A healthy dose of scepticism or a humbug?

Boud Roukema boud w astro.uni.torun.pl
Czw, 9 Sty 2003, 15:21:50 CET


"Healthy skepticism of humbug?"

"humbug" is definitely unfair. Alain is a cool guy and a sincere
scientist. Narlikar, Burbidge (and the late Hoyle) are (was) good
scientists, and they are (was) right to criticise the monothink
(pensée unique) and the fashion of talking about cosmology in a way
which seems simple but in fact is misleading regarding what we have
really measured.

I hope Alain has enough stamina to keep struggling for his favorite
model of  Omega_m \approx 1 as long as Narlikar, Burbidge and Hoyle
have struggled in favour of their model. But just as they brought out
the quasi-steady state model, I guess Alain will come up with the
quasi-Omega_m=1 model... ;)

I'm happy to see that on page 4, Alain has taken notice of my
repeated insistence that approximately flat is not exactly flat,
and that the present results can be approximately expressed as:

R_C = c/ [H_0 (|Omega_total - 1|)^1/2] > R_Horiz \approx 10h^-1 Gpc

or more vaguely as R_C > c/H_0 .

The footnote "a" is rather poorly written - the FLRW model is a
mathematical model. It is still true in cosmology that space is either
flat or it is not flat, the mathematics is still correct.

But saying "nearly flat" is a good habit - it's simply honest. Just as
the Earth has a nearly flat surface, the Universe seems to be nearly flat.

Still on the philosophy of science aspect, I should remind people that
it's rather inconsistent of Alain to insist on empirical measurements
when he considers empirical measurements of the global cosmological
parameters to be a low priority.

However, it remains that to ignore dissidents in astronomy is
extremely hypocritical - we all know the history of astronomy. In the
birthplace of Copernicus, we should be perfectly aware of this!


This is the most interesting bit, especially Fig 4 page 10. This is
where OCRA measurements from the SZ survey will be interesting.

They should hopefully give us independent estimates of the different
luminosity functions of clusters at different redshifts.

Whatever the explanation for Alain's analysis is, we're going to have
to understand it sooner or later if we want to get anything useful
from OCRA. My own guess is the non-Gaussianity of the tail of the
perturbation distribution, but until I start trying some calcuations,
I can't really say anything seriously.

BTW, I'm copying this to Alain just in case he feels like commenting.
(The .htaccess file fails so cosmo-torun became an open list de facto,
unless someone is really paranoid I suggest we keep it open.)


Salut Alain, si tu souhaites savoir ce que fait notre petite équipe,
veuille aller sur :


La page sur OCRA se trouve ici, mais nous n'avons rien mis pour l'instant
sauf un lien vers quelques jolies images :


Tu peux répondre sans ętre abonné, mais il faut confirmer au robot par
la suite.


On Thu, 9 Jan 2003, Andrzej Marecki wrote:

> Paper: astro-ph/0301137
> From: Blanchard Alain <alain.blanchard at ast.obs-mip.fr>
> Date: Wed, 8 Jan 2003 17:45:24 GMT   (138kb)
> Title: Cosmological Parameters: Fashion and Facts
> Authors: A. Blanchard (LAOMP, Toulouse)
> Abstract: [...] I would like to emphasize that some results are established
> beyond reasonable doubt, like the (nearly) flatness of the universe and the
> existence of a dark non-baryonic component of the Universe. But also that
> the evidence for a cosmological constant may not be as strong as needed to
> be considered as established beyond doubt. In this respect, I will argue
> that an Einstein-De Sitter universe might still be a viable option. Three
> global tests: 1) the evolution of the abundance of clusters with redshift 2)
> the baryon fraction measured in local clusters 3) apparent evolution of the
> baryon fraction with redshift might be consistent with a high matter density
> for the Universe in the range $0.6-1.$. I therefore conclude that the
> dominance of vacuum to the various density contributions to the Universe is
> presently an interesting and fascinating possibility, but it is still
> premature to consider it as an established scientific fact.
> -------
> Andrzej


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