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| {{use dmy dates|date=August 2016}} | | {{Infobox theory |
| {{Cosmology}}
| | | name = Non-standard cosmology |
| A '''non-standard cosmology''' is any physical [[physical cosmology|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.
| | | type = Umbrella term for cosmological models outside the mainstream consensus |
| | | author = Many — see the models and researchers listed below |
| | | keywords = cosmology, [[Big Bang]], steady state, [[Plasma Cosmology|plasma cosmology]], [[Electric Universe|electric universe]], [[Redshift|redshift]], non-expanding universe |
| | }} |
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| Several major cosmological disputes have occurred throughout the [[timeline of cosmology|history of cosmology]]. One of the earliest was the [[Copernican Revolution]], which established the [[Heliocentrism|heliocentric model]] of the Solar System. More recent was the [[Great Debate (astronomy)|Great Debate]] of 1920, in the aftermath of which the Milky Way's status as but one of the Universe's many galaxies was established. From the 1940s to the 1960s, the [[astrophysics|astrophysical]] community was equally divided between supporters of the [[Big Bang]] theory and supporters of a rival [[steady state universe]]; this was eventually decided in favour of the Big Bang theory by advances in [[observational cosmology]] in the late 1960s. The current standard model of cosmology is the [[Lambda-CDM]] model, wherein the Universe is governed by [[General Relativity]], began with a Big Bang and today is a nearly-[[Shape of the universe|flat universe]] that consists of approximately 5% baryons, 27% [[cold dark matter]], and 68% [[dark energy]].<ref>See [[Planck (spacecraft)#2015 data release|the Planck Collaboration's 2015 data release]].</ref>
| | '''Non-standard cosmology''' is the umbrella term for any model of the universe proposed as an alternative to the prevailing consensus — today the Lambda-CDM model, in which the universe began in a [[Big Bang]] some 13.8 billion years ago and is composed largely of dark matter and dark energy. |
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| Lambda-CDM has been an extremely successful model, but retains some weaknesses (such as the [[dwarf galaxy problem]]). Research on extensions or modifications to Lambda-CDM, as well as fundamentally different models, is ongoing. Topics investigated include [[quintessence (physics)|quintessence]], [[Modified Newtonian Dynamics]] (MOND) and its relativistic generalization [[TeVeS]], and [[warm dark matter]].
| | The label is relative rather than absolute: it marks only what departs from the current consensus, and the consensus itself shifts. A non-zero cosmological constant was non-standard in 1990 and is orthodox today. On this wiki the term covers the substantial and continuing research tradition that regards the standard model as resting on contestable interpretations — above all the assumption that [[Redshift|redshift]] measures distance and recession — and that seeks better-founded alternatives. |
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| ==The Lambda-CDM model== | | ==Why the standard model is disputed== |
| Before observational evidence was gathered, theorists developed frameworks based on what they understood to be the most general features of [[physics]] and philosophical assumptions about the universe. When [[Albert Einstein]] developed his [[general theory of relativity]] in 1915, this was used as a mathematical starting point for most cosmological theories.<ref>Hoyle, F., ''Home is Where the Wind Blows'', 1994, 1997, 399-423</ref> In order to arrive at a cosmological model, however, theoreticians needed to make assumptions about the nature of the largest scales of the universe. The assumptions that the current standard model of cosmology, Lambda-CDM, relies upon are:
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| # the [[physical law|universality of physical laws]] – that the laws of physics don't change from one place and time to another,
| | The critical case is set out in detail elsewhere on this wiki rather than repeated here. The central lines of objection are: |
| # the [[cosmological principle]] – that the universe is roughly homogeneous and isotropic in space though not necessarily in time, and
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| # the [[Copernican principle]] – that we are not observing the universe from a preferred locale.
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| These assumptions when combined with General Relativity result in a universe that is governed by the [[Friedmann–Robertson–Walker metric]] (FRW metric). The FRW metric allows for a universe that is either expanding or contracting (as well as stationary but unstable universes). When [[Hubble's Law]] was discovered, most astronomers interpreted the law as a sign the universe is expanding. This implies the universe was smaller in the past, and therefore led to the following conclusions:
| | * '''Redshift may not measure distance.''' The expansion of the universe is inferred from the redshift–distance relation. If redshift is produced wholly or partly by other processes, that inference fails. See [[Redshift]] and [[Intrinsic redshift]]. |
| | * '''Discordant associations.''' Objects of very different redshift appear physically connected, most famously in the work of [[Halton C Arp]]. See [[Quasar]]. |
| | * '''Quantized redshifts.''' Redshifts cluster at preferred values rather than varying continuously, which is difficult to reconcile with a simple velocity distribution. See [[Redshift quantization]]. |
| | * '''Reliance on unobserved components.''' Dark matter and dark energy together account for most of the mass-energy of the standard model, yet neither has been detected directly. |
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| # the universe emerged from a hot, dense state at a [[Wikt:finite|finite]] time in the past,
| | A fuller catalogue of objections — covering the microwave background, the singularity and inflation, fine-tuning, and age paradoxes — is collected at '''[[Big Bang#Criticisms of the Big Bang on this wiki|Big Bang § Criticisms]]'''. |
| # because the universe heats up as it contracts and cools as it expands, in the first moments that time existed as we know it, the temperatures were high enough for [[Big Bang nucleosynthesis]] to occur, and
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| # a [[cosmic microwave background]] pervading the entire universe should exist, which is a record of a [[phase transition]] that occurred when the atoms of the universe first formed. | |
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| These features were derived by numerous individuals over a period of years; indeed it was not until the middle of the twentieth century that accurate predictions of the last feature and observations confirming its existence were made. Non-standard theories developed either by starting from different assumptions or by contradicting the features predicted by Lambda-CDM.<ref name="Burbidge, Hoyle">Burbidge, G., Hoyle, F. 1998, ApJ, 509 L1-L3</ref>
| | ==Alternative models documented here== |
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| ==History==
| | * '''[[Plasma Cosmology]]''' — the tradition of Hannes Alfvén and Anthony Peratt, in which electromagnetic forces and plasma dynamics, rather than gravity alone, shape cosmic structure. |
| Modern physical cosmology as it is currently studied first emerged as a scientific discipline in the period after the [[Shapley–Curtis debate]] and discoveries by [[Edwin Hubble]] of a [[cosmic distance ladder]] when astronomers and physicists had to come to terms with a universe that was of a much [[Large-scale structure of the cosmos|larger scale]] than the previously assumed [[Milky Way galaxy|galactic size]]. Theorists who successfully developed cosmologies applicable to the larger-scale universe are remembered today as the founders of modern cosmology. Among these scientists are [[Arthur Milne]], [[Willem de Sitter]], [[Alexander Friedman]], [[Georges Lemaître]], and Albert Einstein himself.
