Gian Francesco Giudice: We are confronted with the need to reconsider the guiding principles that have been used for decades to address the most fundamental questions about the physical world. The nature of dark matter is still unknown. What is changing is the feeling that the paradigm that so successfully led to the Standard Model may not be the right tool to make further progress. There is a widespread sensation that the organizing principles based on symmetry and separation of scales, which follow from an effective quantum field theory approach, in spite of their triumphs, must be superseded by new organizing principles. Physicists are in search for new conceptual paradigms, which is another symptom of a phase of crisis. Crisis means the opportunity to look at a problem with new eyes; it is a moment of change, a discontinuity between past and future. Krisis does not mean a decline of ideas, but the search for a paradigm change.

SA: Is dark matter a scientific theory?

Technically, no.

We have many theories, for example General Relativity is the theory that relates gravitational effects to energy (usually in the form of mass). If we apply that theory (or the Newtonian approximation) to the velocities of galaxies in clusters and the speeds of stars in galactic discs, they predict that there is additional matter which we can't see.

We also have theories that describe sub-atomic physics. When we apply those to the amount of deuterium in the universe, they also predict the same amount of additional unseen matter.

When we look at the way structure grew (galaxies formed very early in the universe), that theory also predicts there must be some additional matter that started clumping together before light decoupled, which means it cannot interact with light in any way.

Dark matter is therefore a hypothesis which satisfies the predictions of multiple theories.

Occam's Razor suggests that if one hypothesis can satisfy multiple requirements, it is to be preferred over multiple different answers that address the evidence in different ways.

MACHOs are dead:

Decades of research have narrowed down the possibilities. Early favourites included not only black holes, but also other massive compact halo objects (MACHOs) made of ordinary matter. A series of studies, however, gradually ruled out most of the possibilities. For example, researchers determined that black holes between about one-thousand billionth and one-billionth the mass of the Sun would destroy neutron stars. The presence of neutron stars in ancient globular clusters therefore suggests that primordial black holes of this size are extremely rare and could not account for all the dark matter in the Universe. Bird's theory was based on the fact that no one had yet ruled out larger black holes. But in the view of theoretical physicist John Ellis of King's College London, “MACHOs are dead.”

Attractive Dark Mater particles, including WIMPs have ruled out:

October 30, 2017• Physics 10, 119

The latest results from two dark matter searches have further ruled out many theoretically attractive dark matter particle candidates:

Two independent experimental collaborations—XENON [1] and PandaX-II —have recently taken the next steps in this relentless march of progress.The recent publications from the XENON and PandaX-II collaborations do not claim to have detected any particles of dark matter.

But even nondetections constitute progress, in that they reveal to us what the dark matter is not !!!

Simeon Bird, one of the physicists at Johns Hopkins says : “When you don't know what something is, you have to consider everything,”

Jeff Hecht Nature 537, S194–S197 (28 September 2016).

The lack of a definitive detection of dark matter particles, in both underground experiments and at the Large Hadron Collider, has had a palpable effect on the community of scientists that study particle dark matter. Even though a discovery could very plausibly be right around the corner, there is a widespread view that many of the most theoretically attractive candidates for dark matter should have been detected by now, based on their predicted properties. In the absence of such a discovery, the field has begun to redirect efforts toward new, and sometimes very different, ideas. Accordingly, again

Does Dark Matter theory constitute a scientific theory?

Could Dark Matter be falsifiable?

SA: Does Dark Matter theory constitute a scientific theory?

I already answered that: "Technically, no. ... Dark matter is therefore a hypothesis which satisfies the predictions of multiple theories."

yet if the missing dark matter does not exist it refutes SCM's assumption of ongoing cosmic expansion. which means the Cosmological redshift (CR )is evidence of something else, such as ..

Unlike SCM, if SPIRAL one would predict the CR, but not the missing dark matter.

So Occam's razor favors SPIRAL over SCM.

RMP: yet if the missing dark matter does not exist it refutes SCM's assumption of ongoing cosmic expansion

No it doesn't Roger. The Hubble Law is empirical and the existence of dark matter or otherwise makes no difference to that.

