Is Dark Matter for real?

[Ken G]

Yet Peebles pretty much summed up my point when he said, in your quote, "We accordingly adopt the simplest physics we can get away with, which is good strategy, but certainly need not be the whole story". Science never has been, nor ever will be, required to provide "the whole story", that will always be a work in progress. The issue at hand is, which is our best current theory, what is the minimal hypothesis that agrees the best with the existing observations and provides the most predictive power and guidance into future observational needs. That is dark matter, and logically, that is also where the lion's share of the research resources should go. I see nothing in Peebles' statements that would suggest otherwise.

[Jerry]

I don't think you understand the mass and size scales at work here. And so what if the gravity wave people came along and had a go at solving this? They haven't, and at the moment cold dark matter fits the bill the best, so what is the point of this idle speculation?

I agree that the bullet cluster studies put forward a good case for CDM. If you read Peebles concerns, and the papers of Milgrom, McGraw and others, there are also many galactic gravitational observations that are difficult to explain with CDM. Weakly interactive CDM should be observable locally. My concern is this is an odd cherry; not a smoking gun.

We need to do the local studies before anyone declares victory. Cassini scientist are scratching their heads over the Titan atmospheric, gravitational, and INMS data. Likewise Enceladas and Iapetus are providing difficult puzzles - planetary geologists are vexed. We need Mossbuer analysis of the outer solar moons, solar Cavendish expirements and other baseline studies.

[Ken G]

If you read Peebles concerns, and the papers of Milgrom, McGraw and others, there are also many galactic gravitational observations that are difficult to explain with CDM.

I don't know about those others on your list, but Peebles was pretty clear, I think, that his concern was not that the observations are difficult to explain with CDM, but rather that they require additional features to be added to the CDM models. His point seems to be that CDM is only a "first cut" solution, and that future versions will need to include richer phenomena. Note that it is perfectly normal for science to progress in that fashion, far from the "we're on the completely wrong track" position you are taking. Hence citing Peebles comments as support for your position is misleading.

[matt.o]

I don't know about those others on your list, but Peebles was pretty clear, I think, that his concern was not that the observations are difficult to explain with CDM, but rather that they require additional features to be added to the CDM models. His point seems to be that CDM is only a "first cut" solution, and that future versions will need to include richer phenomena. Note that it is perfectly normal for science to progress in that fashion, far from the "we're on the completely wrong track" position you are taking. Hence citing Peebles comments as support for your position is misleading.

You've hit the nail on the head Ken G. In fact I saw Peebles give a talk on dark matter a couple of years ago where he proposed a form of evolving dark matter to solve the halo and elliptical galaxy age problems.

[Ken G]

In fact I saw Peebles give a talk on dark matter a couple of years ago where he proposed a form of evolving dark matter to solve the halo and elliptical galaxy age problems.

He's an amazing guy, I took statistical mechanics from him. It sounds like he's well ahead of the pack in his thinking on dark matter.

[folkhemmet]

Right now a variety of methods, independent of each other, come to the same basic conclusion [within reasonable precision] about the Universe's matter density--namely, that it is 20-30% of the critical density. The discovery of dark matter particles, if it occurs, in the quantity that agrees with these other indirect methods will be, whether radical skeptics (like Jerry) like it or not, a super-strong validation of 25% of the current cosmological model (the CDM part of LCDM). It would be stretching credulity for the skeptics to say that "oh, well, it is just a coincidence that the direct dark matter searches, the CMB, galaxy cluster measurements, lensing, etc all arrive at the same conclusion wrt to the Universe's matter density." Now, this ultra-confirmation may not happen, but if it does Jerry and other radical skeptics will have been massively discredited and, most likely, because they are naysayers, massively dismayed. I for one will be along side those "crazy" people who will call such an event a triumph of humanity. There are plenty of things not to be proud over wrt to our civilization; however, our artistic and intellectual achievements are not among them.