| | * '''[[Electric Universe]]''' — a related programme emphasising electric currents in space, associated with [[Wallace Thornhill]] and [[David Talbott]]. |
| | * '''Steady state and quasi-steady state''' — the Hoyle–Bondi–Gold model of continuous matter creation in an unchanging universe, later developed by Hoyle, Burbidge and [[Jayant Narlikar]] as the quasi-steady-state cosmology. |
| | * '''Non-expanding and infinite universe models''' — see ''[[An Infinite Non-Expanding Universe in Dynamic Equilibrium]]'', ''[[Nature of the Non-Expanding Universe]]'', and the work of [[Paul Marmet]]. |
| | * '''Tired-light and photon-energy-loss cosmologies''' — including [[Lyndon E Ashmore|Ashmore's]] New Tired Light and [[Ari Brynjolfsson|Brynjolfsson's]] plasma redshift; see [[Tired Light]]. |
| | * '''[[Autodynamics]]''' — [[Ricardo Carezani]]'s replacement for special relativity, with cosmological consequences. |
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| After confirmation of the Hubble's law by observation, the two most popular cosmological theories became the [[Steady State theory]] of [[Fred Hoyle|Hoyle]], [[Thomas Gold|Gold]] and [[Hermann Bondi|Bondi]], and the [[big bang theory]] of [[Ralph Alpher]], [[George Gamow]], and [[Robert Dicke]] with a small number of supporters of a smattering of alternatives. Since the discovery of the [[Cosmic microwave background radiation]] (CMB) by [[Arno Penzias]] and [[Robert Woodrow Wilson|Robert Wilson]] in 1965, most cosmologists concluded that observations were best explained by the big bang model. Steady State theorists and other non-standard cosmologies were then tasked with providing an explanation for the phenomenon if they were to remain plausible. This led to original approaches including [[integrated starlight]] and [[cosmic iron whiskers]], which were meant to provide a source for a pervasive, all-sky microwave background that was not due to an early universe phase transition.
| | ==On this wiki== |
| [[File:WMAP2.jpg|thumb|left|Artist depiction of the [[WMAP]] spacecraft at the L2 point. Data gathered by this spacecraft has been successfully used to parametrize the features of standard cosmology, but complete analysis of the data in the context of any non-standard cosmology has not yet been achieved.]]
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| Scepticism about the non-standard cosmologies' ability to explain the CMB caused interest in the subject to wane since then, however, there have been two periods in which interest in non-standard cosmology has increased due to observational data which posed difficulties for the big bang. The first occurred was the late 1970s when there were a number of unsolved problems, such as the [[horizon problem]], the [[flatness problem]], and the lack of [[magnetic monopole]]s, which challenged the big bang model. These issues were eventually resolved by [[cosmic inflation]] in the 1980s. This idea subsequently became part of the understanding of the big bang, although alternatives have been proposed from time to time. The second occurred in the mid-1990s when observations of the ages of [[globular cluster]]s and the primordial [[helium]] abundance, apparently disagreed with the big bang. However, by the late 1990s, most astronomers had concluded that these observations did not challenge the big bang and additional data from [[Cosmic Background Explorer|COBE]] and the [[Wilkinson Microwave Anisotropy Probe|WMAP]], provided detailed quantitative measures which were consistent with standard cosmology.
