Letteratura scientifica selezionata sul tema "Expansion of universe"

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Articoli di riviste sul tema "Expansion of universe"

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Wetterich, C. "Universe without expansion". Physics of the Dark Universe 2, n. 4 (dicembre 2013): 184–87. http://dx.doi.org/10.1016/j.dark.2013.10.002.

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Steer, Ian. "Who discovered Universe expansion?" Nature 490, n. 7419 (ottobre 2012): 176. http://dx.doi.org/10.1038/490176c.

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Ne'eman, Yuval. "Inflationary Cosmogony, Copernican Relevelling and Extended Reality". Symposium - International Astronomical Union 168 (1996): 559–62. http://dx.doi.org/10.1017/s0074180900110691.

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“Eternal” Inflation has relevelled the creation of universes, making it a “routine” physical occurence. The mechanism of the Big Bang, from the conditions triggering it, to the eventual creation of the entire matter content of the resulting universe, involves no singular physical processes. However, causal horizons, due to General Relativity, separate the newborn universe from the parent universe in which it was seeded as a localized vacuum energy. The new universe's expansion only occurs “after” infinite time, i.e. “never”, in the parents frame. This forces a reassessment of “reality”. The two universes are connected by the world line of the initial localized vacuum energy, originating in the parent universe. Assuming that the parent universe itself was generated in a similar fashion, etc., an infinite sequence of previous universes is thus connected by one world-line, like a string of beads.
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Gimsa, Dr Andreas. "The Expansion of the Universe". International Journal of Scientific Research and Management 8, n. 07 (18 luglio 2020): 25–31. http://dx.doi.org/10.18535/ijsrm/v8i07.aa01.

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The expansion of the universe is explained, calculated and graphically displayed. The 3K background radiation is examined and interpreted as reflected and distributed stellar radiation. The role of entropy in cosmology is discussed. In our expanding universe it must remain constant. Physical quantities previously assumed to be constant are worked out to be variable. It is explained why the measured redshift is not due to an accelerated growth of the universe.
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Morikawa, Masahiro. "Universe with oscillating expansion rate". Astrophysical Journal 369 (marzo 1991): 20. http://dx.doi.org/10.1086/169734.

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von Brzeski, Georg, e Vadim von Brzeski. "Misconceptions of Universe Expansion, Accelerated Universe Expansion, and Their Sources. Virtual Reality of Inflationary Cosmology". Journal of Modern Physics 09, n. 06 (2018): 1326–59. http://dx.doi.org/10.4236/jmp.2018.96081.

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Phillips, David, Priscilla Heard e Christopher W. Tyler. "Expanding Universe Illusion". i-Perception 10, n. 3 (maggio 2019): 204166951985384. http://dx.doi.org/10.1177/2041669519853848.

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We present a new induced movement illusion from global expansion or contraction in a triangular region filled with rising or falling textures. Objective global expansion or contraction induces lateral movement in the oblique edges of the triangle. The effects may be due to common and relative movements operating within a single texture.
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Bhoja Poojary, Bhushan. "Rotating Space Fabric of Universe Responsible for Expansion of Universe". American Journal of Astronomy and Astrophysics 4, n. 4 (2016): 38. http://dx.doi.org/10.11648/j.ajaa.20160404.11.

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Page, Don N. "No superluminal expansion of the universe". Classical and Quantum Gravity 26, n. 12 (27 maggio 2009): 127001. http://dx.doi.org/10.1088/0264-9381/26/12/127001.

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Freedman, Wendy. "The expansion rate of the universe". Astronomy and Geophysics 43, n. 1 (febbraio 2002): 1.10–1.13. http://dx.doi.org/10.1046/j.1468-4004.2002.43110.x.

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Tesi sul tema "Expansion of universe"

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Burrage, Clare Joanna. "Scalar fields and the accelerated expansion of the universe". Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611090.

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Humphreys, Neil Paul. "Obervational analysis of the inhomogeneous universe". Thesis, University of Portsmouth, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310380.

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Davis, Tamara Maree Physics Faculty of Science UNSW. "Fundamental aspects of the expansion of the universe and cosmic horizons". Awarded by:University of New South Wales. Physics, 2004. http://handle.unsw.edu.au/1959.4/20640.

