�ber die M�glichkeit einer Welt mit konstanter negativer Kr�mmung des Raumes

Friedmann, Alexander

doi:10.1007/bf01328280

Cited by 621 publications

(437 citation statements)

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“…A lack of structure on the largest scales in maps of CMB temperature fluctuations would be a hint that the comoving spatial section of the Universe is multiply connected (de Sitter 1917;Friedmann 1923Friedmann , 1924Lemaître 1931;Robertson 1935) and that its size may have been detected (Starobinsky 1993;Stevens et al 1993). The WMAP observations have confirmed that the large-scale CMB signal analysed either as a quadrupole signal or as a two-point autocorrelation function signal is weak (Spergel et al 2003;Copi et al 2007Copi et al , 2009).…”

Section: Introductionmentioning

confidence: 98%

On the suspected timing error in Wilkinson microwave anisotropy probe map-making

Roukema

2010

A&A

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Context. It has recently been suggested that the compilation of the calibrated time-ordered-data (TOD) of the Wilkinson Microwave Anisotropy Probe (WMAP) observations of the cosmic microwave background (CMB) into full-year or multi-year maps may have been carried out with a small timing interpolation error. A large fraction of the previously estimated WMAP CMB quadrupole signal would be an artefact of incorrect Doppler dipole subtraction if this hypothesis were correct. Aims. Since observations of bright foreground objects constitute part of the TOD, these can be used to test the hypothesis. Methods. Scans of an object in different directions should be shifted by the would-be timing error, causing a blurring effect. For each of several different timing offsets, three half-years of the calibrated, filtered WMAP TOD are compiled individually for the four W band differencing assemblies (DA's), with no masking of bright objects, giving 12 maps for each timing offset. Percentiles of the temperature-fluctuation distribution in each map at HEALPix resolution N side = 2048 are used to determine the dependence of all-sky image sharpness on the timing offset. The Q and V bands are also considered. Results. In the W band, which is the band with the shortest exposure times, the 99.999% percentile, i.e. the temperature fluctuation in the ≈503-rd brightest pixel, is the least noisy percentile as a function of timing offset. Using this statistic, the hypothesis that a −25.6 ms offset relative to the timing adopted by the WMAP collaboration gives a focus at least as sharp as the uncorrected timing is rejected at 4.6σ significance, assuming Gaussian errors and statistical independence between the maps of the 12 DA/observing period combinations. The Q and V band maps also reject the −25.6 ms offset hypothesis at high statistical significance. Conclusions. The requirement that the correct choice of timing offset must maximise image sharpness implies that the hypothesis of a timing error in the WMAP collaboration's compilation of the WMAP calibrated, filtered TOD is rejected at high statistical significance in each of the Q, V and W wavebands. However, the hypothesis that a timing error was applied during calibration of the raw TOD, leading to a dipole-induced difference signal, is not excluded by this method.

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Section: Introductionmentioning

confidence: 98%

On the suspected timing error in Wilkinson microwave anisotropy probe map-making

Roukema

2010

A&A

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“…It represents one of the alternatives offered by Friedmann (1922Friedmann ( , 1924, whose analysis suggested that Einstein"s general relativity theory (GR) allows for expanding as well as for contracting universes, but not for a static one, unless a well-tuned repulsive cosmological constant (Λ) is introduced. Einstein"s own model (1917) relied on such a constant, which Einstein had introduced reluctantly, since it does not reflect anything known from physics.…”

Section: Introductionmentioning

confidence: 99%

From magnitudes and redshifts of supernovae, their light-curves, and angular sizes of galaxies to a tenable cosmology

Traunmüller

2014

Astrophys Space Sci

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Early physical cosmologies were based on interpretations of the cosmic redshift for which there was insufficient evidence and on theories of gravitation that appear to be falsified by galactic dynamics. Eventually, the big bang paradigm came to be guarded against refutation by ad hoc hypotheses (dark matter, cosmic inflation, dark energy) and free parameters. Presently available data allow a more satisfactory phenomenological approach. Using data on magnitude and redshift from 892 type Ia supernovae, it is first shown that these suggest that the redshift factor (1 + z) is simply an exponential function of distance and that, for "standard candles", magnitude m = 5 log[(1 + z) ln(1 + z)] + const. While these functions are incompatible with a big bang, they characterize certain tired light models as well as exponential expansion models. However, the former are falsified by the stretched light curves of distant supernovae and the latter by the absence of a predicted 1+z increase in the angular sizes of galaxies. Instead, the observations suggest that physical processes speed up and objects contract uniformly as an exponential function of time, standards of measurement not excluded, and only free waves being excepted. Distant events proceed, then, more slowly, while angular sizes remain unaffected, approximately as observed. Since all objects contract in proportion, the Universe retains a static appearance. A corresponding physical theory, which should also explain galactic dynamics, remains yet to be derived from first principles. A way to do this, satisfying also Mach"s principle, is vaguely suggested.

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“…Shortly before this, de Sitter (1917) had shown that in presence of Λ the solution for an empty space describes an exponential expansion. Friedmann (1922Friedmann ( , 1924 was the first to obtain exact solutions for the expanding universe that contained matter in presence of the cosmological constant Λ. Another exact solution for the metric in presence of Λ, around the gravitating point mass, was obtained by Carter (1973).…”

Section: Newtonian Approximation In Description Of Dementioning

confidence: 99%

Galaxy clusters in presence of dark energy: a kinetic approach

Merafina

Бисноватый-Коган

Donnari

2014

A&A

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Context. The external regions of galaxy clusters may be under strong influence of the dark energy, which was discovered by observations of supernovae Ia at redshift z < 1. The presence of the dark energy in the gravitational equilibrium equation, with the Einstein Λ term, balances the gravity, and extends the equilibrium configuration more in radius. Aims. We investigate the features of the equilibrium configurations to analyse how the presence of the dark energy affects the density profiles and radial extension by specifying the conditions for which the gravitational equilibrium begins. Methods. We derived the kinetic equation for an equilibrium configuration in presence of dark energy and solved the gravitational equilibrium equation by considering a Maxwell-Boltzmann distribution function with a cut-off in the framework of the Newtonian regime, because the observed velocities of galaxies inside a cluster are much lower than the velocity of light.Results. The prevalence of dark energy effects on the gravity shows a wide region in the W 0 -ρ Λ diagram where equilibrium solutions are not possible. In these particular conditions, the galaxies located in the external regions of a cluster can flow out, following the accelerating expansion of the Universe.

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�ber die M�glichkeit einer Welt mit konstanter negativer Kr�mmung des Raumes

Cited by 621 publications

References 0 publications

On the suspected timing error in Wilkinson microwave anisotropy probe map-making

On the suspected timing error in Wilkinson microwave anisotropy probe map-making

From magnitudes and redshifts of supernovae, their light-curves, and angular sizes of galaxies to a tenable cosmology

Galaxy clusters in presence of dark energy: a kinetic approach

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