Cosmic Magnification;new results bolsters Einstein's idea of a 'cosmological constant.'

Our nonparametric Bayes classification algorithms enabled the first large-scale detection of cosmic magnification, an effect predicted by general relativity.

We present an 8 sigma detection of cosmic magnification measured by the variation of quasar density due to gravitational lensing by foreground large scale structure. To make this measurement we used 3800 square degrees of photometric observations from the Sloan Digital Sky Survey (SDSS) containing ~200,000 quasars and 13 million galaxies. Our measurement of the galaxy-quasar cross-correlation function exhibits the amplitude, angular dependence and change in sign as a function of the slope of the observed quasar number counts that is expected from magnification bias due to weak gravitational lensing. We show that observational uncertainties (stellar contamination, Galactic dust extinction, seeing variations and errors in the photometric redshifts) are well controlled and do not significantly affect the lensing signal. By weighting the quasars with the number count slope, we combine the cross-correlation of quasars for our full magnitude range and detect the lensing signal at > 4 sigma in all five SDSS filters. Our measurements of cosmic magnification probe scales ranging from 60 kpc/h to 10 Mpc/h and are in good agreement with theoretical predictions based on the WMAP concordance cosmology. As with galaxy-galaxy lensing, future measurements of cosmic magnification will provide useful constraints on the galaxy-mass power spectrum.

Einstein was convinced the universe was static, neither expanding nor contracting. Yet his theory of general relativity implied that gravity from all the matter in the universe should cause it to contract. So he introduced the idea of a cosmological constant, a repulsive force that canceled out the contraction. He later discarded the in large part because astronomer Edwin Hubble discovered that the universe was in fact expanding and not static.

With the discovery of dark energy in 1998 and 1999, however, the cosmological constant moved from "blunder" to a leading explanation for the universe's accelerating expansion.

Theoreticians will have to take the latest findings about dark energy's consistent behavior into account as they try to explain the nature and source of dark energy,


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