scholarly journals Connecting cosmological simulations to the real world

2003 ◽  
Vol 208 ◽  
pp. 245-260
Author(s):  
C.S. Frenk
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Astronomical Data ◽  
Cosmic Evolution ◽  
Small Quantum ◽  
The Big Bang ◽  
Current Paradigm ◽  
Coherent Picture

A timely combination of new theoretical ideas and observational discoveries has brought about significant advances in our understanding of cosmic evolution. Computer simulations have played a key role in these developments by providing the means to interpret astronomical data in the context of physical and cosmological theory. In the current paradigm, our Universe has a flat geometry, is undergoing accelerated expansion and is gravitationaly dominated by elementary particles that make up cold dark matter. Within this framework, it is possible to simulate in a computer the emergence of galaxies and other structures from small quantum fluctuations imprinted during an epoch of inflationary expansion shortly after the Big Bang. The simulations must take into account the evolution of the dark matter as well as the gaseous processes involved in the formation of stars and other visible components. Although many unresolved questions remain, a coherent picture for the formation of cosmic structure in now beginning to emerge.

A classical non-quantum all-time time-symmetrical zero-energy single-bounce model for the creation, big bang, and death of the universe

2019 ◽  
Vol 28 (14) ◽  
pp. 1944024 ◽  
Author(s):  
Arthur E. Fischer
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Final States ◽  
Level Curve ◽  
Zero Energy ◽  
Time Model ◽  
Gravitational Effects ◽  
The Big Bang ◽  
The Universe

In this paper, we show how the [Formula: see text]CDM (Lambda Cold Dark Matter) Standard Model for cosmology can be extrapolated backwards through the big bang into the infinite past to yield an all-time model of the universe with scale factor given by [Formula: see text] defined and continuous for all [Formula: see text] and smooth ([Formula: see text] and satisfying Friedmann’s equation for all [Formula: see text]. At the big bang [Formula: see text], there is a nondifferentiable cusp singularity and our model shows some details of the behavior of the universe at this singularity. Our model is a zero-energy single-bounce model and an examination of the [Formula: see text]-plot of the [Formula: see text] level curve gives critical information about the initial and final states of the universe, about the evolution of the universe, and about the behavior of the universe at the big bang. Our results show that much can be said classically about the birth, big bang and death of the universe before one needs to reach for quantum gravitational effects.

scholarly journals SOLVING THE INVERSE PROBLEM WITH INHOMOGENEOUS UNIVERSES

2011 ◽  
Vol 01 ◽  
pp. 234-239
Author(s):  
CHUL-MOON YOO ◽  
TOMOHIRO KAI ◽  
KEN-ICHI NAKAO
Keyword(s):  
Inverse Problem ◽  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Universe Model ◽  
Cosmological Redshift ◽  
Λcdm Model ◽  
The Big Bang ◽  
The Universe ◽  
Dust Universe

We construct the Lemaître-Tolman-Bondi (LTB) dust universe whose distance-redshift relation is equivalent to that in the concordance Λ cold dark matter (ΛCDM) cosmological model. In our model, the density distribution and velocity field are not homogeneous, whereas the big-bang time is uniform, which implies that the universe is homogeneous at its beginning. We also study the temporal variation of the cosmological redshift and show that, by the observation of this quantity, we can distinguish our LTB universe model from the concordance ΛCDM model, even if their redshift-distance relations are equivalent to each other.

scholarly journals STRUCTURE FORMATION WITH MIRROR DARK MATTER: CMB AND LSS

2005 ◽  
Vol 14 (01) ◽  
pp. 107-119 ◽  
Author(s):  
ZURAB BEREZHIANI ◽  
PAOLO CIARCELLUTI ◽  
DENIS COMELLI ◽  
FRANCESCO L. VILLANTE
Keyword(s):  
Dark Matter ◽  
Structure Formation ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Big Bang ◽  
Dark Matter Candidate ◽  
Microwave Background ◽  
Quantitative Calculation ◽  
World Hypothesis ◽  
The Big Bang

In the mirror world hypothesis, the mirror baryonic component emerges as a possible dark matter candidate. An immediate question arises: how do the mirror baryons behave and what are their differences from the more familiar dark matter candidates such as cold dark matter? In this paper, we answer this question quantitatively. First, we discuss the dependence of the relevant scales for the structure formation (Jeans and Silk scales) on the two macroscopic parameters necessary to define the model: the temperature of the mirror plasma (limited by the Big Bang Nucleosynthesis) and the amount of mirror baryonic matter. Then we perform a complete quantitative calculation of the implications of mirror dark matter on the cosmic microwave background and large scale structure power spectrum. Finally, confronting with the present observational data, we obtain some bounds on the mirror parameter space.

scholarly journals J1342+0928 supports the timeline in the Rh = ct cosmology

2018 ◽  
Vol 615 ◽  
pp. A113 ◽  
Author(s):  
Fulvio Melia
Keyword(s):  
Black Hole ◽  
Dark Matter ◽  
Cold Dark Matter ◽  
Big Bang ◽  
High Mass ◽  
Local Universe ◽  
Time Compression ◽  
The Standard Model ◽  
Accretion Rates ◽  
The Big Bang

