65. The Don’t-Look-Up Syndrome of Cosmology: Chicago Cosmologists at their best; and the Hubble Tension does not exist

(by Pavel Kroupa, Friday 21st January 2022)

We humans are, as any living creature, and by necessity, conservative beings. We need to be, since typically most of us prefer to sustain their comfortable arrangements. The cave person will prefer to stay near their cave if the nearby plains below are full of fodder, and they would kill off threats. The cosmologist prefers to stay with their dark matter that made them big and important. So when a comet/climate crisis is discovered to approach Earth and is calculated, with some margin or uncertainty, that it will extinguish known life, it can be easier for the majority to just ignore this and to trust in everything turning out all right in the end. Keep the high spirits up, don’t worry and keep smiling and do not frown, do not spoil the mood by doomsday blubber, don’t look up to the threat. So let us ignore that the temperature of the oceans has already increased by nearly 2 degrees centigrade and that another increase by three will kill off most plankton as shown by Sekerci & Petrovskii (2018) with Earth’s atmosphere consequently running out of oxygen.

What has this to do with modern cosmology? I would claim: everything. The modern, successful homo cosmologicus vehemently defends their dark matter against all odds, even if it means killing the scientific method (testing and falsification of hypotheses using reproducible logical methods); they resist change to their habitat as long as the vast landscape of rewards, awards, grants and riches remains abundant.

On Friday, January 14th, 2022, I watched the Golden Webinar on the Hubble Tension, and on this same Friday there appeared on the arXiv an Annual Review on cosmology. Both scientists (speaker and author) are from the highbrow Kavli Institute for Cosmological Physics at the University of Chicago, and both contributions I found to be remarkable.

In the Golden Webinar on “Tension in the Hubble Constant – Does it mean new Physics?“, the speaker very nicely explained the measurements of the Hubble constant using different distance ladders and which role the uncertainties play. Three points struck me: (1) The speaker declared that the physical reason for the Hubble Tension remains unknown. (2) The speaker declared there to be no other known major tension between observations and the Standard Model of Cosmology (the SMoC, or LCDM model). (3) During the panel discussion, a long time was spent on Penrose’s Conformal Cyclic Cosmology hypothesis and it was speculated that fading dark matter might account for the Hubble Tension. The panel largely agreed that no one knew what dark matter was – it might have a large number of degrees of freedom, thus allowing the introduction of an arbitrary number of free parameters to fit almost anything.

Concerning the three points above, I wrote into the chat two questions (see Figure 1 below). Essentially, accepting the well-observed Gpc-scale KBC void as being a real structure of the Universe, the Hubble Tension must then arise from it logically (Haslbauer et al. 2020). This is because galaxies are accelerated gravitationally towards the sides of the void, and an observer within the void (as we are) then measures an apparent faster expansion of the local Universe (see figure 2 in 52. Solving both crisis in cosmology: the KBC-void and the Hubble-Tension). The Hubble Tension therefore has a very simple physical explanation.

In fact, a real Hubble Tension does not exist: it is merely an apparent effect caused by the observed KBC void (Haslbauer et al. 2020), and it would have been predicted if Wong, Suyu et al. (2020) and Riess et al. (2021) had not made their observations of expansion. It is the same reason, in essence, why apples fall to the Earth: replace the galaxies by apples, and they will fall to where they are attracted to, which is the side of the underdensity.

It was a wonderfull event and fascinating to see how the panel very happily discussed the entirely speculative fading dark matter concept in the context of the Hubble Tension, but no-one appeared to dare to raise the possibility that it might simply be due to the observed KBC void, as in fact it must be. I tried to help the panel by posting my question into the chat, but it appeared to me that, in the intimidating presence of highbrow scientists, discussing fading dark matter was acceptable, while raising the obvious solution was no-go. After all, who wants to ask a seemingly silly down-to-Earth question (“can the observed Gpc underdensity be responsible for the apparent Hubble Tension?”) in view of such intellectual Mt. Everests.

