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Peebles and Galaxy Formation



 
 
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  #1  
Old May 27th 14, 08:19 PM posted to sci.astro.research
Robert L. Oldershaw
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Default Peebles and Galaxy Formation

Recently the issue of how well we understand galaxy formation came up
at SAR and Dr Helbig said our understanding was quite good.

Here is a quotation by PJE Peebles from a recent dark matter
conference reported on by Matt Strassler.

"But [Peebles] also suggested, alluding to the many puzzles about
galaxies (some of which were mentioned in McGaugh's talk) that we
should view our understanding of galaxies and how they form and evolve
as still quite poor, with room for significant surprises."

I repeat: "still quite POOR" [emphasis added for the hard of hearing].

[Mod. note: reformatted, slight editing for politeness -- mjh]
  #2  
Old May 28th 14, 06:56 AM posted to sci.astro.research
wlandsman
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Default Peebles and Galaxy Formation

On Tuesday, May 27, 2014 3:19:28 PM UTC-4, Robert L. Oldershaw wrote:


Here is a quotation by PJE Peebles from a recent dark matter
conference reported on by Matt Strassler.


I share your admiration for Peebles. Not only did he make a correct
definitive prediction for the light element abundances in his 1966
paper, but he was always questioning the assumptions of cosmologists
and looking for alternative explanations. For example, his 2012
biographical notes for Annual Reviews
(http://www.annualreviews.org/doi/ful...-081811-125526
) include the following notes on structure formation with cold dark
matter (CDM)

"I liked CDM, but distrusted its early use in analyses of structure
formation. I had just made up CDM to save the gravitational
instability picture, which didn't make it right, and I set out to show
that by inventing other viable models. I gave up (a last example is
Peebles 1999) because the rapidly advancing observations were ruling
out my models as fast as I could put them on astro-ph, and they were
agreeing wonderfully well with lambda-CDM. "

Now about his quote on galaxy formation. It would be better if you
also quoted the previous line from Strassler's report:

"Jim Peebles pointed out just how broad is the cosmological evidence
for dark matter, from a wide variety of independent sources. He views
the basic notion of dark matter as an idea that is not just widely
accepted, but has been established by data."

But unlike cold dark matter, the baryons in galaxies are incredibly
messy -- you have rotating gas in many phases from 30 K to 10^6 K,
with magnetic fields, cosmic rays, energetic supernovae, and intense
radiation fields. I doubt there are any researchers who would call our
understanding of galaxy formation "quite good", although it is
certainly improving. It might well be that more realistic models of
galaxy formation will somewhat modify our models of large-scale
structure formation, although most of these details will probably be
smoothed out. --Wayne

P.S. I tried to google in SAR where Dr. Helbig said that our
understanding of galaxy formation was "quite good". I couldn't find
any such quotes and in fact found the opposite e.g. he writes "the
details of galaxy and star formation are less certain than the Big
Bang (not the details of it, but rather the existence of it). " or "In
particular, not understanding galaxy formation doesn't imply that
there is any reason at all to doubt the big bang in the narrower sense
of the term. " Anyway, I am sure that Phillip can set the record
straight.

[Mod. note: reformatted, non-ASCII characters replaced -- mjh]
  #3  
Old May 28th 14, 07:16 AM posted to sci.astro.research
Phillip Helbig---undress to reply
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Posts: 629
Default Peebles and Galaxy Formation

In article , "Robert L.
Oldershaw" writes:

Recently the issue of how well we understand galaxy formation came up
at SAR and Dr Helbig said our understanding was quite good.

Here is a quotation by PJE Peebles from a recent dark matter
conference reported on by Matt Strassler.

"But [Peebles] also suggested, alluding to the many puzzles about
galaxies (some of which were mentioned in McGaugh's talk) that we
should view our understanding of galaxies and how they form and evolve
as still quite poor, with room for significant surprises."

I repeat: "still quite POOR" [emphasis added for the hard of hearing].


It is quite good compared to various alternative theories touted here in
the newsgroup. That it is quite poor by Peebles's standards is a
different matter entirely. :-)
  #4  
Old May 29th 14, 07:44 AM posted to sci.astro.research
Phillip Helbig---undress to reply
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Posts: 629
Default Peebles and Galaxy Formation

In article , "Robert L.
Oldershaw" writes:

Recently the issue of how well we understand galaxy formation came up
at SAR and Dr Helbig said our understanding was quite good.

Here is a quotation by PJE Peebles from a recent dark matter
conference reported on by Matt Strassler.

"But [Peebles] also suggested, alluding to the many puzzles about
galaxies (some of which were mentioned in McGaugh's talk) that we
should view our understanding of galaxies and how they form and evolve
as still quite poor, with room for significant surprises."


Here is the full quotation from http://profmattstrassler.com/2014/05...atter-debates/

But in his Wednesday evening talk, the famous astrophysicist and
cosmologist Jim Peebles pointed out just how broad is the
cosmological evidence for dark matter, from a wide variety of
independent sources. He views the basic notion of dark matter as an
idea that is not just widely accepted, but has been established by
data. But he also suggested, alluding to the many puzzles about
galaxies (some of which were mentioned in McGaugh's talk) that we
should view our understanding of galaxies and how they form and
evolve as still quite poor, with room for significant surprises.

