61. The crisis in the dark matter problem becomes a historically unparalleled failure in the scientific method

This year, Pavel Kroupa was asked to hold a Golden Webinar in Astrophysics on the dark matter problem. This contribution provides the link to the recording of this presentation which has now become available on YouTube. In this presentation, Pavel Kroupa argues that the dark matter problem has developed to become the greatest crisis in the history of science, ever. This contribution also provides links to recordings available on YouTube of previous related talks by the same speaker from 2010 (the Dark Matter Debate with Simon White in Bonn) and 2013 (in Heidelberg). This might allow some insight into how the debate and the research field have developed over the past dozen or more years.

1) Golden Webinar: “From Belief to Realism and Beauty: Given the Non-Existence of Dark Matter, how do I navigate amongst the Stars and between Galaxies?”

On April 9th, 2021, Prof. Pavel Kroupa presented a talk in the Golden Webinars in Astrophysics series on “From Belief to Realism and Beauty: Given the Non-Existence of Dark Matter, how do I navigate amongst the Stars and between Galaxies?”. The talk is now available on Youtube:

The slides to the talk without the fictitious story can be downloaded here:

If you are interested in other talks presented during The Golden Webinars in Astrophysics series, you can find the record of those already presented on their Youtube Channel, and here is a list of upcoming talks. The Golden Webinars are provided as a free public service and have no registration fees.

2) The vast polar structures around the Milky Way and Andromeda

In November 2013, Prof. Pavel Kroupa presented “The vast polar structures around the Milky Way and Andromeda” in the Heidelberg Joint Astronomical Colloquium. In the talk he discussed the failures of the Standard model of cosmology and the implications for fundamental physics.

A blog entry from 2012 on the vast polar structure (VPOS) of satellite objects around the Milky Way can be found here.

3) Bethe-Kolloquium “Dark Matter: A Debate”

In November 2010, Prof. Simon White (Max Planck Institute of Astrophysics, Garching) and Prof. Pavel Kroupa (University of Bonn) debated on the concept and existence of dark matter during the Bethe Colloquium in Bonn. Their presentations and the subsequent debate are available here:

a) Presentations by Prof. White and Prof. Kroupa

Summary of both presentations:

b) The Debate

The German-language television channel 3sat produced a TV report on the Bethe Colloquium, which can be also found on Youtube (available only in German):

Part I

Part II


In The Dark Matter Crisis by Moritz Haslbauer, Marcel Pawlowski and Pavel Kroupa. A listing of contents of all contributions is available here.

59. Are “darker psychological mechanisms” at work ?

(by Pavel Kroupa)

Two related essays have been published by aeon :

1) David Merritt wrote an essay for aeon with the title “A non-Standard model”. It is a very short version of his prize-winning Cambridge Universe Press book “A philosophical approach to MOND” and addresses the problem the cosmological scientist is faced with when needing to reach a conclusion as to the merit of a theory, given the data

Note that “true prediction” is used throughout this text to mean a prediction of some phenomenon before observations have been performed. Today, many numerical cosmologists and an increasing number of astrophysicists appear to be using a redefinition of “prediction” as simply being an adjusted calculation. Thus, the modern scientists observes data, then calculates what the cosmological model would give, adjusts the calculation to agree with the data, and then publishes this as a model prediction.

On the one hand side there is the standard dark matter based model which never made a successful true prediction (in the sense of pre-data) but is believed widely in the community to be true,

while on the other hand side Milgromian dynamics has made many successful true predictions of new phenomena but is deplored by the community.

David concludes this essay with “But I hope that scientists and educators can begin creating an environment in which the next generation of cosmologists will feel comfortable exploring alternative theories of cosmology.”

In addition to the performance of a model in terms of true predictions, a model can also be judged in terms of its capability to be consistent with data. This is a line of approach of model-testing followed by me and collaborators, and essentially applies the straight-forward concept that a model is ruled out if it is significantly falsified by data. Rigor of the falsification can be tested for using very different independent tests (e.g. as already applied in Kroupa et al. 2010). We have been covering this extensively in this blog. For example, the existence of dark matter particles is falsified by applying the Chandrasekhar dynamical friction test (as explained in Kroupa 2012 and Kroupa 2015): Satellite galaxies slow down and sink to the centre of their primary galaxy because of dynamical friction on the dark matter haloes. This test has been applied by Angus et al. (2011) demonstrating lack of evidence for the slow down. The motions of the galaxies in the nearby galaxy group M81 likewise show no evidence of dynamical friction (Oehm et al. 2017). Most recently, the detailed investigation of how rapidly galactic bars rotate again disproves their slow-down by dynamical friction on the dark matter halos of their hosting galaxies, in addition to the dark-matter based models having a completely incompatible fraction of disk galaxies with bars in comparison to the observed galaxies (Roshan et al. 2021a; Roshan et al. 2021b). All these tests show dark matter to not exist. Completely unrelated and different tests based on the larger-scale matter distribution and high-redshift galaxy clusters have been performed in great detail by, respectively, Haslbauer et al. (2020) and Asencio et al. (2021). Again, each of these individually falsify the standard dark-matter based models with more than five sigma confidence.

In summary: (a) By applying the formalisms of the philosophy of science to the problem whether the dark-matter-based models or the Milgromian models are the better theories in terms of their track record in true predictions, David Merritt demonstrates the latter to be far superior. (b) By applying the model-falsification approach by calculating the significance of how the models mismatch the data, we have come to the exact same conclusion.

As alluded to by David Merritt, the frightening aspect of our times is that the vast majority of cosmological scientists seem either not capable or willing to understand this. The lectures given by the leaders of cosmological physics, as can be witnessed in the Golden Webinars in Astrophysics series, collate an excellent documentation of the current disastrous state of affairs in this community. In my Golden Webinar in Astrophysics I describe, on April 9th 2021, this situation as

the greatest scientific crisis in history ever,

because never before have there been so many ivy-league educated researchers who en masse are so completely off the track by being convinced that a wrong theory (in this case dark matter cosmology) is correct while at the same time ignoring the success of another theory (in this case Milgromian dynamics). At next-to-all institutions, students appear to be indoctrinated by the “accepted” approach, with not few students in my lectures being surprised that the data appear to tell a different story. Many students even come to class believing that elliptical galaxies are the dominant type of galaxy, thus having an entirely wrong image of the Universe in their heads than what is truly out there. Once before there was a great clash of ideas, famously epitomised by Galileo Galilei‘s struggle with the Church. But this was very different, because traditional religious beliefs collided with modern scientific notions. Today, the Great Crisis is within the scientific community, whereby scientists ought to be following the evidence rather than belief. Belief should not even be a word used by scientists, as it implies a non-factual, not logical approach. Rather than belief, we as scientists need to objectively test hypotheses which need to be clearly stated and the results of the tests must be documented in terms of significance levels.

