Dark Matter: The Situation has Changed...according to Sabine

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Dark Matter: The Situation has Changed...according to Sabine

#1

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Quote "Today I tell you how my opinion about dark matter has changed an why. Is modified gravity better or worse? What evidence speaks for one side or the other, and is the case really as clear-cut as many astrophysicists claim?"

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Re: Dark Matter: The Situation has Changed...according to Sabine

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Well this is a profound disappointment. She's wrong and this video is a blunder. She assesses the observational situation poorly and cherry picks arguments. I think that writing a detailed response is necessary and will take a little time.


In the meanwhile: :popcorn: A detailed refutation is coming. I need to rewatch for key moments and marshall the refuting evidence. She selectively omits many considerations.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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Re: Dark Matter: The Situation has Changed...according to Sabine

#3

Post by notFritzArgelander »

It is impractical to do a comprehensive debunking of this unfortunate video in only one post. I have other things to do today so I'll have to make several passes at it. I'll include time elapsed in video and a signal when I've finished.

The first misstatement in the video happens as early as ~1:50.


It is the claim that no dark matter particle has yet been found. This is false. Dark matter is simply matter that 1) does not participate in electromagnetic interactions and so does not absorb or emit light and 2) have very little non electromagnetic interaction either. The first dark matter particle, the neutrino, was proposed in 1930 by Pauli and was detected in 1956. Neutrinos are believed to be only capable of making up 0.5 to 1.5% of the total budget of DM. See for example the comprehensive treatment of "How Much Of The Dark Matter Could Neutrinos Be?" at https://www.forbes.com/sites/startswith ... 70655541e2

Now the reason neutrinos fail to account for all the dark matter budget is attributable to the fact that neutrinos are HOT dark matter. That is to say that their rest masses are much smaller than the ambient temperatures in the environments where DM is found. Observationally the bulk of DM must be cold, with masses much greater than the ambient temperatures in the universe today.

Since we know that neutrinos make up a small fraction of DM, the hot portion, it is the simplest hypothesis that particles make up the cold portion too.

The second egregious error in the video occurs in the elapsed time range 2:30-5:15.

It is an error of omission from the list of observations supporting particle DM. Deuterium is only marginally stable and is not formed in after the Big Bang. These the abundance of deuterium is a sensitive indicator of the non baryonic dark matter to baryonic matter ratio. Observations indicate that during the Big Bang the deuterium formed is consistent with a cold DM to normal particle mass density of about 5. This is a very independent measure of DM mass density that is in full accord with current measures. More details can be found at: https://en.wikipedia.org/wiki/Big_Bang_ ... #Deuterium
During the 1970s, there were major efforts to find processes that could produce deuterium, but those revealed ways of producing isotopes other than deuterium. The problem was that while the concentration of deuterium in the universe is consistent with the Big Bang model as a whole, it is too high to be consistent with a model that presumes that most of the universe is composed of protons and neutrons. If one assumes that all of the universe consists of protons and neutrons, the density of the universe is such that much of the currently observed deuterium would have been burned into helium-4.[citation needed] The standard explanation now used for the abundance of deuterium is that the universe does not consist mostly of baryons, but that non-baryonic matter (also known as dark matter) makes up most of the mass of the universe.[citation needed] This explanation is also consistent with calculations that show that a universe made mostly of protons and neutrons would be far more clumpy than is observed.[13]
This result on deuterium abundance is routinely ignored by MONDophiles as it the most embarrassing result for the claim that alternative gravity theories are better than particle DM. I have never seen this evidence for particle DM addressed by any of the proponents of alternative gravity ideas.

The third error in the video and the last I will deal with until time permits is at 5:17.

Dr H states that there is a problem with the matter distribution in galaxies. This is known as the core-cusp problem.

https://en.wikipedia.org/wiki/Cuspy_halo_problem

The problem arises when simulations are run for galaxy formation and evolution that make the simple assumption that particle DM does not interact with itself and only has a gravitational interaction. The the distribution of mass in the small galaxies produced should peak sharply at the centers. This is not observed. HOWEVER, if DM particles have some small or large self interaction, there is no problem. Feedback mechanisms such as supernovae and galactic winds can also smooth out cusps by perturbing the baryonic matter distribution.