The second point above by the speaker I also found impressive, given that other independent falsifications of the LCDM model at more than five sigma confidence have been published, see the list A-F below. It seems that these contributions were missed in Chicago, or that Chicago Cosmologists “do not look up”. I guess they do not need to look up, since they are already on Mt. Everest.

I am still trying to digest this, which is why I wrote the above first paragraph.

Figure 1: My chat contribution. It received 7 votes, the highest of all questions, but the panel did not raise this issue with the speaker.

Why was neither the Golden Webinar speaker nor the panel willing to delve into the true physical reason for the Hubble Tension? I think that the problem is that the KBC void, which causes the Hubble Tension, falsifies the SMoC with more than 5sigma confidence (Haslbauer et al. 2020), because the SMoC cannot grow such large and deep under densities within a Hubble time. And furthermore, the Chicago Cosmologists, as represented by the speaker and author (next), seem adamantly to refuse to discuss MOND seriously. But MOND is the only known modern non-relativistic theory of gravitation in which the Universe can grow such a large observed void and observed early very massive interacting galaxy clusters (Asencio et al. 2021). We covered this galaxy-cluster problem on a previous occasion. In MOND, there is no Hubble tension (since the voids form naturally) and very massive interacting galaxy clusters also form naturally in the earlier Universe.

On the same day as the above Webinar, an Annual Review on “The Road to Precision Cosmology” was published on the arXiv: It is to appear in Ann.Rev.Nucl.Part.Sci. 72:1-33, https://arxiv.org/abs/2201.04741v1 .

I was interested, since the author is viewed by many to be an outstanding cosmologist, and I expected a fair, balanced and up-to-date review of cosmology for the community of Nuclear and Particle Physicists. This is an important review: Annual Reviews are corner stones of literature. Often they are the first entry point into a research field. Their role is thus truly important. On contemplating the review, I decided to write the following letter – let it speak for itself:

Letter sent on 17th of January 2022 to those addressed (with minute modifications for this forum):

Dear author,

(CC to Editors, Committee Members and Staff of the Annual Review of Nuclear and Particle Physics, and researchers working on MOND),

Concerning your review article "The Road to Precision Cosmology" which is to appear in Ann.Rev.Nucl.Part.Sci. 72:1-33,     https://arxiv.org/abs/2201.04741v1 :

I kindly ask you to adjust this article to represent the modern state of affairs truthfully: As it stands, the article is not a review but a biased misrepresentation of the state-of-the art in the research field. It misrepresents the entire field of cosmology to the research community in Nuclear and Particle Physics. 

If not-citing highly relevant research literature is considered to be equivalent to plagiarism, then you have provided a major example of such ill conduct: "Papers published in A&A should cite previously published papers that are directly relevant to the results being presented. Improper attribution — i.e., the deliberate refusal to cite prior, corroborating, or contradicting results — represents an ethical breach comparable to plagiarism." (citing from "Ethical issues: the A&A policy concerning plagiarism and improper attribution: https://www.aanda.org/index.php?option=com_content&view=article&id=136#Ethical_issues ).

In your article, we read "Sec. 3.1.2. False starts. In 1983, Milgrom noticed...."

This is an unacceptable representation of an entire highly successful and vibrant research field in which an increasing number of brilliant young physicists are active in.  You claim in this section that MOND cannot be falsified. This is wrong. We are actively working on falsifying this theory. MOND can be falsified by, for example, finding systems that do not obey the non-linear MOND Poisson equation.

Your article is not aware of or purposefully ignores that 

  1. The LCDM standard model of cosmology is in tension with the data on many different scales with significantly more than 5 sigma confidence.
  2. The data which are in tension with LCDM are at the same time naturally (i.e. without adjustment of any parameter) explained in a cosmological model which is based on Milgromian gravitation (MOND) without cold or warm dark matter.