2) And the reader of this blog would probably also be interested in the very related earlier aeon essay by myself on Has dogma derailed the scientific search for dark matter?.


In The Dark Matter Crisis by Moritz Haslbauer, Marcel Pawlowski and Pavel Kroupa. A listing of contents of all contributions is available here.

58. The tidal stability of Fornax cluster dwarf galaxies in Newtonian and Milgromian dynamics

(Guest post by Indranil Banik and Elena Asencio, August 2nd, 2021)

A directly-related presentation by Elena Asencio is available here:

The tidal stability of Fornax cluster dwarf galaxies in Newtonian and Milgromian gravity

The slides of the presentation can be downloaded here:

A large number of dwarf galaxies in the Fornax cluster (Figure 1) appear to be disturbed, most likely due to tides from the cluster gravity. In the standard cosmological model (ΛCDM) , the observable structure of the dwarfs is barely susceptible to gravitational effects of the cluster environment, as the dwarfs are surrounded by a dark matter halo. Because of this, it is very hard to explain the observations of the perturbed Fornax dwarfs in this theory. However, these observations can be easily explained in MOND, where dwarfs are much more susceptible to tides due to their lack of protective dark matter halos and the fact that they become quasi-Newtonian as they approach the cluster center due to the external field effect.

Figure 1: Fornax galaxy cluster. The yellow crosses mark all the objects identified in the Fornax deep survey (FDS) for this region of the sky, the black circles are masks for the spikes and reflection haloes, and the red crosses mark the objects that pass the selection criteria to be included in the FDS catalog. Image taken from Venhola et al. 2018.

The impact of tides on what the dwarfs look like is illustrated in Figure 2, which shows the fraction of disturbed galaxies as a function of tidal susceptibility η in ΛCDM and MOND, with η = 1 being the theoretical limit above which the dwarf would be unstable to cluster tides. Moreover, there is a lack of diffuse galaxies (large size and low mass) towards the cluster center. This is illustrated in Figure 3, which shows how at low projected separation from the cluster center, dwarfs of any given mass cannot be too large, but larger sizes are allowed further away. Figure 3 thus shows a clear tidal edge that cannot be explained by selection effects, since the survey detection limit would be a horizontal line at 1 on this plot such that dwarfs above it cannot be detected. Diffuse dwarf galaxies are clearly detectable, but are missing close to the cluster center. Another crucial detail in Figure 3 is that dwarfs close to the tidal edge are much more likely to appear disturbed, which is better quantified in Figure 2 in the rising fraction of disturbed galaxies with tidal stability η. The tidal edge is also evident in Figure 2 in that the dwarfs only go up to some maximum value of η, which should be close to the theoretical stability limit of 1. This is roughly correct in MOND, but not in ΛCDM.

Figure 2: Fraction of disturbed galaxies for each tidal susceptibility bin in MOND (red) and ΛCDM (blue). Larger error bars in a bin indicate that it has fewer dwarfs. The bin width of the tidal susceptibility η is 0.5 in MOND and 0.1 in ΛCDM (each data point is plotted at the center of the bin). Notice the rising trend and the maximum η that arises in each theory.

Figure 3: Projected distances of Fornax dwarfs to the cluster center against the ratio Re/rmax, where Re is the dwarf radius containing half of its total stellar mass, and rmax is the maximum Re at fixed stellar mass above which the dwarf would not be detectable given the survey sensitivity. The dwarfs are classified as “disturbed” (red) “undisturbed” (blue). The black dashed line shows a clear tidal edge – at any given mass, large (diffuse) dwarfs are present only far from the cluster center. This is not a selection effect, as the survey limit is a horizontal line at 1 (though e.g. some nights could be particularly clear and allow us to discover a dwarf slightly above this).

We therefore conclude that MOND and its corresponding cosmological model νHDM (see blog post “Solving both crises in cosmology: the KBC-void and the Hubble-Tension” by Moritz Haslbauer) is capable of explaining not only the appearance of dwarf galaxies in the Fornax cluster, but also other ΛCDM problems related to clusters such as the early formation of El Gordo, a massive pair of interacting galaxy clusters. νHDM also better addresses larger scale problems such as the Hubble tension and the large local supervoid (KBC void) that probably causes it by means of enhanced structure formation in the non-local universe. These larger scale successes build on the long-standing success of MOND with galaxy rotation curves (“Hypothesis testing with gas rich galaxies”). MOND also offers a natural explanation for the Local Group satellite planes as tidal dwarf galaxies (“Modified gravity in plane sight”), and has achieved many other successes too numerous to list here (see other posts). Given all these results, the MOND framework appears better suited than the current cosmological model (ΛCDM) to solve the new astrophysical challenges that keep arising with the increase and improvement of the available astronomical data, which far surpass what was known in 1983 when MOND was first proposed.


In The Dark Matter Crisis by Moritz Haslbauer, Marcel Pawlowski and Pavel Kroupa. A listing of contents of all contributions is available here.

56. From Belief to Realism and Beauty: Given the Non-Existence of Dark Matter, how do I navigate amongst the Stars and between Galaxies?

(by Pavel Kroupa, 4th of April, 2021, 11:11)

Update (April 15th): After receiving some queries, the slides to the talk w/o the fictitious story can be downloaded here

On April 9th, 2021, I will give this public talk:

If interested, you can join the public lecture by registering here.

The talk, held via zoom, is on April 9that 11:00 Chilean Time (CLT = UTC-4),  8am Pacific Daylight Time (PDT = UTC-7),11am Eastern Daylight Time (EDT = UTC-4), 17:00 Central European Summer Time (CEST = UTC+2)

The Golden Webinars are provided as a free public service and have no registration fees. They are recorded and made available for later viewing via youtube.


In The Dark Matter Crisis by Moritz Haslbauer, Marcel Pawlowski and Pavel Kroupa. A listing of contents of all contributions is available here.

50. Update on the Dark Matter Crisis…

and are we at the beginning of a major historical paradigm shift?

(by Pavel Kroupa and Moritz Haslbauer, 07th Nov. 2020; 15:00)

There have not been posts on this blog for some time.  The reason is certainly not that the dark matter crisis has gone away.  Quite the contrary — the dark matter crisis, or more generally the cosmological crisis, has worsened and is now quite catastrophic. More on this in the next blog “The Crisis in Cosmology is now catastrophic”. With this contribution we provide an update on recent developments and some philosophical contemplation concerning paradigm shifts.