More later.... Only about a third of the way through.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Thank you for taking the time to do this, nFA. It’s much appreciated.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

Gmetric wrote: Sun May 02, 2021 2:41 am Thank you for taking the time to do this, nFA. It’s much appreciated.
There’s more to come. Sneak preview: her measure of “simplicity” is merely “parametric simplicity”, the number of parameters needed by the theories. This doesn’t reflect “conceptual” simplicity at all. Her suggestion that particle dark matter and alternative gravity theory needing to be combined has a precedent in astronomy: Tycho’s solar system in which the inner planets are Copernican and the outer planets are Ptolemaic. :)
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by Gmetric »

Once again, thanks for your time, nFA. I've read through some of the material posted in your first response, and I have a question about Neutrinos and such. Ethan mentions sterile neutrinos as a hypothetical/theoretical possibility for the remainder of DM. As far as I understand, big bang nucleosynthesis places fairly heavy constraints on the mass of sterile neutrinos. Given the constraints, is it still possible for sterile neutrinos to fall within the mass requirements for cold dark matter?

According to this paper, https://arxiv.org/pdf/2005.06721v2.pdf. It is theorised that a lepton asymmetry would relax those constraints leading to the current state concerning Helium-4 and deuterium abundance and resolve the local and early universe measurements of the Hubble constant. How do you feel about lepton asymmetries in the early universe? And is it a plausible idea for the abundances noted?

This is just conjecture but, Is it possible that sterile neutrino overdensities in the early universe would have spawned the creation of Pop III stars? Pop III stars are theorized to have been massive, short-lived and would have produced energetic supernovae, distributing the first elements through their nucleosynthetic process. see here https://en.wikipedia.org/wiki/Stellar_population

Pair instability would have led these stars to go supernovae without leaving stellar remnants, as far as I understand. see here, https://en.wikipedia.org/wiki/Pair-inst ... _supernova.

Also, is it possible that lower mass Pop III stars (lower than the pair-instability mass range for Pop III stars) or Pop II stars forming inside these sterile neutrino bubbles could have gone supernova, leaving a black hole that would have accreted mass from the sterile neutrino overdensity and local baryonic matter creating the supermassive black holes we see now and also leaving behind a dark matter halo of sterile neutrinos in the galaxies surrounding those SMBH's ????
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

OK to continue my critique of Dr H's video.

At about 5:47 a list is presented of alleged problems with particle DM.

This is after the "cusp problem" which is well known to be solvable by self interacting DM and other ideas. The list includes:
  • the satellite galaxy problem
    the Tully-Fisher relation
    the Renza rule
    and galaxy cluster collisions
The "satellite galaxy problem" is also commonly referred to as the "dwarf galaxy problem". On the surface it looks like a severe difficulty.

https://en.wikipedia.org/wiki/Dwarf_galaxy_problem
For example, around 38 dwarf galaxies have been observed in the Local Group, and only around 11 orbiting the Milky Way,[2][a] yet dark matter simulations predict that there should be around 500 dwarf satellites for the Milky Way alone.[3][4]
However there are two popular proposed solutions. One is that there are undetected dwarf galaxy sized blobs of DM that have failed to attract enough baryonic matter to make stars and shine. The other is that the dwarfs are rapidly absorbed or tidally disrupted by the neighboring major galaxy. Favoring the first idea is this observation.

https://iopscience.iop.org/article/10.1086/521816
We present Keck DEIMOS spectroscopy of stars in eight of the newly discovered ultra-faint dwarf galaxies around the Milky Way. We measure the velocity dispersions of Canes Venatici I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, Leo T, Ursa Major I, and Ursa Major II from the velocities of 18-214 stars in each galaxy and find dispersions ranging from 3.3 to 7.6 km s-1. The six galaxies with absolute magnitudes MV < -4 are highly dark matter dominated, with mass-to-light ratios approaching 1000 M☉/L☉,V. For the fainter galaxies we find tentative evidence for tidal disruption. The measured velocity dispersions of the ultra-faint dwarfs are correlated with their luminosities, indicating that a minimum mass for luminous galactic systems may not yet have been reached. We also measure the metallicities of the observed stars and find that the new dwarfs have mean metallicities of [Fe/H] = -2.0 to -2.3; these galaxies represent some of the most metal-poor stellar systems known. The six brightest of the ultra-faint dwarfs extend the luminosity-metallicity relationship followed by more luminous dwarfs by a factor of ~30 in luminosity. We detect metallicity spreads of up to 0.5 dex in several objects, suggesting multiple star formation epochs. UMa II and Com, despite their exceptionally low luminosities, have higher metallicities that suggest they may once have been much more massive. Having established the masses of the ultra-faint dwarfs, we re-examine the missing satellite problem. After correcting for the sky coverage of the Sloan Digital Sky Survey, we find that the ultra-faint dwarfs substantially alleviate the discrepancy between the predicted and observed numbers of satellites around the Milky Way, but there are still a factor of ~4 too few dwarf galaxies over a significant range of masses. We show that if galaxy formation in low-mass dark matter halos is strongly suppressed after reionization, the simulated circular velocity function of CDM subhalos can be brought into approximate agreement with the observed circular velocity function of Milky Way satellite galaxies.
The mass to light ratio of 1000 is enormous! In general it's in the range of 2-10 with the universe as a whole 100. This means several things:
1) the DM effect varies from galaxy to galaxy so a particle DM model is more reasonable and an alternative gravity model is not feasible
2) the evidence that some of these dwarfs have been stripped is a testimony to the Milky Way's cannibalistic tendencies.

