Archive for June 2, 2020

Cristo Redentor – Donald Byrd

Posted in Jazz with tags , on June 2, 2020 by telescoper

Duke Pearson was inspired by the famous statue that looks down over Rio de Janeiro to write this tune, of which this is the very first version, put on record in 1963 and released a year later in 1964 to become an instant classic. It’s a wonderful fusion of jazz, blues and gospel music but above all it’s a gentle hymn to peace and respect.I don’t think I have to explain why I think it’s apt to put it up today.

Front and centre is Donald Byrd on trumpet, but the rest of the band includes Hank Mobley (tenor), Herbie Hancock (piano), Donald Best (vibes), Kenny Burrell (guitar), Butch Warren (bass) and Lex Humphries (drums). The choir consists of 8 voices (4 male, four female) but sadly they are not named on the liner notes.


Cosmology Talks – Colin Hill on Early Dark Energy

Posted in The Universe and Stuff with tags , , , , , on June 2, 2020 by telescoper

Here is another one of those Cosmology Talks curated on YouTube by Shaun Hotchkiss.

In the talk, Colin Hill explains how even though early dark energy can alleviate the Hubble tension, it does so at the expense of increasing other tension. Early dark energy can raise the predicted expansion rate inferred from the cosmic microwave background (CMB), by changing the sound horizon at the last scattering surface. However, the early dark energy also suppresses the growth of perturbations that are within the horizon while it is active. This mean that, in order to fit the CMB power spectrum the matter density must increase (and the spectral index becomes more blue tilted) and the amplitude of the matter power spectrum should get bigger. In their paper, Colin and his coauthors show that this affects the weak lensing measurements by DES, KiDS and HSC, so that including those experiments in a full data analysis makes things discordant again. The Hubble parameter is pulled back down, restoring most of the tension between local and CMB measurements of H0, and the tension in S_8 gets magnified by the increased mismatch in the predicted and measured matter power spectrum.

The overall moral of this story is the current cosmological models are so heavily constrained by the data that a relatively simple fix in one one part of the model space tends to cause problems elsewhere. It’s a bit like one of those puzzles in which you have to arrange all the pieces in a magic square but every time you move one bit you mess up the others.

The paper that accompanies this talk can be found here.

And here’s my long-running poll about the Hubble tension: