I agree with most of what you say. Effectively MOND “kills DM+GR at Galactic Scales” and effectively this means that “GR needs modification“.

I did not say that MOND works very well beyond Galactic scales. I said just the contrary and even explained why one must wait discrepancies: “MOND is being applied outside its range of empirical validity“.

I also wrote in this blog how, thanks to a new theory, we do not need DM (neither DE) to explain observations beyond the Galactic scale anymore.

FQXi Essays are limited in size by Contest rules, therefore I could not write about all the advantages beyond GR (my first draft Essay was over the size limit and I was forced to eliminate many interesting stuff! For instance, I gave some additional technical details, on how the new canonical theory goes beyond M-theory and the rest of quantum gravity approaches, in Dr. Tejinder Pal Singh Essay).

In despite of size limitations, details and further info are given in the cited literature and in the technical notes in my Essay. In the technical note in page 9, I explain the assumptions and approximations over the which GR is based and how we derive GR from a more fundamental theory. I explain how well-known problems of GR as “the lack of gravitational energy-momentum-stress tensor“, “spacetime singularities“, “the problem of the systems of reference“, “violation of the usual conservation laws“, and “the impossibility to obtain a consistent quantization of such [geo]metric theory” are absent in the new theory.

Moreover, I have commented in Dr. Corda Essay how we can already go beyond MOND, PCG, TeVeS… explaining data that those theories cannot explain, and also commented I have not still studied Pioneer anomaly enough to say.

There is a third solution:

1′) DM does not exist at all.

“The fact that MOND does not work as well at cluster or higher scales…” This is only partially true

http://arxiv.org/abs/0704.0381

and, of course, discrepancies with MOND do not imply existence of DM, (ΛCDM has also difficulties http://adsabs.harvard.edu/abs/2010ApJ…718…60L), but that MOND is being applied outside its range of empirical validity and that a more general theory beyond MOND is needed.

As commented above (#101), MOND (and generalizations of it) can be derived from a truly general gravitational theory. You are right on that “the encompassing physical theory” was “discovered from a totally unexpected direction”!

Our goal was to correct other known deficiencies of GR (see the FQXi Essays cited above) and, as a bonus, we discovered that MOND and its acceleration scale were natural outcomes from the new theory.

If you look to my FQXi Essay, you will discover that the recent theory is much more general than Verlinde’s theory, which is based in a number of approximations and controversial assumptions.

So the real solution is that DM does not exist at the galactic scale.
I would have had no problem with DM, if MOND did not work so well at galactic scale.

The fact that MOND does not work as well at cluster or higher scales makes no difference. It is probably an indication that some form of DM exists on those scales. I don’t even think that MOND can be enhanced to form a theory. TeVeS is just a toy theory that shows how to build one, but I am pretty sure the encompassing physical theory will be discovered from a totally unexpected direction. The recent Verlinde’s theory of Entropic gravity looks interesting.

I liken MOND to an Empirical law. Any quantum theory of gravity needs to bring out MOND or it is not physical. Since GR in its present form does not predict MOND, it is not physical.

It is as simple as that. Empirical laws must be explained by all physical theories. If Newtons gravitational theory did not explain Kepler’s laws, it would be as useless (at the solar system scale) as GR is presently (at the galactic scale).

Extended rotation curves of spiral galaxies – Dark haloes and modified dynamics. Mon. Not. R. astr. Soc. 1991: 249, 523-537. Begeman, K. G.; Broeils, A. H.; Sanders, R. H.

Authors compare three-parameter dark-matter fits (M/L for the visible disk, plus two parameters for the dark matter halo: the core radius and the asymptotic circular velocity of the halo) with one-parameter MOND fits (M/L for the visible disk).

They find that MOND works well and “in some cases better than multi-parameter dark-halo fits.”

I am sorry to say this to dark-matter enthusiasts, but MOND rocks…

MOND has zero parameters. It is the dark matter model which uses “free parameters that can be chosen to improve any fit” (as Question Mark says).

