Administrator
Please, if you can't follow the math, don't post your gut-feeling doubts in every thread you can find that touches on this. Whether you intend it this way or not, this is a known strategy for the anti-science misinformationists. It resolves nothing except to make the more serious scientists tire of responding to your empty doubts. We have a rule about creating a nuisance, and this falls under it.Originally Posted by TooMany
Forming opinions as we speak
Established Member
What these two papers prove, taken together, is that if you have a computer model with lots of adjustable parameters, you can prove anything you want
The serious flaw with the original paper is said to be that the circular velocity is constant with z (perpendicular distance from the disc mid-plane).
However, just under equation (25), Bovy et al themselves say (quote):
Thus, the circular-speed curve of the Milky Way remains close to its value in the plane
throughout the region |Z| < 4 kpc that we are investigating.
So that seems to contradict their own position.
Also, I'm sure naively, I would've thought that the circular velocity was not important in the argument. Surely it is only movement in the z-component that we are interested in here ? Or is this a trap that Moni Bidin et al fell into ?
Suspended
My doubts are not just invented, they represent some doubts expressed by other scientists. I agree with you that my personal opinions carry no weight. Nevertheless I think you might agree that evidence is drawn (e.g. for BAO) from complex statistical arguments that seek out very subtle effects. It is not easy for the uninitiated to see how so much can be known with certainty and precision from the detailed analysis of these slight variations, while at the same time an obvious feature like that dark spot at 5 o'clock high is just an artifact of a certain analysis.
If you think I'm anti-science you are mistaken. I get the same feelings that you appear to have toward me, when I hear from GW deniers. But I know that thermometers and melting ice don't lie and I know who is supporting the deniers and why they do so. That issue is politics, not science.
Regardless of what you may think, I am trying to learn and understand as best I can. I do read many papers (unfortunately skipping most of the mathematical details). What I find somewhat unfortunate about this forum is that "non-mainstream" ideas cannot be discussed except in the context of a special sub-forum where you must personally defend them against a regiment of critics. This is especially unfortunate because the "mainstream" appears to be so narrowly defined as to coincide precisely with LCDM as espoused e.g. by Ned Wright.
I have emphasized alternate possibilities (concerning DM) and pointed out that there are things that (IMO) we simply don't know all that much about. I am willing to read papers both in agreement and contrary to mainstream ideas. You have pointed out for example a paper contradicting the one that I referenced in starting this thread. I read that paper (as best I can). It sounds like they may have a point but I am not personally competent to judge.
I'll take a break here (because I don't want to be a nuisance) and wait for more to come. If I find something interesting perhaps I'll start another thread. If I do, it will be based on something published in peer review as anything else is summarily dismissed.
Suspended
I think they are making a distinction between azimuthal velocity (in cylindrical coordinates about the galactic axis) and circular velocity about the center of mass. The first paper assumes constant velocity in azimuth, the second argues that constant circular velocity makes more sense and, applying the latter assumption, they still find sufficient DM to allow for the various proposed LCDM distributions of non-baryonic matter.What these two papers prove, taken together, is that if you have a computer model with lots of adjustable parameters, you can prove anything you want
The serious flaw with the original paper is said to be that the circular velocity is constant with z (perpendicular distance from the disc mid-plane).
However, just under equation (25), Bovy et al themselves say (quote):
Thus, the circular-speed curve of the Milky Way remains close to its value in the plane
throughout the region |Z| < 4 kpc that we are investigating.
So that seems to contradict their own position.
Also, I'm sure naively, I would've thought that the circular velocity was not important in the argument. Surely it is only movement in the z-component that we are interested in here ? Or is this a trap that Moni Bidin et al fell into ?
I can't explain the apparent contradiction, I'll have to read the paper again.
I just looked again and I think the argument under eq (27) is what leads to their conclusion that the assumption of constant velocity in azimuth is wrong. Perhaps if the circular velocity is constant, then the projection on the azimuth is not? It's not completely clear to me.
