almost every scholarly subject of his time, displayed and unfolded according to his demonstrative-deductive, mathematical method, which perhaps represents the peak of Enlightenment rationality in Germany.
Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation myths and eschatology.
Religious cosmology is an explanation of the origin, evolution, and eventual fate of the universe, from a religious perspective. This may include beliefs on origin in the form of a creation myth, subsequent evolution, current organizational form and nature, and eventual fate or destiny. There are various traditions in religion or religious mythology asserting how and why everything is the way it is and the significance of it all. Religious cosmologies describe the spatial lay-out of the universe in terms of the world in which people typically dwell as well as other dimensions, such as the seven dimensions of religion; these are ritual, experience and emotional, narrative and mythical, doctrinal, ethical, social, and material. Religious mythologies may include descriptions of an act or process of creation by a creator deity or a larger pantheon of deities, explanations of the transformation of chaos into order, or the assertion that existence is a matter of endless cyclical transformations. Religious cosmology differs from a strictly scientific cosmology informed by the results of the study of astronomy and similar fields, and may differ in conceptualizations of the world's physical structure and place in the universe, its creation, and forecasts or predictions on its future. The scope of religious cosmology is more inclusive than a strictly scientific cosmology in that religious cosmology is not limited to experiential observation, testing of hypotheses, and proposals of theories; for example, religious cosmology may explain why everything is the way it is or seems to be the way it is and prescribing what humans should do in context. Variations in religious cosmology include those of Indian origin, such as Buddhism, Hindu, and Jain; the religious beliefs of China; and, the beliefs of the Abrahamic faiths, such as Judaism, Christianity, and Islam. Religious cosmologies have often developed into the formal logics of metaphysical systems, such as Platonism, Neoplatonism, Gnosticism, Daoism, Kabbalah, or the great chain of being.
Religion is a social-cultural system of designated behaviors and practices, morals, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that relates humanity to supernatural, transcendental, or spiritual elements. However, there is no scholarly consensus over what precisely constitutes a religion.
Cosmogony (from the Koine Greek Greek: κοσμογονία and the root of γί νομαι / γέγονα is any model concerning the origin of either the cosmos or the universe.
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 cannot 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.
Physics is the natural science that studies matter, its motion and behavior through space and time, and that studies the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.
Philosophy is the study of general and fundamental questions about existence, knowledge, values, reason, mind, and language. Such questions are often posed as problems to be studied or resolved. The term was probably coined by Pythagoras. Philosophical methods include questioning, critical discussion, rational argument, and systematic presentation. Classic philosophical questions include: Is it possible to know anything and to prove it? What is most real? Philosophers also pose more practical and concrete questions such as: Is there a best way to live? Is it better to be just or unjust? Do humans have free will?
Metaphysics is the branch of philosophy that examines the fundamental nature of reality, including the relationship between mind and matter, between substance and attribute, and between potentiality and actuality. The word "metaphysics" comes from two Greek words that, together, literally mean "after or behind or among [the study of] the natural". It has been suggested that the term might have been coined by a first century CE editor who assembled various small selections of Aristotle’s works into the treatise we now know by the name Metaphysics.
Theoretical astrophysicist David 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 the speed of light.
David Nathaniel Spergel, is an American theoretical astrophysicist and Princeton University professor known for his work on the WMAP mission. Spergel is a MacArthur Fellow. He is a member of the NASA Advisory Council and is chair of the Space Studies Board. He was once the W.M. Keck distinguished visiting professor at the Institute for Advanced Study in Princeton, New Jersey. He was part of the team that originated the WMAP mission and designed the spacecraft, and has worked on deciphering the data that it beams back from space. Spergel is playing a leading role in developing the WFIRST, a multibillion-dollar space mission planned for launch in the mid-2020s. Spergel is the Charles A Young Professor of Astronomy and a member of the National Academy of Sciences. Spergel is the Founding Director of the Center for Computational Astrophysics. He shared the 2010 Shaw Prize in astronomy with Charles L. Bennett and Lyman Alexander Page, Jr. for their work on WMAP. He shared the 2015 Dannie Heineman Prize with Marc Kamionkowski "for their outstanding contributions to the investigation of the fluctuations of the cosmic microwave background that have led to major breakthroughs in our understanding of the universe".
