scilogs Dark Matter Crisis

Another reaction to the Dark Matter Debate

Pavel Kroupa | 08. December 2010, 14:30

During the past months there was quite some activity in the German media on the issue of cosmology and the existence of dark matter. Starting with our German paper "The standard cosmological model being tested" (German: Das kosmologische Standardmodell auf dem Pruefstand"), which appeared in the August issue of  Spektrum der Wissenschaft,  some of the leading experts are beginning to re-position themselves, it seems.

In a major German article about himself "Perhaps we are seeking a phantom" (in German: "Vielleicht laufen wir einem Phantom nach"), which appeared in the October issue of Spektrum der Wissenschaft, Prof. Dr. Volker Springel from Heidelberg states that it is quite possible ("Gut möglich") that the current standard model of cosmology is false.

Also, in an interview with the German TV station 3sat/scobel on "MOND - Modified Newtoian Dynamics: A new theory to close gaps" (translated from German: "MOND - Modifizierte Newtonsche Dynamik: Eine neue Theorie, die Lücken schließen soll", on Nov. 25th), Prof. Dr. Matthias Steinmetz from Potsdam also states that, on the long term, we will need a new theory.

Dr. Frederic V. Hessman from the University of Göttingen, upon seeing this blog on The Dark Matter Crisis, wrote a few very interesting comments, some of which we can post here:


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Podcast and presentations to "Dark Matter: A Debate" and the subsequent TV debate are online

Pavel Kroupa | 02. December 2010, 07:53

Note added on 6.04.2012: this page has been translated. See the end of this contribution.

The debate had the following format:

First Simon White had 25 minutes to present his point of view. This was followed  by questions to him from the audience (about 5 minutes). Then Pavel Kroupa had 25 minutestime to present his point of view, again followed by 5 minutes questions. Following this, Simon White and Pavel Kroupa were asked to each give five minute statements summarising their positions. The actual debate then commenced, which also included the audience.

The lecture theatre in the Physics Insitute was overfilled; 300 people attended the event, and another room with a TV monitor showing the life proceedings was also overfilled. Late-arrivals did not find a seat nor standing room. (More)

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Dark Matter: A debate - afterwards while on safari

Pavel Kroupa | 27. November 2010, 12:00

Fleeing  the  European continent to go back to Australia on safari for some satellite-galaxy hunting in Canberra with my friend Dr. Helmut Jerjen, I had a little time on my Quantas  flight and in Singapore and Perth to reflect upon the debate, and I note the following:

Simon White gave an excellent presentation of the impressive agreement of standard cosmology, i.e. the LCDM model, showing some of the available data on large scales and the cosmic background radiation map (his slides are available on his website).  Somebody in the audience during or after the debate was over, mentioned an interesting observation  (unfortunately I do not recall who this was): (More)

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Reactions to the Dark Matter Debate and Another One in German TV

Marcel S. Pawlowski | 24. November 2010, 15:27

While the official video podcast of the Bethe Colloquium "Dark Matter, a Debate" is not available yet, there nevertheless have already been some reactions send via email or posted on astronomy blogs. Some are based on the live blog of the debate. In addition to that, there will be a discussion about Dark Matter in German television this thursday.

Reactions to the Dark Matter Debate

Before the debate, a number of people labeled it as a "MOND vs. Dark Matter" debate, which is simply a wrong statement. This is not the question we as scientists have to ask today. The real issue at hand is the question whether we understand LCDM as being falsified or not. This is independent of the possible existence of an alternative and its successes or failures. Unfortunately, in his report of the debate, Daniel Fisher, who was there himself, also presents it as one between a Dark Matter and a MOND advocate. He shares his impressions (in German) on his Blog Skyweek Zwei Punkt Null.

In contrast to that, Nando Patat, astronomer at ESO, who posts his thoughts on the matter in a post titled "We do not understand nature, we measure it", puts more emphasis on the sociological points Pavel Kroupa raised. He even backs up the statement that it is difficult to go against the mainstrem by refering to one of his papers about very old stars, which was "brutally but superficially rejected". This is in-line with reports by other scientists who for example had observing proposals rejected because they suggested observing disk galaxies at a high redshift. Because the  time-allocation commission "knew" that these cannot have formed in a LCDM universe, the observing time was not granted.

