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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] |
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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] |
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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. :-) |
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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? |
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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! |
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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. |
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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 |
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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. |
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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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