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We use standard general relativity to clarify common misconceptions about fundamental aspects of the expansion of the Universe. In the context of the new standard Lambda-CDM cosmology we resolve conflicts in the literature regarding cosmic horizons and the Hubble sphere (distance at which recession velocity equals c) and we link these concepts to observational tests. We derive the dynamics of a non-comoving galaxy and generalize previous analyses to arbitrary FRW universes. We also derive the counter-intuitive result that objects at constant proper distance have a non-zero redshift. Receding galaxies can be blueshifted and approaching galaxies can be redshifted, even in an empty universe for which one might expect special relativity to apply. Using the empty universe model we demonstrate the relationship between special relativity and Friedmann-Robertson-Walker cosmology. We test the generalized second law of thermodynamics (GSL) and its extension to incorporate cosmological event horizons. In spite of the fact that cosmological horizons do not generally have well-defined thermal properties, we find that the GSL is satisfied for a wide range of models. We explore in particular the relative entropic "eworth"e of black hole versus cosmological horizon area. An intriguing set of models show an apparent entropy decrease but we anticipate this apparent violation of the GSL will disappear when solutions are available for black holes embedded in arbitrary backgrounds. Recent evidence suggests a slow increase in the fine structure constant over cosmological time scales. This raises the question of which fundamental quantities are truly constant and which might vary. We show that black hole thermodynamics may provide a means to discriminate between alternative theories invoking varying constants, because some variations in the fundamental "econstants"e could lead to a violation of the generalized second law of thermodynamics.
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QUIROGA, ALEXANDER ARGUELLO. "IMPACT OF THE COSMIC NEUTRINO BACKGROUND IN THE EXPANSION OF THE UNIVERSE". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14883@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Os neutrinos são produzidos copiosamente no Universo primordial e são hoje as espécies mais abundantes de partículas após os fótons. Com a descoberta da oscilação de neutrinos sabe-se que eles possuem massa. Os efeitos de neutrinos na formação de estruturas têm sido muito estudados e a comparação com os dados observacionais estabelece limites sobre a soma de suas massas. Nesta monografia abordamos outro aspecto dos neutrinos em cosmologia que tem sido pouco estudado na literatura: a sua influência na expansão global e suas possíveis implicações observacionais. Um aspecto interessante dos neutrinos do fundo cósmico é que, dentro dos limites actuais em suas massas, ao menos uma espécie deve ter passado de um regime relativístico a não-relativístico desde o desacoplamento matéria-radiação até o presente. Essa mudança de regime poderia acarretar em efeitos observacionais característicos desse processo. Neste trabalho investigamos a equação de estado dos neutrinos em função de sua massa e sua temperatura. A partir desse resultado, obtemos a taxa de expansão e a distância de luminosidade em função do desvio para o vermelho para um Universo contendo neutrinos massivos, além de matéria escura, constante cosmológica e radiação. Embora espera-se que o impacto dos neutrinos nessas quantidades observáveis seja pequeno, o objetivo deste trabalho é verificar se ele pode ser mensurável no contexto da emergente cosmologia de presição.
Neutrinos are produced copiously in the primordial Universe and today they are the most abundant specie of particles after the photons. With the discovery of neutrinos oscillation it is known that at least two of them have mass, although the absolute values are unknown. The effects of massive neutrinos in the large scale structure formation have been much studied and the comparison with observational data establishes limits over the neutrinos mass sum. In this dissertation we broach other aspect of neutrinos in cosmology which has been few studied in literature: its influence in the global expansion and the possible observational implications. An interesting aspect of cosmic neutrinos background is that inside the present masses limits at least one specie must have passed from a relativistic regime to a non-relativist one, since the matter-radiation decoupling until now. This change in regime could cause observational effects characteristics of this process. In this research we investigate the neutrinos state equation in function of their mass and temperature. From this result, we obtain the expansion rate and the luminosity distance in function of the Universe red-shift considering the presence of massive neutrinos, besides the dark matter, cosmological constant and radiation. Even through we expect that the neutrinos impact in these observable be small, the objective of this work is to verify if it can be measured in the context of the emergent precision cosmology.
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Ali, Sahba Yahya Hamid. "Probing the expansion history of the universe using upernovae and Baryon Acoustic Oscillations". University of the Western Cape, 2016. http://hdl.handle.net/11394/5054.

