arXiv subjects
Publications and source records attributed to Charles H. Lineweaver.
This article briefly summarizes the increasingly precise observational estimates of the cosmological parameters. After three years on the stump, the Lambda-CDM model is still the leading candidate. Although the Universe is expanding, our picture of it is coming together.
I attempt to piece together a consistent scenario based on current estimates of the evolution of the star formation rate of the Universe, the metallicity evolution of the star-forming regions of the Universe and the most recent observations of extrasolar planets. The precision of all of these data sets is improving rapidly, but they can already be combined to yield an estimate of the age distribution of earth-like planets in the Universe (Lineweaver 2001, astro-ph/0012399).
Planets like the Earth cannot form unless elements heavier than helium are available. These heavy elements, or `metals', were not produced in the big bang. They result from fusion inside stars and have been gradually building up over the lifetime of the Universe. Recent observations indicate that the presence of giant extrasolar planets at small distances from their host stars, is strongly correlated with high metallicity of the host stars. The presence of these close-orbiting giants is incompatible with the existence of earth-like planets. Thus, there may be a Goldilocks selection effect: with too little metallicity, earths are unable to form for lack of material, with too much metallicity giant planets destroy earths. Here I quantify these effects and obtain the probability, as a function of metallicity, for a stellar system to harbour an earth-like planet. I combine this probability with current estimates of the star formation rate and of the gradual build up of metals in the Universe to obtain an estimate of the age distribution of earth-like planets in the Universe. The analysis done here indicates that three quarters of the earth-like planets in the Universe are older than the Earth and that their average age is 1.8 +/- 0.9 billion years older than the Earth. If life forms readily on earth-like planets - as suggested by the rapid appearance of life on Earth - this analysis gives us an age distribution for life on such planets and a rare clue about how we compare to other life which may inhabit the Universe.
Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D=c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally.
I present a series of diagrams which illustrate why the cosmic microwave background (CMB) data favor certain values for the cosmological parameters. Various methods to extract these parameters from CMB and non-CMB observations are forming an ever-tightening network of interlocking constraints. I review the increasingly precise constraints in the Omega_m - Omega_Lambda plane and show why more cosmologists now prefer Lambda-CDM cosmologies to any other leading model.
The age of the universe in the Big Bang model can be calculated from three parameters: Hubble's constant, h; the mass density of the universe, Omega_m; and the cosmological constant, Omega_lambda. Recent observations of the cosmic microwave background and six other cosmological measurements reduce the uncertainty in these three parameters, yielding an age for the universe of 13.4 +/- 1.6 billion years, which is a billion years younger than other recent age estimates. A different standard Big Bang model, which includes cold dark matter with a cosmological constant, provides a consistent and absolutely time-calibrated evolutionary sequence for the universe.
For the past 15 years most astronomers have assumed that 95% of the Universe was in some mysterious form of cold dark matter. They also assumed that the cosmological constant, Omega_Lambda, was Einstein's biggest blunder and could be ignored. However, recent measurements of the cosmic microwave background combined with other cosmological observations strongly suggest that 75% of the Universe is made of cosmological constant (vacuum energy), while only 20% is made of non-baryonic cold dark matter. Normal baryonic matter, the stuff most physicists study, makes up about 5% of the Universe. If these results are correct, an unknown 75% of the Universe has been identified. Estimates of the age of the Universe depend upon what it is made of. Thus, our new inventory gives us a new age for the Universe: 13.4 +/- 1.6 Gyr.
The details of the CMB power spectrum are being revealed through the combined efforts of the world's CMBologists. The current data set constrains several cosmological parameters. A combination with other (non-lensing) constraints yields estimates of the cosmological constant: Omega_Lambda = 0.65 +/- 0.13, the mass density: Omega_m = 0.23 +/- 0.08 and the age of the Universe: t_o = 13.4 +/- 1.6 Gyr. Lensing data is not yet comfortable with these values.