As a reminder: this blog on the Dark Matter Crisis was started in 2010 through the pressure (which I first resisted) by staff of the journal Spektrum der Wissenschaft in Germany (equivalent to Scientific American) who wanted Marcel Pawlowski (then a PhD student in the SPODYR group in Bonn) and me to blog about the developing crisis. This was related to the research I was involved with at that time leading me to the conclusion that the astronomical data rule out the standard dark-matter-based cosmological model as being relevant for a description of the Universe. This was in tension with my peers. 

In January 2013 the blog was moved, along with all English blogs on Spectrum,  to Scilogs.com. Later this same year there was a temporarily successful attempt by an amateur-science blogger (a sworn MOND enemy) to have the Dark Matter Crisis close down. This failed and the Dark Matter Crisis continued, simply because it’s content is scientifically solid. In 2016 SciLogs.com decided not to host the English Spektrum blogs any longer, and they were transferred to WordPress.com, where they are now. We have not blogged since this last move which had not gone perfectly well technically, with quite a few images having been lost. Just now we repaired most of the losses after some historical digging and with the help of Srikanth Togere Nagesh, MSc student at the University of Bonn. The corrections are continuing, and we are finding that some old links out of the Dark Matter Crisis blogs do not work any longer – we are trying to update them as far as possible and given the limited time available. This has taught me that documentation developed for the internet is fleeting. But we hope the WordPress platform will remain stable. 

Much has happened since the move to WordPress: Indranil Banik, who had contributed the last piece obtained his PhD and is now an Alexander von Humboldt Fellow in the SPODYR group in Bonn. Marcel Pawlowski obtained a Hubble Fellowship and is now a Schwarzschild Fellow at the Leibniz-Institute for Astrophysics in Potsdam, Germany.  Moritz Haslbauer, who is now researching towards his PhD in the SPODYR group at Bonn University, joined our editorial team just now and will publish his first post in the next contribution based on his own research on the Keenan-Barger-Cowie void and the Hubble tension.  He already published two other research papers, one on galaxies lacking dark matter in cosmological simulations (Haslbauer et al. 2019a), and one on ultra-faint dwarf galaxies in cosmological simulations (Haslbauer et al. 2019b), both finding that the observed galaxies are in conflict with the standard model of cosmology (the SMoC).  Concerning myself (PK), I have taken up a joint affiliation with Charles University in golden Prague and have been spending much time travelling there and beyond. I guess the beer, the knedliky and the scientific and cultural importance as well as the open atmosphere at the institutes and the multi-cultural nature and safety of historically extraordinarily beautiful Prague resonate with me. In Bonn, we hosted the large international conference BonnGravity2019: The functioning of galaxies in 2019 and I disjoined myself from the astronomers and have administratively joined a pure-baryonic-physics institute, namely the theory group at the Helmholtz-Institut für Strahlen- und Kernphysik at the University of Bonn. In this context:

Scientists have explorative minds and we know science evolves into new and often unforeseen directions and we should keep our minds open to these in order to allow science to progress rather than stopping scientific advance. It is also important to continue discussions between people working on different ideas without being dismissive. History shows that changes of paradigm can last decades and for those involved it may be impossible at the time to know if they are on the right track.

from Tereza Jerabkova
But are we in a paradigm shift and are we on the right track? The indications for being on the right track come, of course, from constant comparison of the theory one is developing with the observational data, and this blog will be covering this in the future. But are there perhaps some apparently unassociated hints or indications for an ongoing true major paradigm shift?

From the historical record: Very major paradigm changes in world view (religious, scientific) seem to be associated with significant relatively rapid transformations in the arts and with dramatic historical upheavals. Examples of this are (1) the fall of the Roman Empire went along with large-scale change to benign [thou shalt neither lie to nor kill anyone, but love and forgive everyone and all are equal in front of God] monotheism in Europe which improved local social cohesion, removed slavery from Europe and constituted an essentially critical mental step in abstracting the workings of the Universe. This abstraction is critically important because, simply put, until the abstraction there was a deity for every phenomenon (e.g. god of war). (2) The [first] 30 year war in the 17th century which was associated with the Keplerian revolution. In music, the first opera “L’Orfeo” by Monteverdi appeared in 1607. (3) In the early 19th century, the social transformations and associated Napoleonic wars with their large orchestrated battles outside of cities and the “Revolutions of 1848” appear to go in-hand with the development of thermodynamics and electricity as well as the emergence of romantic music and the symphonies by large orchestras (Schumann, Verdi, Wagner, Bruckner, Brahms, Tschaikowsky, and others). (4) The [second] 30 year war in the 20th century (i.e. the first and second world wars combined) happening in-parallel to the Einsteinian/Planckian revolution and being accompanied by the appearance of the twelve-tone technique by Schönberg and the music by the Russian composers Shostakovich, Prokofjew, Stravinsky, and Rachmaninow. (5?) The current world-wide geopolitical developments which appear with rising tensions and increasing dissociation of the power-blocks from each other, the accelerating demographic and potentially negative cultural-religious shifts in Western Europe, the societal changes concerning personal individualism, cancel culture and political correctness, and all of this in combination with the accelerating over-population, climate, micro-plastic-pollution crisis and on-going mass extinction, do seem to be suggestive of a major upheaval which is in the process of unfolding.

The next blog explains why cosmology is in a catastrophic crisis.

Given my affiliation with Charles University, I have been travelling to Prague and beyond frequently and now the CORONA Pandemic has stopped this flying about the planet — I have already written about the first wave and my getting marooned on a beautiful island next to the Strand. Being this time stranded in Bonn without a Strand during the second wave, I have a little more time on my hands I guess. So here we are, back to the Crisis.

In The Dark Matter Crisis by Moritz Haslbauer and Pavel Kroupa. A listing of contents of all contributions is available here.

48. The Weizmann Experience: discussions on the future of cosmology

Together with Francoise Combes, who was recently appointed as a professor in the most prestigeous institution in France, Le College de France, and Benoit Famaey, who is an expert on Milgromian dynamics and its deeper foundations (e.g. Famaey & McGaugh 2012), we were invited by Mordehai (Moti) Milgrom to spend a whole week at the Department of Particle Physics and Astrophysics in the Weizmann Institute in Rehovot, Israel. A link to the video (dubbed in English) of the inaugural lecture given by Francoise Combes for her new chair and the introduction by Serge Haroche (Nobel Prize 2012 in physics) is available here (alternatives to the dark matter approach are explicitly mentioned by both).