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Philosophiae Doctor - PhD
The standard model of cosmology (the ɅCDM model) has been very successful and is compatible with all observational data up to now. However, it remains an important task to develop and apply null tests of this model. These tests are based on observables that probe cosmic distances and cosmic evolution history. Supernovae observations use the so-called `standard candle' property of SNIa to probe cosmic distances D(z). The evolution of the expansion rate H(z) is probed by the baryon acoustic oscillation (BAO) feature in the galaxy distribution, which serves as an effective `standard ruler'. The observables D(z) and H(z) are used in various consistency tests of ɅCDM that have been developed. We review the consistency tests, also looking for possible new tests. Then the tests are applied, first using existing data, and then using mock data from future planned experiments. In particular we use data from the recently commissioned Dark Energy Survey (DES) for SNIa. Gaussian Processes, and possibly other non-parametric methods, used to reconstruct the derivatives of D (z) and H (z) that are needed to apply the null tests of the standard cosmological model. This allows us to estimate the current and future power of observations to probe the ɅCDM model, which is the foundation of modern cosmology. In addition, we present an improved model of the HI galaxy number counts and bias from semi-analytic simulations, and we use it to calculate the expected yield of HI galaxies from surveys with a variety of phase 1 and 2 SKA configurations. We illustrate the relative performance of the different surveys by forecasting errors on the radial and transverse scales of the BAO feature. We use the Fisher matrix method to estimate the error bars on the cosmological parameters from future SKA HI galaxy surveys. We find that the SKA phase 1 galaxy surveys will not contend with surveys such as the Baryon Oscillation Spectroscopic Survey (BOSS) whereas the full "billion galaxy survey" with SKA phase 2 will deliver the largest dark energy Figure of Merit of any current or future large-scale structure survey.
South African Square Kilometre Array Project (SKA) and German Academic Exchange Service (DAAD)
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Gupta, Rahul. "Supernova Cosmology in an Inhomogeneous Universe". Thesis, Stockholm University, Stockholm University, Department of Physics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-42162.

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The propagation of light beams originating from synthetic ‘Type Ia’ supernovae, through an inhomogeneous universe with simplified dynamics, is simulated using a Monte-Carlo Ray-Tracing method. The accumulated statistical (redshift-magnitude) distribution for these synthetic supernovae observations, which is illustrated in the form of a Hubble diagram, produces a luminosity profile similar to the form predicted for a Dark-Energy dominated universe. Further, the amount of mimicked Dark-Energy is found to increase along with the variance in the matter distribution in the universe, converging at a value of ΩX ≈ 0.7.

It can be thus postulated that at least under the assumption of simplified dynamics, it is possible to replicate the observed supernovae data in a universe with inhomogeneous matter distribution. This also implies that it is demonstrably not possible to make a direct correspondence between the observed luminosity and redshift with the distance of a cosmological source and the expansion rate of the universe, respectively, at a particular epoch in an inhomogeneous universe. Such a correspondences feigns an apparent variation in dynamics, which creates the illusion of Dark-Energy.

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Mazumdar, Anupam. "Dynamics of inflation". Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325580.

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de, Cruz Pérez Javier. "Implications of Dynamical Dark Energy in the expansion of the Universe and the Structure Formation". Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/671792.