[Jerry]

The discovery of dark matter particles, if it occurs, in the quantity that agrees with these other indirect methods will be, whether radical skeptics (like Jerry) like it or not, a super-strong validation of 25% of the current cosmological model (the CDM part of LCDM).

It will/would be wonderful confirmation...just as the actual local observation of gravitational waves will/would validate the Nobel effort of Hulse.

What is good for the goose is good for the gandor: As the local detection limits improve, the lack of any local detections of either Dark Matter or Gravitational waves can render the current explanations for distant gravimetric analysis null and void. (As you have said: I am of the opinion they already have. My world-view requires thermaldynamic balance - that is a philosophical choice.)

[Richard L.]

The point about distributed gravitation on a star within a galexy is well taken, However, if the individual stars in a galexy were locked in place and rotated as points on a wheel as you suggest, then how is it be possible for galexies to look so different from what one would expect of a wheel? How do we explain spirals all those arms and bard spirals with stars trailing from the ends like water out of a rotating sprinkler. They don't look like wheels do they? Note my analogy about the bucket of rotating white paint where black paint is poured into the center and because of the viscosity of the paint, forms spiral arms as the black paint works its way from the center.

[Jerry]

The point about distributed gravitation on a star within a galexy is well taken, However, if the individual stars in a galexy were locked in place and rotated as points on a wheel as you suggest, then how is it be possible for galexies to look so different from what one would expect of a wheel?

I've never suggested that. I have hypothesized that the permiability and permitivity of a vacuum are not constant, but rather a function of the total mass of the system. This would generally (using Newtonian mechanics) cause the baryonic mass of the system to be underestimated.

[nutant gene 71]

Here’s where ‘missing dark matter’ is really missing. NewScientist article: Galaxy without dark matter puzzles astronomers says this galaxy, NGC 4736, doesn’t exhibit any dark matter. Curious that they should say:

” Even then, one exceptional dark-matter-less galaxy would be a great puzzle. "The current picture is that galaxies form inside of dark matter halos," Diemand told New Scientist. The dark matter's gravity attracts ordinary gas, which can then coagulate into stars.
"It is unclear how one would form a galaxy without a dark halo, or how one could remove the halo without destroying the galaxy," says Diemand. "A galaxy without dark matter really does not fit into our current understanding of cosmology and galaxy formation."
Nor can galaxies with declining rotation curves be easily explained by MOND, says McGaugh. So for now, it seems that some of our missing mass is missing.”

However, if the ‘missing dark matter’ attracts cosmic dust and gas into stellar combustion, it may have been either consumed or somehow ‘modified’ into non-dark matter, and now acts as ordinary baryonic matter instead. Either way, dark matter was instrumental in coagulating into stars out of ordinary gas, since it acts gravitationally on a higher order of magnitude than ordinary matter gravity, but per this article it is no longer detectable. This could be, however, because of the assumptions involved in measuring hydrogen gas on galaxy’s perimeter, which may be a flawed assumption, so expected declining rotation curves are not self evident. I for one think so called ‘dark matter’ is merely non-luminous higher G ordinary matter, for the record.

[Buzz-Lite-Punch]

There’s a bit of discussion on NASA TV at the moment, about (Dark Matter and Chandra), most of this is way over my head for clear understanding on how our universe works?

Can (Dark Matter), be consumed by a (Black Hole)?? Or is (Dark Matter) a member or family to (Black Holes)??

[Jerry]

Here’s where ‘missing dark matter’ is really missing. NewScientist article: Galaxy without dark matter puzzles astronomers says this galaxy, NGC 4736, doesn’t exhibit any dark matter. Curious that they should say:

Such a galaxy is easier on Dark Matter theories than other alternatives: Dark Matter could be missing, modified gravity could not.

Still, one galaxy, and a number of assumptions about this rare, exceptional observations does not make or break a theory, any more that the unusual 'bullet cluster' provides proof positive of dark matter. Curious objects are observed. Normal objects look curious when they are shouded in gas or warped by [distance effects].