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| In the 1990s, a dawning of a "golden age of cosmology" was accompanied by a startling discovery that the expansion of the universe was, in fact, accelerating. Previous to this, it had been assumed that matter either in its visible or invisible [[dark matter]] form was the dominant [[energy density]] in the universe. This "classical" big bang cosmology was overthrown when it was discovered that nearly 70% of the energy in the universe was attributable to the cosmological constant, often referred to as "dark energy". This has led to the development of a so-called concordance [[ΛCDM model]] which combines detailed data obtained with new telescopes and techniques in observational astrophysics with an expanding, density-changing universe. Today, it is more common to find in the scientific literature proposals for "non-standard cosmologies" that actually accept the basic tenets of the big bang cosmology, while modifying parts of the concordance model. Such theories include alternative models of dark energy, such as quintessence, [[phantom energy]] and some ideas in [[brane cosmology]]; alternative models of dark matter, such as modified Newtonian dynamics; alternatives or extensions to inflation such as [[chaotic inflation]] and the [[ekpyrotic|ekpyrotic model]]; and proposals to supplement the universe with a first cause, such as the [[Hartle–Hawking state|Hartle–Hawking boundary condition]], the [[cyclic model]], and the [[string landscape]]. There is no consensus about these ideas amongst cosmologists, but they are nonetheless active fields of academic inquiry.
| | Several thousand papers and biographies bearing on cosmology are catalogued here; see [[:Category:Cosmology]]. Researchers with pages include [[Halton C Arp]], [[Paul Marmet]], [[Ari Brynjolfsson]], [[John W Kierein]], [[Amitabha Ghosh]], [[Lyndon E Ashmore]] and many others. |
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| Today, heterodox non-standard cosmologies are generally considered unworthy of consideration by cosmologists while many of the historically significant nonstandard cosmologies are considered to have been [[Falsifiability|falsified]]. The essentials of the big bang theory have been confirmed by a wide range of complementary and detailed observations, and no non-standard cosmologies have reproduced the range of successes of the big bang model. Speculations about alternatives are not normally part of research or pedagogical discussions, except as object lessons or for their historical importance. An open letter started by some remaining advocates of non-standard cosmology has affirmed that: "today, virtually all financial and experimental resources in cosmology are devoted to big bang studies...."<ref name="cosmologystatement">{{cite web|url=http://www.cosmologystatement.org|title=cosmologystatement.org|work=cosmologystatement.org}}</ref>
| | ==See also== |
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| ==Alternative gravity==
| | * [[Big Bang]] |
| {{main article|Alternatives to general relativity}}
| | * [[Redshift]] |
| General relativity, upon which the FRW metric is based, is an extremely successful theory which has met every observational test so far. However, at a fundamental level it is incompatible with [[quantum mechanics]], and by predicting [[gravitational singularity|singularities]], it also predicts its own breakdown. Any alternative theory of gravity would imply immediately an alternative cosmological theory since current modeling is dependent on general relativity as a framework assumption. There are many different motivations to modify general relativity, such as to eliminate the need for dark matter or dark energy, or to avoid such paradoxes as the [[Firewall (physics)|firewall]].
| | * [[Intrinsic redshift]] |
| | * [[Quasar]] |
| | * [[Plasma Cosmology]] |
| | * [[Electric Universe]] |
| | * [[:Category:Cosmology|Category: Cosmology]] |
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| ===Machian universe===
| | [[Category:Cosmology|Non-standard cosmology]] |
| {{See also|Brans–Dicke theory|Mach's principle}}
| | [[Category:Theory & Models|Non-standard cosmology]] |
| [[Ernst Mach]] developed a kind of extension to general relativity which proposed that [[inertia]] was due to gravitational effects of the mass distribution of the universe. This led naturally to speculation about the cosmological implications for such a proposal. [[Carl Brans]] and Robert Dicke were able to successfully incorporate Mach's principle into general relativity which admitted for cosmological solutions that would imply a variable mass. The homogeneously distributed mass of the universe would result in a roughly [[scalar field]] that permeated the universe and would serve as a source for Newton's [[gravitational constant]]; creating a theory of [[quantum gravity]]. | |
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| ===MOND===
| | [[Category:Redshift]] |
| {{main article|Modified Newtonian Dynamics}}
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| Modified Newtonian Dynamics (MOND) is a relatively modern proposal to explain the [[galaxy rotation problem]] based on a variation of [[Newton's Second Law]] of Dynamics at low accelerations. This would produce a large-scale variation of [[Newtonian gravity|Newton's universal theory of gravity]]. A modification of Newton's theory would also imply a modification of general relativistic cosmology in as much as Newtonian cosmology is the limit of Friedman cosmology. While almost all astrophysicists today reject MOND in favor of dark matter, a small number of researchers continue to enhance it, recently incorporating Brans–Dicke theories into treatments that attempt to account for cosmological observations.
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| ===TeVeS===
| | [[Category:Big Bang]] |
| {{main article|Tensor–vector–scalar gravity}}
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| Tensor–vector–scalar gravity (TeVeS) is a proposed relativistic theory that is equivalent to Modified Newtonian dynamics (MOND) in the non-relativistic limit, which purports to explain the galaxy rotation problem without invoking dark matter. Originated by [[Jacob Bekenstein]] in 2004, it incorporates various dynamical and non-dynamical [[tensor field]]s, [[vector field]]s and scalar fields.