On her Blog "One Small Step", Sarah Kendrew, a Post-Doc in Heidelberg, posts a good introduction to the background of the debate. She also mentiones that Pavel Kroupas main point was not to fighting for a particular alternative theory. She writes: "I get the impression that a large part of Kroupa’s argument is actually sociological: he’s calling for research into paradigm-challenging cosmologies like MOND to be given more attention (without smirking) and funding, rather than creating ever more patches to cover the holes in concordance cosmology." Concerning Simon Whites position, she makes an interesting statement: "White acknowledges the problems yet doesn’t think that a radical new line of thought is needed either [...]. Given his views on the future of astronomy [...] I would have thought he’d be all in favour of setting bright students’ creative minds loose on a problem like this."

As a last point, there was an email by a colleague. He shares some of his thoughts about the debate, which he attended himself. However, he asked us not to mention his name because he does not have a permanent position yet. He is afraid that articulating his point of view publicly will reduce his chances to ever get one. Of course we follow his request by citing him anonymously and would like to thank him for his trust in us which he showed by sending this email.

Simon White's statement that Pavel Kroupa is arguing with a "proof through assertion" is an insolence, as it supposes that the arguments lack any evidence. Consistently, in the following Simon White did not really adress the problems of Dark Matter. Instead, he showed where the standard model works. Ignoring criticism is bad scientific practice. In addition to this, Simon White tried to reduce Pavel Kroupa's arguments to a pro-MOND position, while the failures of the concordance cosmology have nothing to do with the question whether MOND is valid or not. While Simon White initially said that alternatives have to be investigated, he later argued that he gets a lot of letters each day proposing alternative cosmologies. This made Professor Klaas de Boer protest, as it puts theories like MOND on the same level as, for example, crackpot-ideas of non-academics claiming to have disprooven Einstein.

But there was also criticism concerning Pavel Kroupas presentation during the debate. His statement that he does not see any possibility to verify LCDM was perceived as a too fixed position. He might also have insisted more on discussing the small-scale problems of LCDM and that they can not simply be dismissed by stating that the physics at these scales is too complicated. This might have made the debate more ground-breaking, as a lot of people were hoping to see if there are proper counter-arguments to the findings presented in the recent paper. Furthermore, he could have reacted to Simon White's claim that Fornax fits excellently in LCDM, using the isophote-plots of the satellite galaxy he showed in his talk: If the galaxy were embedded in a dark matter halo, it could not be too asymmetric but would mostly be spherically and non-structured, which is not the case. During the debate, Pavel Kroupa did not raise this contradiction between Fornax and the LCDM model.

Another Debate (on TV)

This Thursday (November 25th 2010), at 9pm, there will be another discussion about dark matter in the TV show "scobel". It will be broadcasted on 3sat, a TV station in German providing a common program for Germany, Austria and Swizerland. The title is: "Dark Matter - New Studies Question its Existence". Guests in the show will be Arnold Benz, Gerhard Hensler and Simon White. A TV team of 3sat was filming at the Dark Matter Debate between Simon White and Pavel Kroupa last week, so this will probably be the first chance to see some footage of the event. Furthermore, Pavel Kroupa and Robert Sanders were interviewed for the show. Unfortunately, it is in German. It will be available online in the 3sat mediathek afterwards.

by Pavel Kroupa and Marcel Pawlowski (24.11.2010): "Reactions to the Dark Matter Debate and Another One in German TV" in "The Dark Matter Crisis - the rise and fall of a cosmological hypothesis" on SciLogs. See the overview of topics in  The Dark Matter Crisis.

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Slides of the Dark Matter Debate and of Robert Sanders' MOND Talk

Marcel S. Pawlowski | 22. November 2010, 16:37

On November 18th 2010, Pavel Kroupa and Simon White met in Bonn for a special Bethe Colloquium: "Dark Matter, a Debate". While the video podcast is not available yet, there is a replay of the live blog. Furthermore, Pavel Kroupa's presentation slides can be downloaded as a pdf file.  (More)

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Live Blog of the Dark Matter Debate in Bonn

Marcel S. Pawlowski | 18. November 2010, 10:28

Starting at 3pm local time (Germany), Andreas (AHW) and Marcel (8minutesold) will try to live blog from the debate about Dark Matter between Simon White and Pavel Kroupa in Bonn. As there is no live video stream available, this seems to be the only live coverage of the event. You can follow the report in the field below and even send in a comment or two. (More)

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Dark Matter: A debate at the Bethe Center for Theoretical Physics at Bonn University