This is a situation where, because of the complex dynamics history and the long time scale several scenarios are reasonable. The data simply rules out alternative gravity. So this observation supports BOTH of the proposed solutions to the satellite galaxy problem that particle DM overcomes.

Lastly there is a personal suggestion. I've posted links to many studies of globular clusters which shoe evidence of multiple generations of star formation with differing metallicities. I see no reason why the population of GCs should not count toward the census of satellite dwarf galaxies. Indeed this possibility has been recognized for Omega Centauri (https://en.wikipedia.org/wiki/Omega_Cen ... arf_galaxy) and I firmly believe that as more results come in about diversity of chemical make up in globulars that this view is eventually going to prevail: globs are remnant cores of dwarf satellites.

The video states that the Tully-Fisher relation is a problem for cold dark matter.

That USED to be true. But the problem was solved in 2017. https://arxiv.org/abs/1706.07106
GalICS 2.0 is a new semianalytic code to model the formation and evolution of galaxies in a cosmological context. N-body simulations based on a Planck cosmology are used to construct halo merger trees, track subhaloes, compute spins and measure concentrations. The accretion of gas onto galaxies and the morphological evolution of galaxies are modelled with prescriptions derived from hydrodynamic simulations. Star formation and stellar feedback are described with phenomenological models (as in other semianalytic codes). GalICS 2.0 computes rotation speeds from the gravitational potential of the dark matter, the disc and the central bulge. As the rotation speed depends not only on the virial velocity but also on the ratio of baryons to dark matter within a galaxy, our calculation predicts a different Tully-Fisher relation from models in which the rotation speed is proportional to the virial velocity. This is why GalICS 2.0 is able to reproduce the galaxy stellar mass function and the Tully-Fisher relation simultaneously. Our results are also in agreement with halo masses from weak lensing and satellite kinematics, gas fractions, the relation between star formation rate (SFR) and stellar mass, the evolution of the cosmic SFR density, bulge-to-disc ratios, disc sizes and the Faber-Jackson relation.
The bold is my emphasis.

Renzo's Rule.

Renzo's rule simply states that where there is a feature in the luminosity profile of galaxy there will be a corresponding feature in the velocity curve. MOND proponents often state that this is a problem for particle DM. It isn't. It's obviously false.

That's all for tonight. Next I will take up the outrageous claim that galaxy cluster collisions are a problem for particle DM.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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Re: Dark Matter: The Situation has Changed...according to Sabine

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notFritzArgelander wrote: Sun May 02, 2021 5:31 am OK to continue my critique of Dr H's video.

At about 5:47 a list is presented of alleged problems with particle DM.

This is after the "cusp problem" which is well known to be solvable by self interacting DM and other ideas. The list includes:
  • the satellite galaxy problem
    the Tully-Fisher relation
    the Renza rule
    and galaxy cluster collisions
The "satellite galaxy problem" is also commonly referred to as the "dwarf galaxy problem". On the surface it looks like a severe difficulty.

https://en.wikipedia.org/wiki/Dwarf_galaxy_problem
For example, around 38 dwarf galaxies have been observed in the Local Group, and only around 11 orbiting the Milky Way,[2][a] yet dark matter simulations predict that there should be around 500 dwarf satellites for the Milky Way alone.[3][4]
However there are two popular proposed solutions. One is that there are undetected dwarf galaxy sized blobs of DM that have failed to attract enough baryonic matter to make stars and shine. The other is that the dwarfs are rapidly absorbed or tidally disrupted by the neighboring major galaxy. Favoring the first idea is this observation.