Note how Peebles sees evidence for dark matter as something which is
extremely well established. McGaugh is a noted proponent of MOND. I
think most astrophysicists agree that, whether or not they think MOND
is right, it does tackle some real problems (though it is not clear
that they could not be tackled by other means). So, in the last
sentence, Peebles is talking about the detailed kinematics of
individual galaxies. The evidence for cosmological dark matter is
independent of this, and possibly unrelated to it. Peebles isn't
talking about structure formation or the CMB in that last sentence.

How does DSR explain McGaugh's concerns?
  #5  
Old May 29th 14, 07:45 AM posted to sci.astro.research
Phillip Helbig---undress to reply
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Posts: 629
Default Peebles and Galaxy Formation

In article , wlandsman
writes:

I share your admiration for Peebles. Not only did he make a correct
definitive prediction for the light element abundances in his 1966
paper, but he was always questioning the assumptions of cosmologists
and looking for alternative explanations.


Not always. As he says below, at some point he stopped.

For example, his 2012
biographical notes for Annual Reviews
(http://www.annualreviews.org/doi/ful...-081811-125526
) include the following notes on structure formation with cold dark
matter (CDM)

"I liked CDM, but distrusted its early use in analyses of structure
formation. I had just made up CDM to save the gravitational
instability picture, which didn't make it right, and I set out to show
that by inventing other viable models. I gave up (a last example is
Peebles 1999) because the rapidly advancing observations were ruling
out my models as fast as I could put them on astro-ph, and they were
agreeing wonderfully well with lambda-CDM. "


In other words, until 1999, he was something of a devil's advocate,
which is a good thing to have. It is good to question the models. But
then his alternative models became so contrived that Occam's razor
indicated that lambda-CDM was probably correct.

Now about his quote on galaxy formation. It would be better if you
also quoted the previous line from Strassler's report:

"Jim Peebles pointed out just how broad is the cosmological evidence
for dark matter, from a wide variety of independent sources. He views
the basic notion of dark matter as an idea that is not just widely
accepted, but has been established by data."


Hear, hear!
  #6  
Old May 29th 14, 07:52 AM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default Peebles and Galaxy Formation

On Wednesday, May 28, 2014 1:56:26 AM UTC-4, wlandsman wrote:

I share your admiration for Peebles. Not only did he make a correct

definitive prediction for the light element abundances in his 1966

paper, but he was always questioning the assumptions of cosmologists

and looking for alternative explanations.


Here is a partial comment from Peebles [Science 235, 372, 1987)
regarding the status of theoretical cosmology in the 1980s, and
specifically the vague WIMP conjectures and inflation.

"This is a lot of activity to be fed by the thin gruel of theory and
negative observational results, with no prediction or experimental
verification of the sort that, according to the usual rules of
evidence in physics, would lead us to think we are on the right
track..."

In my opinion, the situation has not improved. Rather the alarming
trends noted by Peebles are now pandemic in theoretical physics. The
"usual rules of evidence in physics" have been largely replaced by the
aesthetics dictated by a small but influential group of people. They
use esoteric mathematics and oft-repeated assumptions as a obscuring
cover for their pseudo-science.
  #7  
Old May 29th 14, 07:34 PM posted to sci.astro.research
Jos Bergervoet
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Posts: 126
Default Peebles and Galaxy Formation

On 5/29/2014 8:52 AM, Robert L. Oldershaw wrote:
In my opinion, the situation has not improved. Rather the alarming
trends noted by Peebles are now pandemic in theoretical physics. The
"usual rules of evidence in physics" have been largely replaced by the
aesthetics dictated by a small but influential group of people.


As far as I know the rule of 5-sigma evidence is still
unaltered before discovery is accepted, and independent
verification is still required, regardless whether it is
the Higgs particle or a new exoplanet, so what exactly
is this "replacement" of evidence you believe to be seeing?

.. They use esoteric mathematics


Some people have been using "fluxions" which were pretty
esoteric at that time.. (I think they wrote complete
books about it!)

--
Jos
  #8  
Old May 29th 14, 07:49 PM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default Peebles and Galaxy Formation

On Thursday, May 29, 2014 2:44:52 AM UTC-4, Phillip Helbig---undress to reply wrote:

Here is the full quotation from http://profmattstrassler.com/2014/05...atter-debates/


This thread is not about DSR (how many times do I have to point this
out to you?).

A proponent of MOND has just as much right as you or anyone else to
comment on our understanding of galaxies (structure and formation).

I agree with Peebles that the scientific evidence for dark matter is
strong. I just don't think it is in the form of hypothetical and
poorly motivated no-show WIMPs.
  #9  
Old June 1st 14, 06:58 AM posted to sci.astro.research
Robert L. Oldershaw
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Posts: 617
Default Peebles and Galaxy Formation

On Thursday, May 29, 2014 2:49:32 PM UTC-4, Robert L. Oldershaw wrote:
[mod. note: no actual quoted text provided -- mjh]


I am reading a paper by Walker and Loeb:
http://arxiv.org/abs/1401.1146 , which argues that there may be much
yet to learn about galactic formation, structure and dynamics. The
arguments are based on well-observed characteristics of galaxies, not
theoretical hand-waving. Very refreshing. Note scaling of fundamental
galaxy properties.

[Mod. note: reformatted -- mjh]
 




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