Recent cosmic microwave background measurements combined with recent supernovae limits and other observational data have ambushed Omega_lambda and Omega_m. These cosmological culprits are trapped in a small pocket of parameter space: Omega_lambda = 0.62 +/- 0.16 and Omega_m = 0.24 +/- 0.10. If this is correct then an unknown 2/3 of the Universe has been identified.
I use the most recent cosmic microwave background (CMB) anisotropy measurements to constrain the leading cold dark matter models in the Omega_m - Omega_lambda plane. A narrow triangular region is preferred. This triangle is elongated in such a way that its intersection with even conservative versions of recent supernovae, cluster mass-to-light ratios and double radio source constraints, is small and provides the current best limits in the Omega_m - Omega_lambda plane: Omega_lambda = 0.62 +/- 0.16 and Omega_m = 0.24 +/- 0.10. This complementarity between CMB and other observations rules out Omega_lambda = 0 models at more than the 99% confidence level.
I present several simple figures to illustrate cosmology and structure formation in a nutshell. Then I discuss the following argument: if we assume that Omega_{Lambda} = 0 then the CMB results favor high Omega_{m} while the supernova results favor low Omega_{m}. This large inconsistency is strong evidence for the incorrectness of the Omega_{Lambda} = 0 assumption. Finally I discuss recent CMB results on the slope and normalization of the primordial power spectrum.
We use a combination of the most recent cosmic microwave background (CMB) flat -band power measurements to place constraints on Hubble's constant h and the total density of the Universe Omega_o in the context of inflation-based cold dark matter (CDM) models with no cosmological constant. We use chisquared minimization to explore the 4-dimensional parameter space having as free parameters, h, Omega_o, the power spectrum slope n and the power spectrum normalization at L=10. Conditioning on Omega_o=1 we obtain h=0.33 +/- 0.08. Allowing Omega_o to be a free parameter reduces the ability of the CMB data to constrain h and we obtain 0.26 < h < 0.97 with a best-fit value at h=0.40. We obtain Omega_o=0.85 and set a lower limit Omega_o > 0.53. A strong correlation between acceptable h and Omega_o values leads to a new constraint: Omega_o h^1/2=0.55 +/- 0.10. A favored open model with Omega_o=0.3 and h=0.70 is more than ~4 sigma from the CMB data best-fit model and is rejected at the 99% CL. High baryonic models (Omega_b h^2 ~0.026) yield the best CMB chi-squared fits and are more consistent with other cosmological constraints. The best-fit model has n=0.91^{+0.29}_{-0.09} and Q=18.0^+1.2_-1.5 uK. The amplitude and position of the dominant peak in the best-fit power spectrum are A_peak=76^+3_-7 uK and L_peak = 260^+30_-20. Unlike the Omega_o=1 case we considered previously, CMB h results are now consistent with the higher values favored by local measurements of h but only if 0.55 >~ Omega_o >~ 0.85. Using an approximate joint likelihood to combine our CMB constraint on Omegta_o h^{1/2} with other cosmological constraints we obtain h=0.58 +/- 0.11 and Omega_o=0.65^+0.16_-0.15.
The CMB is already one of the pillars of the Big Bang model. However it may also become our most powerful tool to distinguish contending models and to determine their cosmological parameters. To realize this goal, more than 20 observational groups and two new satellites are gearing up to make precise measurements of the CMB at small angular scales. In such a situation it is important to keep track of what the CMB data can already say about cosmological parameters. Current CMB data can already be used to constrain cosmological parameters. The results are model dependent. We have obtained contraints on Hubble's constant h and the density of the Universe Omega_{o} in the context of open and critical density CDM models with Lambda=0. In critical density models we obtain h=0.30^{+0.18}_{-0.07}. This low value is inconsistent with direct measurements of h but fully consistent with four other cosmological measurements: Big Bang nucleosynthesis, cluster baryonic fraction, age constraints from globular clusters and limits on the shape parameter Gamma of matter power spectra (in Omega_{o}=1 models). If Omega_{o} is left as a free parameter the constraints on h are less restrictive: h=0.40^{+0.57}_{-0.14}. This is fully consistent with local $h$ measurements and the four other cosmological measurements mentioned above. The best-fit density is Omega_{o}= 0.85 and we set an upper limit of Omega_{o} > 0.4 at ~ 95% CL. At this conference Ostriker has claimed that open-CDM models with Omega_{o} ~ 0.3 and h ~ 0.70 are compatible with all current data. However our new CMB data analysis rules this model out at more than ~ 4 sigma.
