oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 51 )

2019 ( 539 )

2018 ( 611 )

2017 ( 632 )

Custom range...

Search Results: 1 - 10 of 366252 matches for " Michael S Turner "
All listed articles are free for downloading (OA Articles)
Page 1 /366252
Display every page Item
Inflation After COBE: Lectures on Inflationary Cosmology
Michael S. Turner
Physics , 1993,
Abstract: In these lectures I review the standard hot big-bang cosmology, emphasizing its successes, its shortcomings, and its major challenge---a detailed understanding of the formation of structure in the Universe. I then discuss the motivations for---and the fundamentals of---inflationary cosmology, particularly emphasizing the quantum origin of metric (density and gravity-wave) perturbations. Inflation addresses the shortcomings of the standard cosmology and provides the ``initial data'' for structure formation. I conclude by addressing the implications of inflation for structure formation, evaluating the various cold dark matter models in the light of the recent detection of temperature anisotropies in the cosmic background radiation by COBE. In the near term, the study of structure formation offers a powerful probe of inflation, as well as specific inflationary models.
Big-bang Nucleosynthesis: Is the Glass Half Full or Half Empty?
Michael S. Turner
Physics , 1996,
Abstract: The current state of affairs in big-bang nucleosynthesis is reviewed and controversies are discussed. The author concludes that the glass is half full.
Dark Matter and Energy in the Universe
Michael S. Turner
Physics , 1999, DOI: 10.1238/Physica.Topical.085a00210
Abstract: For the first time, we have a plausible and complete accounting of matter and energy in the Universe. Expressed a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, between 0.3% and 0.6%; baryons (total), 5% +/- 0.5%; matter (total), 40% +/- 10%; smooth, dark energy, 80% +/- 20%; totaling to the critical density (within the errors). This accounting is consistent with the inflationary prediction of a flat Universe and defines three dark-matter problems: Where are the dark baryons? What is the nonbaryonic dark matter? What is the nature of the dark energy? The leading candidate for the (optically) dark baryons is diffuse hot gas; the leading candidates for the nonbaryonic dark matter are slowly moving elementary particles left over from the earliest moments (cold dark matter), such as axions or neutralinos; the leading candidates for the dark energy involve fundamental physics and include a cosmological constant (vacuum energy), a rolling scalar field (quintessence), and a network of light, frustrated topological defects.
Cosmological Parameters
Michael S. Turner
Physics , 1999, DOI: 10.1063/1.59381
Abstract: The discussion of cosmological parameters used to be a source of embarrassment to cosmologists. Today, measurements of the cosmological parameters are leading the way into the era of precision cosmology. The CMB temperature is measured to four significant figures, T_0=2.7277+/-0.002 K; the Hubble constant is now determined with a reliable error estimate, H_0=(65+/-5) km sec^-1 Mpc^-1; the mass density of baryons is precisely determined by big-bang nucleosynthesis Omega_B = (0.019+/-0.001) h^-2; and the age of the Universe inferred from the ages of the oldest stars is 14+/-1.5 Gyr, which is consistent the expansion age. Further, we have the first full accounting of matter and energy in the Universe, complete with a self consistency check. Expressed as a fraction of the critical density it goes like this: neutrinos, between 0.3% and 15%; stars, between 0.3% and 0.6%; baryons (total), 5+/-0.5%; matter (total),40% +/- 10%; smooth, dark energy, 80% +/- 20%; totaling to the critical density (within the errors).
Why Cosmologists Believe the Universe is Accelerating
Michael S. Turner
Physics , 1999,
Abstract: Theoretical cosmologists were quick to be convinced by the evidence presented in 1998 for the accelerating Universe. I explain how this remarkable discovery was the missing piece in the grand cosmological puzzle. When found, it fit perfectly. For cosmologists, this added extra weight to the strong evidence of the SN Ia measurements themselves, making the result all the more believable.
Cosmology Update 1998
Michael S. Turner
Physics , 1999,
Abstract: For two decades the hot big-bang model has been referred to as the standard cosmology -- and for good reason. For just as long cosmologists have known that there are fundamental questions that are not addressed by the standard cosmology and point to a grander theory. The best candidate for that grander theory is inflation + cold dark matter. It holds that the Universe is flat, that slowly moving elementary particles left over from the earliest moments provide the cosmic infrastructure, and that the primeval density inhomogeneities that seed all large-scale structure arose from quantum fluctuations. There is now prima facie evidence that supports two basic tenets of this paradigm, and an avalanche of high-quality cosmological observations will soon make this case stronger or will break it. Key questions remain to be answered; foremost among them are: identification and detection of the cold dark matter particles and elucidation of the mysterious dark-energy component. These are exciting times in cosmology!
The Meaning of Eros/Macho
Michael S. Turner
Physics , 1993,
Abstract: Most of the mass density in the Universe---and in the halo of our own galaxy---exists in the form of dark matter. Overall, the contribution of luminous matter (in stars) to the mass density of the Universe is less than 1\%; primordial nucleosynthesis indicates that baryons contribute between 1\% and 10\% of the critical density ($0.01h^{-2}\la \Omega_B\la 0.02h^{-2}$; $h=$ the Hubble constant in units of $100\kms\Mpc^{-1}$); and other evidence indicates that the total mass density is at least 10\% of critical density, and likely much greater. If the universal density is as low as 10\% of the critical density there may be but one kind of dark matter. More likely, the universal density is greater than 10\%, and there are two kinds of dark matter, and thus two dark matter problems: In what form does the baryonic dark matter exist? and In what form does the nonbaryonic dark matter exist? The MACHO and EROS collaborations have presented evidence for the microlensing of stars in the LMC by $10^{-1\pm 1}M_\odot$ dark objects in the halo of our own galaxy and may well have solved {\it one} of the dark matter puzzles by identifying the form of the baryonic dark matter.
The Hot Big Bang and Beyond
Michael S. Turner
Physics , 1995, DOI: 10.1063/1.48810
Abstract: The hot big-bang cosmology provides a reliable accounting of the Universe from about $10^{-2}\sec$ after the bang until the present, as well as a robust framework for speculating back to times as early as $10^{-43}\sec$. 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 $10^{-32}\sec$ 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 $30\kms\Mpc^{-1}$), 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.
Detectability of inflation-produced gravitational waves
Michael S. Turner
Physics , 1996, DOI: 10.1103/PhysRevD.55.R435
Abstract: Detection of the gravitational waves excited during inflation as quantum mechanical fluctuations is a key test of inflation and crucial to learning about the specifics of the inflationary model. We discuss the potential of Cosmic Background Radiation (CBR) anisotropy and polarization and of laser interferometers such as LIGO, VIRGO/GEO and LISA to detect these gravity waves.
Cosmology
Michael S. Turner
Physics , 1997, DOI: 10.1016/S0920-5632(97)00448-9
Abstract: Cosmology is very exciting for three reasons. There is a very successful standard model - the hot big bang - which describes the evolution of the Universe from 10^{-2} sec onward. There are bold ideas, foremost among them are inflation and cold dark matter, which can extend the standard cosmology to within 10^{-32} sec of the bang and address some of the most fundamental questions in cosmology. There is a flood of data - from determinations of the Hubble constant to measurements of CBR anisotropy - that are testing inflation and cold dark matter.
Page 1 /366252
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.