Pavel Kroupa | 01. November 2010, 11:25

On July 15th, 2010, Pavel Kroupa held an invited colloquium on "Local Group galaxies as critical tests of the contemporary cosmological model and its failure" at the Helmholtz-Institut fuer Strahlen und Kernphysik of the University of Bonn. The venue had to be shifted to a larger lecture theatre.
The Bethe Center for Theoretical Physics invited Prof. Dr. Simon White (Max Planck Institue for Astrophysics, Garching) and on July 16th Pavel Kroupa (AIfA, Bonn) to hold the Bethe Colloquium on "Dark Matter: a debate".
It will take place on November 18th, 2010, at 3:15 pm, in Lecture Hall 1 of the Physikalisches Institut, Nussallee 12, 53115 Bonn. It is open for all interested. However, it is not likely to be easily accessible for the lay person. The abstract of the Nov.18th Bethe Colloquium reads:
"The subject of this months Bethe Colloquium concerns a question at the interface of cosmology, astrophysics and elementary particle physics: the possible existence of Dark Matter. The existence of Dark Matter is the most prominent proposal to account for the discrepancy between measurements of the mass of galaxies, clusters of galaxies and the entire universe, and measurements based on the mass of the visible matter. So far the existence of Dark Matter is inferred from gravitational effects on visible matter and background radiation and not through direct detection. In his talk Professor S. White introduces the dark matter paradigm and explains its virtues. An alternative proposal to explain the observed discrepancies is introduced by Professor P. Kroupa. He argues that these effects could be due to a modification of the laws of gravity without the need of Dark Matter. The talks are followed by a discussion."
The web-site of the Bethe Colloquia can be found here, and the poster advertising the debate is provided below. A higher resolution pdf version of the poster can be downloaded here. Uni-Bonn-TV will prepare a videopodcast of the event.
 See the overview of topics in  The Dark Matter Crisis.

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Another Conference: New Directions in Modern Cosmology

Marcel S. Pawlowski | 23. September 2010, 10:00

Poster for the conference After the succsessful AG Meeting, next week we will be at another conference, titled "New Directions in Modern Cosmology", to which Prof. Pavel Kroupa was invited. It will take place at the Lorentz Center in Leiden (in the Netherlands) from September 27 through October 1st. As the title suggests, the workshop is about the increasing amount of observational challenges of LCDM cosmology. From the website:

This workshop concentrates on the discussion of recent cosmological observations which present challenges to the standard LCDM model. These observations include: the large scale flows, the sizes and amplitude of galaxy large scale structures, the systematic effects biasing the analysis of CMB data and the lack of large-angle correlations, the anisotropy of the Hubble flow, the evolution of galaxy size, and the failure to find the sub-halo building blocks left over from the primordial fluctuation spectrum.  Last and not least, it is disturbing that in the LCDM model 95% of the Universe have not been observed 'directly'.

While each of these observations can be seen as an anomaly that the model would possibly explain, the bulk of them calls for a more careful analysis of the model foundations, particularly the amount and role of dark substances.


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The standard model of cosmology

Pavel Kroupa | 19. September 2010, 20:30

At the conference "Zooming in: The Cosmos at High Resolution" Prof. Matthias Bartelmann from Heidelberg University gave a didactively beautiful presentation about the standard cosmological model for the general public.

Here is his argument why it is believed that this model is an excellent description of the universe: (More)

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Our contributions at the annual meeting of the "Astronomische Gesellschaft"

Marcel S. Pawlowski | 10. September 2010, 12:10

This coming week we will have the annual meeting of the "Astronomische Gesellschaft" (the German astronomical society) in Bonn. The conference with the topic "Zoomin in: The Cosmos at High Resolution"  starts on Monday (September 13) and will last until Friday. You can find the schedule here. In the afternoons there are a number of splinter meetings on different astronomical topics. For those participating in the meeting and interested in the Dark Matter Crisis, we would like to point out some of our contributions. Of course we will also be around during the week, so feel free to approach us for discussions. (More)

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II. The Fritz Zwicky Paradox and its solution

Pavel Kroupa | 08. September 2010, 10:00

What is the Fritz Zwicky Paradox?