I met Benoit at Frankfurt airport in the very early morning (he was heading in some random direction) since we had booked the same Lufthansa flight to Tel Aviv. We arrived on Sunday, March 6th, and met Moti at his office in the late afternoon.

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In the entrance hall of the Department. From left to right: Einstein’s field equation without Lambda, Francoise Combes, Mordehai Milgrom, Pavel Kroupa and Benoit Famaey.

Coming to know the place and first discussions

I am very impressed by the size and beautiful campus of the whole Weizmann Institut, and how pleasant the entire ambiente is.

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Chairs and a pond in front of the Department.

The people are very friendly and  helpful. And interested. I was staying at the spacious and luxurious San Martin Faculty Clubhouse. At night the various buildings and park areas in the Weizmann Institute are illuminated beautifully, with warm lights setting accents and emphasizing a welcoming atmosphere.

The highly-ranked  Weizmann Institute consists of many departments of various natural sciences and seems to be perfectly created for academic pursuit, including leisure areas. Its success in the pursuit of basic research in the natural and exact sciences and in acquiring funding is evident through the architecture, spaciousness, and general design.

There was no planned agenda for us, apart that Benoit was to give a talk on Wednesday, 9th of March, at 11:15, and for Francoise Combes to give a departmental colloquium on Thursday, 10th of March at 11:15. In between these talks we could do either nothing and hang about enjoying the sunshine and exquisite weather and pool, or engage in intense discussions. Perhaps due to the ambiente and of course our comparable research interests, we largely chose the latter.

On Monday, 7th of March, we had a very relaxed day, meeting with Moti at the Department in the late morning and spending our time debating. Typical discussion points (largely between Francoise, Benoit and myself) throughout the visit were the local major underdensity and its possible implications on the value of the cosmological Lambda, the underlying theory of MOND and whether it is due to a “dark” fluid which behaves like dark matter on large scales (e.g. Luc Blanchet’s dipoles and Justin Khoury’s condensate)

Given that Lambda was missing in the equation displayed in the entrance hall of the Department (see first photo above), we began to discuss it. And this is where the “local” underdensity now plays a possibly important role, see this figure from Kroupa (2015),

K_K_Underdensity

The underdensity is significant, according to the shown data, and may challenge any cosmological model. From Kroupa (2015).

and in contrast the very recent work by Whitbourn & Shanks where the authors explicitly state agreement with the previous survey by Kennen et al. (2014). The independent finding by Karachentsev (2012) on the local 50 Mpc scale appears to naturally continue the trend evident from the Kennan et al. data (see the figure on the left), IF one assumes the same baryonic to dark-matter ratio as at larger distances. The actually measured stellar density remains similar to the Keenan et al. value at small distance. So the baryonic density (assuming the gas to star ratio and the contribution by dwarf galaxies to remain unchanged out to distances of 800 Mpc [redshift of 0.2]) then within 300 Mpc there is at least a decrease in the baryonic density by factor of two. Conversely, taking Karachentsev’s measurement, we would see a disappearance of dark matter nearby to us since the stellar density remains similar to the Kennen measurement within 150 Mpc while the dark matter density decreases further. So the measurements appear to imply the following picture: within 400 Mpc the luminous (and thus baryonic) matter density decreases significantly by a factor of two. At the same time, the ratio of dark matter to baryonic matter decreases even more. Both findings violate the cosmological principle.

The work by David Wiltshire (his lecture notes) and Thomas Buchert already indicates that inhomogeneities could possibly make the Universe appear to an observer situated within such an underdensity as if it’s expansion is accelerating, although in truth it is not. That is, the inhomogeneities appear to be of the correct magnitude to eliminate the need for Lambda, Lambda (dark energy) merely being an apparent effect mis-interpreted by the supernova type 1a data. The reason lies in that a distant object’s observed redshift depends in reality on the exact paths the photons travel in a universe which consists of time-changing voids and over-densities, and this is a different redshift computed assuming a homogeneous and isotropic expanding Universe.

But we need more detailed calculations taking into account the constraints from the observed under-density shown in the figure to be assured that Lamba=0. It is certainly true that Lambda=0 may be more in line with theoretical ideas than the very small value deduced to explain an apparently accelerating Universe, because it is actually predicted, from quantum field theoretical calculations of the vacuum (for details see e.g. Padilla 2015), to have a value some 60 to 120 orders of magnitude larger. It should be emphasized, though, that “MOND likes Lambda“, in the words of Moti. The reason is that the Lambda derived from astronomical observations (e.g. from supernovae of type 1a observations) and Milgrom’s constant a_0 appear to be naturally related, and MOND may be derivable from vacuum processes (Milgrom 1999).

Within about 300 Mpc, where we can say that we have the best measurements, the Universe is nicely consistent with MOND. The mass-to-light ratios of galaxy groups are less than 10 (Milgrom 1998 and Milgrom 2002), i.e. there is only baryonic matter. The observationally inferred increased density of baryonic matter at distances larger than 300 Mpc would then perhaps be due to cosmological models being inappropriate, i.e. that the currently used red-shift–distance relation may be wrong.

We also debated galaxy evolution, the fraction of elliptical galaxies and the redshift dependence of this fraction. Notably, fig.7 in Conselice (2012)  shows that the observed fraction of massive galaxies does not evolve although the LCDM model predicts a strong evolution due to merging. This is consistent with the independent finding by Sachdeva & Saha (2016) that mergers are not a driving mechanism for galaxy evolution, and this is in turn consistent with the independent findings reached by Lena et al. (2014)  on the same issue.

We further talked about how LCDM is faring on large, intermediate and small  scales, how stellar populations change with physical conditions, the variation of the IMF, as well as political topics. The discussions were far from reaching consensus, we had different views and data sets we could quote on various problems, and time flew by such that we barely noticed.

However, Moti managed to drag us away from his Department, and showed us around the Weizmann institute. An particular station was the famous landmark tower which once housed the Koffler Accelerator and which now houses, in its “bubble”,

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The tower which housed the Koffler Accelerator and which now houses a conference room (in its “bubble”) and the Martin S. Kraar Observatory.

a conference room and also the Martin S. Kraar     observatory which is also used in international top-level    research projects. The director of the observatory, Ilan   Manulis, kindly explained to us in much detail its   functionality and design for full remote-observations   without human interference.

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Viewing the lands from the top of the Koffler Accelerator Building. From left to right: Benoit Famaey, Francoise Combes and Mordehai Milgrom.