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| The break-through of TeVeS over MOND is that it can explain the phenomenon of [[gravitational lensing]], a cosmic optical illusion in which matter bends light, which has been confirmed many times. A recent preliminary finding is that it can explain [[structure formation]] without CDM, but requiring a ~2eV massive [[neutrino]] (they are also required to fit some [[Clusters of galaxies]], including the [[Bullet Cluster]]).<ref>{{Cite journal|arxiv=astro-ph/0608602|title=[astro-ph/0608602] Can Cosmic Structure form without Dark Matter?|journal=Physical Review Letters|volume=97|issue=23|last1=Dodelson|first1=Scott|last2=Liguori|first2=Michele|year=2006|doi=10.1103/PhysRevLett.97.231301|bibcode=2006PhRvL..97w1301D}}</ref><ref>{{Cite journal|arxiv=astro-ph/0505519|title=[astro-ph/0505519] Large Scale Structure in Bekenstein's theory of relativistic Modified Newtonian Dynamics|journal=Physical Review Letters|volume=96|issue=11301|last1= Skordis|first1=C.|last2= Mota|first2=D. F.|last3= Ferreira|first3=P. G.|last4= Boehm|first4=C.|year=2005|doi=10.1103/PhysRevLett.96.011301|bibcode=2006PhRvL..96a1301S}}</ref> However, other authors (see Slosar, Melchiorri and Silk)<ref>{{Cite journal|arxiv=astro-ph/0508048|title=[astro-ph/0508048] Did Boomerang hit MOND?|journal=Physical Review D|volume=72|issue=10|last1=Slosar|first1=Anze|last2=Melchiorri|first2=Alessandro|last3=Silk|first3=Joseph|year=2005|doi=10.1103/PhysRevD.72.101301|bibcode = 2005PhRvD..72j1301S }}</ref> claim that TeVeS can't explain cosmic microwave background anisotropies and structure formation at the same time, i.e. ruling out those models at high significance.
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| ===f(R) gravity===
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| {{main article|f(R) gravity}}
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| ''f''(''R'') gravity is a family of theories that modify general relativity by defining a different function of the [[Scalar curvature|Ricci scalar]]. The simplest case is just the function being equal to the scalar; this is general relativity. As a consequence of introducing an arbitrary function, there may be freedom to explain the [[Accelerating universe|accelerated expansion]] and structure formation of the Universe without adding unknown forms of dark energy or dark matter. Some functional forms may be inspired by corrections arising from a [[Quantum gravity|quantum theory of gravity]]. ''f''(''R'') gravity was first proposed in 1970 by [[Hans Adolph Buchdahl]]<ref>{{cite journal| title = Non-linear Lagrangians and cosmological theory| last=Buchdahl |first=H. A.| journal = [[Monthly Notices of the Royal Astronomical Society]]| volume = 150| pages = 1–8| year = 1970| url = http://adsabs.harvard.edu/abs/1970MNRAS.150....1B| bibcode = 1970MNRAS.150....1B| doi=10.1093/mnras/150.1.1}}</ref> (although ''φ'' was used rather than ''f'' for the name of the arbitrary function). It has become an active field of research following work by Starobinsky on [[Inflation (cosmology)|cosmic inflation]].<ref>{{cite journal| title = A new type of isotropic cosmological models without singularity| last=Starobinsky |first=A. A.| journal = [[Physics Letters B]] | volume = 91| pages = 99–102| year = 1980|doi = 10.1016/0370-2693(80)90670-X| bibcode = 1980PhLB...91...99S }}</ref> A wide range of phenomena can be produced from this theory by adopting different functions; however, many functional forms can now be ruled out on observational grounds, or because of pathological theoretical problems.
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| ==Steady State theories==
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| {{main article|Steady State theory}}
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| The Steady State theory challenges the [[homogeneity (physics)|homogeneity]] assumption of the cosmological principle to reflect a homogeneity in [[time]] as well as in [[space]]. This "perfect cosmological principle" as it would come to be called asserted that the universe looks the same everywhere (on the large scale), the same as it always has and always will. This is in contrast to Lambda-CDM, in which the universe looked very different in the past and will look very different in the future. Steady State theory was proposed in 1948 by [[Fred Hoyle]], [[Thomas Gold]], [[Hermann Bondi]] and others. In order to maintain the perfect cosmological principle in an expanding universe, steady state cosmology had to posit a "matter-creation field" (the so-called [[C-field]]) that would insert matter into the universe in order to maintain a constant density.<ref name="Burbidge, Hoyle" />
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| The debate between the Big Bang and the Steady State models would happen for 15 years with camps roughly evenly divided until the discovery of the cosmic microwave background radiation. This radiation is a natural feature of the Big Bang model which demands a "time of last scattering" where photons [[Decoupling (cosmology)|decouple]] with [[baryon]]ic matter. The Steady State model proposed that this radiation could be accounted for by so-called "integrated starlight" which was a background caused in part by [[Olbers' paradox]] in an infinite universe. In order to account for the uniformity of the background, steady state proponents posited a fog effect associated with microscopic iron particles that would scatter radio waves in such a manner as to produce an isotropic CMB. The proposed phenomena was whimsically named "cosmic iron whiskers" and served as the [[Thermalisation|thermalization]] mechanism. The Steady State theory did not have the horizon problem of the Big Bang because it assumed an infinite amount of time was available for thermalizing the background.<ref name="Burbidge, Hoyle" />
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| As more cosmological data began to be collected, cosmologists began to realize that the Big Bang correctly predicted the abundance of light elements observed in the cosmos. What was a coincidental ratio of [[hydrogen]] to [[deuterium]] and helium in the steady state model was a feature of the Big Bang model. Additionally, detailed measurements of the CMB since the 1990s with the [[Cosmic Background Explorer|COBE]], [[WMAP]] and [[Planck Satellite|Planck]] observations indicated that the [[spectrum]] of the background was closer to a [[blackbody]] than any other source in nature. The best integrated starlight models could predict was a thermalization to the level of 10% while the COBE satellite measured the deviation at one part in 10<sup>5</sup>. After this dramatic discovery, the majority of cosmologists became convinced that the steady state theory could not explain the observed CMB properties.