Recent cosmic microwave background (CMB) measurements over a large range of angular scales have become sensitive enough to provide interesting constraints on cosmological parameters within a restricted class of models. We use the CMB measurements to study inflation-based, cold dark matter (CDM) critical density universes. We explore the 4-dimensional parameter space having as free parameters, Hubble's constant Ho, baryonic fraction Omega_b, the spectral slope of scalar perturbations n and the power spectrum quadrupole normalization Q. We calculate chi-squared minimization values and likelihood intervals for these parameters. Within the models considered, a low value for the Hubble constant is preferred: Ho= 30^{+18}_{-7} km/s/Mpc. The baryonic fraction is not as well-constrained by the CMB data: Omega_b = 0.07^{+ 0.24}_{-0.07}. The power spectrum slope is n=0.91^{+0.20}_{-0.12}. The power spectrum normalization is Q=18 +/- 2.5 uK. The error bars on each parameter are approximately 1 sigma and are for the case where the other 3 parameters have been marginalized. If we condition on n=1 we obtain the normalization Q = 17 +/- 1.0 uK. The permitted regions of the 4-D parameter space are presented in a series of 2-D projections. In the context of the CDM critical density universes considered here, current CMB data favor a low value for the Hubble constant. Such low-Ho models are consistent with Big Bang nucleosynthesis, cluster baryonic fractions, the large-scale distribution of galaxies and the ages of globular clusters; although in disagreement with direct determinations of the Hubble constant.
In this paper we compare data to theory. We use a compilation of the most recent cosmic microwave background (CMB) measurements to constrain Hubble's constant h, the baryon fraction Omega_b, and the cosmological constant lambda. We fit h-, Omega_b- and lambda-dependent power spectra to the data. The models we consider are flat cold dark matter (CDM) dominated universes with flat (n=1) power spectra, thus the results obtained apply only to these models. CMB observations can exclude more than half of the h - Omega_b parameter space explored. The CMB data favor low values of Hubble's constant; h \approx 0.35. Low values of Omega_b are preferred (Omega_b ~ 0.03) but the chi-squared minimum is shallow and we obtain Omega_b < 0.28. A model with h \approx 0.40, Omega_b \approx 0.15 and Omega_CDM \approx 0.85 is permitted by constraints from the CMB data, BBN, cluster baryon fractions and the shape parameter Gamma derived from the mass density power spectra of galaxies and clusters. For flat-lambda models, the CMB data, combined with BBN constraints exclude most of the h - lambda plane. Models with Omega_o \approx 0.3, lambda \approx 0.7 with h \approx 0.75 are fully consistent with the CMB data but are excluded by the strict new q_{o} limits from supernovae (Perlmutter et al. 1996). A combination of CMB data goodness-of-fit statistics, BBN and supernovae constraints in the h-lambda plane, limits Hubble's constant to the interval 0.23 < h < 0.72.
The largest anisotropy in the cosmic microwave background (CMB) is the $\approx 3$ mK dipole assumed to be due to our velocity with respect to the CMB. Over the past ten years the precision of our knowledge of the dipole has increased by a factor of ten. We discuss the most recent measurement of this dipole obtained from the four year COBE Differential Microwave Radiometers (DMR) as reported by Lineweaver \etal (1996). The inferred velocity of the Local Group is $v_{LG}= 627 \pm 22$ km/s in the direction $\ell = 276°\pm 3$, $b= 30°\pm 2$. We compare this most recent measurement to a compilation of more than 30 years of dipole observations.