Aims. The discovery of quasar J1342+0928 (z = 7.54) reinforces the time compression problem associated with the premature formation of structure in Λ cold dark matter (ΛCDM). Adopting the Planck parameters, we see this quasar barely 690 Myr after the big bang, no more than several hundred Myr after the transition from Pop III to Pop II star formation. Yet conventional astrophysics would tell us that a 10 M⊙ seed, created by a Pop II/III supernova, should have taken at least 820 Myr to grow via Eddington-limited accretion. This failure by ΛCDM constitutes one of its most serious challenges, requiring exotic “fixes”, such as anomalously high accretion rates, or the creation of enormously massive (~ 105 M⊙) seeds, neither of which is ever seen in the local Universe, or anywhere else for that matter. Indeed, to emphasize this point, J1342+0928 is seen to be accreting at about the Eddington rate, negating any attempt at explaining its unusually high mass due to such exotic means. In this paper, we aim to demonstrate that the discovery of this quasar instead strongly confirms the cosmological timeline predicted by the Rh = ct Universe. Methods. We assume conventional Eddington-limited accretion and the time versus redshift relation in this model to calculate when a seed needed to start growing as a function of its mass in order to reach the observed mass of J1342+0928 at z = 7.54. Results. Contrary to the tension created in the standard model by the appearance of this massive quasar so early in its history, we find that in the Rh = ct cosmology, a 10 M⊙ seed at z ~ 15 (the start of the Epoch of Reionization at t ~ 878 Myr) would have easily grown into an 8 × 108 M⊙ black hole at z = 7.54 (t ~ 1.65 Gyr) via conventional Eddington-limited accretion.

scholarly journals The Hot Big Bang and Beyond

1996 ◽  
Vol 168 ◽  
pp. 301-320
Author(s):  
Michael S. Turner
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Big Bang ◽  
Small Admixture ◽  
Matter Theory ◽  
Density Perturbations ◽  
The Big Bang ◽  
The Universe

The hot big-bang cosmology provides a reliable accounting of the Universe from about 10−2sec after the bang until the present, as well as a robust framework for speculating back to times as early as 10−43sec. Cosmology faces a number of important challenges; foremost among them are determining the quantity and composition of matter in the Universe and developing a detailed and coherent picture of how structure (galaxies, clusters of galaxies, superclusters, voids, great walls, and so on) developed. At present there is a working hypothesis—cold dark matter—which is based upon inflation and which, if correct, would extend the big bang model back to 10−32sec and cast important light on the unification of the forces. Many experiments and observations, from CBR anisotropy experiments to Hubble Space Telescope observations to experiments at Fermilab and CERN, are now putting the cold dark matter theory to the test. At present it appears that the theory is viable only if the Hubble constant is smaller than current measurements indicate (around 30 km s−1Mpc−1), or if the theory is modified slightly, e.g., by the addition of a cosmological constant, a small admixture of hot dark matter (5 eV “worth of neutrinos”), more relativistic particles, or a tilted spectrum of density perturbations.

scholarly journals The Radiation-Dominated Universe in Nonstandard Cosmology

2020 ◽  
Vol 5 (4) ◽  
Author(s):  
Günter Scharf ◽  
Keyword(s):  
Evolution Equations ◽  
Big Bang ◽  
The Other ◽  
Spherically Symmetric ◽  
Velocity Perturbation ◽  
Model Universe ◽  
Cosmic Evolution ◽  
Big Crunch ◽  
The Big Bang ◽  
Irregular Singular Points

We continue the recent study of our model theory of low-density cosmology without dark matter. We assume a purely radiative spherically symmetric background and treat matter as anisotropic perturbations. Einstein’s equations for the background are solved numerically. We find two irregular singular points, one is the Big Bang and the other a Big Crunch. The radiation temperature continues to decrease for another 0.21 Hubble times and then starts to increase towards infinity. Then we derive the four evolution equations for the anisotropic perturbations. In the Regge- Wheeler gauge there are three metric perturbations and a radial velocity perturbation. The solution of these equations allow a detailed discussion of the cosmic evolution of the model universe under study.

scholarly journals The holographic spacetime model of cosmology

2018 ◽  
Vol 27 (14) ◽  
pp. 1846005 ◽  
Author(s):  
Tom Banks ◽  
W. Fischler
Keyword(s):  
Dark Matter ◽  
Gravitational Waves ◽  
Structure Formation ◽  
Big Bang ◽  
Baryon Asymmetry ◽  
Gaussian Fluctuations ◽  
Primordial Gravitational Waves ◽  
Conventional Models ◽  
Non Gaussian ◽  
The Big Bang