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| Although the original steady state model is now considered to be contrary to observations (particularly the CMB) even by its one-time supporters, modifications of the steady state model has been proposed, including a model that envisions the universe as originating through many little bangs rather than one big bang (the so-called "quasi-steady state cosmology"). It supposes that the universe goes through periodic expansion and contraction phases, with a soft "rebound" in place of the Big Bang. Thus the Hubble Law is explained by the fact that the universe is currently in an expansion phase. Work continues on this model (most notably by [[Jayant V. Narlikar]]), although it has yet to gain widespread mainstream acceptance.<ref>{{cite web |last=Wright |first=E. L. |date=20 December 2010 |title=Errors in the Steady State and Quasi-SS Models |url=http://www.astro.ucla.edu/~wright/stdystat.htm
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| |publisher=[[UCLA]], Physics & Astronomy Department}}</ref>
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| ==Anisotropic universe==
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| {{see also|Dark flow}}
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| Isotropicity – the idea that the universe looks the same in all directions – is one of the core assumptions that enters into the FRW equations. In 2008 however, scientists working on Wilkinson Microwave Anisotropy Probe data claimed to have detected a 600–1000 km/s flow of clusters toward a 20-degree patch of sky between the constellations of Centaurus and Vela.<ref>{{cite journal|author1=A. Kashlinsky |author2=F. Atrio-Barandela |author3=D. Kocevski |author4=H. Ebeling | title = A measurement of large-scale peculiar velocities of clusters of galaxies: technical details| journal = Astrophys. J.| volume = 691|issue=2 | year = 2009| pages = 1479–1493| url = http://www.nasa.gov/centers/goddard/pdf/276175main_ApJ_inpress.pdf| accessdate = 2010-07-15|bibcode = 2009ApJ...691.1479K |doi = 10.1088/0004-637X/691/2/1479 |arxiv = 0809.3733 }}</ref> They suggested that the motion may be a remnant of the influence of no-longer-visible regions of the universe prior to inflation. The detection is controversial, and other scientists have found that the universe is isotropic to a great degree.<ref>{{citeweb|url=http://www.earlyuniverse.org/does-the-universe-look-the-same-in-all-directions/|title=Does the Universe look the same in all directions?|author=Daniela Saadeh|date=22 September 2016|accessdate=16 December 2016}}</ref>
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| ==Exotic dark matter and dark energy==
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| {{main article|Dark matter|Dark energy}}
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| In Lambda-CDM, dark matter is an extremely inert form of matter that does not interact with both ordinary matter (baryons) and light, but still exerts gravitational effects. To produce the large-scale structure we see today, dark matter is "cold" (the 'C' in Lambda-CDM), i.e. non-relativistic. Dark energy is an unknown form of energy that tends to accelerate the expansion of the universe. Both dark matter and dark energy have not been conclusively identified, and their exact nature is the subject of intense study. For example, scientists have hypothesized that dark matter could decay into dark energy, or that both dark matter and dark energy are different facets of the same underlying fluid (see [[dark fluid]]). Other theories that aim to explain one or the other, such as warm dark matter and quintessence, also fall into this category.
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| ==Proposals based on observational skepticism==
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| As the observational cosmology began to develop, certain astronomers began to offer alternative speculations regarding the interpretation of various phenomena that occasionally became parts of non-standard cosmologies.
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| ===Tired light===
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| {{main article|Tired light}}
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| Tired light theories challenge the common interpretation of Hubble's Law as a sign the universe is expanding. It was proposed by [[Fritz Zwicky]] in 1929. The basic proposal amounted to light losing energy ("getting tired") due to the distance it traveled rather than any metric expansion or physical recession of sources from observers. A traditional explanation of this effect was to attribute a [[dynamical friction]] to photons; the photons' gravitational interactions with stars and other material will progressively reduce their momentum, thus producing a redshift. Other proposals for explaining how photons could lose energy included the [[scattering]] of light by intervening material in a process similar to observed [[interstellar reddening]]. However, all these processes would also tend to blur images of distant objects, and no such blurring has been detected.<ref>{{cite web|url=http://www.astro.ucla.edu/~wright/tiredlit.htm|title=Errors in Tired Light Cosmology|work=ucla.edu}}</ref>
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| Traditional tired light has been found incompatible with the observed [[time dilation]] that is associated with the cosmological redshift.<ref>{{citeweb|url=http://www.sciencemag.org/news/2001/06/tired-light-hypothesis-gets-re-tired|title="Tired-Light" Hypothesis Gets Re-Tired|publisher=Science|date=28 June 2001|accessdate=16 December 2016}}</ref> This idea is mostly remembered as a falsified alternative explanation for Hubble's law in most astronomy or cosmology discussions.
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| ===Dirac large numbers hypothesis===
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| {{main article|Dirac large numbers hypothesis}}
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| The Dirac large numbers hypothesis uses the ratio of the size of the visible universe to the radius of quantum particle to predict the age of the universe. The coincidence of various ratios being close in [[orders of magnitude|order of magnitude]] may ultimately prove meaningless or the indication of a deeper connection between concepts in a future [[theory of everything]]. Nevertheless, attempts to use such ideas have been criticized as [[numerology]].