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Part of the Weizmann Institute as viewed from the top of the Koffler Accelerator Building.

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The Group at the Koffler Accelerator. From right to left: Benoit Famaey, Francoise Combes, Mordehai Milgrom and Pavel Kroupa

On this Monday Moti took us to lunch at the Lebanese restaurant Petra located in Nes-Ziona, a town 5 minutes drive from the Weizmann Institute. The Lebanese cuisine was fabulous, and I ate far too much.

A diversion to history

And, on Tuesday, 8th of March, Moti and his wife Ivon took us on a drive-around nearby Israel. This trip, involved about 4 hours of driving by Moti, and while driving we discussed, amongst other topics, the new study by Papastergis et al. (2016) in which they use 97 gas-dominated galaxies from the ALFALFA 21cm survey to construct their estimate of the baryonic Tully-Fisher relation showing excellent agreement with the expectations from Milgromian dynamics.

The drive was incredible, as we saw places with many thousands of years of history dating back to the Caananite peoples. It is this land which took the central role in the evolution of the Mediteranean-Sea-engulfing Roman Empire to a Christian empire. It contains the scars of the episodes of the invasion by a newer religion of christian lands, christian reconquest, and reconquest by the newer religion, till the foundation of Israel, issues which remain current to this day.

We visited Caesarea:

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The author amongst the ruins of Caesarea. “What was the fate of Caesarea’s inhabitants when it fell to the Mamluks?”

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Caesarea, once a thriving port for many centuries, from where Paulus was imprissioned and sent to Rome for his hearing at the emperor’s court, was wiped out in the 13th century.

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The Group in front of the Roman ampitheater in windy Caesarea, nearly but not quite ready. From right to left: Mordehai Milgrom, Francoise Combes, Benoit Famaey, Pavel Kroupa.

The thriving thousand-year old medieval city of Caesarea, named by King Herod after Octavian (i.e. Augustus Caesar) and which was once the main port in his kingdom, was finally obliterated from existence after a siege by a Mamluk army in the thirteenth century.

Acre: the chief port in Palestine  during the crusader epoch still boasting major remains of the huge crusader’s fortress:

Acre: the remains of the Crusader port.

Acre: the remains of the Crusader port.

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Acre, once a blossoming port and a gate-way to the holy lands for christian pilgrims.

After a wonderful dinner at the seashore between Tel Aviv and old Jaffa at the restaurant Manta Ray, where some action happened just before we arrived judging from the large number of police and other forces around, we visited very beautiful Old Jaffa:

Old Jaffa, which dates back to a history of 4000 years and where alrady the Egyptian empire stationed a garrison.

Old Jaffa, which dates back to a history of 4000 years and where alrady the Egyptian empire stationed a garrison.

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Old Jaffa.

The restoration of the archeological sites of   Caesarea, Acre and of Old Jaffa brings to mind   how  incredibly rich and beautiful the thousand   year old places are along the Mediterranean coast   throughout the middle East and northern Africa, if   upheld with the corresponding desire to show   this history.

Back to science

On Wednesday, 9th of March, we spend the whole day in discussions with staff of the Institute. It began with Benoit Famaey’s presentation on the latest numerical results of modelling the Sagittarius satellite galaxy and its stream in Milgromian dynamics by Strasbourg-PhD student Guillaume Thomas. Natural solutions appear to emerge and this will, once published, clearly add spice to the discussions, given that the only solutions available in LCDM by Law & Majewski (2010) are unnatural in that the dark matter halo of the Milky Way needs to be oblate at right angle to the Milky Way, a solution which poses severe dynamical instabilities for the Milky Way disk. Notably, this polar oblate dark matter halo of the Milky Way alignes with the vast-polar structure (the VPOS) of all satellite galaxies, young halo globular clusters and stellar and gas streams.

In these discussions with the staff members during the aftenoon, we dealt with supernova rates and explosions and types in different galaxies, the relevance to the variation of the IMF in various environments (e.g. metal-poor dwarf galaxies vs metal-rich massive galaxies and the dependency of the IMF on density and metallicity), and cosmological problems such as the local massive under-density mentioned above.

An important point I tried to emphasize repeatedly is that if Milgromian dynamics is the correct description of galactic dynamics, then we must keep an open mind concerning the possibility that all of cosmological theory may have to be rewritten and the large-redshift data may need to be reinterpreted in terms of different redshift–distance and redshift–age relations.

In the evening of Wednesday I tried out the swimming pool on campus, and their sauna as well. I had access to this swimming pool by staying in The San Martin Faculty Clubhouse and the Hermann Mayer Campus Guesthouse – Maison de France. I must admit, that the day was near to being perfect with the sunshine and a closing dinner with Francoise and Benoit again in our meanwhile standard kosher restaurant (Cafe Mada) nearby the San Martin guest house.

On Thursday, 10th of March, Francoise Combes gave her interdepartmental presentation on “The Molecular Universe” which was well visited, and afterwards we went together with some staff of the Weizmann Institute for lunch at Cafe Mada, where a lively and very entertaining discussion ensued on religeos questions. In the late afternoon we joined the Whisky lounge, in which anyone traveling back to Rehovot from abroad can bring a duty-free bottle of Whisky to and donate it to this lounge.

The Local Group of galaxies is highly symmetrical, with all non-satellite dwarf galaxies lying in two planes symmetrically and equidistantly situated around the axis joining the Milky Way and Andromeda. From Pawlowski et al. (2013).

The Local Group of galaxies is highly symmetrical, with all non-satellite dwarf galaxies lying in two planes symmetrically and equidistantly situated around the axis joining the Milky Way and Andromeda. From Pawlowski et al. (2013).

Young researchers meet every Thursday (remember, this is in Israel the end of the week) to sip Whisky and thereby to elaborate on various problems, such as in our case on the local underdensity, or how the two critical constraints we have from the highly organized structure of the Local Group of galaxies and the CMB together constrain the cosmological model.

An interesting statement made was that while one needs about ten LCDM Universes to get one Bullet cluster (Kraljic & Sarkar 2015), an infinite number of LCDM Universes will not give a single Local Group with its symmetries.

At least these are some of the questions we discussed while there on this Thursday. We were also impressed by all the connections of this Department with Princeton, Caltech and Harvard.

Friday and Saturday

Shops begin to close down and it becomes a challenge to find food and Francoise left for France. In the morning I went for a swim and sauna, and for luch Benoit and myself had to go out of the Weizmann Institute (exit Main Gate and turn left) to find a sandwich place.

photo

The Basha Bar in Tel Aviv.

