Re: Request for review and approval: Big Bang FAQ

feuerbac@xxxxxxxxxxxxxxxxxxxxxxxx wrote:
> Ulf Torkelsson schrieb:
>
> Hello Ulf! Thanks for providing your comments! :-)
>
> I'd really appreciate if you also looked at my FAQ and gave
> some comments on it...

Hi Björn,

Since I was on vacation when you first posted your FAQ,
and since you did receive some feedback from Ned Wright and
Ryan Scranton, I thought that there was not much more that
I could contribute, but I will give you a few comments, mostly
really minor points, since I think it looks quite good already:

Firstly, I would hesitate to describe Kippenhahn as a
cosmologist. He is surely an important astronomer or
astrophysicist (whichever you prefer), but his most
important contributions has been in the theory of stellar
evolution, not in cosmology.

Secondly, according to Hoyle himself, he did not invent
the term Big Bang to ridicule the theory. He needed two
short catchy terms for a radio programme to contrast Gamow's
theory of a universe that had its origin in a dense state at
a finite time in the past with his own theory, in which the
universe had existed forever and always looked the same.
These two terms were "Big Bang" and "Steady State"; please
note the alliterations.

I feel that you are getting a bit too technical in Sect.
1c. I am afraid that the complete layman will get lost
here trying to understand what everything means. In my
opinion it would be better to save the technical details
until later in the FAQ, and keep Sect. 1 so simple that
anyone without any background in physics can get an idea
of what the big bang theory is about. Later on, you can,
and should, provide more of the technical details, but
keep the beginning simple.

The issue of the polarisation of the microwave background
is much more complicated than you present it. I have not
been keeping track of this for some time, so take what I
write here with a grain of salt. Both DASI and WMAP have
detected polarisation though on different angular scales.
WMAP has detected a polarisation over a large angular
scale. This is due to that the photons in the microwave
background have scattered of electrons in the intergalactic
medium. This shows that the intergalactic medium today is
ionised, though the gas became neutral at the time that
the CMB was first formed. The obvious conclusion is that
the intergalactic medium since then has become re-ionised
presumably due to radiation from hot stars or quasars
(most researchers seem to favour ionisation by hot stars).
The large amount of polarisation that WMAP has measured
shows that this reionisation occured already at a redshift
of 15 to 20, which is surprisingly early. DASI has
measured polarisation on much shorter angular scales.
This is due to processes at the time that the microwave
background was formed, and is a result of that the
universe was not fully homogeneous at that time, but
rather already contained small inhomogeneities.
Another possible source of this polarisation would be a
background of gravitational radiation from the early
universe, but as far as I know the jury is still out in
this case, and they are awaiting the results from
Planck, which will be launched in 2007(?).

When you talk about structure formation and computer
simulations of that you describe articles from the second
half of the 90s as early, but people have been working
on such simulations at least from the early 1980s.
Look for instance for papers by Efstathiou, Frenk, Davis
and White in different permutations.

May I also suggest a couple of fairly good and recent
books and articles on cosmology for inclusion in your
biography:

Coles, P., 2001, Cosmology: A very short introduction,
Oxford paperbacks

Ferreira, P. G., 2003, The cosmic microwave background,
Physics World, April, p. 27

Harrison, E. R., 2000, Cosmology. The science of the
universe, Cambridge University Press

I doubt that there is any other book that explains
equally carefully what the big bang is and is not as
Harrrison does with very little use of mathematics,
so that book is warmly recommended to anyone.

>
> I don't think that it makes much sense to argue with Ken; over at
> sci.physics, he just said that Ned Wright does not understand General
> Relativity and cosmology. He's *way* beyond help.
>
I would tend to agree, so let us close that part of
the discussion. I stopped reading sci.physics when
sci.physics.research was created in order to avoid the
worst crackpots.
>
>
>>dynamics@xxxxxxxxxxxx wrote:
>>
>>>Ulf Torkelsson wrote:
>>

[text snipped]

>>>> Björn may be only a physics student,
>
>
> In fact, I've got a PhD and work as a researcher, in theoretical
> chemistry.

Oops, I thought you were still a PhD student. I apologise for
that.

Ulf Torkelsson

.

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