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| ===Redshift periodicity and intrinsic redshifts===
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| [[File:Halton-arp.jpg|thumb|200px|[[Halton Arp]] in London, Oct 2000]]
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| {{See also|Redshift quantization}}
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| Some astrophysicists were unconvinced that the cosmological redshifts are caused by universal cosmological [[metric expansion of space|expansion]].<ref>Segal, I.E., Nicoll, J.F., Wu, P., Zhou, Z. 1993, ''Statistically Efficient Testing of the Hubble and Lundmark Laws on IRAS Galaxy Samples'', Astrophys. J. 465-484</ref><ref name="Arp 1998">Arp, H., ''Seeing Red, Redshifts, Cosmology and Academic Science'', 1998</ref> Skepticism and alternative explanations began appearing in the scientific literature in the 1960s. In particular, [[Geoffrey Burbidge]], [[William Tifft]] and [[Halton Arp]] were all observational astrophysicists who proposed that there were inconsistencies in the redshift observations of [[galaxy|galaxies]] and [[quasar]]s. The first two were famous for suggesting that there were [[redshift quantization|periodicities in the redshift distributions]] of galaxies and quasars. Subsequent statistical analyses of [[redshift survey]]s, however, have not confirmed the existence of these periodicities.<ref>{{cite journal | last1 = Schneider | display-authors =etal | date=2007| title = The Sloan Digital Sky Survey Quasar Catalog. IV. Fifth Data Release| bibcode=2007AJ....134..102S | journal = The Astronomical Journal | volume = 134 | issue = 1| pages = 102–117 |doi = 10.1086/518474 |arxiv = 0704.0806 }}</ref>
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| During the quasar controversies of the 1970s, these same astronomers were also of the opinion that quasars exhibited high redshifts not due to their incredible distance but rather due to unexplained ''intrinsic redshift'' mechanisms that would cause the periodicities and cast doubt on the Big Bang.<ref name="Arp 1998" /> Arguments over how distant quasars were took the form of debates surrounding quasar energy production mechanisms, their [[light curve]]s, and whether quasars exhibited any [[proper motion]]. Astronomers who believed quasars were not at cosmological distances argued that the [[Eddington luminosity]] set limits on how distant the quasars could be since the energy output required to explain the [[apparent brightness]] of cosmologically-distant quasars was far too high to be explainable by [[nuclear fusion]] alone. This objection was made moot by the improved models of gravity-powered [[accretion disk]]s which for sufficiently dense material (such as [[black hole]]s) can be more efficient at energy production than nuclear reactions. The controversy was laid to rest by the 1990s when evidence became available that observed quasars were actually the ultra-luminous cores of distant [[active galactic nuclei]] and that the major components of their redshift were in fact due to the [[Hubble flow]].<ref>{{Cite journal
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| | last = Antonucci
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| | first = R.
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| | title = Unified Models for Active Galactic Nuclei and Quasars
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| | journal = Annual Review of Astronomy and Astrophysics
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| | date = 1993
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| | doi = 10.1146/annurev.aa.31.090193.002353
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| | bibcode=1993ARA&A..31..473A
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| }}</ref><ref>{{Cite journal
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| | volume = 107
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| | pages = 803–845
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| | last = Urry
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| | first = P.
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| | author2= Paolo Padovani
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| | title = Unified schemes for radioloud AGN
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| | journal = Publications of the Astronomical Society of the Pacific
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| | date = 1995
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| | doi = 10.1086/133630
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| | bibcode=1995PASP..107..803U
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| | arxiv = astro-ph/9506063 }}</ref>
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| Throughout his career, Halton Arp maintained that there were anomalies in his observations of quasars and galaxies, and that those anomalies served as a refutation of the Big Bang.<ref name="Arp 1998" /> In particular, Arp pointed out examples of quasars that were close to the line of sight of (relatively) nearby [[active galactic nucleus|active galactic nuclei]] (AGN). He claimed that clusters of quasars were in alignment around AGN cores and that quasars, rather than being the cores of distant AGN, were actually much closer and were starlike-objects ejected from the centers of nearby AGN with high intrinsic redshifts. Arp also contended that they gradually lost their non-cosmological redshift component and eventually evolved into full-fledged galaxies.<ref>Arp and others who agree with him have been known to support the argument for a varying non-cosmological redshift by referring to a so-called "magnitude-redshift discrepancy". When a Hubble's law-type plot of quasar magnitudes versus redshift is made, a graph with a diffuse scatter and no clear linear relation is generated. However, since [[absolute magnitude]]s can only be independently calibrated to an upper limit using size constraints from variability and an Eddington luminosity, it is likely that quasars are exhibiting differing luminosities that cannot necessarily be derived from such simplistic first principles. Arp, Burbidge, and others maintain that the scatter in these plots further supports the idea that quasars have a ''non-cosmological'' component to their redshift, but nearly everyone else in the field accepts that quasars have variable luminosity.</ref><ref name="Burbidge, Hoyle" /><ref name="Arp 1998" /> This stands in stark contradiction to the accepted models of [[galaxy formation]].
