Dark Matter, On the Ropes?

*Saul*

What comes next if the dark matter hypothesis fails? A hypothesis that is fundamentally incorrect blocks any progress. The entire effort is trying to make a round peg fit in a square hole as opposed to looking for the correct mechanism. What theorist and modeler do is try to change the free parameters to make the model fit what is observed. If the fundamental mechanisms are correct the process has meaning and value. The purpose also of comparing simulations to observations is to kill off incorrect mechanisms.

Computer simulations of galaxy formation with Dark Matter do not match how galaxies are observed to form and do not match the observed properties of galaxies.

The simulations for example have half the observed angular momentum as compared to observations of spiral galaxies and the galaxies that form in simulation are significantly smaller than observed. The problem is dark matter thermalizes the motion of the gas clouds which causes them to clump earlier before forming large galaxies and reducing the angular momentum of the resultant galaxy. In addition the thermalization causes in the simulations a larger galaxy bulge than is observed.

A third problem is how the angular momentum (rotational velocity) changes as one approaches the center of the simulated galaxy as compared to observational data. The computer simulations show dark matter should clump at the galaxy's center which should reduce the total angular momentum (rotational velocity) at the center of the galaxy. This is not observed. The spiral galaxy continues to rotate as one moves to the center of the spiral. This clumping of dark matter in the center of galaxy's also breaks up the bars in spiral galaxy in simulations, which makes it difficult to even form bar, which does not make sense as the observational data indicates spiral bars form and have a long lifetime.

The dark matter detection experiments have not been able to detect dark matter. The point of the dark matter detection is to determine if dark matter does or does not exist.

It is telling that there multiple very fundamental observations that dark matter cannot explain and no one has been able to detect dark matter.

There is currently no viable alternative (MOND has at least as many problems as dark matter) to dark matter, which is curious as there is observational evidence that provides a clue as to what is causing the observational anomalies which dark matter does not in computer simulation explain.

To use an analogy, think of the logical methodology that is used to solve crimes. When there is repeating peculiar evidence at multiple murder scenes, the investigators look for a serial criminal as they expect independent murders to have not have the same peculiar evidence.

This next paper shows eight spiral galaxy properties are interrelate including angular momentum, non random. This is likely a clue to what is really the physical cause of the angular momentum and related anomalies, such the large scale structure anomalies, and the large scale velocity anomalies. (Velocities are higher than the would be expected based on the estimated masses.)

As the authors of the paper note when dark matter was hypothesized there was not large survey data available to test the dark matter hypothesis.

http://arxiv.org/abs/0811.1554

http://www.nature.com/nature/journal...ture07366.html

Galaxies appear (my comment Non random) simpler than expected

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes (1). The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter (2, 3, 4). The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects (5), shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our data set. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology (6).

nicksauce

I think the main problems is that simulating galaxy formation is very hard. There's lots of complex physics involved, we don't quite know how to handle it.

I mean, we also don't know how to simulate star formation, but that doesn't mean there's a problem with Hydrogen.

*Saul*

Quote by nicksauce

I think the main problems is that simulating galaxy formation is very hard. There's lots of complex physics involved, we don't quite know how to handle it.

I mean, we also don't know how to simulate star formation, but that doesn't mean there's a problem with Hydrogen.

Of course we know hydrogen exists and that fusion (hydrogen to helium) creates a great deal of energy. What is the connection with hydrogen and stellar fusion to dark matter and the rotational anomaly of spiral galaxies?

What I have said in my comment is consistent with published papers.

Based on two decades of observation (the more recent and more accurate observational data and computer analysis continues to support the earlier findings) searching for direct evidence of the "dark matter particle" and computer simulations and analysis of what is predicted, to what is observed, is not in agreement. The analysis and the observation supports the assertion that dark matter does not physically exist and if dark matter did exist it could not explain the evolution and morphology of galaxies.

Dark matter appears based on observations and theoretical analysis, in published papers to be an incorrect mechanism.

