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trinitree88
2012-Jul-20, 12:46 PM
Forty-seven new papers today and a lot of good stuff.
...
http://xxx.lanl.gov/abs/1207.4692 Looks at the types of errors that arise when we assume 'round cow' gravitational lenses and concludes such assumptions lead to 'artificial' conclusions. The degeneracy can be minimized when time delay information is available; but it rarely is.

Jerry. In the last paper on gravitational lensing...it would appear that the computer generated images of the distribution of putative dark matter in galaxy clusters is pretty sketchy..note Figure 5, page 6 in the paper. Makes Schiaparelli's canals look pretty good on Mars. pete

SEE:http://www.google.com/imgres?q=giovanni+schiaparelli+canals+on+mars&um=1&hl=en&sa=N&biw=946&bih=674&tbm=isch&tbnid=j79BJMzkaT9qQM:&imgrefurl=http://dungeonsndigressions.blogspot.com/2011/04/google-mars-as-campaign-map.html&docid=osHfZizYPt9uoM&imgurl=http://images.suite101.com/918107_com_mars.jpg&w=1393&h=826&ei=PFMJUKOzK8iw6QGqssykCg&zoom=1&iact=hc&vpx=417&vpy=334&dur=15&hovh=173&hovw=292&tx=137&ty=85&sig=100937898454694408931&page=1&tbnh=128&tbnw=216&start=0&ndsp=13&ved=1t:429,r:7,s:0,i:97

On the other hand, carbon monoxide the putative tracer of molecular hydrogen, seems not to be associated with it here:
SEE:http://adsabs.harvard.edu/full/1989PASJ...41..113S Note well p.118 figure 4, and the authors'. comments that the association is asymmetric on page 121...the carbon monoxide seems to be where the molecular hydrogen isn't and vice versa. This close association is one of the putative reasons that the missing baryonic dark matter is not molecular hydrogen hiding in the halos of galaxies. pete

antoniseb
2012-Jul-20, 02:49 PM
I moved this thread from "Fun Papers". Also, side note to trinitree88, I sent you a PM yesterday, but you haven't responded yet.

TooMany
2012-Jul-21, 12:58 AM
On the other hand, carbon monoxide the putative tracer of molecular hydrogen, seems not to be associated with it here:
SEE:http://adsabs.harvard.edu/full/1989PASJ...41..113S Note well p.118 figure 4, and the authors'. comments that the association is asymmetric on page 121...the carbon monoxide seems to be where the molecular hydrogen isn't and vice versa. This close association is one of the putative reasons that the missing baryonic dark matter is not molecular hydrogen hiding in the halos of galaxies. pete

There is a problem with trusting a tracer. If the stuff is there, but not traced, you won't discover that your tracer doesn't trace it.

kzb
2012-Jul-24, 12:01 PM
I've had a quick look at the first paper Lensing degeneracies and mass substructure. It's very technical ! Trinitree88, for those of us too thick to fully understand this paper, do you have any insights as how this would support or not support the NASA-publicised study below? Or is it not relevant at all?

http://arxiv.org/abs/1207.4466 An evidence for indirect detection of dark matter from galaxy clusters in Fermi-LAT data
Andi Hektor, Martti Raidal, Elmo Tempel

I'll try and read the paper properly tonight, hopefully some lightbulbs will light up when I get chance to concentrate :)

trinitree88
2012-Jul-24, 02:36 PM
I moved this thread from "Fun Papers". Also, side note to trinitree88, I sent you a PM yesterday, but you haven't responded yet.

Antoniseb. Hi. I responded...pro bono it is. pete Danke.

trinitree88
2012-Jul-24, 02:41 PM
I've had a quick look at the first paper Lensing degeneracies and mass substructure. It's very technical ! Trinitree88, for those of us too thick to fully understand this paper, do you have any insights as how this would support or not support the NASA-publicised study below? Or is it not relevant at all?

http://arxiv.org/abs/1207.4466 An evidence for indirect detection of dark matter from galaxy clusters in Fermi-LAT data
Andi Hektor, Martti Raidal, Elmo Tempel

I'll try and read the paper properly tonight, hopefully some lightbulbs will light up when I get chance to concentrate :)