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| The biggest problem with Arp's analysis is that today there are hundreds of thousands of quasars with known redshifts discovered by various sky surveys. The vast majority of these quasars are not correlated in any way with nearby AGN. Indeed, with improved observing techniques, a number of host galaxies have been observed around quasars which indicates that those quasars at least really are at [[cosmological distances]] and are not the kind of objects Arp proposes.<ref>The first instance of observing the host galaxies around quasars was announced in 1983 by Gehren as published in the ''Proceedings of the Twenty-fourth Liege International Astrophysical Colloquium''. p. 489-493.</ref> Arp's analysis, according to most scientists, suffers from being based on [[Hasty generalization|small number statistics]] and hunting for peculiar coincidences and odd associations.<ref>https://www.nytimes.com/2014/01/07/science/space/halton-c-arp-astronomer-who-challenged-big-bang-theory-dies-at-86.html</ref> Unbiased samples of sources, taken from numerous [[galaxy survey]]s of the sky show none of the proposed 'irregularities', nor that any [[statistically significant]] correlations exist.<ref>{{cite arXiv|eprint=0807.2641|title= Evidence against non-cosmological redshifts of QSOs in SDSS data|last1= Tang|first1= Sumin|author2= Shuang Nan Zhang|class= astro-ph|year= 2008}}</ref>
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| In addition, it is not clear what mechanism would be responsible for intrinsic redshifts or their gradual dissipation over time. It is also unclear how nearby quasars would explain some features in the spectrum of quasars which the standard model easily explains. In the standard cosmology, [[intergalactic medium|clouds of neutral hydrogen]] between the quasar and the [[earth]] create [[Lyman alpha]] [[absorption lines]] having different redshifts up to that of the quasar itself; this feature is called the [[Lyman-alpha forest]]. Moreover, in extreme quasars one can observe the absorption of neutral hydrogen which has not yet been [[reionization|reionized]] in a feature known as the [[Gunn–Peterson trough]]. Most cosmologists see this missing theoretical work as sufficient reason to explain the observations as either chance or error.<ref>For a description of mainstream cosmology's view of Arp's suggestions in this regard see Jones, H. ''What makes an astronomical controversy?'' ''Astronomy Now'' Vol. 19, No. 3, p. 58–61 (2005).</ref>
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| Halton Arp has proposed an explanation for his observations by a [[Mach's principle|Machian]] "variable mass hypothesis".<ref>[http://adsabs.harvard.edu/full/1993ApJ...405...51N Flat Spacetime Cosmology: A unified framework for extragalactic redshifts in ''Astrophysical Journal'' by J Narlikar and H Arp]</ref> The variable-mass theory invokes constant matter creation from active galactic nuclei, which puts it into the class of steady-state theories. With the passing of Halton Arp, this cosmology has been relegated to a dismissed theory.<ref>“When he died, he took a whole cosmology with him,” said Barry F. Madore, a senior research associate at the Carnegie Observatories in Pasadena, Calif. https://www.nytimes.com/2014/01/07/science/space/halton-c-arp-astronomer-who-challenged-big-bang-theory-dies-at-86.html</ref>
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| ===Plasma cosmology===
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| {{main article|Plasma cosmology}}
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| In 1965, [[Hannes Alfvén]] proposed a "plasma cosmology" theory of the universe based in part on [[plasma scaling|scaling]] observations of [[space physics|space plasma physics]] and experiments on [[plasma (physics)|plasmas]] in terrestrial laboratories to cosmological scales [[order of magnitude|orders of magnitude]] greater.<ref name=scaling>Hannes Alfvén, "[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1983Ap%26SS..89..313A&db_key=AST&data_type=HTML&format=&high=4521318e0206333 On hierarchical cosmology]" (1983) ''Astrophysics and Space Science'' (ISSN 0004-640X), vol. 89, no. 2, Jan. 1983, p. 313-324.</ref> Taking [[CP-violation|matter–antimatter symmetry]] as a starting point, Alfvén together with [[Oskar Klein]] proposed the [[Plasma cosmology#Alfvén-Klein cosmology|Alfvén-Klein cosmology]] model, based on the fact that since most of the local universe was composed of [[matter]] and not [[antimatter]] there may be large bubbles of matter and antimatter that would globally balance to equality. The difficulties with this model were apparent almost immediately. Matter–antimatter [[annihilation]] results in the production of high energy [[photon]]s which were not observed. While it was possible that the local "matter-dominated" cell was simply larger than the [[observable universe]], this proposition did not lend itself to observational tests.
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| Like the [[steady state theory]], plasma cosmology includes a Strong Cosmological Principle which assumes that the universe is isotropic in time as well as in space. Matter is explicitly assumed to have always existed, or at least that it formed at a time so far in the past as to be forever beyond humanity's empirical methods of investigation.
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| While plasma cosmology has never had the support of most [[astronomers]] or [[physicists]], a small number of plasma researchers have continued to promote and develop the approach, and publish in the special issues of the IEEE [[Transactions on Plasma Science]].<ref>(See IEEE Transactions on Plasma Science, issues in [http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&sim_query=YES&ned_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=12&start_year=1986&end_mon=12&end_year=1986&ttl_logic=OR&title=&txt_logic=OR&text=&nr_to_return=100&start_nr=1&jou_pick=ALL&ref_stems=ITPS.&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 1986], [http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=1989&isnumber=928 1989], [http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=1990&isnumber=1720 1990], [http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=1992&isnumber=5186 1992], [http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=2000&isnumber=19507 2000], [http://ieeexplore.ieee.org/xpl/tocresult.jsp?isYear=2003&isnumber=28301 2003], and 2007 Announcement [http://plasmascience.net/ieeetps/SpecialIssuesUpcoming/SpacePlasmas.html 2007] {{webarchive|url=https://web.archive.org/web/20070928115503/http://plasmascience.net/ieeetps/SpecialIssuesUpcoming/SpacePlasmas.html |date=28 September 2007 }} here)</ref> A few papers regarding plasma cosmology were published in other mainstream journals until the 1990s. Additionally, in 1991, [[Eric J. Lerner]], an independent researcher in [[plasma physics]] and nuclear fusion, wrote a popular-level book supporting plasma cosmology called ''The Big Bang Never Happened''. At that time there was renewed interest in the subject among the cosmological community along with other non-standard cosmologies. This was due to anomalous results reported in 1987 by Andrew Lange and Paul Richardson of UC Berkeley and Toshio Matsumoto of Nagoya University that indicated the cosmic microwave background might not have a [[blackbody spectrum]].<ref>{{cite book|title=Echo of the Big Bang|author=[[Michael Lemonick]]|publisher=Princeton University Press|year=2003|pages=63–64|isbn=0-691-10278-3}}</ref> However, the final announcement (in April 1992) of COBE satellite data corrected the earlier contradiction of the Big Bang; the popularity of plasma cosmology has since fallen.