A failed hypothesis should be treated as a failed hypothesis. Physics has moved on from phlogiston. Physics should and will move on from "Dark Matter". The first step in that process is public criticism of the mechanism in question.

nicksauce

Please find a citation for me from a published paper on what constraints, from not directly detecting dark matter particles, can be placed. From my understanding, the constraints aren't very significant.

Edit: My point, and I know that a lot of people agree, is that computer simulations that show that galaxy formation with dark matter doesn't work isn't evidence against dark matter, it just shows that we don't know how to simulate galaxy formation.

*Saul*

Dark matter has not passed the first hurdle which is that it physically exists. Dark matter requires the creation of a particle that has the necessary properties which simulations indicate unfortunately is not possible.

The observational tests with increasingly sophisticated experimental apparatus does not support the assertion that dark matter exists. The computer simulation results are irrelevant if the "dark matter" particle does exist.

Primarily Zeon100 results are negative for the detection of dark matter.

http://blogs.nature.com/news/thegrea...tays_dark.html

XENON 100 is in a class all its own. It uses around 50 kilograms of a liquid xenon compound that is supposed to emit a flash of light if it gets knocked by a passing dark matter particle. It's the size of the detector that really makes it stand out from the crowd: most dark matter experiments to date measure the size of their detectors in grams rather than kilos. More mass makes an interaction more likely and so even after just 11 days of running XENON 100 has something to say about dark matter.

http://arxiv.org/abs/1005.0380

First Dark Matter Results from the XENON100 Experiment

The XENON100 experiment, in operation at the Laboratori Nazionali del Gran Sasso in Italy, is designed to search for dark matter WIMPs scattering off 62 kg of liquid xenon in an ultra-low background dual-phase time projection chamber. In this letter, we present first dark matter results from the analysis of 11.17 live days of non-blind data, acquired in October and November 2009. In the selected fiducial target of 40 kg, and within the pre-defined signal region, we observe no events and hence exclude spin-independent WIMP-nucleon elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs at 90% confidence level. Below 20 GeV/c^2, this result challenges the interpretation of the CoGeNT and DAMA signals as being due to spin-independent, elastic, light mass WIMP interactions.

As numerous people have stated the first group to find the dark matter particle will be awarded a Nobel prize. However, if the dark matter particle does not exists how does one prove it does not exist? Will the first team that proves the dark matter particle does not exist be awarded a Nobel Prize?

A competing team are arguing that the ZEON100 finding is not definitive. The competing team of course erroneously announced that they had found evidence of dark matter's existence which was not supported by other teams and which was not replicated.

http://arxiv.org/PS_cache/arxiv/pdf/...005.0838v2.pdf

nicksauce

"and hence exclude spin-independent WIMP-nucleon elastic scattering cross-sections above 3.4 x 10^-44 cm^2 for 55 GeV/c^2 WIMPs at 90% confidence level"

Isn't nearly convincing enough to conclude that dark matter is a failed hypothesis, as you say.

*Saul*

As I said, the simulations with dark matter produce galaxies with half the angular momentum of real physical galaxies and galaxies that are an order of magnitude smaller than observed galaxies.

The authors of this paper acknowledge the problem and then propose unrealistic heating and unrealistic lack of cooling of the massive gas clouds to try to rectify the problem. What they are proposing does not agree with observations and analysis of how intergalactic gas cools. As they note in the paper that theoretical toy model assumption creates other problems which does not agree with observations.

http://arxiv.org/PS_cache/astro-ph/p.../0308117v1.pdf

The Angular Momentum of Gas in Proto-Galaxies: II – The Impact of Preheating by
Frank C. van den Bosch, Tom Abel, and Lars Hernquist