After some work and then in the evening and at about 18:00 we decided to take a taxi to Tel Aviv. We arrived at the Basha Bar by about 18:30 and stayed for three hours (see photo).

image

The Basha Bar, enjoying a three-hour shisha smoke and many Tuborg beers.

On Saturday, the kosher breakfast in the guest    house was as excellent as ever, but it was    interesting for me to note that neither the   toaster nor the coffee machine were to be  used,  while the water boiler was   on so we  could still have hot Turkish coffee (which we  also drink in Bohemia, by the way, so not   much      new for me here). Nearly everything is closed. Benoit   and myself met for lunch and walked outside the Main   Gate turning right, over the bridge to reach the   Science Park finding bistro Cezar for lunch.

In the evening Moti picked us up for a dinner at his home with Ivon, where we had a long discussion also on the dynamic situation in Germany, Europe and the future.

At the home of Moti in Rehovot.

At the home of Moti in Rehovot. From right to left: Moti, Benoit and the author.

Final comments

Benoit and myself stayed on until Monday, joining the astrophysics journal club which serves lunch at the Department on Sunday. I spent most of the afternoon discussing with Boaz Katz how star clusters may be relevant for type 1a supernovae. In the evening of Monday Benoit and I went again to Cafe Mada for a final dinner and drinks. On Monday, 14.03., we flew out around 16:00, taking a taxi to the Tel Aviv airport at 13:00 from the Department. We shared the same flight back. Again the 4+ hour long Lufthansa stretch without personal-screen-based entertainment system! But, this gave Benoit and myself a chance to further discuss at length the above mentioned Khoury condensate and the Blanchet dipoles as models for galaxy-scale MOND and cosmology-scale dark-matter-like behaviour. But I note that these are not dark matter models. During pauses my thinking was that as the coastal line of Tel Aviv receded in the setting Sun we left a small fraction of the Levant and northernmost Africa, all once pat of the Roman Empire, at a level of civilisation mirrored by the clear, brllliantly lit vast and dynamic power- and resource-hungry central-European night with full autobahns, radiant towns and illuminated football fields in nearly every village. In Frankfurt our ways parted after a last small dinner in the train station, Benoit taking a bus to Strasbourg at about 21:30, and me starting my odessey to Bonn at the same time using the available train connections (German trains all too often run late, these days).

The visit was most memorable for all of us, and Benoit and myself agree that we would like to return. We did not reach any conclusions but we came to know many new people and perhaps helped to underscore the very seriousness of alternative concepts to dark matter and the many failures of the LCDM model.

In closing it is probably fair to say that Milgrom contributed the greatest advance on gravitational physics since Newton and Einstein.

In The Dark Matter Crisis by Pavel Kroupa and Marcel Pawlowski. A listing of contents of all contributions is available here.

46. First Workshop on Progress in Modelling Galaxy Formation and Evolution in Milgromian dynamics — first results achieved with the Phantom of Ramses (PoR) code

[Note: This web-page is being updated continuously:
current status: 26.09.15]

LOCATION and TIME:
Observatoire astronomique de Strasbourg, Universite de Strasbourg, CNRS UMR 7550, Sept. 21st - 25th 2015

Below are provided
1.BACKGROUND/MOTIVATION
2.HOW TO REGISTER
3.PARTICIPANTS
4.HOTELS
5.PROGRAMME
6.PHANTOM WIKI
ORGANISERS: Benoit Famaey (Strasbourg) and Pavel Kroupa (Bonn)

1.BACKGROUND / MOTIVATION: Galaxy-scale data seem to be in accordance with the hypothesis that the extrapolation of Newtonian gravitation by orders of magnitude below the Solar system space-time curvature breaks down completely, and that collisionless astronomical systems behave according to space-time scale-invariant dynamics, as postulated by Mordehai Milgrom (2015). The classical theories of dynamics and gravitation underlying this symmetry, often referred to as MOND  theories, show a richer dynamical behaviour with new phenomena which appear non-intuitive to a Newtonian mind. Very successful analytical results have been obtained in this dynamics framework, such as accounting for the hitherto not understood properties of polar-ring galaxies (Lueghausen et al. 2013), accounting for the Bullet cluster (Angus, Fmaey & Zhao 2006Angus & McGaugh 2008) and the properties of disk galaxies (MOND reviews by Scarpa 2006; Famaey & McGaugh 2012;Trippe 2014) and elliptical galaxies (Sanders 2000; Milgrom & Sanders 2003; Scarpa 2006).

But little understanding of the dynamical behaviour of live Milgromian systems has been gathered. Live calculations, i.e. simulations of galaxies, are required in order to test, to possibly refine or to falsify this approach. The implications for fundamental physics are major in any case!

A series of Milgromian-dynamics workshops is planned to begin remedying this situation.

With this first “Phantom of Ramses” (PoR) meeting, the aim is to bring together the pioneers who have been daring footsteps into applying Milgromian dynamics to simulate live galaxies. First simulations of galaxies within MOND have been achieved with the first Milgromian Nbody code without gas (Brada & Milgrom 1999). Tiret & Combes (2007) re-visited this problem with their own code. The PhD thesis of Tiret is available here (in French). For spheroidal geometries MOND simulations have become possible with the NMODY code by Nipoti, Londrillo & Ciotti (2007), see e.g. the application of this code to the phase-transition of spheroidal systems on radial orbits (Wu & Kroupa 2013). A MOND code has also been developed for studies of cosmological structure formation by Ilinares, Knebe & Zhao (2008). While being highly successful in their ability to represent observed galaxies, all of these attempts have died-off due to a lack of long-term sustainability.

Now much more involved and more numerous studies has become possible with the first publicly available Milgromian dynamics computer code including star formation, i.e. baryonic physics (Lueghausen, Famaey & Kroupa 2015) with which even full-scale simulations of cosmological structure formation have become achievable, PoR being an official patch to Teyssier’s RAMSES code. A similar computer code (RAyMOND) has been developed independently by a Chilean research group (Candlish, Smith & Fellhauer 2015).

Because non-linear Milgromian dynamics is largely non-intuitive for researchers trained to think within the framework of linear Newtonian gravitation, this group of pioneers needs to find the chance to discuss, in as great depth as is required, the issues arising with initialising, setting-up and evolving Milgromian galaxies in virial equilibrium, including gas dynamics and star formation. The first scientific results which have already been achieved with the PoR code will be discussed at this occasion, but research related to Milgromian dynamics (e.g. by adoption of zeroth-order approximations by adding dark matter particles to Newtonan systems) will also be discussed.