https://iopscience.iop.org/article/10.1086/521816
We present Keck DEIMOS spectroscopy of stars in eight of the newly discovered ultra-faint dwarf galaxies around the Milky Way. We measure the velocity dispersions of Canes Venatici I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, Leo T, Ursa Major I, and Ursa Major II from the velocities of 18-214 stars in each galaxy and find dispersions ranging from 3.3 to 7.6 km s-1. The six galaxies with absolute magnitudes MV < -4 are highly dark matter dominated, with mass-to-light ratios approaching 1000 M☉/L☉,V. For the fainter galaxies we find tentative evidence for tidal disruption. The measured velocity dispersions of the ultra-faint dwarfs are correlated with their luminosities, indicating that a minimum mass for luminous galactic systems may not yet have been reached. We also measure the metallicities of the observed stars and find that the new dwarfs have mean metallicities of [Fe/H] = -2.0 to -2.3; these galaxies represent some of the most metal-poor stellar systems known. The six brightest of the ultra-faint dwarfs extend the luminosity-metallicity relationship followed by more luminous dwarfs by a factor of ~30 in luminosity. We detect metallicity spreads of up to 0.5 dex in several objects, suggesting multiple star formation epochs. UMa II and Com, despite their exceptionally low luminosities, have higher metallicities that suggest they may once have been much more massive. Having established the masses of the ultra-faint dwarfs, we re-examine the missing satellite problem. After correcting for the sky coverage of the Sloan Digital Sky Survey, we find that the ultra-faint dwarfs substantially alleviate the discrepancy between the predicted and observed numbers of satellites around the Milky Way, but there are still a factor of ~4 too few dwarf galaxies over a significant range of masses. We show that if galaxy formation in low-mass dark matter halos is strongly suppressed after reionization, the simulated circular velocity function of CDM subhalos can be brought into approximate agreement with the observed circular velocity function of Milky Way satellite galaxies.
The mass to light ratio of 1000 is enormous! In general it's in the range of 2-10 with the universe as a whole 100. This means several things:
1) the DM effect varies from galaxy to galaxy so a particle DM model is more reasonable and an alternative gravity model is not feasible
2) the evidence that some of these dwarfs have been stripped is a testimony to the Milky Way's cannibalistic tendencies.

This is a situation where, because of the complex dynamics history and the long time scale several scenarios are reasonable. The data simply rules out alternative gravity. So this observation supports BOTH of the proposed solutions to the satellite galaxy problem that particle DM overcomes.

Lastly there is a personal suggestion. I've posted links to many studies of globular clusters which shoe evidence of multiple generations of star formation with differing metallicities. I see no reason why the population of GCs should not count toward the census of satellite dwarf galaxies. Indeed this possibility has been recognized for Omega Centauri (https://en.wikipedia.org/wiki/Omega_Cen ... arf_galaxy) and I firmly believe that as more results come in about diversity of chemical make up in globulars that this view is eventually going to prevail: globs are remnant cores of dwarf satellites.

The video states that the Tully-Fisher relation is a problem for cold dark matter.

That USED to be true. But the problem was solved in 2017. https://arxiv.org/abs/1706.07106
GalICS 2.0 is a new semianalytic code to model the formation and evolution of galaxies in a cosmological context. N-body simulations based on a Planck cosmology are used to construct halo merger trees, track subhaloes, compute spins and measure concentrations. The accretion of gas onto galaxies and the morphological evolution of galaxies are modelled with prescriptions derived from hydrodynamic simulations. Star formation and stellar feedback are described with phenomenological models (as in other semianalytic codes). GalICS 2.0 computes rotation speeds from the gravitational potential of the dark matter, the disc and the central bulge. As the rotation speed depends not only on the virial velocity but also on the ratio of baryons to dark matter within a galaxy, our calculation predicts a different Tully-Fisher relation from models in which the rotation speed is proportional to the virial velocity. This is why GalICS 2.0 is able to reproduce the galaxy stellar mass function and the Tully-Fisher relation simultaneously. Our results are also in agreement with halo masses from weak lensing and satellite kinematics, gas fractions, the relation between star formation rate (SFR) and stellar mass, the evolution of the cosmic SFR density, bulge-to-disc ratios, disc sizes and the Faber-Jackson relation.
The bold is my emphasis.

Renzo's Rule.

Renzo's rule simply states that where there is a feature in the luminosity profile of galaxy there will be a corresponding feature in the velocity curve. MOND proponents often state that this is a problem for particle DM. It isn't. It's obviously false.

That's all for tonight. Next I will take up the outrageous claim that galaxy cluster collisions are a problem for particle DM.
Thanks for all the info, I'll read through it today. looking forward to the next instalment. :)
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Re: Dark Matter: The Situation has Changed...according to Sabine

#9

Post by notFritzArgelander »

Gmetric wrote: Sun May 02, 2021 5:06 am Once again, thanks for your time, nFA. I've read through some of the material posted in your first response, and I have a question about Neutrinos and such. Ethan mentions sterile neutrinos as a hypothetical/theoretical possibility for the remainder of DM. As far as I understand, big bang nucleosynthesis places fairly heavy constraints on the mass of sterile neutrinos. Given the constraints, is it still possible for sterile neutrinos to fall within the mass requirements for cold dark matter?