Administrator
Thanks. I think the point I was trying to make is that it's not helping anything to say "It's too complex and subtle so I have unfixable doubts" to everything in cosmology. It wastes our time to respond to that message written over and over again by one person. We do discuss things that are on the fringe of detectability, and it is fine to question the specifics of what can and can't be known about that topic. No problem. We all do it. Our concern about your posts have been a broader tendency to claim in the mainstream part of the forum that things which are now pretty well established by good observation, but which were marginal several years ago, are still unknowable... and in some cases, when you've been brought up to date, you later come back and seem to have ignored what was said.
I am asking you to please continue your reading and learning, and use your energy in the threads where you *do* know what you are talking about. It seems obvious that you will be broadening that range very rapidly.
Forming opinions as we speak
Suspended
For example? (Because I'm not sure what you are saying I've ignored.)
Fair enough!
Perhaps you can shed some light on the issue raised by kzb above. The paper does not go into great detail, apparently because they feel that their assumption of constant circular velocity contradicts the assumption of constant azimuthal velocity. I don't really see that cleary and would appreciate any insight you might have.
Order of Kilopi
Not strictly true. They can be discussed and frequently are. Some have been mentioned in this thread, I think. I have started one or two threads about non-standard cosmologies myself to find out what those with more expertise think about them. These are usually based on papers in "proper" journals (rather than pseudo/fringe websites etc. - but those get asked about as well).
The "ATM" section is for people who want to advocate for such an idea. However, the overwhelming majority of stuff there is not even science.
Suspended
Yep, the ATM section contains quite a bit of really fringe stuff that (IMO) is barely worth discussing. I just hope that limiting discussion to "proper" journals is not also a limitation to "proper ideas". For example, there was a recent news article concerning a paper that strongly suggests a different (bottom heavy) IMF for ellipticals than has been assumed. Dr. Pavel Kroupa was quoted in that article of being a bit ticked in that he presented a paper concerning variance in IMF before that, but the referees would not publish it. Completely anecdotal of course, but somewhat disturbing. Not surprisingly claims of such bias come mainly from those who find disagreement with mainstream ideas.
Order of Kilopi
Well, no. They said ...the mean azimuthal (or rotational) velocity of their tracer population is assumed to be independent of the Galactocentric cylindrical radius R at all heights. Which is "not supported by the data."
I'm no expert, but it appears to me that Moni Bidin, et al., just neglected to consider the asymmetric drift...
"The asymmetric drift is expected to vary with R, although this variation cannot be measured for [Moni Bidin's] sample as the data do not span a large enough range in R."
That also explains why Jo Bovy said:
...which isn't a contradiction.
Everyone is entitled to his own opinion, but not his own facts.
Established Member
On its own, no it isn't. You have no idea about the quality of the paper, of the consistency with evidence or anything - and yet because it is on a subject you support make some vague insinuation that it was thrown out for no good reason. Even good scientists write bad papers, or have papers sent back for revision. But no, your first instinct is, again, to hint that he was censored thanks to the content. A position for which you have no evidence and, as you have said, could not evaluate the evidence if you had it. Despite this, because the referees disagreed it has to be "disturbing"...Dr. Pavel Kroupa was quoted in that article of being a bit ticked in that he presented a paper concerning variance in IMF before that, but the referees would not publish it. Completely anecdotal of course, but somewhat disturbing.
Moderator
And that is the problem with "doing science" per press release. Then you get "an interesting anecdote" but no science.
(But as an aside, you can also have no science or junk science in a Science or Nature paper, I could easily give two recent examples in space physics, but that is OT and would derail this discussion.)
All comments made in red are moderator comments. Please, read the rules of the forum here and read the additional rules for ATM, and for conspiracy theories. If you think a post is inappropriate, don't comment on it in thread but report it using the /!\ button in the lower left corner of each message. But most of all, have fun!