The meeting will take place at the Observatoire astronomique de Strasbourg. We are planning a whole week for this event, whereby there will be one to two (at most three)  presentations per day interrupted with long discussion breaks to dwell upon problems that have been encountered and that may need solutions. Also, the breaks are intended to allow new persons to learn using PoR. The meeting will take place in the *MEETING ROOM* (with a capacity of about 20) at the Observatoire, and the presentations can be of any duration, but must have a break after the first 45 minutes if longer. After the last presentation each day discussions may continue at will, and Strasbourg offers many excellent culinary opportunities for the evening entertainments.

2.HOW TO REGISTER / IF INTERESTED:
Please register by sending an e-mail to Benoit Famaey <benoit.famaey_at_astro.unistra.fr> and to Pavel Kroupa <pavel_at_astro.uni-bonn.de>.

Note that this meeting does not have invited talks. The attendance is limited to 20.
3.PARTICIPANTS (preliminary):

Garry Angus (Brussel, Belgium)
Indranil Banik (St. Andrews, UK)
Christian Boily (Strasbourg, France)
Joerg Dabringhausen (remotely from Concepcion, Chile)
Benoit Famaey (Strasbourg, France) [SOC]
Martin Feix (Paris, France)
Hector Flores (Paris, France)
Alistair Hodson (St. Andrews, UK)
Rodrigo Ibata (Strasbourg, France)
Tereza Jerabkova (Praha, Czech Rep.)
Pavel Kroupa (Bonn, Germany) [SOC]
Fabian Lüghausen (Bonn, em.; tbc)
Marcel Pawlowski (Cleveland, USA)
Florent Renaud (Surrey, UK)
Jean-Babtiste Salomon (Strasbourg, France)
Ingo Thies (Bonn, Germany)
Guillaume Thomas (Strasbourg, France)
Yanbin Yang (Pairs, France)
HongSheng Zhao (St. Andrews, UK)

Conference Photo (24.09.2015):

        PoR_group

Left to right:  Yanbin Yang, Indranil Banik, Ingo Thies, Guillaume Thomas, Garry Angus, Jean-Babtiste Salomon, Tereza Jerabkova, HongSheng Zhao, Rodrigo Ibata, Marcel Pawlowski, Hector Flores, Alistair Hodson, Florent Renaud, Benoit Famaey, Fabian Lueghausen, Pavel Kroupa
4.HOTELS:

Hotel Esplanade
ETC Hotel
Hotel Roses
Hotel21
Au Cerf d’Or
des Princes
5.PROGRAME:
The programme, abstracts and list of participants are available here as a pdf file:
PoR_Programme.pdf


PROGRAM (with downloadable presentations):  

First Workshop on Progress in Modelling Galaxy Formation and Evolution in Milgromian dynamics —
first results achieved with the Phantom of Ramses (PoR) code.
At the Observatoire astronomique de Strasbourg, 21.09.-25.09.2015.

PoR-code talks are scheduled for the afternoons allowing for discussion and learning time.  A few scientific talks relevant to the mass-deficit problem are scheduled for the mornings.


******* Sunday, 20th September

evening, approximately 18:00-
Meet for drink and food at Au Brasseur
ACCUEIL
******* Monday, 21st September 10:00 MORNING COFFEE 10:30 Welcome/Introduction/First presentation and discussion: Setting the scene: 1. Kroupa_PoR.pdf: Why is the dark-matter approach ill-fated? (Pavel Kroupa) 2. Famaey.pdf: The basics of Milgromian dynamics/MOND (Benoit Famaey) LUNCH (12:15-14:45) 15:00-16:15 1. Lueghausen_PoR.pdf: The PoR code (Fabian Lueghausen) 2. Thies_PoR.pdf: Setting up a stable disc galaxy in PoR (Ingo Thies) 16:30 AFTERNOON TEA 17:00-18:00  Open Discussion ******* Tuesday, 22nd September 10:00 MORNING COFFEE 10:45-11:15 (30 minutes) Angus_PoR.pdf: The DiskMass Survey’s implications for MOND, CDM and itself  (Garry Angus) LUNCH (12:15-14:45)   14:45-15:15 (30 minutes) Banik.pdf: The External Field Effect In QUMOND: Application To Tidal Streams (Indranil Banik) 16:10 AFTERNOON TEA 16:30 Thomas_PoR.pdf: Simulating Tidal Streams with PoR (Guillaume Thomas) PoR Movie (dSph Sgr, slide 19 in presentation): YouTubelink 17:00-18:00  Open Discussion - decision to set up PhantomWIKI ******* Wednesday, 23rd September 10:00 MORNING COFFEE 10:45-11:15 Yang_PoR.pdf: (30 minutes) Reproducing properties of MW dSphs as descendants of DM-free TDGs (Yanbin Yang) MEETING PHOTO  (12:15) LUNCH (12:20-14:45) 14:15-14:45 Angus2_PoR.pdf: The sub-subhalo connection to M31’s plane of satellites (Garry Angus) 14:45-15:15 Pawlowski_PoR.pdf: (30 minutes) Small-scale problems of cosmology and how modified dynamics might address them (Marcel Pawlowski) 16:00 AFTERNOON TEA 16:30 Renaud_PoR.pdf: Gravitation-triggered star formation in interacting galaxies (Florent Renaud) 17:30-18:00  Open Discussion 18:30--  Workshop dinner at Au Brasseur
ACCUEIL
******* Thursday, 24th September 10:30 MORNING COFFEE 10:45-11:15 Hodson_PoR.pdf: (30 minutes)  EMOND (Extended MOND) and effective galaxy cluster masses (Alistair Hodson) 11:30-12:00 Preliminary results on QMOND forces between point masses (HongSheng Zhao) LUNCH (12:15-14:45) 14:45-15:15  Salomon_PoR.pdf: The tangential motion of the Andromeda System (Jean-Babtiste Salomon) 15:15-15:45 Dabringhausen_PoR.pdf: Early-type galaxies in Milgromian dynamics (Joerg Dabringhausen, remotely from Concepcion, Chile) 16:15 AFTERNOON TEA 16:45-17:15 Banik2_PoR.pdf: Evidence for Dynamical Heating in The Local Group (Indranil Banik) 17:15-18:00  Open Discussion ******* Friday, 25th September 10:00 MORNING COFFEE 10:30-12:00 Kroupa_IMF_Strasbrourg.pdf Main Seminar of the Observatory: Is the stellar IMF a probability distribution function, or is star formation highly regulated? (Pavel Kroupa) LUNCH (12:15-14:45) 15:00 Final discussion and FAREWELL
6.PHANTOM WIKI

PhantomWIKI
This wiki is dedicated to supporting the research making use of the “Phantom of RAMSES” (PoR) patch.

