Established Member
You are certainly the expert this. I admit to nearly complete ignorance. What is a bit strange is that the WMAP folks published this stuff knowing that it was likely leading to false ideas? Or was that concluded later when this anomaly was discussed? Do you feel there is a general consensus that it's just an artifact? If so, how extensive are the implications on the rest of the data/conclusions?Originally Posted by Shaula
Established Member
Going back a few years to COBE, the uniformity of the CMB was a huge surprise, not a predication, and inflation was invented to explain it. That's an example of the kind of adaption of the theory and failure to predict I"m referring to. Recently the idea of "cosmic texture" was proposed to explain the "Cold Spot". This could go on endlessly and what would it really illuminate?
Regarding MOND/TeVeS, there seems to be serious disagreement about how this or that disproves it, depending on which side of the issue you have taken.
Personally I don't like it, partly for the same reason as other things. It seems a bit concocted.
Administrator
Now you are just talking through your hat. Inflation was proposed in Jan 1980 by Alan Guth. COBE was launched in 1989, and the results weren't known for a couple years. If you're going to argue for your position, can you please stick to arguments that leave yourself sounding credible?
Forming opinions as we speak
Established Member
If you could provide a citation that suggests that any of the modified gravity models can produce the BAO feature in the matter correlation function or power spectrum without resorting to dark matter, I'd love to see it. This problem with MOND has been known for quite a while. If you don't understand what I mean by the BAO, you can ask.
As it is, you seem to be trying to play a "he said, she said" game with people who know the relevant literature. Unless you provide citations to relevant papers, there's not much point in arguing. This goes along with antoniseb's comment about your hyperbole regarding inflation; I think you've been trying to learn too much astronomy via press release.
Established Member
Not an expert - an informed user! Most people applying signal processing techniques, frankly, click the button and accept the results. 9/10 times that is a safe thing to do - the algorithms are usually well behaved. The trouble comes when you hit the one time in ten that a data artefact is an equally valid explanation for what you see. Wavelets and their ilk are pretty complex in the way they interact with data and usually people don't fully understand them. It is rather like applying statistical tests to data. A lot of papers still use significance statistics based on a gaussian assumption without checking how valid this assumption is.
It is usually true that physicists are at best mediocre statisticians. I am 'lucky' in that I have statisticians for friends who never let me forget that. Papers often get through peer review without a full review of the statistical techniques used. Less common in particle physics papers but quite common in astrophysics papers. Does this invalidate all the results out there? No. But it does mean that blindly quoting papers can get you in to trouble.
Short version: Statistics are tricky things. This confusion most directly affects any papers claiming to have found an anomalous feature in the background. It is all about how you drive down the background reliably to find one anomalous patch. Papers looking at larger, periodic patterns are going to be safer from this sort of issue because they tend to ignore single occurrence anomalies (to an extent). So the BAO work is safe.
However I do not think that the matter is closed. For now the most likely answer is artefact. What is not clear is where this artefact came from. If it is actually in the data then it is not the same as a cold spot but it is still a significant deviation from the background pattern. So I would say it is not evidence you can use against the LCDM model yet - but equally it is not explained away and cannot be discounted as uninteresting.
Established Member
I've got the history wrong. Reading a brief account, it appears that the theory was actually motivated by the magnetic monopole problem.
"Guth was to find that the decay of the false vacuum at the beginning of the universe would produce amazing results, namely the exponential expansion of space." Thus somehow diluting the monopoles sufficiently to make them unlikely to be detected.
Then there was also the flatness problem. Omega = 1 exactly. So apparently he had a solution for that too.
According to what I read, shortly after formulating this theory (weeks), he was told that the CMB was very uniform, too uniform to explain (long before COBE, as you pointed out). But bingo, inflation explains that too and we've killed three fatal BBT problems with one stone!
What is the physical basis for inflation? Is it directly predicted from GR and QM and the standard model of particles? Or is it just a conjecture created to solve a problem that already existed with BBT thirty years ago? I know now that it is taken for granted as fact by most cosmologists. However, I don't believe that it is based on any known physics, so you cannot make any precise predictions about inflation. Instead you just assume it occurred and then you juggle your inflation parameters until they match some observations and then declare that it is correct.
With this theory we now invoke an expansion by a factor of 10^74 that happen during a time period (< 10^-33 s) many orders of magnitude smaller than the time that light requires to traverse the length of a proton. (A realm that seems way beyond any knowledge we currently have of physical law or that we can even hope to experiment with.)