Bi-weekly space physics research "blog" at tusenfem.blogspot.co.at
Suspended
He implied it was thrown out simple because it was considered an incorrect idea! Eventually it appears that it did get published. but only after someone else published other evidence of a similar nature.
I'm sorry but if you guys seriously think that the study of cosmology is completely unbiased and purely objective science, you are living in a dream world. Just look at your own threads. Anything written that does not support your theory is so abhorrent that you summarily declare it false. You scramble to find a contradiction. You constantly use old assumptions to prove arguments. Assumptions that may indeed be wrong and are turning out to be wrong. One of these is a universal IMF. That is going the way of the Dodo. No matter though, the conclusions drawn therefrom will last for many years to come.
I'm reading a thread mentioned by Reality Check and it's just wonderful in terms of the group psychology apparent. I've got to call a spade a spade. There is some serious close-mindedness evident in this forum and in the astonomy community. People like Ned Wright believe that they have the science behind them to falsify all other interpretations of the Universe. In other words, any other interpretation is wrong a priori. However, Ned's own view of the Universe requires you to accept at least two un-falsifiable assumptions, Inflation and Dark Matter (not to mention that you must accept that the CMB is the fading flash of the BB). Yet standing on those flimsy crutches all of you make the claim that ONLY YOUR THEORY can possibly be right. This is group belief, not science.
Now, if some large percentage of senior astronomers share Ned's belief, then what do you suppose they tell their students about what direction they should take in their PhD thesis, papers and research? Get real, there is bias and it's always been this way in science throughout history, because human nature has not changed. It's these same senior academics and scientists, firmly set in their beliefs, that review papers and reject papers containing non-conforming ideas. They already know that the papers must be wrong. Oh sure, a few innovative ones leak through, but very few.
There is no scientific credibility here because there is no willingness to give up existing assumptions in pursuit of other possibilities. There is a rush to judgement to dismiss anything that assails your theory and fantastic assumptions. Many of the papers that I see from the LCDM crowd are dedicated to making up yet another excuse for why observations do not match their predictions. This THEORY is tying up billions of dollars in research funds looking for the DM particles and trying to explain the universe from the subtle variations in the feeble background of deep space. Never mind that these predictions fail to explain the here and now. No, that doesn't matter. What matters is that the theory is so wonderfully self-consistent at explaining the things that it has been carefully tailored to explain.
Further, this group has the gall to present their story to the public as the undisputed truth about the universe. Consider this, if you are wrong, and I mean completely wrong, what is that going to do the public image of science? When a theory is based on speculations, it has no business being close-minded and presenting a false image of certainty to the public. Science should be quite modest about claims of what it knows until it really knows something (free from speculation). But alas it is not. Yet, this is understandable because scientist are not objective computational engines; they are human animals subject to the same tendencies, desires and biases as all of us.
Your theory may be completely right, but it's certainly not looking that way. Before I'm banned for this, I urge all of you to keep an open mind, to listen, to challenge your own assumptions and to deeply consider other ideas. What have you made this "forum" into, except a platform for expousing your own beliefs and denigrating all challenges?
Established Member
A couple of problems: You do not cite this news article. You do not show that this paper was rejected by the editor because the reviewers stated that it was not within the "proper ideas".
And I think that you mean top-heavy IMFs since that is the subject of a couple of his latest pre-prints.
Dr. Pavel Kroupa has published at least one paper on this topic: A top-heavy stellar initial mass function in starbursts as an explanation for the high mass-to-light ratios of ultra compact dwarf galaxies, Monthly Notices of the Royal Astronomical Society (2009).
Established Member
Ned's own view of the Universe suggests that you accept that strong evidence exists for at least two falsifiable observations (dark matter and dark energy), one falsifiable theory (inflation) and that the properties of the CMB are best explained by the universe once being in a hot dense state (the CMB temperature, perfect black body spectrum and power spectrum). The issues with dark matter and dark energy are not to do with their existence but to do with their causes.