[Ken G]

Such a galaxy is easier on Dark Matter theories than other alternatives: Dark Matter could be missing, modified gravity could not.

That's a pretty good point-- and how ironic, it is in effect a true case of the exception that proves the rule!

[Jerry]

A theory (I won't mention who's) that hypothesizes that Newtonian mechanics underestimate the mass of galactic centers has a chance of surviving, if this galaxy core is truly undermassive relative to the core luminosity - that could be true if the baryonic mass in the core is burning much more brightly than the norm. This is certainly a system worthly of further study.

[schlaugh]

Physicists Renew Claim, in New Experiment, of Detecting Dark Matter Particles

By DENNIS OVERBYE
Published: April 17, 2008
A team of Italian and Chinese physicists on Wednesday renewed a controversial claim that they had detected the mysterious dark matter particles that astronomers say swaddle the galaxies in halos and direct the evolution of the universe.

The team, called Dama, from “DArk MAtter,” and led by Rita Bernabei of the University of Rome, has maintained since 2000 that a yearly modulation in the rate of flashes in a detector nearly a mile underneath the Gran Sasso mountain in Italy is the result of the Earth’s passage through a “wind” of dark matter particles as it goes around the Sun. Other groups of hunters of dark matter have just as consistently failed to find any evidence of the putative particles.

At a meeting in Venice, Dr. Bernabei reported that a new, bigger experiment named Dama/Libra had now observed the same modulation. “No other experiment whose result can be directly compared in a model-independent way is available so far,” she said. The findings increase the chances that the modulation is real, outside dark matter experts say.

Dark matter has taunted astronomers and physicists ever since the astronomer Fritz Zwicky of the California Institute of Technology pointed out in the 1930s that clusters of galaxies appear to be missing enough visible matter to hold them together gravitationally. Speculation has centered on the possibility that the dark matter consists of hypothetical elementary particles left over from the Big Bang — so-called WIMPs, or weakly interacting massive particles, that are immune to most forces of nature and so can pass through us and the Earth like ghosts.

[borman]

DAMA paper

For those who would like more details, the paper has been posted on the arxiv:

First results from DAMA/LIBRA and the combined results with DAMA/NaI

Abstract: http://arxiv.org/abs/0804.2741

[loglo]

They are reporting an 8 sigma confidence limit of detection with the combined data. That seems fairly significant. Is there any other experiment of similar sensitivity being run that will be able to confirm?

[borman]

They are reporting an 8 sigma confidence limit of detection with the combined data. That seems fairly significant. Is there any other experiment of similar sensitivity being run that will be able to confirm?

There are other WIMP seaches going on such as CDMS and XENON and they have not detected anything yet and so place limits on the supposed cross section of WIMPs. It is a quiestion of WIMPs or NIMPs where the latter only interact gavitationally and do not go "bump" in the night.

To verify, there would need to be other LIBRA testing sites at differeing lattitudes and orientations. The DAMA team suggests their setup is different from the other searches and their null results do not impact as much upon their results.

The signal does seem believalbe, but it is a different thing to conclude that it is Dark Matter. For example they may be successfully monitoring neutral spallation byproducts from UHECR striking dust from the ISM that is not deflected by the solar magnetic field and is allowed entrance into the solar system.

One thing to keep in mind though is that, from planetary ephemeris, no Dark Matter Effect is seen within the solar system while it is apparent in the paths and velocites of stars moving in galactic orbit. The effect is also seen on scales as small as globular clusters. So one is left wondering why WIMPs cluster at that scale and not others.

One of the other branches of theories hold that maybe gravity is altered, either a dotG theory like MOG or a threshold theory like MOND.

While there are a variety of theories each of which has had some success in capturing the Dark Matter Effect, whether LCDM or the modified gravity or modified inetria theories, they all also have their failures. Many times the failure of one is covered the success of another, but there exists at least one example where they all fail at the same time. So a final correct theory may still be off in the future yet.