KZB. page 9 "we do not have a firm handle on the mass distribution between the images"....says it all. Computers are very fast, fabulous for crunching lots of data, and wrong when fed the wrong algorithms. The authors simply state that the inferred mass distributions causing the nevertheless very real gravitational lensing....are uncertain as insufficient data streams are usually not available. So when you see "purple dark matter distributions" modeled for the Bullet cluster...maybe that's correct. pete

trinitree88
2012-Jul-24, 03:00 PM
KZB. page 9 "we do not have a firm handle on the mass distribution between the images"....says it all. Computers are very fast, fabulous for crunching lots of data, and wrong when fed the wrong algorithms. The authors simply state that the inferred mass distributions causing the nevertheless very real gravitational lensing....are uncertain as insufficient data streams are usually not available. So when you see "purple dark matter distributions" modeled for the Bullet cluster...maybe that's correct. pete

Note that I am not disputing that the rotation curves of galaxies determined via Doppler shifts, or that the lensing from clusters is unreal ,.. they indicate that something is amiss with Keplerian / Newtonian kinematics....but the picture shown in the following link is quite uncertain, and the likely culprit is untraced molecular hydrogen. Baryonic. Standard Model. No new laws of physics needed, or old ones to throw out then. Too simple for the front page of the Times. pete

kzb
2012-Jul-24, 05:45 PM
Note that I am not disputing that the rotation curves of galaxies determined via Doppler shifts, or that the lensing from clusters is unreal ,.. they indicate that something is amiss with Keplerian / Newtonian kinematics....but the picture shown in the following link is quite uncertain, and the likely culprit is untraced molecular hydrogen. Baryonic. Standard Model. No new laws of physics needed, or old ones to throw out then. Too simple for the front page of the Times. pete

OK ta. Now of course the molecular gas hypothesis attracted much criticism on those other threads. Virtually everyone said it was totally untenable, and clearly excluded by observations on many fronts.

You reference a paper that is (a) 23 years old and (b) appears to be about an atypical galaxy. So get ready for some flack...

Jerry
2012-Jul-25, 03:42 PM
Decades ago, I ran a dinosaur emission spectrophotometer. The calibration was pretty straight forward: spike a series of carbon cup electrodes with the elements we are interested in and do a log/log plot to quantify the spectral line density in the sample...but there are almost always the dreaded matrix effects when new samples are introduced. Spike a sample with the same proportion as a standard, and the spectral lines could be much weaker and occasionally stronger than expected. The density of any given volume of mixed gases and unkown dusts will produce spectral lines that are semi quantitative at best; iffy lower limits at worst. We don't know the density of the gases in the bullet cluster. The presence or absense of dark matter in this one weird event cannot be well constrained.

Still, it is fun to try, and round cows are a good starting point to test the sanity of any theory. It takes much better cows to establish a new one.

trinitree88
2012-Jul-25, 04:26 PM
Note that I am not disputing that the rotation curves of galaxies determined via Doppler shifts, or that the lensing from clusters is unreal ,.. they indicate that something is amiss with Keplerian / Newtonian kinematics....but the picture shown in the following link is quite uncertain, and the likely culprit is untraced molecular hydrogen. Baryonic. Standard Model. No new laws of physics needed, or old ones to throw out then. Too simple for the front page of the Times. pete

SEE:http://blogs.discovermagazine.com/cosmicvariance/2006/08/21/dark-matter-exists/

kzb
2012-Jul-25, 05:32 PM
Trinitree88: I'm easy to confude at my age! One minute you are telling me about untracead molecular hydrogen, the next you are giving links to articles extolling the virtues of non-baryonic DM ?

trinitree88
2012-Jul-25, 06:48 PM
Trinitree88: I'm easy to confude at my age! One minute you are telling me about untracead molecular hydrogen, the next you are giving links to articles extolling the virtues of non-baryonic DM ?

kzb. The link to Sean Carroll's image refers to the fact that the geometry of the putative dark matter "shown" is completely uncertain. The fact that some dark matter must be there is certain....the shape is what's unknown.
Here's another more recent article also indicating that the putative CO/H2 ratio is uncertain not only in different "local" clouds, but in different areas within an individual cloud, due to CO freezing out on dust grains and depleting. SEE:http://ethesis.helsinki.fi/julkaisut/mat/tahti/vk/harjunpaa/carbonmo.pdf

SEE also:
http://iopscience.iop.org/0004-637X/659/1/426/fulltext/70647.text.html

TooMany
2012-Jul-26, 12:49 AM
My understanding is that the BB nucleosynthesis calculations demand that the unseen mass is non-baryonic. Hence there is an intensive search for non-baryonic matter. The nucleosynthesis calculations have another problem; the expected abundance of 7Li is seriously in conflict with observations. All sorts of explanations for this have been tried; lately there is the suggestion that the solution lies in new physics.