Some of the relevant very recent major peer-reviewed research contributions (ignored by your article) on this are:

A) The existence of LCDM dark matter particles is in more than 5sigma tension with observed bar pattern speeds through the test based on Chandrasekhar dynamical friction published in 2021: Fast galaxy bars continue to challenge standard cosmology.

B) Very massive galaxy clusters form and interact at high redshift being in more than 5sigma tension with LCDM published in 2021: A massive blow for ΛCDM - the high redshift, mass, and collision velocity of the interacting galaxy cluster El Gordo contradicts concordance cosmology.

C) The observed local Gpc scale underdensity causes the Hubble tension and is in more than 5sigma tension with LCDM published in 2020: The KBC void and Hubble tension contradict ΛCDM on a Gpc scale - Milgromian dynamics as a possible solution,

Apart from the above extreme inconsistencies of the LCDM model with the respective data (spanning kpc to Gpc scales), MOND accounts for these naturally and it also naturally accounts for:

D) A planar group of galaxies recedes too rapidly from the Local Group (in >3.96 sigma tension with LCDM) published in 2021: On the absence of backsplash analogues to NGC 3109 in the ΛCDM framework.

E) The lack of a bar in the nearby disk galaxy M33 could not be explained in LCDM published in 2020: The Global Stability of M33 in MOND.

F) The planar (disk-like) distribution of satellite galaxies is inconsistent with LCDM but arises naturally in MOND published in 2018: MOND simulation suggests an origin for some peculiarities in the Local Group and Origin of the Local Group satellite planes.

Your article neither cites nor discusses these, and falsely implies the LCDM model to be consistent with the data at the precision level. Further, the review appears to suggest there to be no other model (without dark matter) that can claim comparable success. Claiming today that the LCDM model is a "triumph of precision cosmology" (Sec. 4.1 in your article) is purposefully propagating outdated misinterpretations to an audience who are non-experts in this research field. 

I will publish the contents of this email as an open letter, and I hope to receive a constructive reaction. 


Sincerely,

Pavel Kroupa

(Helmholtz-Institut for Nuclear and Radiation Physics, Bonn;                        Astronomy Institute, Charles University, Prague)


The interested reader might also consult “It’s time for some plane speaking” published by Marcel Pawlowski (2021) in Nature Astronomy. Although Marcel suggests there to be no obvious solution in sight, in MOND, the solution is quite trivial. The planes of satellites come from galaxy-galaxy encounters, as explicitly demonstrated by Bilek et al. (2018, A&A and 2021, Galaxies) and Banik et al. (2018, MNRAS).


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

64. Youtube playlist full of MOND talks, debates and more

(Guest post by Mark Huisjes, December 8th, 2021)

In the following guest post by Mark Huisjes (GIS Analyst and master student at Utrecht University) we would like to promote a Youtube playlist, which includes talks, debates, Q&A’s, and more videos related to MilgrOmiaN Dynamics (MOND). This playlist is aimed for anyone who is interested in this research field.

Over the past year I’ve built a Youtube playlist of videos related to MOND, which is available online here.

Youtube playlist of talks, debates, interviews, Q&A sessions, and much more hosted by Mark Huisjes.

It contains more than 70 hours of talks, debates, interviews, Q&A sessions, and much more. Most of the listed videos are in English, but videos in French, Spanish, German, and Czech are also available at the end of the playlist. Subjects covered include fundamental MOND phenomenology such as rotation curves, the baryonic Tully-Fisher relation, the central density relation, and the radial acceleration relation, but also more advanced topics such as the external field effect, satellite galaxy planes, wide binaries, TeVeS, superfluid dark matter, and νHDM cosmology, and scientific tests of the hypothesis that dark matter exists.

This way people can easily find a talk if it is available online and delve deeper into the theory of MOND!