[01101001]

Cosmic Variance Blog: Juan Collar on Dark Matter Detection

I’ll start with the most negative, so as to end up on a brighter note:

The modulation is undeniable by now. I don’t know of any colleagues who doubted these data were blatantly modulated already back in 2003, when “the lady” (DAMA) decided to keep mum for a while. However, to conclude from something this mundane that the experiment “confirms evidence of Dark Matter particles in the galactic halo with high confidence level” or that there is “an evidence for the presence of dark matter particles in the galactic halo at 8.2 sigma confidence level” is simply delusional. There is evidence for a modulation in the data at 8.2 sigma, stop. Compatible with what would be expected from some dark matter particles in some galactic halo models, full stop. Anything beyond this is wanting to believe, and it smears on the rest of us in the field. Of course, of course… there is no other observed process in nature that peaks in the summer and goes through a low in winter, so this must be dark matter, right? [...]

[loglo]

Cheers borman and 01, that sounds far more reasonable.

I liked this bit from 01's link, says it all:

(Occam is turning in his grave, rusty razor still in hand. He is thinking a remake of that opening scene in “Un chien andalou”, with help from this little lady. I am channeling him loud and clear).

[borman]

While it is important to run more controls and calibrations to strengthen the reality of the signal, one can not rule out just yet that it is Dark Matter. As WIMPs it is hard to reconcile with the other experiments who are out to see the WIMPs too.

As the article linked by 01 mentioned, it may be that the single hit event is detected at the atomic or possibly even lattice level considering how pure the NaI is.

One thing that seems missing from the DAMA data is whether there is a modulating role for the time of day apparent in the data. When the detector travels in the direction of enhancement during the summer, does the fact that the Earth is in the path of detection every 12 hours cause a fall off of the signal only to see it get stronger when only around 2 km is overhead 12 hours later yet? Sizeable particles such as alpha and neutrons may get scatttered by the planet from the energy of the signature seen. There could well be a modulation signature upon all WIMPs travelling through the Earth as opposed to the little bit afforded by being in a deep mine.

The absence of the daily modulation upon the signal could help point to what is being seen. Most useful would be the data from the WMAP mission where the direction and speed of the Earth figure into the temperature variations. What WMAP sees are the cosmological photons that have been stretched to where they are in the microwave range. At the same time, there were generated cosmological neutrinos that also have stretched in presumeably the same ratio. Unlike photons, neutrinos can pass easily through Earth from the bottom up as from top down without giving any strong evidence of scattering or modulation.

However, in recent years, experiments have suggested that neutrinos appear to oscillate through their three flavors. There is still an outstanding problem of how they do this without a rest mass to permit them to move at light speed. Nevertheless, the signal appears at the low end of the detector energy range, around 2-6 keV. And so one should wonder if LIBRA is somehow able to detect the oscillation into the more massive flavor of neutrino as it passes into one of the detector bars. At least the cosmological neutrino density profile should have something incommon with the WMAP results as regards how Earth's movement affects the observed temperature variations that would correlate with the signal seen by DAMA.

[borman]

A standard isothermal galactic halo of WIMPs is ruled out for the DAMA/LIBRA annual modulation signal.

Experimental constraints on a dark matter origin
for the DAMA annual modulation effect

Abstract: http://arxiv.org/abs/0807.0879

PDF (4 pages): http://arxiv.org/PS_cache/arxiv/pdf/...807.0879v1.pdf

[pie33]

"Einstein theorized that gravity is not a force between two objects but the bending of space-time as a property of mass." - Maybe the greater distance between massive stars, the stronger the property of gravity becomes.

Dark matter maybe the results of the expanding universe. Whereby the property of gravity is pushing dark matter faster to its conclusion. A total voild of everthing there is the universe.