According to this paper, https://arxiv.org/pdf/2005.06721v2.pdf. It is theorised that a lepton asymmetry would relax those constraints leading to the current state concerning Helium-4 and deuterium abundance and resolve the local and early universe measurements of the Hubble constant. How do you feel about lepton asymmetries in the early universe? And is it a plausible idea for the abundances noted?
A quick scan of the paper leaves a favorable impression. I need to reread it at leisure. I have a queasy gut when it comes to lepton asymmetries....... A sterile neutrino might provide some of the DM but needn't provide it all. I think that there is some evidence for bosons in DM which would not be sterile neutrinos, of course. The evidence (need to find the reference) is that there are two phases of DM, a superfluid (hence boson) and non superfluid.
This is just conjecture but, Is it possible that sterile neutrino overdensities in the early universe would have spawned the creation of Pop III stars? Pop III stars are theorized to have been massive, short-lived and would have produced energetic supernovae, distributing the first elements through their nucleosynthetic process. see here https://en.wikipedia.org/wiki/Stellar_population

Pair instability would have led these stars to go supernovae without leaving stellar remnants, as far as I understand. see here, https://en.wikipedia.org/wiki/Pair-inst ... _supernova.

Also, is it possible that lower mass Pop III stars (lower than the pair-instability mass range for Pop III stars) or Pop II stars forming inside these sterile neutrino bubbles could have gone supernova, leaving a black hole that would have accreted mass from the sterile neutrino overdensity and local baryonic matter creating the supermassive black holes we see now and also leaving behind a dark matter halo of sterile neutrinos in the galaxies surrounding those SMBH's ????
The only caveat I have about this is the "lower mass Pop III". I'm not sure that they could form without being seeded with the heavy elements required for cooling and condensation of protostars of low mass. The initial mass function for Pop III was very top heavy. Other than that I have no quibbles.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
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Re: Dark Matter: The Situation has Changed...according to Sabine

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So to resume the critique we were discussing the list of successes for alternative gravity starting at 5:37 with cusps, satellite galaxies, Tully-Fisher and Renzo which are incorrectly claimed as problems for particle DM and successes for alternative gravity. The last item in the list is perhaps the most astonishing mishandling of the observational data.

At ~7:04 it is falsely claimed that gravitational lensing studies of colliding galaxy clusters are a problem for particle DM.

This portion is the most outrageous abuse of data and shows, when combined with the discussion of the "cusp problem" how alternative gravity proponents cherry pick data and arguments without regard for avoiding self contradiction!

The only stated problem for particle DM with the Bullet Cluster is that the velocities are too high to be due to DM because of friction. This argument fails if the self interaction cross section of DM is properly constrained. So rather than being a problem for particle DM, observations of colliding galaxy clusters can be used to constrain the self interaction cross section of particle DM. This has been done.

https://arxiv.org/pdf/astro-ph/0309303.pdf
We compare new maps of the hot gas, dark matter, and galaxies for 1E0657-56 (nFA: note this is the Bullet Cluster), a cluster with a rare, high-velocity merger occurring nearly in the plane of the sky. The X-ray observations reveal a bullet-like gas subcluster just exiting the collision site. A prominent bow shock gives an estimate of the subcluster velocity, 4500 km/s, which lies mostly in the plane of the sky. The optical image shows that the gas lags behind the subcluster galaxies. The weak-lensing mass map reveals a dark matter clump lying ahead of the collisional gas bullet, but coincident with the effectively collisionless galaxies. From these observations, one can directly estimate the cross-section of the dark matter self-interaction. That the dark matter is not fluid-like is seen directly in the X-ray -- lensing mass overlay; more quantitative limits can be derived from three simple independent arguments. The most sensitive constraint, sigma/m<1 cm^2/g, comes from the consistency of the subcluster mass-to-light ratio with the main cluster (and universal) value, which rules out a significant mass loss due to dark matter particle collisions. This limit excludes most of the 0.5-5 cm^2/g interval proposed to explain the flat mass profiles in galaxies. Our result is only an order-of-magnitude estimate which involves a number of simplifying, but always conservative, assumptions; stronger constraints may be derived using hydrodynamic simulations of this cluster.
Now it sounds at the end like this might conflict with the required self interaction for solution of the "cusp problem". But in the conclusions to this paper the authors note that
Within the SIDM paradigm, the galaxy profiles and the tight cross-section limits coming from clusters can still be reconciled if the cross-section were velocity-dependent, so that it would be smaller on average in clusters than in galaxies (e.g., Firmani et al. 2000, 2001;Hennawi & Ostriker 2002; Colín et al. 2002). However, it is difficult to justify this additional degree of freedom in the model until a nonzero cross-section is detected at any velocity.
So we are learning that the self interaction cross section of particle DM may well be velocity dependent.

