http://xxx.lanl.gov/PS_cache/arxiv/p...803.3836v1.pdf

TEMPERATURE DIFFERENCES IN THE CEPHEID INSTABILITY STRIP REQUIRE DIFFERENCES IN THE PERIOD-LUMINOSITY RELATION IN SLOPE AND ZERO POINT

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jwj

If you always believe what you already know, you can't learn anything - Liz

This is an interesting paper. I'd like to point out that Sandage is part of the Arp team, and while that doesn't disqualify the paper and its conclusions by itself, it does mean that the paper should be read carefully noting that they are looking for cracks in mainstream cosmology, and sometimes post things they claim are trends by prove to be anomalies.

I haven't seen an obvious flaw in this paper yet, but I've only skimmed it. Thanks to Jerry for bringing it to our attention.

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Forming opinions as we speak

What??!?!! Sandage is a friend of Arp, but scientifically they could scarcely be further apart on almost any issue of cosmological significance (for decades, Sandage's work defined what was mainstream in observational cosmology). These days, Sandage apparently feels his legacy is ignored simply because the Hubble Key Project team made different (and to his mind inferior) choices of how to handle a number of effects in data analysis, leading to a different (and to his mind quite wrong) value of H0.

It was in Pasadena that a colleague claimed to have seen a bumper sticker saying HONK IF YOU THINK THEY"RE COSMOLOGICAL.

Ya, according to Keel, Sandage eventually caved in and accepted a higher HO value - but not completely. It is interesting that the metallicity-corrected Cepheid HO values are closer to Sandages.

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jwj

If you always believe what you already know, you can't learn anything - Liz

Not altogether too surprising. All the "standard" candles have some uniformity issues.Subtle differences in metallicities affecting P-L slopes. Doesn't look like it will be earth shattering, though, just some tweaking of parameters.
Like supernovae, this is not necessarily a homogeneous population of objects, but rather a population of similar objects. I appreciate Sandage & Tammann's candor though. Nice work by a couple of pros. Pete.

edit: on second thought, if it weakens the distance scale....the need for dark matter might soften/or strengthen quite a bit. This might be much more interesting than my cursory inspection. I'll leave it to the distance-scale pros to sort it out though.

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A third rate theory forbids
A second rate theory explains after the fact
A first rate theory predicts...A. Lomonosov

The place it makes the biggest difference, is in the interpretation of the WMAP results. WMAP 5 year data tightens the age of the universe to a specific, narrow range; but if and only if the HKP HO value is spot on. Tweaking is always permissable, but never desireable.

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jwj

If you always believe what you already know, you can't learn anything - Liz

Absolutely, Arp and Sandage strongly and spiritedly disagree where intrinsic redshifts are concerned.

Sandage attributes too much effect to Malmquist bias. He argues that the larger value favored by the HKP results from their failure to properly account for bias at multiple stages in their analysis. For example, he claims that the Tully-Fisher relation has an intrinsic scatter on the order of +/0.70 mag. If the intrinsic TFR scatter was that large, then Malmquist bias would be a serious issue. However the observed TFR scatter from cluster templates is typically ~+/-0.30 mag with liberal selection criteria. If one tightens the criteria by eliminating the slower rotators known to have larger intrinsic TFR scatter, the observed TFR scatter becomes even smaller. Sandage's argument that intrinsic TFR scatter is about +/- 0.70 mag is just not supported by the data from cluster samples.

His Cepheid distance scale also relies upon a slope much steeper than what most others have found.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Sandage seems to have split the difference. In the late 80's and early 90's he was advocating H0=50. Lately he finds H0=~62, so he's accepting a higher value, but still not where the HKP is at.

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"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Here's an interesting paper (http://arxiv.org/abs/0803.4015v1) whose authors describe the use of gravitationally lensed quasars to measure the value of the Hubble constant. Their technique is independent of Sandage, HKP, and WMAP. The value they measure for Ho is:

"Our estimate of H0 agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H0 = 67 +13−10 km s−1 Mpc−1, while the Single Isothermal Sphere model yields H0 = 63 +7−3 km s−1 Mpc−1(68% confidence level)."

In other words, their analysis puts Ho in between the Sandage value and the HKP value.

I like the gist of the Sandage et al paper that Jerry mentioned, as it pin-points uncertainties/limitations to Cepheid-based measurements of Ho. You have to first admit there is a problem before you can take steps to improve your situation. However, the fact that several different methods (including the SZ effect) are now giving us roughly similar values for Ho (60-80) shows that there has been undeniable progress in this area of observational astronomy and we seem to be at least closing in on the "true value" of Ho. Now, what would really be nice, will be if gravitational waves are detected and then used to (i) most importantly, independently confirm that the Universe is expanding, and (ii) measure Ho to a couple percent precision. Gravitational waves, unlike light, are not effected by as many contaminating factors (extinction, reddening, etc).

Caution! Before everyone gets too excited about my last point, note what a scientist involved in one of the gravitational wave experiments recently said about gravitational wave detection (from http://www.wired.com/science/space/n...tional_waves):

"And now LIGO scientists have begun searching their data for this gravitational wave signature. If scientists continue to detect nothing, however, Einstein's theories may well need modifying.

"If we don't see anything in four years," Foffa said, "then it will be the time to start questioning."

Aren't scientists alway supposed to question? We should wait another three years? Nobody ever tells me anything!

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jwj

If you always believe what you already know, you can't learn anything - Liz

As long as it is with real questions.

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Forming opinions as we speak

Yes, the scientists are questioning...They are questioning whether or not gravitational waves exist just by looking for them! If they find them the payoff will be huge. If they don't, it will still be progress.