In our previous contribution we gave three historical examples of previous failures of Newtonian mechanics or dynamics. These failures implied quantum mechanics, special and general relativity. While not evident at start, each of these break-throughs lead, many decades later, to very major technological advances with industries worth trillions of dollars today. In the present era physics is experiencing the fourth failure. But how does the failure arise? (More)

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I. The Fritz Zwicky Paradox: the fourth failure of Newton (MOND, MOG, etc)

Pavel Kroupa | 01. September 2010, 10:00

The radical conclusion that Cold- or Warm-Darm-Matter cosmology ought to be discarded as a viable description of physical reality would imply, as a strict logical process, that this physical reality must be non-Newtonian in a certain physical regime which is found on galactic scales and beyond. This goes hand-in-hand with discarding Newtonian dynamics in these regimes.

Indeed, changing dynamics away from Newtonian dynamics is actually already a very well established tradition in physics and results from the desire to understand how objects with "mass" move about and influence each other in our four-dimensional "space-time" world. (More)

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State-of-the-art cosmology: the current status

Pavel Kroupa | 25. August 2010, 10:00

Last week's contribution "Is LambdaCDM or standard cosmology a 4th order speculation, and ought it be further researched?"  was concerned with the recent suggestion by Prof. Abraham Loeb that alternative approaches should be followed to advance science. But at the same time he proposes the alternative approach "MOND plus netrinos" to be a second order speculation not worth the effort.

Following this logic of Loeb, it becomes immediately apparent that LCDM, or standard/concordance cosmology, is at least a 4th order speculation, with the corresponding implications.

Dr. Garry Angus is a very talented young cosmologist currently at the University of Torino, Italy, but shortly moving to the University of Cape Town, South Africa, who has been working in the field of "MOND plus neutrinos". Dr. Angus is the recipient of the Cormack Bequest Prize for his 2007 publication on the topic of the Bullet Cluster, Neutrino Dark Matter and Alternative Gravity. This prize is awarded annually to the most outstanding postgraduate student contribution to astronomical research in Scotland.

Below he directly addresses Abraham Loeb's assertion concerning his field.

It should be noted, before reading Garry's text, that in the LCDM field (4th order speculative science) whole armies of researchers (hundreds?) have been toiling over the past decade to improve the computations and observations. It is the accepted model of cosmology, and over the past 10-15 years the very major professorships in cosmology or extragalactic astrophysics have been filled with experts in this one specific field. In contrast,  "MOND plus neutrinos" (2nd order speculative science according to Abraham) has been worked on by not more than about 2 researchers, while the other alternative, Modified Gravity (MOG), has been worked on by not many more researchers than that as well.

It nevertheless turns out that LCDM sort of works on large scales, and MOND plus neutrinos does at least as well as far as the existing work allows us to judge. Indeed, as Dr. Garry Angus shows below, the cosmic microwave background (CMB) power-spectrum is fitted perfectly well in MOND + neutrinos. On  scales smaller than about ten million light years LCDM fails however, while non-Newtonian/Einsteinian gravity works brilliantly (Kroupa et al. 2010). 

Thus, MOND plus neurinos seems to be the astrophysically most modern and successful cosmological description we have currently. 

Dr. Garry Angus writes:

I'd like to just make a comment on why MOND+neutrinos is not a 2nd order speculation. I  don't know how familiar you are with the literature on MOND+neutrinos, but no one, to my knowledge, has ever suggested that the CMB can be fit by MOND plus the active neutrinos - be they 2.2eV or 0.1eV. Skordis et al. (2006) clearly showed the apparently high 3rd peak is not compatible with even 3x2.75eV in TeVeS, even if the critical MOND acceleration (a_0) is boosted by a factor of 4.

It should be a well known fact to all cosmologists that replacing  Omega_CDM x h2  with the same energy density in sterile neutrinos gives as good a fit to the CMB. The proviso is that this energy density comes in the form of a single, thermal sterile neutrino species. Given a reasonable mixing angle, it is perfectly possible for these sterile neutrinos to be thermalised in the very early Universe. This means the neutrino has a mass of ~11eV. A figure of the MOND + neutrino CMB calculation can be seen here where we fit both WMAP 7 and ACBAR data. As can be seen, the theortical fit is near to perfect to the CMB data.

This has nothing to do with MOND. In fact, it requires MOND to have no influence at redshift z>1000 and a cosmological constant is still required. It just so happens that an 11eV sterile neutrino would resolve all problems MOND has in clusters of galaxies. At 100~kpc (about 300 thousand light years) in basically all clusters there is a 10:1 ratio of DM:baryons (after accounting for MOND), it is only at distances like 1Mpc that there is a 2:1 ratio. Angus, Famaey & Diaferio (2010) looked at 30+ groups and clusters and made the intriguing observation that the Tremaine-Gunn limit for the 11eV neutrinos is reached in every system, but never need be exceeded for very sensible values of the brightest cluster galaxy's mass-to-light ratio.