Another study, widely cited, uses the Bullet Cluster as direct evidence for the existence of particle DM. https://arxiv.org/pdf/astro-ph/0312273.pdf
We present a weak lensing mass reconstruction of the interacting cluster 1E0657−558 in which we detect both the main cluster and a sub-cluster. The sub-cluster is identified as a smaller cluster which has just undergone initial in-fall and pass-through of the primary cluster, and has been previously identified in both optical surveys and X-ray studies. The X-ray gas has been separated from the galax- ies by ram-pressure stripping during the pass-through. The detected mass peak is located between the X-ray peak and galaxy concentration, although the position is consistent with the galaxy centroid within the errors of the mass reconstruction. We find that the mass peak for the main cluster is in good spatial agreement with the cluster galaxies and offset from the X-ray halo at 3.4σ significance, and determine that the mass-to-light ratios of the two components are consistent with those of relaxed clusters. The observed offsets of the lensing mass peaks from the peaks of the dominant visible mass component (the X-ray gas) directly demonstrate the presence, and dominance, of dark matter in this cluster. This proof of the dark matter existence holds true even under the assumption of modified Newtonian gravity (MOND); from the observed gravitational shear to optical light ratios and mass peak – X-ray gas offsets, the dark matter component in a MOND regime has a total mass which is at least equal to the baryonic mass of the system.
The section I have bolded indicates that even assuming MOND to be true, you need particle DM to explain the observations!!

The separation of the concentrations of mass as revered by gravitational lensing FROM the baryonic matter distribution is prima facie evidence for the existence of particle DM and informative about its properties.

Now to Dr H's rhetoric and cherry picking. The "cusp problem" was used against particle DM but it is only applicable to "collisionless DM". Self interacting DM solves the cusp problem. However against the DM interpretation of the Bullet Cluster she uses a self interacting cross section with too high a self interaction. So she is willing to argue against collisionless in one context and against self interaction in another and unwilling to learn that the data is consistent with a velocity dependent self interaction. :shrug: Picking a straw man to suit the occasion is quite lawyerly but not at all scientific.

That concludes my analysis of the abuse of logic and data in this list. Next up I will discuss observations OTHER than the Bullet Cluster that decisively falsify alternative gravity theories and which were not discussed at all in the video.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

PS

Before I go on to that topic I'd like to add a reference I forgot:

https://arxiv.org/abs/2012.06611
We analyze strongly lensed images in 8 galaxy clusters to measure their dark matter density profiles in the radial region between 10 kpc and 100 kpc, and use this to constrain the self-interaction cross section of dark matter (DM) particles. We infer the mass profiles of the central DM halos, bright central galaxies, key member galaxies, and DM subhalos for the member galaxies for all 8 clusters using the QLens code. The inferred DM halo surface densities are fit to a self-interacting dark matter (SIDM) model, which allows us to constrain the self-interaction cross section. When our full method is applied to mock data generated from two clusters in the Illustris-TNG simulation, we find results consistent with no dark matter self-interactions as expected. For the eight observed clusters with maximum circular velocities in the range of 1400 to 2000 km/s, we find that the upper limit for the self-interaction cross section per unit mass of dark matter is 0.065 cm2/g at the 95% confidence level.
From the conclusions we note
Our results for the DM self-interaction applies to clusters with median maximum circular velocities in the range of approximately 1,400 km/s to 2,000 km/s. Since relative particle speeds are much lower in galaxies, the cross sections for dark matter interactions can be larger in galaxies, as many concrete particle physics models predict Tulin & Yu (2018).
The velocity dependent cross section for self interacting dark matter is just what you expect and yet Dr H insists on dismissing it as "adding parametric complexity". Well, alternative gravity theories also add parametric complexity! MOND has a whole family of functions for interpolating small gravitational accelerations with lots of unmotivated adjustable factors. It is unfair to criticize particle DM for adding parameters that are well motivated in standard particle physics theory.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by Michael131313 »

Thanks nFA very much for your time and effort. I am very impressed by your knowledge of this subject, as well as all the other subjects that you have helped me with. 😃
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

There are a number of observations which fatally falsify MOND and other alternative gravity theories that are attempts to make MOND theoretically more palatable. These are not mentioned at all in the video.

MOND and other alternative gravities are falsified by lab results on Earth.

MOND and the other alternative gravity theories modify gravity by having an irreducibly small acceleration. The force does not go to zero as distances become limitlessly large but rather to some constant minimum acceleration. The behavior of the acceleration as it becomes small is not specified but can be a simple hard cutoff constant or a more complex interpolation function (with as many parameters as you need for data fitting, so much for parametric simplicity!).