There is scientific credibility here because there is no willingness to give up existing theories that are supported by evidence in pursuit of other possibilities that are not supported by evidence.
The LCDM predictions about the evolution of the universe including the "here and now" do match the observations quite well.
Established Member
If you are talking about the JREF Lambda-CDM theory - Woo or not? thread then you should be aware that it was started by a rather ignorant crank and most of it is various posters trying to explain science to him. This extended over 2 years and about 5000 posts and he did not seem to learn or understand much!
The basic misconception that he had was "empirical evidence" means only things that can be experimented on in laboratories. So according to him: no dark matter in a lab = dark matter does not exist, no dark energy in a lab = dark energy does not exist, no inflation in a lab = inflation does not exist (thus no stars in a lab = stars do not exist). Empirical evidence includes observations!
The "group psychology" is that that you stick with theories backed with empirical evidence until a better theory (explains the same empirical evidence and new empirical evidence) comes along.
Order of Kilopi
Administrator
TooMany
This rant against the membership of BAUT is a derailment of this thread and is just flat out rude. If you hate this place so much, then just stop posting here. Either that, or learn to live by our rules and to play nice with others. In any case this earns you an infraction.
Established Member
Suspended
I agree that the MM poster displayed substantial ignorance, however it was the arguments of OPs that I found interesting. MM was correct in this - the other posters tended to interpret evidence so as to match their theory, for no good physical reason. That is where the psychology enters. I can give you a couple of examples.If you are talking about the JREF Lambda-CDM theory - Woo or not? thread then you should be aware that it was started by a rather ignorant crank and most of it is various posters trying to explain science to him. This extended over 2 years and about 5000 posts and he did not seem to learn or understand much!
The basic misconception that he had was "empirical evidence" means only things that can be experimented on in laboratories. So according to him: no dark matter in a lab = dark matter does not exist, no dark energy in a lab = dark energy does not exist, no inflation in a lab = inflation does not exist (thus no stars in a lab = stars do not exist
The "group psychology" is that that you stick with theories backed with empirical evidence until a better theory (explains the same empirical evidence and new empirical evidence) comes along.
1) MM pointed to evidence that galaxies were twice as bright as previously thought and thereby concluded that they were twice as heavy (in stars and gas). That seems like the simplest, most direct interpretation. However another poster (TT) argued that twice as bright was equivalent to only 1.2 times as massive. His reasoning was that the luminosity of main sequence stars L is proportional to M^3.5 where M is the stellar mass. Therefore (according to TT) doubling the luminosity implies only a small change in mass.
That argument is just contrived to keep the new stellar mass estimate low. The only way to keep the mass so low that way is to propose that the extra luminosity is only at the very top of the IMF and that the IMF is more top heavy than we have evidence for. That is quite dubious because the high mass stars are the easiest to detect.
Nobody on the thread called out TTs assumption as unlikely. Instead they all tacitly agree. That is group think. The common purpose is to deny the significance of new evidence that does not help the shared belief.
2) MM pointed to evidence that the IMF is more bottom heavy than was previously thought and thereby concluded that mass/luminosity ratio for galaxies was significantly higher than previously thought, so that galaxies for a given luminosity actually have more stellar mass than previously thought. TT countered that this finding had no effect on mass estimates and that mass was derived solely from total luminosity as before. This is quite obviously an incorrect interpretation. If he were just to consider the luminosity formula he gave for main sequence stars (L = kM^3.5), he should see that adding more stars with lower mass increases the mass/luminosity ratio for galaxies, thus increasing the mass estimate of normal matter.
Again, nobody on the thread called out TT on this clear mistake. The other posters are not being objective. They are simply trying defend their theory and don't mind using nonsensical arguments to dismiss evidence that might affect their theory (even if that evidence does not constitute anything close to a disproof of their theory).
Now I was referred to TT as an expert who could demonstrate that Ari Brynjolfsson's plasma redshift ideas were nonsense. They could be nonsense, but after reading some of that thread, I cannot take TT's statements as authoritative.