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

63. Hybrid models may solve mystery of dark matter

(Guest post by Tobias Mistele, December 1st, 2021)

Tobias Mistele is a PhD student at the Frankfurt Institute for Advanced Studies studying hybrid MOND-dark-matter models. Besides his physics research he also works on Scimeter.

Hybrid models, which combine dark matter and modified gravity, were long neglected. In this post, I explain why such models are now attracting attention as a path out of a stalemate.

There is observational evidence for missing baryonic mass on both cosmological and galactic scales. Most notably, the fluctuations in the cosmological microwave background (CMB) on cosmological scales and rotation curves on galactic scales. Traditionally, this is explained by non-relativistic dark matter particles (cold dark matter, CDM) that do not interact much except gravitationally. These CDM particles form a pressureless fluid on cosmological scales and later accumulate around galaxies, forming a dark matter halo. The pressureless fluid explains the fluctuations in the CMB. The mass of the halo around galaxies explains galactic rotation curves. An alternative paradigm is modified gravity. Instead of postulating particles that produce additional mass, modified gravity postulates a different gravitational force. Modified Newtonian Dynamics (MOND) is a modified gravity model that is quite successful on galactic scales. For example, consider the so-called Radial Acceleration Relation (RAR) shown in Figure 1. This is a relation between the standard Newtonian gravitational acceleration due to the stars and gas in a galaxy, gbar = GMb/r2, and the total acceleration gobs we infer from observed rotation curves. In a world without dark matter and without modified gravity, these two are the same, gbar = gobs. In the real world they are not. This is the missing mass problem in galaxies. More importantly, this relation between gobs and gbar has little scatter. Thus, the total acceleration gobs can be predicted just from the baryonic mass distribution, i.e. from gbar.

Figure 1: The Radial Acceleration Relation (RAR). Credits: One Law to Rule Them All: The Radial Acceleration Relation of Galaxies (Lelli et al. 2017). With kind permission by Federico Lelli.

This is non-trivial in DM models. In principle, two galaxies with the same baryonic mass distribution (the same gbar) can have different dark matter halos and thus a different gobs, but this doesn’t happen. In contrast, MOND naturally explains this. In fact, the RAR shows precisely what MOND postulates. At Newtonian accelerations gbar larger than a0 ≈ 10-10 m/s2 nothing new happens. Newton’s gravitational force law remains. But at accelerations gbar smaller than a0, the total acceleration changes to (a0 gbar)1/2.

Unfortunately, both CDM and MOND remain unsatisfactory when considered individually. MOND, for example, cannot explain all the missing mass on galaxy cluster scales. And, so far, no MOND-based models have been able to explain the fluctuations in the CMB, at least not without introducing some type of dark matter after all. CDM, on the other hand, has its own problems. For example, there is so far no convincing explanation for MOND-like scaling relations like the RAR. There’s just no reason why the dominant dark matter halo should be predictable from the visible baryonic mass in such a simple way. Another problem is that observed galactic bars tend to rotate faster than what CDM predicts. The dynamical friction of a CDM fluid slows down galactic bars. Then there’s the plane-of-satellites problem. Satellites of the Milky Way co-orbit in thin, planar structures. A natural explanation would be that these satellites were created from the tidal tails of interacting galaxies. But then they would not have their own dark matter halo which contradicts their high internal velocity dispersion. Also, CDM seems to be too slow to grow large structures. Massive clusters at high redshift like El Gordo are very unlikely to form so early in CDM.

So if not MOND or CDM – then what? One answer is both! That’s what hybrid MOND-dark-matter models are about. These are models that have both a pressureless fluid on cosmological scales (to explain the CMB) and a MOND-like force in galaxies (to explain e.g. the RAR).