That is the point that I was trying to make, although I was quite incorrect in the way I specifically described it. You can consider this a theory, but it is not at all in the same sense as GR or thermodynamics and the like. Currently theorist are also adjusting the properties of CDM to make things come out right. Maybe if we get the right mix of hot, cold, warm and just the right degree of interaction with that stuff we can get it to explain things and then once again declare it firmly part of this theory.
How can I prove that inflation never happened? That's a tough one. Like proving that undetectable particles don't exist.
Established Member
Fair enough. I don't know much about image processing mathematics, but I am somewhat familiar with the sorts of artifacts that can result from JPEG compression which may be analogous. But those tend to be more or less ubiquitous rather than singular.
I agree with your concerns about statistics. They have become the central theme in many papers, so they better get it right. You know the old joke, "there are damn lies and then there's statistics."
Outsiders like myself can get a little uncomfortable when we are told that "everything matches our predictions perfectly, but please ignore that big dark spot; it's just an anomaly".
Anyway, thanks for the info and one more question: Do you think that Planck data will in any way help to resolve the issue?
Administrator
Without getting too involved in String Theory ideas, you can't really say much about what caused inflation... and it is certainly valid to look for alternatives that explain what it explains. Really, at this point, the direction of science of inflation is to quantify what we are seeing well enough that it can eventually give us the framework for some more elegant theory.
One of the things that you've been saying or alluding to in you many posts, is that the Big Bang, and Inflation, and Dark Matter, and Dark Energy are not theories which have some first principles the way General Relativity does. GR is testable (and will eventually need to be superseded by something that can also be compatible with QM). It is so elegant... that it has pretty much spoiled it for you. Nothing less elegant seems right to you, and lets be pragmatic, LCDM is a model and framework for increasing the quality of our measurements, and for giving context to observations.
This whole thing (BBT, GR, DM, DE, etc) is the state of things as we see them today. Some people dismiss it all as "epicycles", by which they (hopefully) mean that we are making measurements that get us to a model that predicts and explains what we see to within the limit of our ability to measure, using tools we know how to use (epicycles were a mathematical technique to make very good predictions of the positions of the planets). Copernicus made an innovation which reduced the number of epicycles from 86 to 43... He was still working with circular motions superimposed on each other. That change came from working with the refined observational data of himself and his predecessors... and then 65 years later, Kepler went one step further, and found the ellipses, and epicycles got their bad name... and then a century and a half later Newton gave some reasonable explanation for Kepler's laws.
So I suspect that you are mostly complaining that we aren't at the equivalent of Newton's place in this parallel to planetary theory... we are still working out the details of how things work and move and more. But let's point out that like the Planetary Theorists, we are right now working (as always) at the very limits of what our technology will let us see, but now the problem we are looking at is something that is intertwined both at the largest possible scale and the smallest, and our ability to have many people working together and in parallel on scientific endeavors is far beyond anything from Copernicus' time.
We know we are working with models, and make no claim that the ultimate truth of these things is known. We are on the hunt for that truth... and we have a pretty good sense of what we know and don't know. We'd be happier with your complaints if you'd listen when we answer them, and maybe read the papers we point you to.
Forming opinions as we speak
Established Member
It may do. It will certainly give us more more data points and allow us to better understand the structure (if it is there in both sets of data) that has caused this. But to be honest more would be got out of a rigorous statistical review of the processing done on the WMAP data. I suspect that what is happening is that people downstream of the pre-processors are perhaps not as familiar with the data conditioning that has already happened, or are perhaps not as conversant with the signal processing that they are doing as they could be. It should be a reminder to anyone who deals with data like this that they need to be careful, methodical and precise in what they do. Maybe I am being unfair on the researchers who first found this but I would personally never trust one filter from my toolbox.Anyway, thanks for the info and one more question: Do you think that Planck data will in any way help to resolve the issue?
Established Member
My grasp of baryonic acoustic oscillations is pretty vague, but I believe these are supposed to be results of collapsing areas of matter that bounce back leaving voids with mostly CDM left behind? (You can laugh now.)
I'm not an advocate of MOND. Perhaps other tests for MOND can be found and dispense with it. It's a theory about gravity, not the CMB. I'm reluctant to take the CMB as first order evidence of much of anything (at this point). You see big conclusions drawn from its ever so subtle texture. To test MOND we need something more direct.
How do I know which papers I should believe and which I should not believe? That's not an easy thing for a beginner. There are plenty of contradictions out there. No sooner than one is published another contradicts it.
