Astronomy

We review properties of theories for the variation of the gravitation and fine structure 'constants'. We highlight some general features of the cosmological models that exist in these theories with reference to recent quasar data that are consistent with time-variation in the fine structure 'constant' since a redshift of 3.5. The behaviour of a simple class of varying-alpha cosmologies is outlined in the light of all the observational constraints.

The classic simulation

a joint Fermilab/SLAC publication

The University of Arizona is honored to be the first public university to lead a mission to Mars. The Phoenix Mars Mission, scheduled to land May 25, 2008, is the first in NASA's "Scout Program." Scouts are designed to be highly innovative and relatively low-cost complements to major missions being planned as part of the agency's Mars Exploration Program.

The basic laws of physics work equally well forward or backward in time, yet we perceive time to move in one direction only-toward the future. Why?

For 25 years, the ADC was a key center for published astronomy data, catalogs, and journal tables. The ADC made these data sets computer readable and developed new methods, tools, and techniques for their preparation and use.

The CDS Service for astronomical Catalogues

Now, new images from NASA's Spitzer Space Telescope are shedding light on the true structure of the Milky Way, revealing that it has just two major arms of stars instead of the four it was previously thought to possess.

Measurements of temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe. In contrast, a multi-field inflationary theory, the curvaton model, can produce this power asymmetry without violating the homogeneity constraint. The mechanism requires the introduction of a large-amplitude superhorizon perturbation to the curvaton field, possibly a pre-inflationary remnant or a superhorizon curvaton-web structure. The model makes several predictions, including non-Gaussianity and modifications to the inflationary consistency relation, that will be tested with forthcoming CMB experiments.