The behavior of Newtonian gravity (and therefore General Relativity) has been tested in terrestrial experiments. The result is that MOND and it's cousins are falsified. No deviation from an inverse square law is found.

https://journals.aps.org/prl/abstract/1 ... .98.150801
We have tested the proportionality of force and acceleration in Newton’s second law, F=ma, in the limit of small forces and accelerations. Our tests reach well below the acceleration scales relevant to understanding several current astrophysical puzzles such as the flatness of galactic rotation curves, the Pioneer anomaly, and the Hubble acceleration. We find good agreement with Newton’s second law at accelerations as small as 5×10^−14 m/s^2.
So while the search for DM particles is incomplete because the possible parameter space has not been searched exhaustively, the parameter space for MOND has been searched and found falsified. The full paper is available at http://www.schlammi.com/pdf/nsl_revised.pdf

I asked Dr H about this and received in reply only "they didn't measure what they thought they were measuring". I asked why she thought that and received no reply.

MOND is an unacceptable field theory because it violates Special Relativity.

Yep. It's a modification of Newtonian action at a distance gravity so you can't make a quantum field theory out of it. Now one can't yet make quantum field theory compatible with General Relativity but at least GR is compatible with Special Relativity and string theorists hold out that there is still hope. Action at a distance is incompatible with special relativistic quantum field theory.

Attempts to make MOND relativity have fatal side effects.

The most [romising attempt to put MOND on a relativistic field basis is the TeVeS theory. A summary is here https://en.wikipedia.org/wiki/Tensor–ve ... ar_gravity

Note that among the problems that TeVeS tries to fix is failure to conserve momentum! :lol: MOND violates Noether's theorem!!

Also
In addition to its ability to account for the flat rotation curves of galaxies (which is what MOND was originally designed to address), TeVeS is claimed to be consistent with a range of other phenomena, such as gravitational lensing and cosmological observations. However, Seifert[6] shows that with Bekenstein's proposed parameters, a TeVeS star is highly unstable, on the scale of approximately 106 seconds (two weeks). The ability of the theory to simultaneously account for galactic dynamics and lensing is also challenged.[7] A possible resolution may be in the form of massive (around 2eV) neutrinos.[8]

A study in August 2006 reported an observation of a pair of colliding galaxy clusters, the Bullet Cluster, whose behavior, it was reported, was not compatible with any current modified gravity theories.[9]

A quantity E_{G} [10] probing general relativity (GR) on large scales (a hundred billion times the size of the solar system) for the first time has been measured with data from the Sloan Digital Sky Survey to be[11] E_{G}=0.392±0.065 (~16%) consistent with GR, GR plus Lambda CDM and the extended form of GR known as f(R) theory, but ruling out a particular TeVeS model predicting E_{G}=0.22. This estimate should improve to ~1% with the next generation of sky surveys and may put tighter constraints on the parameter space of all modified gravity theories.

TeVeS appears inconsistent with recent measurements made by LIGO of gravitational waves.[12]
How do alternative gravity theories violate LIGO results?

It's exquisitely simple. Alternative gravities (when unlike the original MOND, which has no gravitational waves) predict a propagation speed for gravitational waves DIFFERENT from the speed of light. The arrival times difference provides a severe constraint on the difference (if any) in speed because of the very long travel distances. A difference in speed would be huge over the distances of the sources.

https://arxiv.org/abs/1710.06168
On August 17, 2017 the LIGO interferometers detected the gravitational wave (GW) signal (GW170817) from the coalescence of binary neutron stars. This signal was also simultaneously seen throughout the electromagnetic (EM) spectrum from radio waves to gamma-rays. We point out that this simultaneous detection of GW and EM signals rules out a class of modified gravity theories, termed ``dark matter emulators,'' which dispense with the need for dark matter by making ordinary matter couple to a different metric from that of GW. We discuss other kinds of modified gravity theories which dispense with the need for dark matter and are still viable. This simultaneous observation also provides the first observational test of Einstein's Weak Equivalence Principle (WEP) between gravitons and photons. We estimate the Shapiro time delay due to the gravitational potential of the total dark matter distribution along the line of sight (complementary to the calculation in arXiv:1710.05834) to be about 400 days. Using this estimate for the Shapiro delay and from the time difference of 1.7 seconds between the GW signal and gamma-rays, we can constrain violations of WEP using the parameterized post-Newtonian (PPN) parameter γ, and is given by |γGW−γEM|<9.8×10−8.
The title of the paper "GW170817 Falsifies Dark Matter Emulators" makes no bones about alternative gravities in the MOND family being false.

I wonder why Dr H failed to mention this? Best to not speculate.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

Michael131313 wrote: Mon May 03, 2021 1:49 am Thanks nFA very much for your time and effort. I am very impressed by your knowledge of this subject, as well as all the other subjects that you have helped me with. 😃
Thank you. I'm glad you find it interesting. I have kept up, since my school days, with my first love.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by turboscrew »

Very interesting!
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

turboscrew wrote: Mon May 03, 2021 2:55 am Very interesting!
I'm glad you find it so. There is still more to come maybe one or two posts on the substance of the video. ;)
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

At around 10 minutes into the video, Dr H suggests "the reason there has been so little progress with particle Dark Matter" in the last few decades is because "the wrong people are working on it".