I invite you to read again the section 5.2 of Gentile et al.

http://arxiv.org/abs/1004.3421

Two parameters for Burkert dark matter model (central density and core radius).

One/two parameters for the ΛCDM model of Navarro, Frenk & White (concentration and virial mass). Gentile et al. use cosmological simulations to correlate both (see eq. 3), but due to bad fit to the data they repeated the fit leaving both parameters free (read section 6) and still obtained a bad fit and related difficulties.

Zero parameters for MOND (see equation 6).

Regarding http://arxiv.org/abs/1005.5456, the authors use M/L as a free parameter to correlate velocity with light distribution, not because M/L was a free parameter in MOND. MOND are equations 1 and 2 in that preprint and they have zero parameters.

If you were to repeat their analysis using dark matter models you would use one or two parameters (of the dark halo) plus the M/L ratio of the correlation to light.

I.e. using the Burkert dark matter model you have three times more freedom (rho_0, r_{core}, and M/L) and still cannot match MOND predictions.

Precisely, the fact that MOND has zero parameters is the reason which is so sensitive to uncertainties in distances, whereas the dark matter models can absorb distance uncertainties into the halo parameters.

In this comment-page I have introduced six links from Stacy website. Only one part of one of the links discuss the wiggle. The other links discuss MOND predictions (all verified), samples of about a hundred of galaxies explained by MOND…

The same about the Gentile et al paper. They discuss the wiggle and more as ML ratios and overall fits.

MOND ability to fit the wiggle in NGC 1560 is not the reason for which MOND advocates consider “to take MOND seriously”. The reasons are (i) a hundred of galaxies explained by MOND as well as (ii) the dozen of predictions done by MOND and verified up to the date.

Regarding the recent preprint by Gentile et al. they do not claim “to take MOND seriously” because of the wiggle, as you continue to believe, but because they got “good fits using MOND” and “bad fits using the Navarro, Frenk & White halo” (an ‘elegant’ ΛCDM model). Reproducing the wiggle is only one point of an overall score that has given MOND its good empirical status.

As explained in the section 5.2 of Gentile et al., the Burkert dark matter model uses TWO parameters (rho_0 and r_{core} in the eq. 1), whereas MOND uses ZERO parameters (see eqs. 6 and 7). For values of r_{core} = 5.6 kpc and rho_0 = 0.8×10^−24 g cm^−3, the best fit M/L ratio for the Burkert dark matter model is of 2.3. Using ZERO parameters, the best fit M/L ratio for MOND is 0.98. The reference value for the ratio obtained from stellar population analysis is 1.43.

If you take all the points together (chi-squared plus wiggle plus ML ratio plus total number of free parameters…) you will find that MOND works better and, indeed, Gentile et al. affirm that MOND does it better than Burkert model and much much better than ΛCDM (which is empirically falsified).

Regarding http://arxiv.org/abs/1005.5456, the authors claim that “MOND is successful” for roughly three quarters of the galaxies in a sample of 27 dwarf and low surface brightness galaxies and that “This is remarkable, given that MOND is a one parameter fit with only M/L as a free parameter.”

MOND does not adequately explain the observed rotation curves for the remaining one quarter. The authors also emphasize that for the discrepant galaxies poor predictions were expected due to strong uncertainties in inclinations and distances.

If you take a look to their sample, you will find that some of the galaxies (e.g. UGC 5750, UGC 6446) were already covered in the section “Galaxies for which MOND fit is dubious” of a link given in a previous post from mine (http://www.astro.umd.edu/~ssm/mond/fitroster.html). However, UGC 5750 was then listed in that section, whereas now is reported as being in good agreement with MOND predictions.

This sample adds 8 new galaxies to the section of “Galaxies for which the MOND fit is dubious” and 14 new to the section “Galaxies well fit by MOND” and moves UGC 5750. This gives an overall score of about 98-0-18, with the 18 being associated to strong uncertainties.