It's ironic that the most common molecule in existence, H2, is very hard to detect. Nevertheless, apparently most astronomers feel that they have ruled out the possibility that substantially more baryonic matter exists than is predicted. At the same time, the predicted amount of baryonic matter has not been found (although possibilities are being examined).

Nereid
2012-Jul-26, 01:06 AM
My understanding is that the BB nucleosynthesis calculations demand that the unseen mass is non-baryonic.

Could you refresh our collective memories please? I'm especially interested in what constitutes "demand".


Hence there is an intensive search for non-baryonic matter.

Hence?

Hence???

I don't quite follow the logic here; could you clarify please? In particular, are you saying that the only (or only significant) scientific driver behind the search for non-baryonic (cold?) dark matter is baryosynthesis calculations?


The nucleosynthesis calculations have another problem; the expected abundance of 7Li is seriously in conflict with observations. All sorts of explanations for this have been tried; lately there is the suggestion that the solution lies in new physics.

Yep, ain't science wonderful? I myself particular like the part where any proposed "new physics" has to account for the collective total of all relevant, well-established observational and experimental results (at least as well as "old physics" can). A bit like proposing that vast masses of hydrogen in the outer disks of spiral galaxies, in the form of H2 gas, can account those galaxies' rotation curves ... any such proposal is required to also account for every other relevant observation of spiral galaxies, galaxy groups, galaxy clusters, ...

kzb
2012-Jul-26, 11:48 AM
Obesity is reaching epidemic proportions in most western nations and is still on the increase. Even I, whom well-meaning relatives used to feed up because I was too skinny, have developed a slightly middle-aged waistline in recent years.

Throughout the years of increasing obesity, government advice has been to reduce fat intake and eat more starchy, complex carbohydrate. Scientifically very reasonable, because fats are much higher in calories than carbs, plus your body has to expend a lot of energy to turn carbs into fat, whereas fats can go almost straight on your waistline. Low fat and increased complex carbs is still the official line in the UK.

However, people were still getting fatter. I don't know how it started, maybe the Atkins diet. But hardly anyone now believes the official line. Carbs are bad and fat/protein are harmless. Basically, the official line ignores the insulin connection, which it now turns out is probably the key to obesity (or not being obese). It also turned out that Atkins dieters lost weight faster than other diets, and surprisingly enough, also had no worse cholesterol status than other diets.

Anyway, after years of following the scientific consensus advice and getting a kg or so heavier every year, I've switched and will be severely limiting the carbs. Not actually the full Atkins. So far it is working.

Jerry
2012-Jul-26, 03:53 PM
Obesity...I suspect you pulled up the wrong thread, here.


That’s exactly what you’d expect if you believed in dark matter.
That is exactly what you would expect if you believed in angels, too: Behavior in the cosmos that cannot be modeling using the know properties of ordinary matter. That is the problem with dark matter solutions: The only properties of dark matter are the dynamics we cannot model without sprinkling in numbers that really come from nowhere: Floating cows.

kzb
2012-Jul-26, 05:14 PM
I suspect you pulled up the wrong thread, here.

It was meant to be a little parable on scientific consensus. I'm sure there are plenty of other examples, but those should probably be a thread on their own !

Thanks for the links trinitree88 I will read with interest. The first one looks like a good overview presentation.

TooMany
2012-Jul-26, 05:18 PM
However, people were still getting fatter. I don't know how it started, maybe the Atkins diet. But hardly anyone now believes the official line. Carbs are bad and fat/protein are harmless. Basically, the official line ignores the insulin connection, which it now turns out is probably the key to obesity (or not being obese). It also turned out that Atkins dieters lost weight faster than other diets, and surprisingly enough, also had no worse cholesterol status than other diets.


Apparently the science of nutrition is so complex that we really don't have a good handle on it yet. Way back Eskimos ate nothing but meat and fat but did fine. When they started eating carbohydrates they got fat. On the other hand some Asians, e.g. those in Vietnam, who eat a lot of rice (carbohydrate) and relatively little meat are almost all thin. They are not especially tall either, but that could be genetic.

