Topic
Flatness problem
About: Flatness problem is a research topic. Over the lifetime, 2001 publications have been published within this topic receiving 62110 citations. The topic is also known as: oldness problem.
Papers published on a yearly basis
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Papers
TL;DR: In this paper, the authors proposed a model of hot big-bang cosmology where the early universe is assumed to be highly homogeneous, in spite of the fact that separated regions were causally disconnected (horizon problem).
Abstract: The standard model of hot big-bang cosmology requires initial conditions which are problematic in two ways: (1) The early universe is assumed to be highly homogeneous, in spite of the fact that separated regions were causally disconnected (horizon problem); and (2) the initial value of the Hubble constant must be fine tuned to extraordinary accuracy to produce a universe as flat (i.e., near critical mass density) as the one we see today (flatness problem). These problems would disappear if, in its early history, the universe supercooled to temperatures 28 or more orders of magnitude below the critical temperature for some phase transition. A huge expansion factor would then result from a period of exponential growth, and the entropy of the universe would be multiplied by a huge factor when the latent heat is released. Such a scenario is completely natural in the context of grand unified models of elementary-particle interactions. In such models, the supercooling is also relevant to the problem of monopole suppression. Unfortunately, the scenario seems to lead to some unacceptable consequences, so modifications must be sought.
11,265 citations
TL;DR: In this paper, the authors consider a FRW cosmological model with an exotic fluid known as Chaplygin gas and show that the resulting evolution of the universe is not in disagreement with the current observation of cosmic acceleration.
3,002 citations
Sapienza University of Rome1, Queen Mary University of London2, Jet Propulsion Laboratory3, University of Toronto4, Lawrence Berkeley National Laboratory5, University of California, Berkeley6, University of California, Santa Barbara7, California Institute of Technology8, University of Rome Tor Vergata9, University of Oxford10, Collège de France11, ENEA12, Cardiff University13, University of Massachusetts Amherst14
TL;DR: The first images of resolved structure in the microwave background anisotropies over a significant part of the sky are reported, consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.
Abstract: The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73 K cosmic microwave background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the Universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole l_(peak) = (197 ± 6), with an amplitude ΔT_(200) = (69 ± 8) µK. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary models.
2,579 citations
TL;DR: In this article, a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe was proposed.
Abstract: We propose a cosmological scenario in which the hot big bang universe is produced by the collision of a brane in the bulk space with a bounding orbifold plane, beginning from an otherwise cold, vacuous, static universe. The model addresses the cosmological horizon, flatness and monopole problems and generates a nearly scale-invariant spectrum of density perturbations without invoking superluminal expansion (inflation). The scenario relies, instead, on physical phenomena that arise naturally in theories based on extra dimensions and branes. As an example, we present our scenario predominantly within the context of heterotic M theory. A prediction that distinguishes this scenario from standard inflationary cosmology is a strongly blue gravitational wave spectrum, which has consequences for microwave background polarization experiments and gravitational wave detectors.
1,959 citations
TL;DR: In this article, a cyclic model of the universe is proposed based on concepts drawn from the ekpyrotic scenario and M theory, and the universe undergoes an endless sequence of cosmic epochs.
Abstract: Based on concepts drawn from the ekpyrotic scenario and M theory, we elaborate our recent proposal of a cyclic model of the universe. In this model, the universe undergoes an endless sequence of cosmic epochs which begin with the universe expanding from a ``big bang'' and end with the universe contracting to a ``big crunch.'' Matching from ``big crunch'' to ``big bang'' is performed according to the prescription recently proposed with Khoury, Ovrut and Seiberg. The expansion part of the cycle includes a period of radiation and matter domination followed by an extended period of cosmic acceleration at low energies. The cosmic acceleration is crucial in establishing the flat and vacuous initial conditions required for ekpyrosis and for removing the entropy, black holes, and other debris produced in the preceding cycle. By restoring the universe to the same vacuum state before each big crunch, the acceleration ensures that the cycle can repeat and that the cyclic solution is an attractor.
991 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 8 |
| 2024 | 6 |
| 2023 | 14 |
| 2022 | 48 |
| 2021 | 4 |
| 2020 | 12 |