RMP: So Occam's razor favors SPIRAL over SCM.

No Roger, as we have discussed ad nauseam, simple triangulation of distant stars rules out YeC.

Note also that the LIGO detection of gravitational waves gives direct measurements of 'luminosity distance' to black hole mergers that happened over a billion years ago, and most recently to a binary neutron star merger that happened 130 million years ago in a galaxy 130 million light years distant, NGC 4993.

Occam's Razor didn`t say that if one hypothesis can satisfy multiple requirements, it is to be preferred over multiple different answers. He said If you have two theories that both explain the observed facts, then you should use the simplest until more evidence comes along. We didn`t detect dark matter to confirm its existence since 1930, to explain the flat rotation curve. MACHOs, Attractive Dark Mater particles, including WIMPs have ruled out. Supersymmetric particles have not been detected. Again and again we postulate Dark Matter to bridge the gap between observations and multiple theories, those we failed to explain. So, Dark Matter works as a peg to which we attached our failure and inability.

we used speculations to support speculations (Dark Matter, Dark Energy, Inflation...etc). I don`t think science could progress in such manner.

Dark Matter and CMB

"Apart from flat rotation curves, evidence for dark matter comes from the small anisotropies in the cosmic microwave background radiation (CMB), which suggests that forming large scale cosmic structures on time scales shorter than the Hubble time essentially requires substantial amount of gravitating cold dark matter". This is no more than speculations. No equations, no calculations and no rigorous mathematics to support such speculations.

Most early massive galaxies are strongly dominated by normal matter ruled out the speculations that the "Theory of large scale structure formation requires anisotropies in the CMB, but also requires the presence of dark matter in early universe" International Journal of Modern Physics A. Vol. 29, No. 19 (2014) 1443001. DOI:10.1142/S0217751X14430015

Time passes without a confirmed detection, even the most heavily backed theories are beginning to look less likely. A series of experiments have systematically searched for, and failed to find, the theoretical candidates for dark matter. Scientists from two of the world’s biggest dark matter detectors have reported that their latest experiments, like all earlier attempts, have produced no sign of the elusive substance. Scientists from two of the world’s biggest dark matter detectors have reported that their latest experiments, like all earlier attempts, have produced no sign of the elusive substance. In a pair of papers published in Physical Review Letters, researchers from the XENON1T and PandaX-II collaborations have ruled out some theoretical possibilities for dark matter particles. Combined with negative results from American LUX experiment and tests at the Large Hadron Collider, these results are adding to a sense of frustration among researchers. . So, What?

Bullet Cluster contradicted ΛCDM model :

The greatest challenge to modified gravity theories, and also the clearest direct evidence of Dark Matter, comes from observations of a pair of colliding galaxy clusters known as the Bullet Cluster in which the stars and Dark Matter separate from the substantial mass of ionized gas. The Dark Matter follows the less substantial stars and not the more massive gas. Since the new bullet cluster is less massive and the merger slower, weighing its dark matter could be harder. The dark matter hypothesis for the bullet cluster is contradicted by the cold dark matter ΛCDM model. The initial relative velocity of the two colliding clusters would need to be around 3000 km/s in order to explain the observed shock velocity, X-ray brightness ratio and morphology of the main and sub-cluster. Jounghun and Eiichiro (2010) have shown that such a high infall velocity is incompatible with the predictions of the cold dark matter ΛCDM model. The probability that such an event could occur is roughly one in 10 billion!.

Jounghun and Eiichiro arXiv:1003.0939 [astro-ph.CO]]

What is considered in cosmology is not simply some "dark matter" but particular dark matter models.

The most important and relevant one is CDM, cold dark matter. It consists of usual particles, with mass, which does not interact with other matter except via the gravitational field. So, everything is well-defined here, and therefore falsifiable.

An abstract "dark matter" of type "we don't know anything about it" would be unfalsifiable. But this is not what is considered in cosmology.