The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second. It is exact because by international agreement a metre is defined as the length of the path travelled by light in vacuum during a time interval of 1/299792458 second. According to special relativity, c is the upper limit for the speed at which conventional matter and information can travel. Though this speed is most commonly associated with light, it is also the speed at which all massless particles and field perturbations travel in vacuum, including electromagnetic radiation and gravitational waves. Such particles and waves travel at c regardless of the motion of the source or the inertial reference frame of the observer. Particles with nonzero rest mass can approach c, but can never actually reach it. In the special and general theories of relativity, c interrelates space and time, and also appears in the famous equation of mass–energy equivalence E = mc2.
Physics and astrophysics have played a central role in shaping the 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 the Big Bang, followed almost instantaneously by cosmic inflation; an expansion of space from which the universe is thought to have emerged 13.799 ± 0.021 billion years ago.Cosmogony studies the origin of the Universe, and cosmography maps the features of the Universe.
Astrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the astronomical objects, rather than their positions or motions in space". Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background. Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.
Physical cosmology is a branch of cosmology concerned with the studies of the largest-scale structures and dynamics of the universe and with fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood. Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang theory, by Georges Lemaître, as the leading cosmological model. A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory explains the observations better.
The Big Bang theory is the prevailing cosmological model for the observable universe from the earliest known periods through its subsequent large-scale evolution. The model describes how the universe expanded from a very high-density and high-temperature state, and offers a comprehensive explanation for a broad range of phenomena, including the abundance of light elements, the cosmic microwave background (CMB), large-scale structure and Hubble's law. If the observed conditions are extrapolated backwards in time using the known laws of physics, the prediction is that just before a period of very high density there was a singularity which is typically associated with the Big Bang. Current knowledge is insufficient to determine if the singularity was primordial.
In Diderot's Encyclopédie, 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).
Metaphysical cosmology has also been described as the placing of humans in the universe in relationship to all other entities. This is exemplified by Marcus 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."
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 the heavens. Greek philosophers Aristarchus of Samos, Aristotle, and Ptolemy proposed different cosmological theories. The geocentric Ptolemaic system was the prevailing theory until the 16th century when Nicolaus Copernicus, and subsequently Johannes Kepler and Galileo Galilei, proposed a heliocentric system. This is one of the most famous examples of epistemological rupture in physical cosmology.
Isaac Newton's Principia Mathematica , published in 1687, was the first description of the law of universal gravitation. It provided a physical mechanism for Kepler'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 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 its astronomical ramifications, which enhanced the ability of astronomers 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. Around the same time (1917 to 1922) the Great Debate took place, with early cosmologists such as Heber Curtis and Ernst Öpik determining that some nebulae seen in telescopes were separate galaxies far distant from our own.
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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 as island universes. This difference of ideas came to a climax with the organization of the Great Debate on 26 April 1920 at the meeting of the U.S. National Academy of Sciences in Washington, D.C. The debate was resolved when Edwin Hubble detected Cepheid Variables in the Andromeda Galaxy in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way.
Subsequent modelling 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 redshift 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 cosmologies.
Since around 1990, several dramatic advances in observational 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 the COBE, WMAP and Planck satellites, large new galaxy redshift surveys including 2dfGRS and SDSS, and observations of distant supernovae and gravitational lensing. These observations matched the predictions of the cosmic inflation theory, a modified Big Bang theory, and the specific version known as the Lambda-CDM model. This has led many to refer to modern times as the "golden age of cosmology".
On 17 March 2014, astronomers at the Harvard-Smithsonian Center for Astrophysics announced the detection of gravitational waves, providing strong evidence for inflation and the Big Bang.However, on 19 June 2014, lowered confidence in confirming the cosmic inflation findings was reported.
On 1 December 2014, at the Planck 2014 meeting in Ferrara, Italy, astronomers reported that the universe is 13.8 billion years old and is composed of 4.9% atomic matter, 26.6% dark matter and 68.5% dark energy.
Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation and eschatology.
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.In modern use metaphysical cosmology 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 like dialectics. Modern metaphysical cosmology tries to address questions such as:
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|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.[ citation needed ]|
|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|
|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 = 1/2, 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||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||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."[ citation needed ]|
|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.|
|Discovery of Gravitational Waves (LIGO Model)||Laser Interferometer Gravitational-Wave Observatory 2016||Albert Einstein Model Continuation, Gravitational Wave Theory Proven||Following the BICep2 Model failing to prove their findings concerning gravitational waves back in 2014, LIGO, in 2016, were able to detect and prove that gravitational waves are indeed emitted around black holes when two black holes pull together and create one larger black hole.|
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.
In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from 10−36 seconds after the conjectured Big Bang singularity to some time between 10−33 and 10−32 seconds after the singularity. Following the inflationary period, the universe continues to expand, but at a less rapid rate.
The cosmic microwave background, in Big Bang cosmology, is electromagnetic radiation as a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all space. It is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1964 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize in Physics.
The multiverse, also known as a maniverse, megaverse, metaverse, omniverse, or meta-universe, is a hypothetical group of multiple universes. Together, these universes comprise everything that exists: the entirety of space, time, matter, energy, and the physical laws and constants that describe them. The different universes within the multiverse are called "parallel universes", "other universes", or "alternate universes".
In physics, redshift is a phenomenon where electromagnetic radiation from an object undergoes an increase in wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave frequency and photon energy, in accordance with, respectively, the wave and quantum theories of light.
This timeline of cosmological theories and discoveries is a chronological record of the development of humanity's understanding of the cosmos over the last two-plus millennia. Modern cosmological ideas follow the development of the scientific discipline of physical cosmology.
A non-standard cosmology is any physical cosmological model of the universe that was, or still is, proposed as an alternative to the then-current standard model of cosmology. The term non-standard is applied to any theory that does not conform to the scientific consensus. Because the term depends on the prevailing consensus, the meaning of the term changes over time. For example, hot dark matter would not have been considered non-standard in 1990, but would be in 2010. Conversely, a non-zero cosmological constant resulting in an accelerating universe would have been considered non-standard in 1990, but is part of the standard cosmology in 2010.
The observable universe is a spherical region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. There are at least 2 trillion galaxies in the observable universe. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe has a spherical volume centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.
The ΛCDM or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda and associated with dark energy; second, the postulated cold dark matter ; and third, ordinary matter. It is frequently referred to as the standard model of Big Bang cosmology because it is the simplest model that provides a reasonably good account of the following properties of the cosmos:
In physical cosmology the inflationary epoch was the period in the evolution of the early universe when, according to inflation theory, the universe underwent an extremely rapid exponential expansion. This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078. Expansion by a factor of 1026 is equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 62 trillion miles) long.
The history of the Big Bang theory began with the Big Bang's development from observations and theoretical considerations. Much of the theoretical work in cosmology now involves extensions and refinements to the basic Big Bang model.
The expansion of the universe is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. Technically, neither space nor objects in space move. Instead it is the metric governing the size and geometry of spacetime itself that changes in scale. Although light and objects within spacetime cannot travel faster than the speed of light, this limitation does not restrict the metric itself. To an observer it appears that space is expanding and all but the nearest galaxies are receding into the distance.
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. The earliest stages of the universe's existence are estimated as taking place 13.8 billion years ago, with an uncertainty of around 21 million years at the 68% confidence level.
In physical cosmology and astronomy, dark energy is an unknown form of energy which is hypothesized to permeate all of space, tending to accelerate the expansion of the universe. Dark energy is the most accepted hypothesis to explain the observations since the 1990s indicating that the universe is expanding at an accelerating rate.
Andrew E. Lange was an astrophysicist and Goldberger Professor of Physics at the California Institute of Technology in Pasadena, California. Lange came to Caltech in 1993 and was most recently the chair of the Division of Physics, Mathematics and Astronomy. Caltech's president Jean-Lou Chameau called him "a truly great physicist and astronomer who had made seminal discoveries in observational cosmology".
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