37. This blog moves to SciLogs.com

Pavel and I have been too busy to blog for a while (my excuse being that I am in the final stages of my PhD studies). This is also why we did not announce this sooner: Our blog has moved from SciLogs.eu to SciLogs.com. The new site provides an improved blogging system and maybe more international visibility, as well as a pleasant neighborhood of science bloggers. The new URL for “The Dark Matter Crisis” is http://www.scilogs.com/the-dark-matter-crisis/. All future articles will be published there, but the old ones will remain accessible here on SciLogs.eu.

The first article on the ‘new’ blog deals with last week’s Nature article by Rodrigo Ibata and collaborators: “A Vast Thin Plane of Co-rotating Dwarf Galaxies Orbiting the Andromeda Galaxy“. While the media currently focusses on the 15-year old co-author of the Nature study, the scientific implications of the study are no less spectacular. The co-rotating plane of satellite galaxies around Andromeda resembles the VPOS around the Milky Way and therefore similar formation scenarios are plausible, which we discuss in our article “Andromeda’s satellites behave as expected … if they are tidal dwarf galaxies”.

35. A filament of dark matter between two clusters of galaxies: dark matter detected

We briefly comment on the paper by Dietrich, Werner, Clowe et al. on “A filament of dark matter between two clusters of galaxies ” which is now in press with Nature.

The media have it that this may be a direct detection of dark matter.  The abstract of this paper reads

“It is a firm prediction of the concordance Cold Dark Matter (CDM) cosmological model that galaxy clusters live at the intersection of large-scale structure filaments. The thread-like structure of this “cosmic web” has been traced by galaxy redshift surveys for decades. More recently the Warm-Hot Intergalactic Medium (WHIM) residing in low redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying Dark Matter skeleton, which should contain more than half of all matter, remained elusive, as earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignements of dark and luminous matter. Here we report the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft X-ray emission and contributes mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. Combined with X-ray observations, we place an upper limit of 0.09 on the hot gas fraction, the mass of X-ray emitting gas divided by the total mass, in the filament.”

The first sentence of the abstract is undoubtedly correct, but the following sentence here is absolutely true as well:

“It is a firm prediction of any realistic cosmological model that galaxy clusters live at the intersection of large-scale structure filaments.”

Indeed, in any realistic theory of gravity, matter, which has a significant random velocity field, will collapse to filamentary structures. This is amply observed in simulations of molecular clouds without dark matter and is now also beautifully seen in observations of real molecular clouds with the Hershel telescope (e.g. Andre et al. 2010). Filamentary structure is thus nothing special to the  concordance Cold Dark Matter (CDM) cosmological model, and so the abstract can be seen as being somewhat misleading.

Further,  the authors of this paper have only studied the lensing signal using Einstein’s General Relativity. It is true that using Einstein’s General Relativity the signal can only be interpeted with the help of postulating the presence of additional, unseen matter.

But, in a different but nevertheless realistic theory of gravity, the lensing signal may well be explainable without dark matter (e.g. Zhao et al. 2006). It is even possible that in a better theory of gravity, if there is a matter concentration at point A and one at point B then there might be a lensing signal not related to any local matter density at point C in between A and B. Wrongly interpeting such a lensing signal with General Relativity would then lead to the false result that there is unseen matter at C. For instance, in this paper Mordehai Milgrom and Robert Sanders explain how a dark matter effect appears where there is no dark matter at all. The gravitational lensing by filaments in the framework of modified gravity has also been investigated by Feix et al. (2008).

So, the above Nature paper is misleading on this account as well, because “the detection of a dark matter filament connecting the two main components of the Abell 222/223 supercluster system” relies on assuming effective gravity to be described by Einstein’s General Relativity on all scales.

That this cannot be the case has already been shown many times (e.g. “What are the three best reasons for the failure of the LCDM model? Incompatibility with observations” and “Question CII: MOND works far too well!“).  And, an invited review on these problems and matters is available as a freely-downloadable open access CSIRO-publishing paper “The Dark Matter Crisis: Falsification of the Current Standard Model of Cosmology”.

So, while the observations and the results presented in the Nature paper are a major and beautiful feat deserving much attention, a more balanced discussion of the results would have been more appropriate.

By Pavel Kroupa and Marcel Pawlowski  (05.07.2012): “A filament of dark matter between two clusters of galaxies” on SciLogs. See the overview of topics in  The Dark Matter Crisis.

33. Discussing Gravity with Erik Verlinde

We have just returned from a talk by the Bethe colloquium. Erik Verlinde from the university of Amsterdam spoke about “Dark Matter, Dark Energy and the Emergence of Gravity ”.

Verlinde is a dutch theoretical physicist working on string theory and gravity. He became very famous for his theory of entropic gravity and was awarded the Spinoza Prize for his work.

In his talk, he showed that his approach can not only reproduce the MONDian behavior of the different kinds of galaxies. He even gave an explanation on why the centers of galaxy clusters deviate from the baryonic Tully-Fisher relation by a factor of four. The reason, he says, lies in the distribution of matter. Very roughly, galaxies can be approximated by a point mass if we look at their outskirts only. In galaxy clusters, however, the matter is more evenly distributed. Assuming a spatially constant matter density, he can even motivate the amount of the deviation

All in all, his results look very promising. After the talk, Pavel and I discussed with him for about an hour, explaining some of the failures of the LCDM model, but mostly asking about details and implications of his approach. He explained that his intention is to understand gravity by starting from scratch. So not only change and modify the formula used so far, but basing our understanding of gravity on a more fundamental basis. To do so, he looks at the observational evidence unbiased. We agreed that this is not always easy because especially cosmological results are usually analyzed and expressed in a model-dependent form. He does not aim at reproducing MOND, which even its adherents usually describe rather as a phenomenological effect than a new fundamental law. But his model naturally contains MONDian behavior, it seems to explain/give a reason for MOND’s free parameter (the acceleration a0) and he also showed that his approach can predict the ratio of baryonic to (phantom) dark matter correctly: 4% to 22.5%.

What he told was impressive and looks like it could be a major step forward in our understanding of gravity and the universe. Unfortunately, we have to wait some more until he will publish a paper on this topic. But there is good reason to look forward to it.

By Pavel Kroupa and Marcel Pawlowski  (28.06.2012): “Discussing Gravity with Erik Verlinde” on SciLogs. See the overview of topics in  The Dark Matter Crisis.