Foremost, hydrodynamical simulations of disk formation that include cooling indicate that, contrary to the standard assumption, the specific angular momentum distribution of the gas is not conserved. Instead, the gas looses a large fraction of its angular momentum to the dark matter (Navarro & Benz 1991; Navarro & White 1994), yielding disks that are an order of magnitude too small. This problem has become known as the “angular momentum catastrophe”, and is typically associated with the well-known “over-cooling problem” in CDM cosmologies (White & Rees 1978; White & Frenk 1991). At early times gas cooling is very efficient, leading to the formation of dense gas clumps which loose their orbital angular momentum to the surrounding dark matter haloes through dynamical friction, before eventually merging to form the central disk. Therefore, some mechanism is required to prevent or delay the cooling of the gas, so that it can preserve a larger fraction of its angular momentum. Indeed, simulations in which gas cooling is artificially suppressed until z = 1 yield larger, more realistic disks (Weil, Eke & Efstathiou 1998; Eke, Efstathiou & Wright 2000).

In an ongoing attempt to improve our understanding of the origin and evolution of the angular momentum of baryons, we have performed a number of simulations of structure formation in a LCDM cosmology without cooling. While unrealistic, the absence of cooling allows us to better focus attention on the impact of gravity and (shock) heating on the angular momentum of the baryons. Therefore, such simulations are a logical preliminary step to investigate the build-up of angular momentum in proto-galaxies.

5 DISCUSSION & CONCLUSIONS
A full understanding of the structure and formation of disk galaxies within a hierarchical, cold dark matter cosmogony faces a number of intriguing challenges. First, in the absence of any heating, baryons cool extremely efficiently, producing too many satellite galaxies and resulting in what has become known as the angular momentum catastrophe. In addition, the angular momentum distributions of both the gas and the dark matter in numerical simulations reveal an excess of low angular momentum material compared to real disk galaxies.

However, preheating also has some effects that are less favourable for disk formation. First of all, the total specific angular momentum of the gas within the virial radius, and which is thus eligible to cool and form a disk galaxy, is reduced with respect to that of the dark matter. Thus, although the angular momentum loss may be reduced, there is less angular momentum to start with. Second, the detailed angular momentum distributions reveal a clear increase of the baryonic mass fractions with negative specific angular momentum, making the formation of a disk dominated galaxy less plausible. We therefore conclude that understanding disk formation remains an intriguing puzzle, even in a preheated IGM (intergalactic material).

*Saul*

If "Dark Matter" does not exist and even if dark matter did exist it could not explain the observations, at what point does astrophysics abandon the dark matter mechanism?

The galaxy rotational anomaly, the galaxy velocity anomaly, the spiral galaxy morophological anomalies (there are obvious unexplained patterns and processes going on) has a physical explanation. What is interesting is the physical explanation for those anomalies appears based on published papers to not be dark matter and is not MOND.

http://arxiv.org/abs/astro-ph/0012334v1

“Dark Halo and Disk Galaxy Scaling Laws” by J. Navarro.

Normal matter interacts gravitational with “dark matter”, so dark matter can loss or gain energy from the galaxy. Unfortunately for the “dark matter theory”, hydro-dynamic simulations, fundamentally disagree with real galaxies. The simulations create a model disc that is an order of magnitude smaller than what is observed. This discovery, which is called the “angular momentum catastrophe”, was made 8 years ago. There is no solution to the angular momentum catastrophe, which is not surprising; however, as more detail data and observations concerning spiral galaxies shows structures that could not possibly have been created by the interaction of “dark matter” and normal matter.

It should be noted that the ‘angular momentum catastrophe” problem and the “missing satellites problem” is leading some researchers to state that dark matter does not exist which is interesting as LCDM theory will need to change. The “angular momentum catastrophe” and the missing satellites problem” are not the only fundamental disagreements with the “dark matter” theory and reality.

*Saul*

The direct detection attempts to find evidence that dark matter exist have been negative.

Even if dark matter exists, it cannot explain galaxy formation. It seems logically that dark matter does not exist based on the negative results to observe it.