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En aquesta tesi s’estudien diferents models cosmològics, tots ells caracteritzats per considerar, de manera efectiva, una lleu evolució temporal de l’Energia Fosca, en contrast amb l’actual model estàndard de la cosmologia. El terme Energia Fosca s’utilitza per fer referència a una misteriosa forma d’energia que sembla impregnar tots els racons del Univers i que provoca que les galàxies s’allunyin les unes de les altres. El ritme predit d’expansió del Univers varia d’un model a un altre així com la quantitat d’estructura observada i la distribució d’aquesta. Degut al bon moment de la cosmologia observacional tenim a la nostre disposició una gran quantitat de dades que ens permeten posar a prova els diferents models existents. Un exemple d’aquests models, seria el Running Vacuum Model (RVM), que ha estat estudiat en detall en aquesta tesi i que considera una expressió per la densitat d’energia del buit motivada en el context de les Teories Quàntiques de Camp. Un altre exemple de models cosmològics serien els anomenats models de camp escalar que suposen que l’equació d’estat de l’Energia Fosca, en el moment present, és lleugerament diferent del valor predit pel model estàndard. No noées s’han considerat models acomodats dins del marc de la teoria de la Relativitat General, sinó que també s’han estudiat les prediccions teòriques del model presentat per Brans i Dicke al 1961 i que resulta ser el primer intent d’extensió de la teoria d’Einstein. El model de Brans i Dicke està caracteritzat pel fet que la interacció gravitatòria està no només mediada per un camp tensorial, sinó també per un camp escalar. Les prediccions teòriques dels diferents models estudiats, tant a nivell de background com a nivell de pertorbacions, han sigut contrastades amb les mes recents dades cosmològiques revelant que l'anteriorment esmentada evolució temporal de l’Energia Fosca ajuda a rebaixar, de manera considerable, algunes de les tensions que afecten al model estàndard. La comparació teoria-observacions s’ha dut a terme mitjançant una rigorosa metodologia que involucra diferents eines estadístiques. Per tant les conclusions obtingudes al llarg d’aquesta tesi es basen en un procés robust i en un estudi detallat dels diferents models cosmològics considerants.
The high quality observations performed during the last two decades, have allowed to demonstrate, with high confidence range, that the Universe is in expansion and to be more precise in accelerated expansion. In order to explain the accelerated evolution the name of dark energy was coined. It refers to a some mysterious form of diffuse energy presumably permeating all corners of the Universe as a whole. We may say that the canonical picture of our Universe defined in the framework of General Relativity, whose field equation were found by Einstein in 1917, is built upon the assumption that the observed acceleration is caused, in fact, by a rigid cosmological constant term denoted by Λ. Thanks to the aforementioned cosmological measurements, we have been able to pin down its value to an impressive level. Dark energy is not the only element, beyond the conventional baryons and photons, required by the observations since we also need large amounts of what is commonly call as dark matter. We call such an overall picture of the Universe the “concordance (or standard) cosmological model” or simply ΛCDM. Therefore, we attribute the observed accelerated expansion of the Universe to the existence of a repulsive force, exerted by the Λ term, which works against the attractive gravitational force and tends to push the clusters of galaxies apart at a speed continuously increasing with the cosmic expansion. Throughout this thesis a wide variety of models, beyond the standard model have been studied. The corresponding analyses have been carried out by studying in detail the theoretical predictions at the background and perturbation level, with the purpose of testing them with the large amount of cosmological data which we currently we have access to. The ultimate goal is to see if we can detect signals of new physics that help to alleviate some of the tensions that affect the ΛCDM. The concordance model, has remained robust and unbeaten for a long time since it is roughly consistent with a large body of cosmological data. Because of this fact, it is not reasonable to look for models with a very different behaviour than the ΛCDM, but to study models that exhibit small departures with respect to the standard model in key aspects. We have studied the Running Vacuum Models (RVM) in depth. They are characterized by having a time-evolving vacuum energy density, whose functional expression is motivated in the context of Quantum Field Theory in curved space-time. It is fundamental that its expression contains a constant term, which mimics the standard behaviour in order to first generate the transition from a decelerated to an accelerated Universe and to ensure that the fit of the structure formation data is not ruined. We have also studied the Peebles & Ratra model, which is a particularly successful scalar field model φCDM for which the potential takes the form V (φ) ∼ φ−α . The dimensionless parameter α encodes the extra degree of freedom that this model has with respect to the standard model. It is found to be small and positive, therefore V (φ) can mimic and approximate cosmological constant that is decreasing slowly with time. In the late Universe the contribution of the scalar field, φ, surfaces over the matter density, thus becoming the dominant component. Not all the models studied are motivated within a theoretical framework, since we have also considered some interesting phenomenological approaches. Last but not least, at the end of the thesis the Brans & Dicke (BD) gravity model was studied in detail. The main feature of this model is that the Newtonian constant coupling GN is replaced by a dynamical scalar field G(t) = 1/ψ(t), coupled to the curvature. As a consequence the gravitational interaction is not only mediated by the metric field, as in the General Relativity case but also for the aforementioned scalar field ψ. The obtained results clearly point out to an interesting conclusion, those models which consider an effective time-evolving dark energy are able to alleviate some of the tensions affecting the ΛCDM. Among the different tensions there are two that stand out, namely the σ8 -tension and the H0-tension.
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Helou, Alexis. "Beyond the trapping horizon : the apparent universe & the regular black hole". Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC140.