Let me illustrate the general ideas behind hybrid models with an example – a model called superfluid dark matter (SFDM) proposed by Berezhiani & Khoury. This model has various problems, but it serves as a good illustration of the general features of hybrid models. SFDM postulates a specific new type of particle that behaves like standard CDM on cosmological scales and therefore explains the CMB in the standard way. But around galaxies, these particles condense to form a superfluid. The collective excitations of this superfluid, called phonons, then mediate a MOND-like force in galaxies. This MOND-like force is an emergent property of these particles in the superfluid phase. This is how this model explains MOND-like scaling relations like the RAR.

Of course, the superfluid itself has a mass. This produces a standard gravitational force that affects stars and gas. That is to say the superfluid also acts as dark matter in galaxies. So then we have both a MOND-like force and dark matter around galaxies. But does this not solve the missing mass problem twice? So that rotation velocities end up even larger than what we observe?


Figure 2: The Milky Way rotation curve in superfluid dark matter. The dark matter contribution is small, but becomes more important at larger radii. Credits: Tobias Mistele

The answer to that is that the superfluid DM component is usually subdominant within galaxies because the superfluid halo is very cored. Its mass becomes relevant only at larger radii. This is illustrated in Figure 2 for the Milky Way rotation curve.

One might be tempted to adjust one’s models so that the DM contribution becomes even smaller. Just to reproduce the MOND-like scaling relations even more cleanly. But one must be careful with this. Some amount of dark matter is needed in hybrid models to explain the missing mass on galaxy cluster scales for which MOND cannot fully account and, in some models, also to explain gravitational lensing.

Superfluid dark matter is not the only hybrid model. For example, recently Skordis and Złosnik proposed a model that reproduces MOND in galaxies (SZ model). This is also a hybrid model and has, deservedly, received a lot of attention since it is fully-relativistic and it was demonstrated explicitly that this model fits the CMB. Like in SFDM, the MOND and DM components are related to each other in the SZ model.

Such a common origin for the cosmological and galactic phenomena is theoretically appealing. But not all hybrid models have such a common origin. For example, the so-called νHDM model does not. Moreover, such a common origin often brings about internal tensions that must be carefully avoided.

In SFDM, for example, this common origin means that the phonon field is involved both in providing the DM and the MOND components. One technical consequence is that the usual U(1) symmetry of the superfluid must be explicitly broken which has various non-technical implications. For example, the superfluid equilibrium state might not be valid on timescales longer than galactic timescales.

The common origin for the DM and MOND components complicates things also for the SZ model. In this model, there is a kind of mass term for the static gravitational field in galaxies. Mass terms generally make forces short-range. To keep the gravitational force in galaxies long-range, the mass term must be chosen small. But a smaller mass term in galaxies means a larger pressure of the DM-like fluid in cosmology. Observations indicate a very small pressure of the DM fluid. So the galactic and cosmological phenomena push the model in different directions. This has forced the authors to include certain non-linearities as a counter.

Besides these model-specific constraints, there is also a new type of phenomenon that quite generally constrains models with a common origin for the MOND and DM components. Namely, stars often lose energy just by moving through a galaxy. Let me explain.

Accelerated charges produce electromagnetic waves. Accelerated masses produce gravitational waves. In general, whenever matter is coupled to a force carrier (e.g. the electromagnetic or the gravitational field), matter that accelerates produces waves corresponding to that force carrier. But even non-accelerated matter objects can produce waves. Namely if they move faster than the speed with which these waves propagate. For example, in a medium, electromagnetic waves propagate slower than the vacuum speed of light. Charged particles in such a medium emit electromagnetic waves if they move faster than this reduced speed of light. These waves are then called Cherenkov radiation. Such charged particles lose energy and slow down. A similar phenomenon occurs frequently in modified gravity theories whenever gravitational waves propagate at less than the vacuum speed of light. This is called gravitational Cherenkov radiation. Usually, only highly relativistic matter objects emit Cherenkov radiation, both in modified gravity theories and in electromagnetism. This is because the propagation speed of waves is usually relativistic, so that only relativistic particles are fast enough.