If dark matter existed galaxies would be an order of magnitude smaller and would have half the angular momentum than this universe and its galaxies. As this is not observed, it appears "dark matter" does not exist.

http://arxiv.org/abs/astro-ph/0505226v1

“The mass of dwarf spheroidal galaxies and the missing satellite problem” by Read, Wilkinson, Evans, Gilmore, & Kleyna

3. Conclusions
In conclusion, tidal stripping cannot be very strong for many, if not all, of the local group dSphs. Strong tidal stripping, which would produce distorted isodensity contours, also leads to velocity gradients and flat or rising projected velocity dispersions - neither of which are observed in the local group dSphs for which we have good kinematic data (but see also Munoz et al. 2005). This suggests that dSph galaxies must be sufficiently massive such that tidal stripping is of little importance for the stars. Either they are on orbits with large pericentres, in which case they can have masses as low as _ 10^8M⊙ (Kleyna et al. 2001); or they are on more extreme orbits in which case they must be _ 10^9 − 10^10M⊙ depending on the extremity of the orbit. Our current cosmological paradigm would favour the latter hypothesis, but this leaves us with a puzzle: if the dSph are really as massive as _ 10^10M⊙ and have dark matter densities which are cosmologically consistent then they would have central velocity dispersions which are too large to be consistent with Draco or UMi - even after significant tidal stripping and shocking.

SpaceTiger

Unfortunately, galaxy formation is extremely difficult to simulate and the failure to simulate a galaxy from first principles cannot be automatically blamed on the dark matter hypothesis. This isn't because the dark matter itself is difficult to simulate (this part is quite easy), but rather because of uncertainties in the baryonic physics. In a dark-matter dominated universe, we expect galaxies to form in a bottom-up fashion, meaning that little things merge together to form bigger things. To simulate the formation of, for example, the Milky Way, we need to simulate the gas physics, star formation, and AGN and stellar feedback of these little things as they merge together to form bigger things. This means that we need to start our simulations on very small scales and run the simulation until the little things merge together to form the present-day Milky Way (which will be hundreds or thousands of times larger than its original components). Such simulations take tremendous computational resources and even then require us to make a great many approximations.

Direct detection experiments are a more promising avenue for examining the dark matter problem, but unfortunately, we've explored only a very small subset of the parameter space of possible dark matter particles. Even if the dark matter hypothesis is wrong, it will be difficult to rule it out as a possibility anytime in the near future. However, physicists continue to examine possible alternative theories of gravity. If one of these theories were to make a successful prediction that ran contrary to most conventional dark matter theories, I think the community would take notice. Unless that happens, astronomers will continue to work within the dark matter paradigm.

Admittedly, dark matter is difficult to falsify, but that doesn't make it wrong. Rest assured, however, that we are working hard on this problem and you will know as soon as we have hard evidence one way or the other.

SpaceTiger

Quote by Saul

“Dark Halo and Disk Galaxy Scaling Laws” by J. Navarro.

Normal matter interacts gravitational with “dark matter”, so dark matter can loss or gain energy from the galaxy. Unfortunately for the “dark matter theory”, hydro-dynamic simulations, fundamentally disagree with real galaxies. The simulations create a model disc that is an order of magnitude smaller than what is observed. This discovery, which is called the “angular momentum catastrophe”, was made 8 years ago. There is no solution to the angular momentum catastrophe, which is not surprising; however, as more detail data and observations concerning spiral galaxies shows structures that could not possibly have been created by the interaction of “dark matter” and normal matter.

I don't see that anywhere in Julio's paper. Where are you quoting from?

Chronos

It took decades to detect neutrinos after Pauli hypothesized their existence, so, it is unsurprising it is taking time to detect dark matter - a much more difficult endeavor. The evidence in favor of dark matter is overwhelming [e.g., bullet cluster] in the minds of most mainstream scientists. Disney has a history of flamboyant opposition to mainstream ideas, so I would suggest a grain of salt when reading his papers.

AWA

Quote by SpaceTiger

Admittedly, dark matter is difficult to falsify, but that doesn't make it wrong.