I admit to getting leads from the popular press, but I take their interpretation of what was published with a grain of salt and go find the paper they are talking about for starters. I do not take press releases at face value. If I'm interested I look for more papers; not that I fully understand them, but I can read what the writers are actually concluding and more or less understand the methodology.
There is some diversity of opinion about current LCDM, it's not seen as a slam dunk by everyone.
Last edited by TooMany; 2012-May-11 at 11:29 PM.
Established Member
OK, agreed. That's exactly what I'm trying to say about this theory. I would not dismiss it, but I would not assume it's truth either and apply it without doubt in all analysis of observations. In other words, even though the theory is very tempting, doctrines and dogma can be bad for science. Particularly because in this case, the theory in part dictates the interpretation of the observations!
An example of this concern comes in fusion research where almost all the eggs are in one basket, ITER. Other approaches are so underfunded as to approach starvation. The ITER direction has become doctrine in the fusion physics community. It absorbs billions while a paltry few million are left for other innovative paths. I'm sure some career physicist in that community would say something like: "Well it is the best way we know right now so it should continue to absorb most of the available funding". There are some reasons to doubt that ITER, even if it "works", will ever be practical.
Hopefully the same thing is not going on in astronomy with LCDM projects sucking up all the research funds available. I've heard complaints (in papers and news articles) from other astronomers about this. But it's not just funds. It's group think that creates a bias against innovation. E.g., "well I have new idea and I'd like to check it out." "Do you realize that that is impossible in well-established theory? I cannot support you in such a pursuit."
Why do you assume that I do not? I do check into these things. Sometimes the papers are massive and the point that the OP is trying to make is hard to extract. Also, I peruse enough papers to know that the ones often suggested are in disagreement with others. They are often attempts at explaining divergence from theory by considering some other effect to reduce the strain. They are not always very compelling.
Established Member
I'm not talking about the CMB, I'm talking about the matter distribution as traced by galaxies. It's a pretty direct measurement: look for a peak in the galaxy/galaxy correlation function around the 150Mpc scale. And as I said, it was a prediction of LCDM before it was discovered, and no other cosmological theory produces it. As a direct prediction of LCDM, it can be used as a standard ruler to measure the angular diameter distance instead of the luminosity distance of, e.g. supernova searches. The position and amplitude of the peak provides quite strong constraints on the cosmological parameters that are orthogonal to those produced by supernova or CMB measurements.
I've given you two references for the measurement of the BAO feature so far (Eisenstein et al. 2005 and Anderson et al. 2012, which is currently under review); maybe you could read them? If you have trouble with those, the wikipedia page is quite good, as is this page by Martin White and these various links from Daniel Eisenstein, particularly the animations of expanding waves in the 5th bullet and this description.
Also, why are you so quick to reject measurements of the CMB? It's the most perfect blackbody ever observed. We've measured its power spectrum on scales from the whole sky down to below an arcminute at quite astonishing accuracy, and we have a single coherent explanation for the exact amplitude and position of all the peaks in said power spectrum, including the effects of non-linear matter evolution in the universe (gravitational lensing from galaxies and clusters, scattering from hot gas, the Sunyaev-Zeldovich effect, etc.) on the smallest scales.
Focusing on the lowest multipole is kinda like claiming that because 1998 was the warmest year on record in the CRU data, global warming isn't happening. What about the hundreds of other multipoles that have been measured by a dozen or so different surveys? The lowest multipoles are the ones that are most uncertain, because of the windowing effects that Shaula described and because of the effects of non-CMB sources (e.g., the Galaxy!) that are very hard to remove on those scales.
I wonder where you've gotten this idea about "plenty of contradictions?" If you have papers that you are curious about or that you'd like to understand better, you could start a thread about them here on BAUT. But coming in with the view that "astronomers are doing everything wrong" doesn't really endear you to those who might be best placed to answer your questions.
Established Member
I never claimed "astronomers are doing everything wrong". One example of contradictions is in relation to the "cold spot". There were a couple of papers concluding that there was a dearth of galaxies (a large void) way out there. Later there were papers denying these findings and taking issue with the statistical methods used. Out of curiosity I wondered if the authors of one original paper were properly chastened but apparently they were not. I'll put your links in my reading queue and thanks for them. There's an awful lot to absorb.
Established Member
All right, the beginners version in the wiki has gotten me started and it raises an immediate question that maybe you can answer. The shells of concentrated matter created by the acoustic process also entail an under-density of CDM where clusters are now and an over-density in voids. This means the total CDM component is even higher than that derived for clusters. In addition, it implies that voids are massive with CDM since it accounts for at least 80% of all mass overall. We know voids have very few galaxies and thus presumably little baryonic matter. There should be evidence of the extra mass in voids. In fact, most of the mass in the universe should be in the voids. This extra mass would also tend to decrease the expansion rate of voids below the average rate.