But this is different in hybrid MOND-DM models with a common origin for the MOND and DM components. Such models usually contain a force carrier (for the MOND-like force) whose associated waves propagate with non-relativistic speed (because this force is related to the non-relativistic dark matter fluid). Thus, even non-relativistic objects like stars might move faster than the wave propagation speed associated with the MOND force. Such stars will then lose energy and slow down, because they emit a special type of gravitational Cherenkov radiation. For example, in SFDM stars that move faster than the superfluid’s speed of sound will lose energy by emitting sound waves and slow down until they are slower than the superfluid’s speed of sound. This is illustrated in Figure 3. A star may be on a standard circular orbit when it is sufficiently slow, but will otherwise lose energy and circle towards the center of a galaxy.

Figure 3: The orbit of a star in the plane Z = 0 of a galaxy with (dotted orange line) and without (straight blue line) the Cherenkov radiation typical of hybrid MOND-DM models with a common origin for the MOND and DM components. The two cases are labeled as “With friction” and “Without friction” because in the specific approximation used, the Cherenkov radiation acts like an effective friction force on the star. Credits: Tobias Mistele

This reasoning applies only to models with a common origin for the DM and MOND components. So it does apply to SFDM and the SZ model, but not to the νHDM model. When actually doing the calculation one needs to be careful because of the non-linearities that are inherent in any MOND model. Still, it is possible to rule out part of the parameter space of SFDM using the observed Milky Way rotation curve. Basically, one requires that stars that orbit around the Milky Way with the rotation curve velocity do not lose much of their energy during the Milky Way’s lifetime. The SZ model avoids such constraints due to a special property. The coupling to matter is much larger in the static limit than in dynamical situations, which suppresses the energy emitted by Cherenkov radiation. Though I should say that the calculation for this model was done in a simplified setup so that the result should be taken with a grain of salt.

To sum up, the observational evidence for both MOND-like scaling relations on galactic scales and a DM-like fluid on cosmological scales has only become more convincing in recent years. This motivates hybrid MOND-DM models. We may not yet have a completely satisfactory model and much remains to be explored. Still, this general type of model will likely become ever more relevant in the future.


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

62. Mailing list for the MOND community

(Guest post by Indranil Banik, November 22nd, 2021)

In the following guest post by Dr. Indranil Banik (past AvH Fellow in the SPODYR group at Bonn University and now at the St.Andrews University), we would like to promote a mailing list for the MOND community and anybody who is interested in this research field.

Following a request, I have set up a mailing list for the MOND community and anybody who wants to stay updated about our work. The idea is that if someone wants to advertise an upcoming talk or an article they have recently posted but they are at an early career stage and do not know everyone in the MOND community, they can just send an email to the mailing list. Also if some discussions between more senior researchers take place through this list, then any early career researchers signed up to it will be included in the conversation even if nobody thought explicitly to include them in the conversation. Regardless of whether you are signed up, you can send an email to the mailing list and everyone on it should receive the message.

The email address is: mondworkers@gmail.com

Please contact Elena Asencio if you want to sign up to this mailing list and thus receive the emails sent to it, she will be in charge of sending an invitation link which you need to accept in order to complete the sign up: s6elena@uni-bonn.de

We think it is not appropriate to send such invitation links to people who have not requested it, as such a request would take only a little time and we would not ask for any reasons for why you want to sign up.
At the moment, only a very small number of emails have been sent to the mailing list because I have only recently set it up. I envisage that it would not be used all that often for a while, and slowly catch on as more people know about it. Obviously it is not suitable for a great many emails as the sender might only want specific people to see it rather than the whole mailing list. But there are times when people want their email to gain extra visibility, and that is what this is about.