This essay outlines the Holographic Spacetime (HST) theory of cosmology and its relation to conventional theories of inflation. The predictions of the theory are compatible with observations, and one must hope for data on primordial gravitational waves or non-Gaussian fluctuations to distinguish it from conventional models. The model predicts an early era of structure formation, prior to the Big Bang. Understanding the fate of those structures requires complicated simulations that have not yet been done. The result of those calculations might falsify the model, or might provide a very economical framework for explaining dark matter and the generation of the baryon asymmetry.

scholarly journals Nonlinear matter terms in general scalar–tensor braneworld cosmology

2019 ◽  
Vol 28 (11) ◽  
pp. 1950138
Author(s):  
Kevin F. S. Pardede ◽  
Agus Suroso ◽  
Freddy P. Zen
Keyword(s):  
Big Bang ◽  
Accelerated Expansion ◽  
Big Bang Nucleosynthesis ◽  
Braneworld Cosmology ◽  
Strongly Coupled ◽  
Weakly Coupled ◽  
General Scalar ◽  
Bulk Scalar Field ◽  
The Big Bang ◽  
Correction Terms

A five-dimensional braneworld cosmological model in general scalar–tensor action that is comprised of various Horndeski Lagrangians is considered. The Friedmann equations in the case of strongly and weakly coupled [Formula: see text] Horndeski Lagrangians have been obtained. The strongly coupled [Formula: see text] model produces the Cardassian term [Formula: see text] with [Formula: see text], which can serve as an alternative explanation for the accelerated expansion phase of the universe. Furthermore, the latest combined observational facts from BAO, CMB, SNIa, [Formula: see text] and [Formula: see text] value observation suggest that the [Formula: see text] term lies quite close to the constrained value. On the other hand, the weakly coupled [Formula: see text] case has several new correction terms which are omitted in the braneworld Einstein–Hilbert model, e.g. the cubic [Formula: see text] and the dark radiation–matter interaction term [Formula: see text]. Furthermore, this model provides a cosmological constant constructed from the bulk scalar field, requires no brane tension and supports the big bang nucleosynthesis (BBN) constraint naturally.

scholarly journals Is the expansion of universe accelerating or the Photons decelerating?

2015 ◽  
Vol 3 (1) ◽  
pp. 40
Author(s):  
Hasmukh Tank
Keyword(s):  
Big Bang ◽  
Time Dilation ◽  
Red Shift ◽  
Light Curves ◽  
Accelerated Expansion ◽  
Gravitational Acceleration ◽  
Expansion Of The Universe ◽  
Pi Mesons ◽  
The Big Bang ◽  
The Universe

<p>Astronomical observations of the cosmological red-shift are currently interpreted in terms of ‘expansion of universe’ and ‘accelerated-expansion of the universe’, at the rate of <em>H<sub>0</sub> c</em>; here <em>H<sub>0</sub></em> is Hubble’s constant, and c is the speed of light. Whereas a straight-forward derivation presented here suggests that: rather it is the photon which is decelerating, at the rate of <em>H<sub>0</sub> c</em>. Such a deceleration of photons can be caused by virtual electrons, positrons and pi-mesons, contained in the extra galactic quantum vacuum, because: they do have gravitational-acceleration of the same order as <em>H<sub>0</sub> c</em> at their “surfaces”; or by decay of a photon into a lighter photon and a particle of mass <em>h H<sub>0</sub> / c<sup>2</sup></em>. Tired-light interpretations of the cosmological red-shift’ were so far considered as not compatible with the observations of ‘time-dilation of super-novae light-curves’; so in a paper titled: “Wave-theoretical insight into the relativistic ‘length-contraction’ and ‘time-dilation of super-novae light-curves’” (Tank, Hasmukh K. 2013), it has been already shown that any mechanism which can cause ‘cosmological red-shift’ will also cause ‘time-dilation of super-novae light-curves’.  Therefore, we now need not to remain confined to the Big-Bang model of cosmology.</p>

scholarly journals Dark Matter in the Universe

1986 ◽  
Vol 7 ◽  
pp. 27-38 ◽  
Author(s):  
Vera C. Rubin
Keyword(s):  
Dark Matter ◽  
Deceleration Parameter ◽  
Big Bang ◽  
Theoretical Cosmology ◽  
Observational Cosmology ◽  
The Past ◽  
The Galaxy ◽  
Expansion Of The Universe ◽  
The Big Bang ◽  
The Universe

Thirty years ago, observational cosmology consisted of the search for two numbers: Ho, the rate of expansion of the universe at the position of the Galaxy; and qo, the deceleration parameter. Twenty years ago, the discovery of the relic radiation from the Big Bang produced another number, 3oK. But it is the past decade which has seen the enormous development in both observational and theoretical cosmology. The universe is known to be immeasurably richer and more varied than we had thought. There is growing acceptance of a universe in which most of the matter is not luminous. Nature has played a trick on astronomers, for we thought we were studying the universe. We now know that we were studying only the small fraction of it that is luminous. I suspect that this talk this evening is the first IAU Discourse devoted to something that astronomers cannot see at any wavelength: Dark Matter in the Universe.

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