Finally, no you don't "stick with your theory", especially when it based on unsubstantiated new physics. You can certainly use your theory and see where it goes, but you should be open at all times to the possibility that it is wrong. Currently it appears that the senior astronomical community is so attached to that theory that contrary observations are often ignored (e.g. no time dilation in quasars) or attempts are made to stretch new data as far as possible to make the contradictions go away (usually reducing the significance to sigma 1 and then considering the issue closed). Anything, absolutely anything contrary is viewed with suspicion and assumed to be wrong while waiting for a good justification. This creates an atmosphere in the world of astronomy where deeply held assumptions such as expansion, the interpretation of rotation curves and the meaning of the CMB have become dogma that cannot be challenged. Thinking outside of this box is discouraged with "well, given what we know that is just impossible, so you best forget about such nonsense."
Instead of open-minded science what we have is "scientific guardianship" of a commonly held interpretation which requires un-falsifiable conjectures such as inflation and non-baryonic DM in its foundation.
Established Member
Cougar wrote:
I'm no expert, but it appears to me that Moni Bidin, et al., just neglected to consider the asymmetric drift...
"The asymmetric drift is expected to vary with R, although this variation cannot be measured for [Moni Bidin's] sample as the data do not span a large enough range in R."
But if there is no significant range for a variable, how can the effect of that variable on the final measurement be quantified?
In fact this is a common technique in science: hold one variable constant or within a small range, so that the effect of other variables can be quantified.
Obviously I don't know the full details of what either set of authors has done, but this aspect is still a bit puzzling.
Established Member
Have you ever been an astronomer? At undergraduate or postgraduate level? Or are you just basing this on your selective reading of second or third hand evidence? Because I did astronomy at uni, and have plenty of contact with professional astronomers even now. And I can tell you that your characterisation of the community is utter rubbish. You feel like ideas you like (without being able to actually follow them as you have admitted) are ignored so to justify this you malign an entire community you have no direct contact with. Stick to the science.
Administrator
If the purpose of this thread is just to critique a thread on a different forum, and for TooMany to continue his rant against the Astronomical Community and BAUT, then it serves no useful purpose. This thread is closed. If someone thinks it should be reopened, Report this post and explain why you think that.
Administrator
I have reopened this thread on a request from StupendousMan who has more information on the original topic.
I assume he wants to discuss this paper: http://arxiv.org/abs/1205.5397
Forming opinions as we speak
Administrator
I will remind everyone that posts will ONLY be on the subject of Dark Matter, and there will be no further discussion of the general scientific process, nor of the openness of BAUT or its members.
Suspended
That new paper seems to be saying that the statistical analysis by MB is wrong by taking only the "wings" to avoid thin disk contamination? They conclude in part:
So what's the deal? MB says you need to remove the thin disk contamination and these guys say that spoils the accuracy of the velocity dispersion? But isn't the exclusion of the thin disk good because it is not relevant to this issue of what's going on at higher z? I'm confused. They also do some statistical analysis to claim that the errors are actually larger than assumed by MB. They suggest that errors are in the neighborhood of the "Poisson noise" but don't seem to offer proof of that.These authors found a gradient a factor of two higher than MB which MB claim is due to not removing thin disc and halo contaminants in their analysis. We conclude by
following the method used by G06 to test whether their results are more secure than those reported by MB.
Now we have two papers saying MB is wrong (or at least weak) for two different reasons. It will be interesting to see if MB counters, but if I were him, I'd wait a while since someone else may want to throw their hat in the ring, at the rate they are flying in.
Established Member
I've only skimmed the Jason paper briefly. It's worth pointing out that he has not used the same stars as the other two previous papers. In fact he has used a synthetic population based on a model (hmmm...circular argument alert....).
This he has done in order to point out what statistical traps you can fall into with these kind of studies. it also means that both the previous papers we are discussing suffer from this same issue.