Please advertise this to especially early career researchers, it is intended for sharing adverts for upcoming talks, notifying others of articles and blogs, and discussing research ideas you want to share. In general, it is for anything you want to share with everyone on the list, including I suppose asking for advice. It is important that the more senior researchers working on MOND are signed up to it so that early career researchers who want to e.g. advertise a talk or get advice about a project manage to contact everyone on the list without knowing all their names and email addresses. In principle, a fair amount of customisation is possible with the filters that are used, and different filters can be used for different people on the list. At the moment, the only filtering in place is to prevent administrative emails being sent to everyone on the list. Requests to modify filters can be considered, and of course you can be removed from the mailing list if you ask. Thank you to those of you who have already signed up.

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.

60. Recent review talks about MOND, the Hubble tension and MOND cosmology including major problems of the dark matter models to match data

1) To obtain an introduction to MOND and MOND-cosmology, those interested might like to watch the talk below by Dr. Indranil Banik (past AvH Fellow in the SPODYR group at Bonn University, now at St.Andrews University). It was held on Sept. 30th, 2021 at the University of Southampton.

Indranil Banik

https://drive.google.com/file/d/1wJvYvpDWDtDk0xs47H6-Dr0Lr987wf5m/view?usp=sharing

Also, the following two previous talks are relevant:

2) In the recent Newton 1665 physics seminar series on  “MOND, the KBC void and the Hubble tension” by Dr. Indranil Banik and Moritz Haslbauer (SPODYR group):

Moritz Haslbauer

3) And also recently, as a CosmoStat Journal Club seminar on “El Gordo: a massive blow to LCDM cosmology” by Dr. Indranil Banik and Elena Asencio (SPODYR group): 

Elena Asencio


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.

57. A splash too far: “On the absence of backsplash analogues to NGC 3109 in the ΛCDM framework”

The isolated but nearby galaxy NGC 3109 has a very high radial velocity compared to ΛCDM expectations, that is, it is moving away from the Local Group rapidly, as shown by Peebles (2017) and Banik & Zhao (2018). One of the few possible explanations within this framework is that NGC 3109 was once located within the virial radius of the Milky Way or Andromeda, before being flung out at high velocity in a three-body interaction with e.g. a massive satellite. In the new research paper “On the absence of backsplash analogues to NGC 3109 in the ΛCDM framework”, which was led by Dr. Indranil Banik, it is shown that such a backsplash galaxy is extremely unlikely within the ΛCDM framework. Basically, such galaxies cannot occur in ΛCDM because they ought to be slowed-down due to Chandrasekhar dynamical friction exerted on NGC 3109 and its own dark matter halo by the massive and extended dark matter halo of the Milky way. Making it worse, NGC 3109 is in a thin plane of five associated galaxies (the “NGC 3109 association”, rms height 53 kpc; diameter 1.2 Mpc), all of which are moving away from the Local Group (Pawlowski & McGaugh 2014), whereby the dynamical friction ought to slow down the galaxies in dependence of their dark matter halo masses. This makes its thin planar structure today unexplainable in ΛCDM.

Interestingly, the backsplash scenario is favoured by the authors (Banik et al. 2021), but in the context of MOND. In this theory, much more powerful backsplash events are possible for dwarf galaxies near the spacetime location of the past Milky Way-Andromeda flyby because in MOND galaxies do not have dark matter halos made of particles. A galaxy thus orbits through the potential of another galaxy unhindered and ballistically. The envisioned flyby could also explain the otherwise mysterious satellite galaxy planes which are found around the Milky Way and Andromeda. It now seems that the flyby may well be the only way to explain the properties of NGC 3109, since a less powerful three-body interaction is just not strong enough to affect its velocity as much as would be required. But a Milky Way-Andromeda flyby is not possible in ΛCDM as their overlapping dark matter halos would merge.

In a series of Tweets, the co-author Dr. Marcel Pawlowski briefly explains on his Twitter account @8minutesold the main results of this recent publication:

Source: https://twitter.com/8minutesold/status/1392430171240677376

Source: https://twitter.com/8minutesold/status/1392430171240677376


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.