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| ==Nucleosynthesis objections==
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| One of the major successes of the Big Bang theory has been to provide a [[prediction]] that corresponds to the observations of the abundance of light elements in the [[universe]]. Along with the explanation provided for the Hubble's law and for the cosmic microwave background, this observation has proved very difficult for alternative theories to explain.
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| Theories which assert that the universe has an infinite age, including many of the theories described above, fail to account for the abundance of deuterium in the cosmos, because deuterium easily undergoes nuclear fusion in stars and there are no known astrophysical processes other than the Big Bang itself that can produce it in large quantities. Hence the fact that deuterium is not an extremely rare component of the universe suggests that the universe has a finite age.
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| Theories which assert that the universe has a finite life, but that the Big Bang did not happen, have problems with the abundance of helium-4. The observed amount of <sup>4</sup>He is far larger than the amount that should have been created via stars or any other known process. By contrast, the abundance of <sup>4</sup>He in Big Bang models is very insensitive to assumptions about baryon density, changing only a few percent as the baryon density changes by several orders of magnitude. The observed value of <sup>4</sup>He is within the range calculated.
| | [[Category:Plasma]] |
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| ==Notes==
| | [[Category:Plasma Cosmology]] |
| {{Reflist|30em}}
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| == Bibliography ==
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| * Arp, Halton, "''Seeing Red''". Apeiron, Montreal. August 1998. {{ISBN|0-9683689-0-5}}
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| * Hannes, Alfvén D., "''Cosmic Plasma''". Reidel Pub Co., February 1981. {{ISBN|90-277-1151-8}}
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| * Hoyle, Fred, and Geoffrey Burbidge, and Jayant V. Narlikar, "''A Different Approach to Cosmology: From a Static Universe through the Big Bang towards Reality''". Cambridge University Press. February 17, 2000. {{ISBN|0-521-66223-0}}
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| * Lerner. Eric J., "''Big Bang Never Happened''", Vintage Books, October 1992. {{ISBN|0-679-74049-X}}
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| * Mitchell, William C., "''Bye Bye Big Bang: Hello Reality''". Cosmic Sense Books. January 2002. {{ISBN|0-9643188-1-4}}
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| * Narlikar, Jayant Vishnu, "''Introduction to Cosmology''". Jones & Bartlett Pub. January 1983. IUCAA. {{ISBN|0-86720-015-4}}
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| * Peratt, Anthony L., "''Physics of the Plasma Universe''". Springer-Verlag, 1991, {{ISBN|0-387-97575-6}}
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| ==External links and references==
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| * Santanu Das, 2012, ''[https://arxiv.org/abs/1205.4055 Cosmological solution of Machian gravity]''
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| * Lopez-Corredoira, Martín, 2003, ''[https://arxiv.org/abs/astro-ph/0310214 Observational Cosmology: caveats and open questions in the standard model]'', Recent Research Developments in Astronomy & Astrophysics, vol. 1, S. G. Pandalai, Ed., Research Signpost, Kerala, pp. 561–589
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| * Lopez-Corredoira, Martín, 2009, ''[http://cdsads.u-strasbg.fr/abs/2009ASPC..409...66L Sociology of Modern Cosmology]'' (ASP Conf. Ser. 409), in: J. A. Rubiño Martin, J. A. Belmonte, F. Prada, & A. Alberdi, Eds., ''Cosmology across Cultures'', ASP, S. Francisco, pp. 66–73
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| * Narlikar, Jayant V. and T. Padmanabhan, "''[http://adsabs.harvard.edu/cgi-bin/nph-bib_query?2001ARA&A..39..211N Standard Cosmology and Alternatives: A Critical Appraisal]''". [[Annual Review of Astronomy and Astrophysics]], Vol. 39, p. 211-248 (2001).
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| * Tifft, W. G. ''[http://public.lanl.gov/alp/plasma/papers.html Evidence for Quantization and Variable Redshifts in the Cosmic Background Rest Frame]''. Steward Observatory, University of Arizona, Tucson, Arizona
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| * Wright, Edward L. "''[http://www.astro.ucla.edu/~wright/errors.html Cosmological Fads and Fallacies:]''" Errors in some popular attacks on the Big Bang
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| * {{dmoz|Science/Astronomy/Cosmology/|Cosmology}}
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| {{portal bar|Astronomy|Cosmology|Physics}}
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| {{DEFAULTSORT:Non-Standard Cosmology}}
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| [[Category:Physical cosmology]]
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| [[Category:Fringe physics]]
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| [[Category:Astronomical controversies]]
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| [[Category:Big Bang]]
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