Same happens with the Tooth Fairy. Rest assured though we are working hard on it.

SpaceTiger

Quote by AWA

Same happens with the Tooth Fairy. Rest assured though we are working hard on it.

Might I suggest putting a camera in your bedroom.

*Saul*

Quote by SpaceTiger

Unfortunately, galaxy formation is extremely difficult to simulate and the failure to simulate a galaxy from first principles cannot be automatically blamed on the dark matter hypothesis. This isn't because the dark matter itself is difficult to simulate (this part is quite easy), but rather because of uncertainties in the baryonic physics. In a dark-matter dominated universe, we expect galaxies to form in a bottom-up fashion, meaning that little things merge together to form bigger things. To simulate the formation of, for example, the Milky Way, we need to simulate the gas physics, star formation, and AGN and stellar feedback of these little things as they merge together to form bigger things. This means that we need to start our simulations on very small scales and run the simulation until the little things merge together to form the present-day Milky Way (which will be hundreds or thousands of times larger than its original components). Such simulations take tremendous computational resources and even then require us to make a great many approximations.

Spiral galaxies show indicates of patterns which indicates they were not formed from many mergers.

A second problem with the many mergers hypothesis is that simulations indicate multiple mergers of spiral with spiral produces an elliptical galaxy. Observationally that is not observed. The number of spiral galaxies stays roughly constant with redshift at 70%.

It should be noted that the paradox between simulation properties and observed properties are fundamental properties of the spiral. Angular momentum and change in angular momentum as one moves towards the core of the galaxy for example.

Saul's comment:Normal matter interacts gravitational with “dark matter”, so dark matter can loss or gain energy from the galaxy. Unfortunately for the “dark matter theory”, hydro-dynamic simulations, fundamentally disagree with real galaxies. The simulations create a model disc that is an order of magnitude smaller than what is observed. This discovery, which is called the “angular momentum catastrophe”, was made 8 years ago. There is no solution to the angular momentum catastrophe, which is not surprising; however, as more detail data and observations concerning spiral galaxies shows structures that could not possibly have been created by the interaction of “dark matter” and normal matter.

Space Tiger: I don't see that anywhere in Julio's paper. Where are you quoting from?

Saul: My error, I copied and quoted one of my own comments. That specific comment is the issue.

http://arxiv.org/abs/0811.1554

http://www.nature.com/nature/journal...ture07366.html

Galaxies appear (my comment Non random) simpler than expected

Galaxies are complex systems the evolution of which apparently results from the interplay of dynamics, star formation, chemical enrichment and feedback from supernova explosions and supermassive black holes (1). The hierarchical theory of galaxy formation holds that galaxies are assembled from smaller pieces, through numerous mergers of cold dark matter (2, 3, 4). The properties of an individual galaxy should be controlled by six independent parameters including mass, angular momentum, baryon fraction, age and size, as well as by the accidents of its recent haphazard merger history. Here we report that a sample of galaxies that were first detected through their neutral hydrogen radio-frequency emission, and are thus free from optical selection effects (5), shows five independent correlations among six independent observables, despite having a wide range of properties. This implies that the structure of these galaxies must be controlled by a single parameter, although we cannot identify this parameter from our data set. Such a degree of organization appears to be at odds with hierarchical galaxy formation, a central tenet of the cold dark matter model in cosmology (6).

AWA

Quote by SpaceTiger

Might I suggest putting a camera in your bedroom.

You got me there

*Saul*

As noted in my above comments, the dark matter hypothesis does not explain spiral galaxy morphology or evolution. There are multiple specific significant gaps between observation and simulation. For example the simulation spiral galaxies have half the angular momentum and are smaller than physical spiral galaxies.

The claim that there is a gap between simulation and observation due to the complexity of the of performing a many body simulation, misses the issue or more appropriate the problem situation. The observational data is pointing to a difficult physical cause.