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Dans le contexte de la Relativité Générale, le concept d'horizon permet de séparer l'espace-temps en zones de comportement causal différent. En particulier l'horizon apparent, et la notion très proche d'horizon de confinement, sont définis à partir de grandeurs locales. Nous sélectionnons ces horizons comme l'outil pertinent pour décrire les situations dynamiques à symétrie sphérique, telles que le trou noir ou la cosmologie. Le principe d'Holographie indique en effet que l'information contenue dans un volume donné serait encodée sur la surface renfermant le volume. Ainsi l'horizon apparent contiendrait des informations sur le trou noir qu'il délimite ou sur l'Univers qu'il borne. Dans cette optique, nous appliquons les lois de la thermodynamique à l'horizon apparent cosmologique, en utilisant un ensemble d'outils adaptés à la symétrie sphérique : le vecteur de Kodama, l'énergie de Misner-Sharp, la première loi unifiée. Ceci nous permet de retrouver les équations de Friedmann qui régissent la dynamique de notre Univers. Un paramètre de température thermodynamique est ensuite calculé, qui caractérise une émission à l'horizon. Ceci est ensuite généralisé aux trous blancs et cosmologies en contraction. Enfin nous étudierons le rôle de l'horizon apparent dans le paradoxe de l'information des trous noirs
In the context of General Relativity, the concept of horizon divides the spacetime into regions of different causal behaviour. In particular, the apparent horizon and closely related trapping horizon are defined from local quantities. We select these horizons as the relevant tool to describe spherically symmetric, dynamical situations, such as black holes or cosmology. Indeed the Holographic principle indicates that the information contained in the bulk of a given region, would be encoded on the boundary surface of the region. Then the apparent horizon would contain information on the black hole or on the Universe it bounds. In this optic, we apply the laws of thermodynamics to the cosmological apparent horizon, using a set of tools well-suited to spherical symmetry : the Kodama vector, the Misner-Sharp energy, the unified first law. This will allow us to recover the Friedmann equations, which govern the dynamics of our Universe. A thermodynamical parameter identified as a temperature is then computed, which characterizes the emission at the horizon. This is then generalized to white holes and contracting cosmologies. Finally we study the role of the apparent horizon in the information loss paradox for black holes
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Wiegand, Alexander [Verfasser]. "The inhomogeneous Universe : its average expansion and cosmic variance / Alexander Wiegand. Fakultät für Physik - Cosmology and Astroparticle Physics". Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2012. http://d-nb.info/1026077605/34.

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Libri sul tema "Expansion of universe"

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Ehrensperger, Jakob. Energien im Kosmos ; Die Expansion des Kosmos: Die Expansion der Erde. Winterthur: W. Vogel, 1988.

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Lectures on cosmology: Accelerated expansion of the universe. Berlin: Springer, 2010.

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Guth, Alan H. The inflationary universe: The quest for a new theory of cosmic origins. Reading, Mass: Addison-Wesley Publishing, 1997.

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Guth, Alan H. The inflationary universe: The quest for a new theory of cosmic origins. Reading, Mass: Perseus Books, 1997.

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Guth, Alan H. The inflationary universe: The quest for a new theory of cosmic origins. London, UK: Jonathan Cape, 1997.

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B, Madore, Tully R. Brent e North Atlantic Treaty Organization. Scientific Affairs Division., a cura di. Galaxy distances and deviations from universal expansion. Dordrecht: D. Reidel Pub. Co., 1986.

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Silbergleit, Alexander S., e Arthur D. Chernin. Interacting Dark Energy and the Expansion of the Universe. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-57538-4.

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Leffert, Charles B. Time and cosmology: Creation and expansion of our universe. Troy, Mich: Anoka Pub., 1995.

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Brandström, Per. Boundless universe: The culture of expansion among the Sukuma-Nyamwezi of Tanzania. [Uppsala, Sweden]: Dept. of Cultural Anthropology, Uppsala University, 1990.

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Qurʾan on creation and expansion of the universe: A cosmological and astrophysical study. 2a ed. Lahore: Minhaj-ul-Qurʾan Publications, 1996.

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Capitoli di libri sul tema "Expansion of universe"

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Vishveshwara, C. V. "The Universe: Expanse and Expansion". In Astronomers' Universe, 159–76. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-08213-4_13.

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Piattella, Oliver. "The Universe in Expansion". In UNITEXT for Physics, 17–53. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-95570-4_2.

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Bari, Pasquale Di. "Expansion history of the universe". In Cosmology and the Early Universe, 129–40. Boca Raton : CRC Press, [2018] | Series: Series in astronomy and astrophysics: CRC Press, 2018. http://dx.doi.org/10.1201/9781138496903-10.