That's what I've taken from it so far anyhow.
Established Member
First point I'd like to make about the Jason Sanders paper,
quote:
We limit our investigation to just the W component
of the velocity (the component along the z direction).
In other words, JS does not seem to think the problem identified by Bovy et al is much of an issue.
JS illustrates what statistical pitfalls both MB and Bovy et al based their conclusions on. In doing this, he uses a synthetically-generated population of stars, itself based on a model including stellar disk, gas disk, thick disk, and spherical halo. (So we need to have our circular argument goggles firmly attached here.)
However, in mitigation, he then goes on to use a real sample of stars, but not the same sample as the previous two papers under discussion.
It's clear he is saying the statistical methods used in both previous papers lead to bias. What's not so clear is whether he thinks the findings with his sample of real stars backs up one argument or the other.
But I think it's fair to say, Bovy et al, with their claim of finding the most precise estimate to date of the disk DM content from this data, are being rubbished just as much as MB et al in this paper.
Suspended
This situation seems to be common in the field, i.e. contradictory findings or claims about significance. I was just reading some papers about the Integrated Sachs–Wolfe (ISW) effect. This is the effect of large concentrations and voids on the CMB. One paper claims that it does not show up and another claims that too much is detected. When I pointed out this problem earlier (in evaluating papers) I was told that this really doesn't happen. But I keep finding examples.
I would venture to attribute it to the difficultly of accurately measuring the effects sought. Detections of this or that effect are often at the very limit of what S/N allows (as well as highly dependent on assumptions). Depending upon the way the data is analyzed (generally relying heavily on statistics), the assumptions made and the competing effects considered, the conclusions may differ widely, as in this example. One man's evidence of no DM is another's proof of it's existence in the LCDM-expected amounts, and a third's evidence of nothing but noise.
I suppose there is considerable interest in publishing papers to be recognized at the leading edge of investigation. However, one might wonder whether it would not be better to wait until strong data from sufficiently powerful instruments is available before drawing conclusions in papers? In other words, don't bother publishing conclusions unless they have a high degree of certainty. There are a tremendous number of papers published, but the significance of them is obscure. Will a paper stand or be shot down by the next paper?
Claims of incorrect results from improper analysis are common; this undermines faith in publications more generally. One would certainly expect (if the data allows) a true resolution of these conflicts. But how would this ever occur? There is no impartial tribunal that decides who's analysis is correct and who's is wrong. To some degree the problem is to be expected in science, but it seems especially common in cosmology. The reason for this is probably that cosmology differs from other sciences in that generally there is no way to experiment, i.e. to control one variable while containing others. We have observations; but few experiments.
Administrator
Over all, good points. I think that the system has developed this way because we want to know what are good gambles for spending the big bucks on newer better instruments (which instruments do we build? Who gets to use them?). If you find a hint in the margins do you not publish, and then perish? I'd like a little less assertiveness in the conclusions of some papers. Most seem to frame these things fairly accurately.
Forming opinions as we speak
Order of Kilopi
This appears to be a selection effect. Papers that claim to overthrow longstanding mainstream findings are more likely to have response papers pointing out the errors in their analysis. In general, this is not common.
Everyone is entitled to his own opinion, but not his own facts.
Suspended
Lack of density cusps in galactic centers (for example) has lead to a number of mainstream papers attempting to explain why they do not appear. But the lack itself is not often denied.
I think Cougar's comment is accurate. Mainstream-neutral or supportive papers will not receive as much scrutiny as those with unsupportive findings.
Antoniseb makes a good point that uncertain conclusions can lead the community to probe in a direction that resolves an issue. Probably that will be the case here. Better measurements will eventually be available, but there's no guarantee that they will result in resolution if the different sides cannot agree on assumptions and statistical methods.
Administrator
Once again, let's not derail this thread. If you folks want to discuss the scientific method, start a new thread, or Report this post and ask for the discussion to be split off.
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