scholarly journals The Radiation-Dominated Universe in Nonstandard Cosmology

2020 ◽  
Vol 5 (4) ◽  
Author(s):  
Günter Scharf ◽  

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.

2020 ◽  
Vol 500 (3) ◽  
pp. 3750-3762
Author(s):  
Federico Sestito ◽  
Tobias Buck ◽  
Else Starkenburg ◽  
Nicolas F Martin ◽  
Julio F Navarro ◽  
...  

ABSTRACT The kinematics of the most metal-poor stars provide a window into the early formation and accretion history of the Milky Way (MW). Here, we use five high-resolution cosmological zoom-in simulations (∼ 5 × 106 star particles) of MW-like galaxies taken from the NIHAO-UHD project, to investigate the origin of low-metallicity stars ([Fe/H] ≤ −2.5). The simulations show a prominent population of low-metallicity stars confined to the disc plane, as recently discovered in the MW. The ubiquity of this finding suggests that the MW is not unique in this respect. Independently of the accretion history, we find that ≳90 per cent of the retrograde stars in this population are brought in during the initial build-up of the galaxies during the first few Gyr after the Big Bang. Our results therefore highlight the great potential of the retrograde population as a tracer of the early build-up of the MW. The prograde planar population, on the other hand, is accreted during the later assembly phase and samples the full galactic accretion history. In case of a quiet accretion history, this prograde population is mainly brought in during the first half of cosmic evolution (t ≲ 7 Gyr), while, in the case of an ongoing active accretion history, later mergers on prograde orbits are also able to contribute to this population. Finally, we note that the MW shows a rather large population of eccentric, very metal-poor planar stars. This is a feature not seen in most of our simulations, with the exception of one simulation with an exceptionally active early building phase.


2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Koijam Manihar Singh ◽  
Gauranga C. Samanta

The phenomenon of dark energy and its manifestations are studied in a spherically symmetric universe considering the Brans-Dicke scalar tensor theory. In the first model, the dark energy behaves like a phantom type and in such a universe the existence of negative time is validated with an indication that our universe started its evolution before t=0. Dark energy prevalent in this universe is found to be more active at times when other types of energies remain passive. The second model of universe begins with big bang. On the other hand, the dark energy prevalent in the third model is found to be of the quintessence type. Here, it is seen that the dark energy triggers the big bang and after that much of the dark energy reduces to dark matter. One peculiarity in such a model is that the scalar field is prevalent eternally; it never tends to zero.


2009 ◽  
Vol 5 (S268) ◽  
pp. 201-210
Author(s):  
Monique Spite ◽  
François Spite

AbstractThe nuclei of the lithium isotopes are fragile, easily destroyed, so that, at variance with most of the other elements, they cannot be formed in stars through steady hydrostatic nucleosynthesis.The 7Li isotope is synthesized during primordial nucleosynthesis in the first minutes after the Big Bang and later by cosmic rays, by novae and in pulsations of AGB stars (possibly also by the ν process). 6Li is mainly formed by cosmic rays. The oldest (most metal-deficient) warm galactic stars should retain the signature of these processes if, (as it had been often expected) lithium is not depleted in these stars. The existence of a “plateau” of the abundance of 7Li (and of its slope) in the warm metal-poor stars is discussed. At very low metallicity ([Fe/H] < −2.7dex) the star to star scatter increases significantly towards low Li abundances. The highest value of the lithium abundance in the early stellar matter of the Galaxy (logϵ(Li) = A(7Li) = 2.2 dex) is much lower than the the value (logϵ(Li) = 2.72) predicted by the standard Big Bang nucleosynthesis, according to the specifications found by the satellite WMAP. After gathering a homogeneous stellar sample, and analysing its behaviour, possible explanations of the disagreement between Big Bang and stellar abundances are discussed (including early astration and diffusion). On the other hand, possibilities of lower productions of 7Li in the standard and/or non-standard Big Bang nucleosyntheses are briefly evoked.A surprisingly high value (A(6Li)=0.8 dex) of the abundance of the 6Li isotope has been found in a few warm metal-poor stars. Such a high abundance of 6Li independent of the mean metallicity in the early Galaxy cannot be easily explained. But are we really observing 6Li?


Tempo ◽  
1983 ◽  
pp. 12-14
Author(s):  
Robert Simpson

Any imaginative hypothesis must be seminal, and Jonathan Harvey's is no exception. As he points out, a number of composers have been fascinated by the idea of harmonic structures radiating above and below a central axis in reflecting intervals. He says ‘from either side’ rather than ‘above and below’, and perhaps advisedly, for as soon as the concept of ‘below’ is permitted, so is that of gravity. The thesis depends on the removal of gravity in what is essentially a placeless, directionless space, without perceptible ups, downs, or sides. Swedenborg's rarified and not altogether realistic ideas come from a mysticism that is unclear about the nature of space. There are relative directions in space; it has dimensions; it is full of energy and radiation; in it gravity is inescapable. A man floating between earth and moon may not be aware of it, but he will drift in one direction or the other, according to which gravitational pull is the stronger. We can estimate at least roughly the distances between the galaxies, and their relative positions, their rates of movement away from each other if they do not belong to the same group. If the theory that in music the bass has moved to the middle refers to the apparent absence of an absolute bottom to the universe, it can be regarded as at least plausible, though without much basis in actual experience, and scarcely susceptible to proof. Where is this axis from which things radiate? It is not, presumably, a fixed and all too audible persistent internal pedal. No doubt it was there at the beginning, like the Big Bang, to be afterwards detected only by means of some residual musical radiation. It becomes an imaginary, or remembered, point.