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Hentschke, Reinhard, e Christian Hölbling. "Accelerated Expansion of the Universe". In A Short Course in General Relativity and Cosmology, 169–92. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-46384-7_10.

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van den Heuvel, Edward. "Other Galaxies and the Discovery of the Expansion of the Universe". In Astronomers' Universe, 79–96. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-23543-1_6.

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Parker, Barry. "Discovery of the Expansion of the Universe". In The Vindication of the Big Bang, 17–47. Boston, MA: Springer US, 1993. http://dx.doi.org/10.1007/978-1-4899-5980-5_1.

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Wagoner, Robert V. "From the Expansion of SN 1987A to the Expansion of the Universe". In Supernovae, 741–50. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-2988-9_111.

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Melott, Adrian L. "Virgo Infall and the Mass Density of the Universe". In Galaxy Distances and Deviations from Universal Expansion, 225–28. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-009-4702-3_38.

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Manoukian, E. B. "Expansion of the Universe and the Hubble Law". In 100 Years of Fundamental Theoretical Physics in the Palm of Your Hand, 465–68. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-51081-7_76.

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Cohen, M. H., P. D. Barthel, T. J. Pearson e J. A. Zensus. "Expanding Quasars and the Expansion of the Universe". In The Impact of VLBI on Astrophysics and Geophysics, 23–24. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2949-4_6.

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Atti di convegni sul tema "Expansion of universe"

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Lopez-Corredoira, Mart­in. "Tests on the Expansion of the Universe". In Frontiers of Fundamental Physics 14. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.224.0085.

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Linder, Eric V. "Dark Energy, Expansion History of the Universe, and SNAP". In PARTICLE PHYSICS AND COSMOLOGY: Third Tropical Workshop on Particle Physics and Cosmology - Neutrinos, Branes, and Cosmology. AIP, 2003. http://dx.doi.org/10.1063/1.1543500.

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3

Le Delliou, Morgan, Filipe C. Mena, José P. Mimoso, Jean-Michel Alimi e André Fuözfa. "Separating expansion from contraction: generalized TOV condition, LTB models with pressure and ΛCDM". In INVISIBLE UNIVERSE: Proceedings of the Conference. AIP, 2010. http://dx.doi.org/10.1063/1.3462594.

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4

Zeng, Caibin, YangQuan Chen e Igor Podlubny. "Is Our Universe Accelerating Dynamics Fractional Order?" In ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/detc2015-46216.

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Abstract (sommario):
In this paper, a fractional dynamics approach is used to characterize the observed accelerating expansion of the universe. We claim that the evolution of accelerating expansion obeys an α-exponential function, which is the fundamental solution of linear fractional order dynamical equation. We find that the Hubble constant is 67.8807, 68.2546, and 67.9119 for all redshift z < 1.5, z < 1, and z < 0.1 based on the dataset collected by the Supernova Cosmology Project. Furthermore, we verify that the expansion rate of our universe is speeding up and actually obeys a Mittag-Leffler law.
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CARROLL, SEAN M. "WHAT DO WE REALLY KNOW ABOUT THE EXPANSION OF THE UNIVERSE?" In Proceedings of the Second Meeting. WORLD SCIENTIFIC, 2002. http://dx.doi.org/10.1142/9789812778123_0010.

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SPYROU, N. K. "CONFORMAL DYNAMICAL EQUIVALENCE AND THE COSMOLOGICAL EXPANSION OF A REALISTIC UNIVERSE". In Proceedings of the 10th Hellenic Relativity Conference. WORLD SCIENTIFIC, 2003. http://dx.doi.org/10.1142/9789812791238_0008.

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CLINE, J. M. "COSMOLOGICAL EXPANSION IN THE RANDALL-SUNDRUM WARPED COMPACTIFICATION". In Proceedings of the Third International Workshop on Particle Physics and the Early Universe. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812792129_0072.

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Landim, Ricardo C. G. "A model for accelerated expansion of the universe from 𝒩 = 1 supergravity". In Proceedings of the MG14 Meeting on General Relativity. WORLD SCIENTIFIC, 2017. http://dx.doi.org/10.1142/9789813226609_0249.

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Mebarki, N., N. Mebarki e J. Mimouni. "Some Cosmological Models for Poincare Gauge Gravity and Accelerated Expansion of the Universe". In THE THIRD ALGERIAN WORKSHOP ON ASTRONOMY AND ASTROPHYSICS. AIP, 2010. http://dx.doi.org/10.1063/1.3518329.