Has all of this been born out in measurements? I just starting here so I have no idea.
Established Member
Be careful: the BAO is completely separate from the existence of voids and walls. Voids and walls would form in a 100% dark matter universe, with no baryons or neutrinos or photons. The BAO only occurs in a universe with baryons and dark matter. I like to call it "proof that there are baryons in the Universe!"
The BAO is on a scale much larger (~150 Mpc) than the voids (~10-20 Mpc in diameter). The BAO appears because dark matter falls onto the initial baryon overdensity at that large scale, so if there are no baryons somewhere, then there's nothing for the dark matter to be attracted to. It is also a fluctuation of order a few percent above the mean overdensity at that scale, and can only be discovered with a large volume galaxy correlation function/power spectrum survey.
Established Member
OK, I was all excited that they could account for the texture of the voids and their formation, but it has nothing to do with that. You are saying this is a much more subtle over/under density, on the order of a few percent? That scale is just 10 times the extreme baryonic density fluctuations that are seen in the SDSS data. This must be some highly statistical argument that such a thing exists, because the substructure on that scale is so coarse.Be careful: the BAO is completely separate from the existence of voids and walls. Voids and walls would form in a 100% dark matter universe, with no baryons or neutrinos or photons. The BAO only occurs in a universe with baryons and dark matter. I like to call it "proof that there are baryons in the Universe!"
The BAO is on a scale much larger (~150 Mpc) than the voids (~10-20 Mpc in diameter). The BAO appears because dark matter falls onto the initial baryon overdensity at that large scale, so if there are no baryons somewhere, then there's nothing for the dark matter to be attracted to. It is also a fluctuation of order a few percent above the mean overdensity at that scale, and can only be discovered with a large volume galaxy correlation function/power spectrum survey.
I read that this BAO size at recombination is the same as the size now, ~150 Mpc. How can that be if the universe has expanded at lot since then? How far do you think baryons can fall toward a few percent over-density during 13.4 Gy? I'd better read some more. (A 20 Mpc void could barely be cleared even with matter moving at steadily at 1,000km/s in the lifetime of the universe. How do we account for them?)
Administrator
This has gotten pretty off topic... I don't blame anyone, but I *do* suggest starting a new thread if you want to talk about the creation of voids and walls. Otherwise, this discussion will get lost.
Forming opinions as we speak
Order of Kilopi
I know antoniseb has suggested that I not write a post like this (well, he implied it, and it's good advice anyway), but ...
... perhaps you think you didn't; perhaps you actually didn't, in some strict sense.
However, you certainly have - or have had - a habit of very strongly implying that astronomers, in general, are closed-minded, bent on defending widely accepted models and theories (to the exclusion of alternatives), and do not regard observation as primary.
Worse, when various BAUTians put time and effort into trying to answer the actual content/question parts of your (often quite wild) statements, my impression is that you rarely bother to follow up in sufficient detail (when those answers involve, in effect, a demolition of what you seem to have hoped to find).
You've probably noticed that some BAUTians have ceased responding to posts you've written, and that some of those might - just might! - actually be quite well-informed about the topics you seem so interested in. Perhaps you might ponder on why that is.
Chastened? Chastened?!?One example of contradictions is in relation to the "cold spot". There were a couple of papers concluding that there was a dearth of galaxies (a large void) way out there. Later there were papers denying these findings and taking issue with the statistical methods used. Out of curiosity I wondered if the authors of one original paper were properly chastened but apparently they were not.
I'll try one last time: you really, really should make a strong effort to get to know some real astronomers. You know, the people who've spent decades doing astronomy, and (in many cases) nothing but astronomy their entire adult lives (they probably even dream astronomy!), and much of their pre-adult lives too.
Yes, there is. And there are lots of people here who'd be only to happy to help you absorb, and learn.I'll put your links in my reading queue and thanks for them. There's an awful lot to absorb.
Established Member
Using that term implies, to me, a poor understanding of what a paper is and what it means. Science generally is a rather complicated topic. The arguments against the cold spot were quite subtle, a mix of signal processing and statistics. The background to it was probably outside the experience of the people producing the paper, just like precision astrophysics may outside the experience of the people who wrote the counter-paper. No one can be an expert on everything.Chastened? Chastened?!?