2003 ◽  
Vol 208 ◽  
pp. 245-260
Author(s):  
C.S. Frenk

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.


2009 ◽  
Vol 18 (14) ◽  
pp. 2257-2263 ◽  
Author(s):  
VISHNU JEJJALA ◽  
MICHAEL KAVIC ◽  
DJORDJE MINIC ◽  
CHIA-HSIUNG TZE

We present a novel solution to the nature and formation of the initial state of the Universe. It derives from the physics of a generally covariant extension of matrix theory. We focus on the dynamical state space of this background-independent quantum theory of gravity and matter — an infinite-dimensional, complex, nonlinear Grassmannian. When this space is endowed with a Fubini–Study-like metric, the associated geodesic distance between any two of its points is zero. This striking mathematical result translates into a physical description of a hot, zero-entropy Big Bang. The latter is then seen as a far-from-equilibrium, large-fluctuation-driven, metastable ordered transition — a "freezing by heating" jamming transition. Moreover, the subsequent unjamming transition could provide a mechanism for inflation while rejamming may model a Big Crunch, the final state of gravitational collapse.


Religions ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 634
Author(s):  
W. R. Klemm

Human culture has modernized at a much faster pace than has theology and religion. We are at the point where many moderns apparently think that religion is losing relevance. Satisfying the need for relevance and ecumenical harmony requires more reasoned and mature approaches to religion. Science is one of those secular activities that seems to undermine religious faith for many people. Unlike the sciences that give us the Big Bang, relativity, quantum mechanics, and theories of evolution, neuroscience is the one science that applies in everyday life toward developing a faith that promotes nurturing of self and others. Modern neuroscience and the mental health understanding that it creates can contribute to satisfying this need. Neuroscience and religion have numerous shared areas of concern, and each worldview can and should inform and enrich the other. Neuroscience may help us understand why we believe certain religious ideas and not others. It helps to explain our behavior and might even help us live more righteous and fulfilled lives. Religion can show neuroscientists areas of religious debate that scientific research might help resolve. New educational initiatives at all levels (secondary, seminary, and secular college) can provide a way to integrate neuroscience and religion and lead to religious perspectives that are more reasoned, mature, satisfying, and beneficial at both individual and social levels. Neurotheology is an emerging academic discipline that seems to focus on integrating neuroscience and theology. About only 10 years old, neurotheology has not yet consolidated its definition, ideology, purpose, or scholarly or applied strategies. Acceptance by the scholarly community is problematic. This manuscript raises the question of whether neurotheology will survive as a viable discipline and, if so, what form that could take.


2018 ◽  
Vol 51 (2) ◽  
pp. 505-513 ◽  
Author(s):  
Angela Altomare ◽  
Nicola Corriero ◽  
Corrado Cuocci ◽  
Aurelia Falcicchio ◽  
Anna Moliterni ◽  
...  

The hybrid big bang–big crunch algorithm is a combination of a global optimization algorithm inspired by one of the theories of the evolution of the universe, named the big bang and big crunch theory, and the simulated annealing method. The procedure was implemented in the latest version of the programEXPOand applied to crystal-structure solution from powder diffraction data. Several aspects of the hybrid big bang–big crunch algorithm can be further optimized with the aim of obtaining good quality solutions in a shorter computation time. In the present study, the hybrid big bang–big crunch procedure has been combined with the greedy randomized adaptive search procedure (GRASP) and some steps of the algorithm have been improved. The new approach, implemented in theEXPOpackage, has been successfully tested on numerous known crystal structures.


Algorithms ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 146 ◽  
Author(s):  
Abdoalnasir Almabrok ◽  
Mihalis Psarakis ◽  
Anastasios Dounis

This article presents a novel technique for the fast tuning of the parameters of the proportional–integral–derivative (PID) controller of a second-order heat, ventilation, and air conditioning (HVAC) system. The HVAC systems vary greatly in size, control functions and the amount of consumed energy. The optimal design and power efficiency of an HVAC system depend on how fast the integrated controller, e.g., PID controller, is adapted in the changes of the environmental conditions. In this paper, to achieve high tuning speed, we rely on a fast convergence evolution algorithm, called Big Bang–Big Crunch (BB–BC). The BB–BC algorithm is implemented, along with the PID controller, in an FPGA device, in order to further accelerate of the optimization process. The FPGA-in-the-loop (FIL) technique is used to connect the FPGA board (i.e., the PID and BB–BC subsystems) with the plant (i.e., MATLAB/Simulink models of HVAC) in order to emulate and evaluate the entire system. The experimental results demonstrate the efficiency of the proposed technique in terms of optimization accuracy and convergence speed compared with other optimization approaches for the tuning of the PID parameters: sw implementation of the BB–BC, genetic algorithm (GA), and particle swarm optimization (PSO).


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