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Tsuchiya, Asato. "Exponential and power-law expansion of the Universe from the type IIB matrix model". In Proceedings of the Corfu Summer Institute 2015. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.263.0112.

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Rapporti di organizzazioni sul tema "Expansion of universe"

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Zilberman, Mark. “Doppler de-boosting” and the observation of “Standard candles” in cosmology. Intellectual Archive, luglio 2021. http://dx.doi.org/10.32370/iaj.2549.

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“Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the name of relativistic effect observed for receding light sources (e.g. relativistic jets of active galactic nuclei and gamma-ray bursts). “Doppler boosting” changes the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” causes the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard candle adjustment of an Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.
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Zilberman, Mark. PREPRINT. “Doppler de-boosting” and the observation of “Standard candles” in cosmology. Intellectual Archive, giugno 2021. http://dx.doi.org/10.32370/ia_2021_06_23.

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Abstract (sommario):
PREPRINT. “Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the term of the same relativistic effect observed for receding light sources (e.g.relativistic jets of active galactic nuclei and gamma-ray bursts). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) =L/Lo=(Z+1)^(α-3) and for Type Ia supernova appears as ℳ(Z)=L/Lo=(Z+1)^(-2). “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.
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3

Zilberman, Mark. "Doppler De-boosting" and the Observation of "Standard Candles" in Cosmology. Intellectual Archive, luglio 2021. http://dx.doi.org/10.32370/iaj.2552.

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Abstract (sommario):
“Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the same relativistic effect observed but for receding light sources (e.g. relativistic jets of AGN and GRB). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard Candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.
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4

Ferreyra, Maria Marta, Carlos Garriga, Juan D. Martin-Ocampo e Angélica María Sánchez Díaz. Raising College Access and Completion: How Much Can Free College Help? Banco de la República de Colombia, febbraio 2021. http://dx.doi.org/10.32468/be.1155.

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Free college proposals have become increasingly popular in many countries of the world. To evaluate their potential effects, we develop and estimate a dynamic model of college enrollment, performance, and graduation. A central piece of the model, student effort, has a direct effect on class completion, and an indirect effect in mitigating the risk of not completing a class or not remaining in college. We estimate the model using rich, student-level administrative data from Colombia, and use the estimates to simulate free college programs that differ in eligibility requirements. Among these, universal free college expands enrollment the most, but it does not affect graduation rates and has the highest per-graduate cost. Performance-based free college, in contrast, delivers a slightly lower enrollment expansion yet a greater graduation rate at a lower per-graduate cost. Relative to universal free college, performance-based free college places a greater risk on students but is precisely this feature that delivers better outcomes. Nonetheless, the modest increase in graduation rates suggests that additional, complementary policies might be required to elicit the large effort increase needed to raise graduation rates.
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Zilberman, Mark. The "Dimming Effect" Produced by the Application of Doppler Effect on the Quantity of Photons Arriving to a Receiver and its Implication to Astronomy (ver. 2). Intellectual Archive, novembre 2020. http://dx.doi.org/10.32370/iaj.2444.

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This article describes the "Dimming effect" that is produced by the Doppler effect applied to a quantity of individual photons arriving to a receiver from a moving source of light. The corpuscular-wave dualism of light suggests that the well-known Doppler effect, which is currently applied only to the wave component of light, should also be considered for the corpuscular component of light. Application of the Doppler effect on a quantity of photons leads to the "Dimming Effect" - as the faster light source is moving away from observer - the dimmer its brightness appears. While the described dimming effect is negligible for low-speed light sources, it becomes significant for light sources with a velocity comparable to light speed in a vacuum. The relativistic adjustments for time dilation cause the described dimming effect to be even stronger. For example, the "Dimming Effect" for an object moving away from the observer with the speed 0.1c is 0.904 and for an object moving away from the observer with the speed 0.5c is 0.577. Article also provides the formula for the calculation of "Dimming effect" values using the red-shift parameter Z widely used in astronomy as N/N0=1/(Z+1). If confirmed, the "Dimming effect" must be taken into account in calculations of astronomical "Standard Candles" and in particular in the "Supernova Cosmology Project", which has claimed the acceleration of the Universe's expansion and led to the introduction of dark energy.
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