Juan, NGC 1560 has ‘iconic status’ for MOND, i.e. the ‘remarkable’ ability to fit the wiggle is widely quoted as a good reason to take MOND seriously. As for the hundred other galaxies ‘perfectly well described’ by MOND, I advise you to read
http://arxiv.org/abs/1005.5456 where more counterexamples are discussed. Good distances might indeed tighten the constraints on MOND, since now de facto distance is used as a free parameter in MOND fits, in addition to the M/L ratio. Note that the M/L ratio is not predicted by MOND, contrary to your statement that MOND has ZERO free parameters. M/L ratios are rather uncertain, since the IMF is not very well constrained.

thanks for pointing to the figure in the reference page. In early posts, I did a series of corrections to unfounded attacks on MOND and added information about a hundred of galaxies being perfectly described by MOND as well as about a dozen of predictions done by MOND and that have been verified.

You have only focused in one wiggle around 300” in one galaxy! Still, I commented about this wiggle and about how this would not hide the subsequent difficulties for the ΛCDM model, which, I repeat, has been experimentally falsified in galaxies (ΛCDM systematically fails to reproduce both the velocities and the shape of the observed rotation curves).

In fact, you cite now the “core-cusp” problem in ΛCDM and confirm the attitude of cosmologists as Sean Caroll to ignore empirical evidences and to make unfounded comments against MOND.

You affirm that “by eye” the Burkert model gives a better fit than MOND. I find that you again are missing the whole picture because you are ignoring (i) the fit to the wiggle (curiously the best-fit curve in the Burkert model goes through the region of the wiggle), (ii) the number of FREE parameters used in each fit (TWO in the Burkert model, ZERO in MOND), (iii) that MOND gives better M/L ratio that Burkert, and (iv) that ΛCDM gives a bad fit.

There is not inconsistency about distances but uncertainty. Adopting the 3.45+-0.36 Mpc in MOND reduces the fit quality (chi-square) about a 0.13 and there is lower distances than 2.94 Mpc reported by other methods. The comments in Stacy McGaugh’s page are about the Broeils 1992 data not about Gentile et al. recent data. McGaugh emphasizes that “The CDM fit is not unique” and that “Its prediction is more vague than that of MOND, and misses the mark by a wider margin.” The same conclusions are found by Gentile et al.: “bad fits using the a Navarro, Frenk & White halo” (CDM), “and good fits using MOND”.

Now cosmologists as Sean Carroll would explain how is possible than the ‘beautiful’ ΛCDM model once again fails to explain data, whereas ‘ugly’ models as MOND explain the data (without free parameters).

Gentile et al. don’t give a chi-squared for the fits, but by eye the Burkert model gives a better fit than MOND. Furthermore, they assume a distance of 3.45 Mpc when fitting DM models, and for MOND they adopt a distance of 2.94 Mpc. The 3.45+-0.36 Mpc distance comes from the tip of the red giant branch method. So there is an inconsistency here – the best MOND fit is for a distance different from the best distance estimate -, as is also known for NGC 3198. Note that on Stacy’s page the comments are the other way around : the Begeman et al. fit for D = 3.0 Mpc was not good enough, so they said the galaxy ought to be at 3.4 Mpc for a good fit! So not all is well here (OK, a 13% problem).

The dip in the wiggle in NGC 1560 coincides with a relative depletion of the HI in the northern part. Interestingly enough, there is an extension in the vertical direction in the HI there, see Figure 3 of the paper of Gentile et al. This is not further discussed in that paper, but it could be related to the uneven gas distribution in the main plane.

As for the Burkert model fitting better than a model using the NFW profile (Figures 10 and 11), this graphically illustrates the ‘core-cusp’ problem in LCDM. It is indeed true that it took observers a lot of time to convince cosmologists that LCDM had that problem : their general attitude was (and partly is) still very close to the attitude displayed above by Sean (attitude of saying DM doing “just fine”, despite all the glaring problems; declaring MOND is ugly, as if 4% baryons + 23% unknown matter + 73% ‘dark energy’ is not messy). In that sense, LCDM was, and continues to be, oversold. But that does not mean that MOND should be oversold as well: it also has subtle problems, such as the one I am pointing out about NGC 1560.