The goal of a paper is not to lay out the truth but to present findings, findings people can then assess and respond to in the hope that the community of scientists as a whole can bring along their collective skills/knowledge and either support or refute the work. Dozens of papers and analyses later and you might have something that has run the gauntlet, been tested and is accepted. Which is why it is usually so pointless throwing arxiv quotes at each other.
People seem to want to know the latest and best ideas too much now. They skip the whole 'letting the community test it' phase and then complain that 'science' cannot make up its mind! It is rather like claiming a business is headless because it doesn't follow through on every bid proposal its R&D department put forwards.
Established Member
It also implies a poor understanding of how science works.
Science is not so much about being right as it is about discovering the unknown. In science being wrong is not a sin or failure but is part of the process, it's why there is peer-review.
Chastening for being wrong would discourage scientists to try, in order to avoid the risk of being chastened, and thus would hinder progression of science.
Established Member
Well, we all agree about the way science should work. I cannot say with any certainty that there is prejudice against new or different ideas, but I have seen that claimed by a number of astronomers who's ideas are not strictly mainstream. I certainly agree that every new paper that comes out is not necessarily correct. Deductions that lead to conclusions are so complicated that the conclusion are somewhat fragile (on any side of the issue). Only time and more research will resolve the issues. In the meantime I'll remain open minded about the possibilities. In my mind (being blissfully ignorant) everything is on the table and nothing is truly written in stone.
Established Member
Apparently any prejudice against new (initially non-mainstream) ideas is not so strong that science can not progress, as it has done for centuries.
Established Member
No, it just takes a few decades after the idea is introduced. Ultimately it could only be stopped by absolute authorities and history shows that those fade within ~ 1,000 years.
Order of Kilopi
This is ridiculous. You imply that scientists are brainless automatons. I beg to differ.
Everyone is entitled to his own opinion, but not his own facts.
Order of Kilopi
TooMany has been infracted (in a different thread) for extending this view of science into a general slur against BAUT members. Let's all drop that side topic from this thread.
Get up, a get-get, get down.
Established Member
OK, let's get back on subject. In recent years some corrections have been made in that galaxies have more baryonic matter than previously thought due to 1) underestimated dust (which hides stars), 2) larger contribution in the low mass IMF, 3) miscount of small stars because they are hidden in bright clusters with large stars, 4) the existence of a hot corona of plasma surrounding galaxies and perhaps others. I don't know what all of this actually adds up to now. There are various estimates of how much missing mass there is in galaxies. I'm not sure how sensitive they are to assumptions about the distribution of that mass. Let's forget about the CMB conclusions for a second and just think about the distribution of matter and DM in a typical spiral. How much ordinary matter is actually required to account for rotation curves if that extra ordinary matter is optimally distributed? I ask this because the usual assumption is that the DM is non-baryonic and more or less spherically distributed over a much larger volume than the ordinary matter. I suppose the amount of DM required to explain the rotation curves is based on this type of distribution. Certainly one baryonic possibility is that it is in fact distributed like the proposed non-baronic matter, but that doesn't seem likely because the properties are so different.
Would anyone care to offer some information? In this case you have to imagine that there is no non-baryonic matter, but instead there is some "hidden" baryonic matter. What is the minimum amount needed? Do you have a reference?
Established Member
I'm giving an exam soon. One of the problems is related to this question, so why don't I throw it out for BAUTers to do?
Below is the rotation curve of a relatively nearby galaxy. It shows radial velocity (km/s) on the vertical axis, and angular distance (arcsec) from the center of the galaxy on the horizontal axis. The distance modulus to this galaxy is about (m-M) = 27.9 mag, so the distance is about 4 Mpc.
(If you can't see the picture, look at http://stupendous.rit.edu/richmond/temp/ugc7321_rot.gif)
ugc7321_rot.gif
Please estimate the amount of mass the galaxy must have (out to some radius) in order to explain the observed rotation curve. Feel free to distribute the mass in any way you wish.
The apparent V-band magnitude of this galaxy is around m(V) = 11.4. What is the absolute magnitude? Express the galaxy's luminosity in solar units.
What is the mass-to-light ratio of the galaxy you derived? Could that ratio be explained by any reasonable stellar mass function? If so, what are the parameters of that mass function?
Have fun!
Order of Kilopi
What's with the negative angular distance from the center?
Everyone is entitled to his own opinion, but not his own facts.
Established Member
In essence, positive = East of center, negative = West of center.
Order of Kilopi
Thank you.
Everyone is entitled to his own opinion, but not his own facts.
Posting Permissions
Reply With Quote
