Topic

# Universe

About: Universe is a research topic. Over the lifetime, 22699 publications have been published within this topic receiving 619559 citations. The topic is also known as: cosmos & space.

##### Papers published on a yearly basis

##### Papers

More filters

01 Jan 1998

TL;DR: The spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 � z � 0.62 were presented in this paper.

Abstract: We present spectral and photometric observations of 10 type Ia supernovae (SNe Ia) in the redshift range 0.16 � z � 0.62. The luminosity distances of these objects are determined by methods that employ relations between SN Ia luminosity and light curve shape. Combined with previous data from our High-Z Supernova Search Team (Garnavich et al. 1998; Schmidt et al. 1998) and Riess et al. (1998a), this expanded set of 16 high-redshift supernovae and a set of 34 nearby supernovae are used to place constraints on the following cosmological parameters: the Hubble constant (H0), the mass density (M), the cosmological constant (i.e., the vacuum energy density, �), the deceleration parameter (q0), and the dynamical age of the Universe (t0). The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (M = 0.2) Universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., � > 0) and a current acceleration of the expansion (i.e., q0 < 0). With no prior constraint on mass density other than M � 0, the spectroscopically confirmed SNe Ia are statistically consistent with q0 < 0 at the 2.8�

11,197 citations

•

[...]

01 Jan 1990

TL;DR: In this article, the Robertson-Walker Metric is used to measure the radius of the Planck Epoch in the expanding universe, which is a measure of the number of atoms in the universe.

Abstract: * Editors Foreword * The Universe Observed * Robertson-Walker Metric * Standard Cosmology * Big-Bang Nucleosynthesis * Thermodynamics in the Expanding Universe * Baryogenesis * Phase Transitions * Inflation * Structure Formation * Axions * Toward the Planck Epoch * Finale

6,319 citations

••

TL;DR: In this article, the treatment of first-order phase transitions for standard grand unified theories is shown to break down for models with radiatively induced spontaneous symmetry breaking, leading to an explanation of the cosmological homogeneity, flatness, and monopole puzzles.

Abstract: The treatment of first-order phase transitions for standard grand unified theories is shown to break down for models with radiatively induced spontaneous symmetry breaking. It is argued that proper analysis of these transitions which would take place in the early history of the universe can lead to an explanation of the cosmological homogeneity, flatness, and monopole puzzles.

4,298 citations

01 Jan 1980

TL;DR: Peebles as discussed by the authors argues that the evolution of the early universe went from a nearly uniform initial state to a progressively more irregular and clumpy universe, based on the largest known structures of the universe.

Abstract: Opinions on the large-scale structure of the early universe range widely from primeval chaos to a well-ordered mass distribution. P.J.E. Peebles argues that the evolution proceeded from a nearly uniform initial state to a progressively more irregular and clumpy universe. The discussion centers on the largest known structures, the clusters of galaxies, the empirical evidence of the nature of the clustering, and the theories of how the clustering evolves in an expanding universe. In Chapter One the author provides an historical introduction to the subject. Chapter Two contains a survey of methods used to deal with the Newtonian approximation to the theory of the evolution of the mass distribution. Recent progress in the use of statistical measures of the clustering is described in Chapter Three. Chapters Four and Five return to techniques for dealing with cosmic evolution, in the statistical measures of clustering and under general relativity theory. Lastly, in Chapter Six Professor Peebles assesses the progress in attempts to link theory and observation to arrive at a well established physical picture of the nature and evolution of the universe.

4,288 citations

••

Abstract: We present full sky microwave maps in five bands (23 to 94 GHz) from the WMAP first year sky survey. Calibration errors are 1 per mode to l=658. The temperature-polarization cross-power spectrum reveals both acoustic features and a large angle correlation from reionization. The optical depth of reionization is 0.17 +/- 0.04, which implies a reionization epoch of 180+220-80 Myr (95% CL) after the Big Bang at a redshift of 20+10-9 (95% CL) for a range of ionization scenarios. This early reionization is incompatible with the presence of a significant warm dark matter density. The age of the best-fit universe is 13.7 +/- 0.2 Gyr old. Decoupling was 379+8-7 kyr after the Big Bang at a redshift of 1089 +/- 1. The thickness of the decoupling surface was dz=195 +/- 2. The matter density is Omega_m h^2 = 0.135 +0.008 -0.009, the baryon density is Omega_b h^2 = 0.0224 +/- 0.0009, and the total mass-energy of the universe is Omega_tot = 1.02 +/- 0.02. The spectral index of scalar fluctuations is fit as n_s = 0.93 +/- 0.03 at wavenumber k_0 = 0.05 Mpc^-1, with a running index slope of dn_s/d ln k = -0.031 +0.016 -0.018 in the best-fit model. This flat universe model is composed of 4.4% baryons, 22% dark matter and 73% dark energy. The dark energy equation of state is limited to w<-0.78 (95% CL). Inflation theory is supported with n_s~1, Omega_tot~1, Gaussian random phases of the CMB anisotropy, and superhorizon fluctuations. An admixture of isocurvature modes does not improve the fit. The tensor-to-scalar ratio is r(k_0=0.002 Mpc^-1)<0.90 (95% CL).

3,868 citations