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.