Oxford astro-ph Coffee

This looks like it might be interesting - new optical spectra and Spitzer IR data for 4 galaxies at z=2 show that the dust in these systems is rather different than in the local universe. The high magnification provided gravitational lenses arranged in front of them helped a lot!

Well, alright it just looks like SMC dust instead of MW dust but still, cool that we can measure it in galaxies at z=2!

A long paper on measures in Cosmology, which I haven't read in its entireity yet. However, I found the final comment in the abstract quite provocative and interesting: "In a universe where the second law of thermodynamics holds, one cannot make use of our knowledge of the present state of the universe to "retrodict" the likelihood of past conditions." This is due to laws being time symmetric, while in practice we have the second law. In practice we *must* resort to Occam's razor and/or beauty arguments. Later: "if one wishes to make an argument in favor of inflation having occurred in the early universe, this argument must be based upon its being a simple and/or elegant hypothesis that accounts for observed phenomena. Any argument about the "likelihood" of inflation based upon the Liouville (or other) measure on phase space will require a justification for the use of this measure." Sometimes, beauty and Occam's razor are incompatible, or rather scale dependent (as in the case of the string landscape), and from a purely philosophical point of view I don't feel entriely comfortable with either being used as a criterion of truth when trying to discover things about the universe. However, this paper makes this seem inevitable. Certainly food for thought.

"We argue using simple models that all successful practical uses of probabilities originate in quantum fluctuations in the microscopic physical world around us, often propagated to macroscopic scales. Thus we claim there is no physically verified fully classical theory of probability. We comment on the general implications of this view, and specifically question the application of classical probability theory to cosmology in cases where key questions are known to have no quantum answer."

Discovery of a group of quasars which appear to form a structure over 1 Gpc across. This is much larger than any previously-suggested homogeneity scale in LambdaCDM.

Modern MCMC method for cosmological parameter estimation. "While Metropolis-Hastings is constrained by overheads, CosmoHammer is able to accelerate the sampling process from a wall time of 30 hours on a single machine to 16 minutes by the efficient use of 2048 cores. Such short wall times for complex data sets opens possibilities for extensive model testing and control of systematics."

Perhaps an ACT team member could give us a verdict on this?

There's been a growing awareness that the 'free' functions used to parameterise modified gravity aren't really as arbitrary as one might first think. This methods paper suggests how to use these ideas - although the forecast isn't all that encouraging. Still, the proof of the pudding is yet to come.

I'll let Phil do the talking on this one!