A different observational problem that I noted in my above comment, is mergers of spiral galaxies with spiral galaxies should produce an elliptical galaxy. The observation that the percentage of spiral galaxies does not vary with redshift and remains at 70% is interesting as it is a clue to what causing the rotational anomaly in spiral galaxies and the systematic morphology changes in spiral galaxies. A second related question is what is causing the difference between spiral and elliptical galaxies? (i.e. What is causing the two very different galaxy types to form.)

An elliptical galaxy's stars do not all rotate about the galaxy's gravitational center in the same direction. That observational fact makes sense based on conservation of angular momentum and the random direction of merging galaxies. What one would expect, if elliptical galaxies formed from multiple mergers of gas clouds or other galaxies is the elliptical would have a small net rotation (its stars rotate in both directions and hence the angular momentum cancels) and should have multiple rotational axises which is what is observed.

The reason that there has been no theoretical progress to explain the spiral galaxy observations is the initial proposed hypothesis "dark matter" was proposed at a time when there has not very accurate survey data showing how galaxies evolve with redshift.

http://arxiv.org/abs/astro-ph/0702585v1

“The Milky Way: An Exceptionally Quiet Galaxy; Implications for the formation of spiral galaxies”, by F. Hammer, M. Puech, L. Chemin, H. Flores, M. Lehnert

Disk galaxies constitute the majority of the galaxy population observed in the local universe. They represent 70% of intermediate mass galaxies (stellar masses ranging from 3× 10^10 to 3 × 10^11 M⊙), which themselves include at least two-third of the present-day stellar mass (e.g., Hammer et al. 2005). Early studies of the Milky Way have led to a general description of the formation of a disk galaxy embedded in a halo (Eggen, Lynden-Bell, & Sandage 1962). Fall & Efstathiou (1980) set out a model of galaxy formation assuming that disks form from gas cooling and condensing in dark halos. Protogalactic disks are assumed to be made of gas containing substantial amount of angular momentum, which condenses into stars to form thin disks (Larson 1976). These disks then evolve only through secular processes.

However, there are several outstanding difficulties with this standard scenario. One such difficulty is the so-called angular momentum problem. That is, simulated galaxies cannot reproduce the large angular momentum observed in nearby spiral galaxies (e.g., Steinmetz & Navarro 1999). Another is the assumed absence of collisions during and after the gas condensation process. Indeed, the hierarchical nature of the _CDM cosmology predicts that galaxies have assembled a significant fraction of their masses through collisions with other galaxies. It is likely that such collisions would easily destroy galactic disks (e.g., Toth & Ostriker 1992).

Using arguments based on either dynamical friction (Binney & Tremaine 1987) or simple orbital time-scale (e.g.,Bell et al. 2006), this time scale has been estimated to be about 0.35Gyrs. Combining the pair fraction and characteristic time scale estimates suggests that for a present-day galaxy with a stellar mass larger than 3 × 10^10 M⊙, the chance it has experienced a major merger since z=1 is 50±17%, 75±25% and 70% according to Lotz et al. (2006), Hammer et al. (2005), and Bell et al. (2006), respectively1. Although less certain, integrating the merger rate to higher redshift implies that a typical bright galaxy may have experienced up to four to five major merging events since z=3 (Conselice et al. 2003).

The widely accepted assumption that a major merger would unavoidably lead to an elliptical is perhaps no longer tenable: accounting for the large number of major mergers that have apparently occurred since z=3 would imply that all present day galaxies should be ellipticals. This is obviously not the case. So it is likely that disks either can survive or are “rebuilt” after a major merger, through whatever mechanism as yet perhaps unknown in detail (see, for example, Robertson et al. 2006).

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nicksauce Recognitions: Homework Help Science Advisor	I think the main problems is that simulating galaxy formation is very hard. There's lots of complex physics involved, we don't quite know how to handle it. I mean, we also don't know how to simulate star formation, but that doesn't mean there's a problem with Hydrogen.