There are two reasons why this remark is ill considered.

1) I think she has forgotten the neutrino. After all it took nearly 3 decades to coax a signal out of neutrinos. That was possible only because neutrinos participate in the weak nuclear force and can be induced (rarely) to interact with an atomic nucleus and create an inverse beta decay that emits charged particles that can be detected. It is unknown whether particle DM participates in the weak nuclear force and so strategies that worked for the neutrino (which is mostly what gets tried for WIMPs anyway) would completely fail to find DM. If the cold DM particles have a very small participation in the weak nuclear force they might never be seen since there is a noise floor that experiments are close to reaching: the hot dark matter background due to neutrinos from the Big Bang. Weaker interaction than that and they are forever undetectable, I fear.

2) She suggests that condensed matter physicists are better qualified to work on the problem since they can handle the problem of an alleged "phase transition" between where DM is a good idea and alternative gravity is (according to her, not me) a good idea. Back in my days in physics graduate school I was in a research group that worked in condensed matter physics and astrophysics theory. So such folks exist.

Well.... the condensed matter physics approach has been applied to the DM problem, but not in the way she would like. The work proposes that outside galaxies DM particles behave like a normal gaseous fluid but within galaxies where it is more dense it undergoes a phase transition to a superfluid state.

Here are some popular links to descriptions of the work:

https://penntoday.upenn.edu/news/physic ... superfluid

https://www.quantamagazine.org/dark-mat ... -20170613/

The technical details can be found at https://arxiv.org/abs/1507.01019
We propose a novel theory of dark matter (DM) superfluidity that matches the successes of the LambdaCDM model on cosmological scales while simultaneously reproducing the MOdified Newtonian Dynamics (MOND) phenomenology on galactic scales. The DM and MOND components have a common origin, representing different phases of a single underlying substance. DM consists of axion-like particles with mass of order eV and strong self-interactions. The condensate has a polytropic equation of state P~rho^3 giving rise to a superfluid core within galaxies. Instead of behaving as individual collisionless particles, the DM superfluid is more aptly described as collective excitations. Superfluid phonons, in particular, are assumed to be governed by a MOND-like effective action and mediate a MONDian acceleration between baryonic matter particles. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): due to the higher velocity dispersion in clusters, and correspondingly higher temperature, the DM in clusters is either in a mixture of superfluid and normal phase, or fully in the normal phase. The rich and well-studied physics of superfluidity leads to a number of observational signatures: array of low-density vortices in galaxies, merger dynamics that depend on the infall velocity vs phonon sound speed; distinct mass peaks in bullet-like cluster mergers, corresponding to superfluid and normal components; interference patters in super-critical mergers. Remarkably, the superfluid phonon effective theory is strikingly similar to that of the unitary Fermi gas, which has attracted much excitement in the cold atom community in recent years. The critical temperature for DM superfluidity is of order mK, comparable to known cold atom Bose-Einstein condensates.
With DM particles forming a Bose Einstein condensate (a superfluid) there is need for a MOND et al.

It's really odd that Dr H speaks in the video about the need for condensed matter folks to look at the DM problem, that they are the right folks to solve it. Perhaps she forgot about this video.....



Anyway this older video also contains her plea for combining particle DM and alternative gravity to get the best of both worlds. This is incoherent. If GR is correct and superfluid particle DM and normal fluid particle DM can explain all the observations then the observational need for alternative gravity theories can be well approximated by zero.

OK. I think I've written out my objections. Cheers.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by notFritzArgelander »

Oops. I forgot one huge falsifying set of observations for alternative gravity. The existence of under luminous galaxies that have no dark matter content is important and also omitted from Dr H’s video. If alternative gravity is good it should work out of the box with no need to adjust parameters for individual galaxies. However there are galaxies where the apparent DM to normal matter ranges from nearly zero to 1000 IIRC. This is easy to understand with particle dark matter: different formation and tidal interaction histories can and should lead to abundances of DM that differ from the universe average of 5. For alternative gravity theory to be viable the value should be 5 period with slight deviations only due to observation errors. So I’m not quite done yet.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by SkyHiker »

This discussion is happening on backreaction now, I am curious what Sabines answer would be to your comments nFA. She says that she is not talking about MOND and that MOND is wrong so maybe there is some misunderstanding. Why there are two theories necessary, looks like more complexity to me.
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Re: Dark Matter: The Situation has Changed...according to Sabine

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Post by pakarinen »

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