[trinitree88]

There's a little news here. Results from DAMA not confirmed with regards to dark matter. 6-8 standard deviations not. pete

see:http://arxiv.org/PS_cache/arxiv/pdf/...907.1438v1.pdf

[Jerry]

http://arxiv.org/PS_cache/arxiv/pdf/...907.2731v2.pdf
IMPROVED CMB MAP FROM WMAP DATA

The cosmic microwave background (CMB) temperature maps published by the Wilkinson Microwave Anisotropy Probe (WMAP) team are found to be inconsistent with the differential time-ordered data (TOD), from which the maps are reconstructed. The inconsistency indicates that there is a serious problem in the map making routine of the WMAP team, and it is necessary to reprocess the WMAP data. We develop a self-consistent software package of map-making and power spectrum estimation independently of the WMAP team. Our software passes a variety of tests. New CMB maps are then reconstructed, which are significantly different with the official WMAP maps. In the new maps, the inconsistency disappeared, along with the hitherto unexplained high level alignment between the CMB quadrupole and octopole components detected in released WMAP maps. An improved CMB cross-power spectrum is then derived from the new maps which better agrees with that of BOOMRANG.

Two important results are hence obtained: the CMB quadrupole drops to nearly zero, and the power in multiple moment range between 200 and 675 decreases on average by about 13%, causing the best-fit cosmological parameters to change considerably, e.g., the total matter density increases from 0.26 up to 0.32 and the dark energy density decreases from 0.74 down to 0.68. These new parameters match with improved accuracy those of other independent experiments. Our results indicate that there is still room for significant revision in the cosmological model parameters.

Fluffing the data removes some rather quirky track marks, but gives us nothing absolute: If the baseline calabration errors were this bad, all bets are off. Hopefully, Planck will give us new, improved absolutes...possibly very different absolutes.

[Jerry]

arXiv:0907.3940

Kai Schmidt-Hoberg, Martin Wolfgang Winkler

Abstract

We perform an extensive study of the DAMA annual modulation data in the context of inelastic dark matter. We find that inelastic dark matter with mass m > 15 GeV is excluded at the 95% confidence level by the combination of DAMA spectral information and results from other direct detection experiments. However, at smaller m, inelastic dark matter constitutes a possible solution to the DAMA puzzle.

[borman]

Some Additional Constraints of the DAMA signal

Analysis of the low-energy electron-recoil spectrum of the CDMS experiment

http://arxiv.org/abs/0907.1438

DAMA/LIBRA and leptonically interacting Dark Matter

http://arxiv.org/abs/0907.3159

With the later paper, the question as to the lack of evidence from other Dark Matter Particle searches to support the DAMA/LIBRA signal might stem from the possibility that the DAMA/LIBRA signal might be due to lepton-Dark Matter interactions rather than hadron-Dark Matter interactions that are the foundation of most searches is considered. The arguments and conclusions are that this approach will not succeed in addressing the incompatible results between the DAMA/LIBRA interpretation of their discovered signal and the other negative CDM search results.

[Jerry]

http://arxiv.org/abs/0910.4480v1

No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured lightest Kaluza-Klein particle (LKP) WIMPs in the Sun and converted to limits on the LKP-proton cross-sections for LKP masses in the range 250 -- 3000 GeV. These results are the most stringent limits to date on LKP annihilation in the Sun.

Dark Matter still remains the difference between what gravitational theories predict, and what we observe.

A place holder we do not understand.

[borman]

Adler has written a paper stating that inelastic WIMP collisions with normal matter should produce noticeable calorimeter values compared to elastic collisions where the difference is around nine orders. It would be a test of the idea he persues regarding elasitc and inelastic Dark Matter Particles being responsible for the flyby anomaly. Some of the GPS craft with eccentric orbits should cross enough "flux" lines to heat up enough to test the hypothesis of "dual" Dark Matter Particles.

[borman]

More constraints

Observations of Milky Way Dwarf Spheroidal galaxies with the Fermi-LAT detector and constraints on Dark Matter models
http://arxiv.org/abs/1001.4531