These neutrinos would free stream out of Milky Way type galaxies, so all the successes of MOND at galaxy scales would be unaltered. The ramification of this is that the galaxies must collapse under their own gravity (enhanced by MOND) without the aid of a cold dark matter halo (see Sanders 2008). Linked to this, we have run preliminary cosmological simulations that incorporate MOND and 11eV sterile neutrinos and the conclusion is that they form roughly the correct number of clusters of galaxies as a function of cluster mass. It could just as  easily have ended up in a big black hole or with no structure forming at all.  If we run numerical simulations with the 11eV neutrino and no MOND, then no structures form i.e. MOND is essential for massive neutrinos to work.

Whether the correct number of galaxies form is an incredibly difficult question to answer and the numerical tools are nowhere near ready - basically because the 2 or 3 people with the necessary expertise to develop the codes can't get jobs for love nor money. However, based on the successes of MOND at galaxy scales, we do expect that MOND+sterile neutrinos can reproduce that observed properties of galaxies with no effort, unlike CDM. For example, as long as a galaxy forms, we know trivially that it will conform to the baryonic Tully-Fisher relation. Furthermore, the highly organised distribution of satellite galaxies surrounding the Milky Way (see Kroupa, Theis & Boily 2005; Metz et al. (2009); Kroupa et al. 2010)  will immediately be explained to be tidal dwarf galaxies. Currently they have no explanation in LCDM.

For these reasons I don't see how MOND+neutrinos is a second order speculation. If one has MOND, then there is an incredibly high chance that 11eV sterile neutrinos must exist and by the same token, if sterile neutrinos at 11eV exist then MOND is needed. In the former case it is possible that a deeper theory of MOND will spring a surprise which conspires at cluster scales, for the expansion history, during the formation of the acoustic peaks of the CMB and during structure formation to resemble an 11eV sterile neutrino. Abraham Loeb mentioned briefly that the baryonic acoustic oscillations appear at the scale predicted by LCDM. I don't believe this is fully accurate. They appear at the scale defined by a scale factor that evolves as if it has a dominant dark matter component, hot, cold or warm. The peaks themselves do not require the dark matter to be cold.

A lot of people talk about neutrinos being against the design, spirit or original intention of MOND. I feel this is never very helpful. As Professor Milgrom clearly states above, the state of observational astronomy was very different in the early 80s. That MOND works at all highly disfavours the need for any type of Warm or Cold dark matter, but if that dark matter is hot and hot enough to free stream from galaxies then MOND (in the 80s) made no predictions about its presence. Nowadays, MOND without sterile neutrinos and MOND with sterile neutrinos are two different models with very different predictions for cosmology.

In addition to the cosmological evidence for 11eV sterile neutrinos, there also exists tentative particle physics evidence from Miniboone (see Giunti & Laveder 2008). And, more experiments are in the pipeline, for instance the T2K experiment will be able to put excellent constraints on 11eV sterile neutrinos, with results probably released in early 2012. Unfortunately, Planck will not offer any evidence for the specific mass of sterile neutrinos because the CDM model with a very low mass (say <0.1eV) thermal sterile neutrino would generate an identical power spectrum. It can, however, rule out the existence of further thermalised neutrino species (i.e. if N_eff=3).

I should add that although 11eV sterile neutrinos is my preferred solution that extends MOND to cosmology, there are others. HongSheng Zhao & Baojiu Li are working very hard testing a model that combines the MOND effect, the cosmological dark matter and dark energy into the same field that behaves differently depending on environment, which is a very nice idea. It boils down to the same essential ingredient for cosmology, however, and that is hot dark matter plus MOND.

by Anton Ippendorf, Pavel Kroupa and Marcel Pawlowski (25.08.2010, "State-of-the-art cosmology: the current status" in "The Dark Matter Crisis - the rise and fall of a cosmological hypothesis" on SciLog. See the overview of topics in  The Dark Matter Crisis.

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Is LambdaCDM or standard cosmology a 4th order speculation, and ought it be further researched ?

Pavel Kroupa | 18. August 2010, 10:00

On August 9th, 2010  Prof. Abraham Loeb from Harvad University  published a stimulating paper on the electronic preprint server with the title "Taking "The Road Not Taken'': On the Benefits of Diversifying Your Academic Portfolio".

In this paper he takes issue with which type of research ought to be supported, making the much noted suggestion that innovative projects not following the main stream should be invested in by young researchers, in addition to following more secure research directions.  Abraham points out that even if one in a million new ideas bear fruit, this may completely transform our understanding of reality justifying the entire effort of using a certain fraction of funding for new, risky ideas.  To achieve this goal, he recommends that each researcher should spend up to about 50 per cent time on non-standard research, while individuals will naturally develop their own strategy based on personal and social factors. His suggestion is further that senior members of the community should find better strategies for rewarding innovation. (More)

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The Train Wreck Cluster - an "anti-Bullet-Cluster": disproof of Cold or Warm Dark Matter

Marcel S. Pawlowski | 11. August 2010, 10:00

This is the final part of our small series on the Bullet Cluster (and galaxy clusters in general). In the first part we have already argued that the Bullet Custer can not be used as a "smoking gun" for dark matter and even poses a problem for concordance cosmology. The second part laid out that theories of modified gravity can account for galaxy clusters and expecially for the Bullet Cluster, too.

There is one cluster which, in some respects, resembles the Bullet Cluster: Abell 520 (see also: Cosmic 'train wreck' defies dark matter theories).  

Source: Chandra X-ray observatory site, Harvard University.

Similar to the Bullet Cluster two galaxy clusters have collided recently. Consequently, the hot gas is again found in the middle of the clusters. And again one expects Dark Matter, as it is collisionless in contrast to the gas (which, when atoms collide, radiates its energy in the form of light and thus cools and slows down), to be centered on the two galaxy clusters. But to the surprise of the Dark-Matter community, Mahdavi et al. (2007) found a “Dark Core in Abell 520”, that is, there is Dark Matter in the center where no galaxies are.

This object therefore looks like the inverse of the Bullet Cluster. Things look messed up, that's why the object got the name “Train Wreck Cluster”. We did not find an explanation for it in the literature and one of us, Marcel Pawlowski, even discussed it's case with standard cosmologists. Up to now, they all agree that we do not understand it in Standard Cosmology. Interestingly, the alternative gravity community has come up with an explanation, such as Moffat and Toth (2009) for MOG.

After finding out about the existence of this “Train Wreck Cluster”, one question cames to mind: How is it that everybody mentions the Bullet Cluster as a proof of Dark Matter, but (almost) nobody ever talks about the Train Wreck Cluster? Does an object for which the theory gives a good explanation have more "evidence-value" than an object which seems to be at odds with the theory?  Isn't that a bit too selective for scientists? In fact, while during discussions everybody points at the Bullet Cluster, many people and even a lot of astronomers do not even know about Abell 520!

We have to be really careful here. Always pointing at one object as the ultimate proof for dark matter and not mentioning a counter-example isn't good science. In fact, this selective reporting distorts the evidence especially towards people who do not and cannot acquire the objecitve information - the public gets a wrong impression. 

And stating that galaxy clusters can not be explained in modified gravity theories while there are peer-reviewed papers doing exactly that is very bad style and positively unscientific. The whole problem of the existence of Cold or Warm Dark Matter should not be about opinions, but about science. And the evidence is defintely not in-favour of its existence.

A Radical Conclusion

Why can we make such a radical statement depite the vast majority of fellow-scientists expressing the oposing view?

Well, given the material on galaxy clusters presented here it is very clear that the Cold- or Warm-Dark-Matter hypothesis has problems with galaxy clusters, particularly with the Bullet and Train-Weck Clusters. Non-Newtonian approaches on the other hand seem to easily account for them. And, the Local Group of galaxies (and thus us humans) cannot really exist in a Cold- or Warm-Dark-Matter universe.

Putting this together we get a positively dark view of Dark Matter Cosmology, while the alternative models (MOND or MOG or ... ?) yield a notably bright window towards a much more superior description of cosmological reality.  

by Anton Ippendorf, Pavel Kroupa and Marcel Pawlowski (11.08.2010): "The Train Wreck Cluster - an anti-Bullet-Cluster: disproof of Cold or Warm Dark Matter" in "The Dark Matter Crisis - the rise and fall of a cosmological hypothesis" on SciLog. See the overview of topics in  The Dark Matter Crisis.

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