Go figure. Where knowledge is lacking, people can speculate as they please. I wonder how many diet books have been published versus physics books?

TooMany
2012-Jul-26, 05:27 PM
That is exactly what you would expect if you believed in angels, too: Behavior in the cosmos that cannot be modeling using the know properties of ordinary matter. That is the problem with dark matter solutions: The only properties of dark matter are the dynamics we cannot model without sprinkling in numbers that really come from nowhere: Floating cows.

Yes, but be fair, you have to appreciate the value of it in bolstering the theory.

PetersCreek
2012-Jul-26, 05:57 PM
It was meant to be a little parable on scientific consensus.

Please be more clear with your posts. On its face, without your subsequent explanation, it has every appearance of an out-of-the-blue hijack. TooMany and others, please do not continue this in an off-topic direction.

trinitree88
2012-Jul-26, 07:13 PM
Please be more clear with your posts. On its face, without your subsequent explanation, it has every appearance of an out-of-the-blue hijack. TooMany and others, please do not continue this in an off-topic direction.

Ok. In 1997 Andersson et al found that although the conversion factor for CO to implicit H2 seemed to be a variable in their data....they would nevertheless use a constant conversion factor. surprising. pete
SEE:http://webcache.googleusercontent.com/search?q=cache:FupseLZvnOkJ:ftp://ftp.astro.su.se/andreas/pinwheel.ps.gz+carbon+monoxide+fails+as+hydrogen+g as+tracer+in+galaxies&cd=30&hl=en&ct=clnk&gl=us

Jerry
2012-Jul-27, 11:08 PM
Yes, but be fair, you have to appreciate the value of it in bolstering the theory.

Within limits that is true. I think is was Pamala who called 'Dark Matter' a placeholder for something we are trying really hard to get a better handle on.

The point I was making when talking about the emission spectrophotometer is that when you have a mess like the Bullet cluster, there are only best guesses about how much matter is here or there; and what kind of matter is driving the observables. The mainstream should not sound as shrill (nor as confident) as many of the detractors.

Jerry
2012-Jul-28, 12:44 AM
My understanding is that the BB nucleosynthesis calculations demand that the unseen mass is non-baryonic.
Sort of. I'm rusty here to; but I remember a couple of peaks everyone expected to find in the Cobe CMB that did not mature. The DM/DE ratio is built upon a solution to this quagmire.

Jerry
2012-Jul-29, 04:20 PM
I've had a quick look at the first paper Lensing degeneracies and mass substructure. It's very technical ! Trinitree88, for those of us too thick to fully understand this paper.
When you get a chance, study the features on the bottom of a wave-agitated pool after all of the swimmers are out. The wave patterns on the surface alternatively magnify, then diminish features on the bottom of the pool. Looking into cosmological space is like looking into a frozen wave. There is both gravitational lensing and neutral gas density lensing - we find galaxies much more distant than any one expected to be able to see such; but much of the structure is also hidden. I'm not even certain such features as the great wall actually exist - we could be viewing an area of space greatly magnified by an almost inconceivable macrolens.

kzb
2012-Jul-30, 12:08 PM
^ thanks Jerry, that's a good way of picturing it. However, I think what the paper is getting at is not the neutral gas/non-baryonic DM degeneracy per se - I think they are saying it is not possible to definitively interpret the lensing in terms of a mass distribution, full stop?

kzb
2012-Jul-30, 12:16 PM
Please be more clear with your posts. On its face, without your subsequent explanation, it has every appearance of an out-of-the-blue hijack. TooMany and others, please do not continue this in an off-topic direction.

Sorry if people did not "get it". I think looking to other areas of science and scientific consensus is a valid argument. I certainly did not want to derail the thread into diet and nutrition, simply to point out an official scientific position that hardly anyone has faith in anymore.

Jerry
2012-Jul-31, 04:28 AM
^ thanks Jerry, that's a good way of picturing it. However, I think what the paper is getting at is not the neutral gas/non-baryonic DM degeneracy per se - I think they are saying it is not possible to definitively interpret the lensing in terms of a mass distribution, full stop?

Agreed - one-of-a-kind events like this are funner than hell to study, but it is broad, statistical studies of more common phenomenon that have the best chance of revealing the cosmos.