The various attempts to find dark matter try other models of dark matter, namely uncharged dark matter which can interact with usual matter, or with weak or with strong interactions. So, also some particular assumption about the properties of the dark matter, which makes it possible to test the hypothesis - and each "dark matter not found" means one such particular model of dark matter has been falsified.

Ilja Schmelzer

“When you don't know what something is, you have to consider everything,”

The process of ruling out dark matter candidates would continue indefinitely, by this sense it seems not falsifiable. Like supersymmetric particles, every time we fail to detect them we move the constraints to untouchable level !!!

Yes. In this sense, the abstract "dark matter" without specification of properties of the dark matter is not falsifiable. Whatever we observe, we can take the observable error in the Einstein equations G_mn - T_mn and name it "energy-momentum tensor of unknown dark matter".

But in fact there is not much ruling out. What is ruled out is essentially not dark matter, but various variants of "almost dark matter". The most important variant, which is CDM (cold dark matter), which is simply some unknown massive particle which does not interact at all with usual matter, is not ruled out at all. So, the process has in this sense not even started.

Dark matter has appeared as one of the few observational cosmological features which can open new physics in this area of knowledge. Unfortunately I think that we have too many logic and few experiments for determining so huge scales from our small Earth and the same that it has happen with the small scale (quantum effects), perhaps the high scale of the Universe scapes to the straightforword laws of gravitation assumed to follow Einstein's equations or so on.

There are two recent physical review that tries put some limits to the dark matter that I think they deserve a reading for this discussion

Article Dark Matter Results from 54-Ton-Day Exposure of PandaX-II Experiment

Article First dark matter search results from the XENON1T experiment

MOND is almost ruled out

An alternative to Dark Matter is to explain the missing mass by means of modification of gravity at large distances or more specifically at small accelerations. There have been suggestions that the law of gravity could be different over galactic scales and could perhaps resolve the problem of Dark Matter implied by flat rotation curves. A 1/r force law, rather than an inverse square law for gravity. The theory, known as Modified Newtonian Dynamics (MOND).

The paper arXiv:1710.06168 [astro-ph.HE] rules out all modified gravity theories that predict gravitational waves which pass differently through the gravitational potential of galaxies than electromagenetic waves do. The recently reported gravitational wave detection, GW170817, was accompanied by electromagnetic radiation. Both signals arrived on Earth almost simultaneously, within a time-window of a few seconds. The observation is difficult to explain with some variants of modified gravity because in these models electromagnetic and gravitational radiation travel differently. This is a big problem for some alternatives to dark matter (such as Bekenstein’s TeVeS and Moffat’s Scalar-Vector-Tensor theory) as this new paper lays out: GW170817 Falsifies Dark Matter Emulators arXiv:1710.06168 [astro-ph.HE]

MOND is non-relativistic where the physics of the large structure should b relativistic. MOND deals with gravity as a force that is weak at large structure scale, in contrast to GR that deals with gravity as a curvature. Curvature locally is undetectable, but its significant at large structure.

Virial theorem (V=√(MG/r) fails to predict Mercury`s orbit where the gravitational field (curvature) is very strong near the sun and consequently the spacetime is not flat. Virial theorem didn`t cover the overall space of the solar system. How correctly we assume it should be valid over the large structure spacetime of the galaxies and the cluster of galaxies. We need a rigorous mathematics to generalize the domain of applicability of the Virial theorem to survive at large structure scale. According to the Equivalence Principle, its impossible to detect the gravitational field (curvature) locally. The imprint of the curvature is noticeable and significant over the large structure spacetime. Virial theorem is valid only for flat space and fails to be valid for non-Euclidean spacetime. Hence the discrepancy between the mass of the galaxy due to its brightness and that due to its rotation velocity is due to the failure of applying Virial theorem at large structure non-Euclidean spacetime of the galaxy to detect its mass. Our main mistake is that we accept an unverifiable assumption that the portion of the universe which can be observed is representative of the whole, and that the laws of physics are the same throughout the whole universe. It is an oversimplification to generalize that the universe is globally flat and the laws of physics are the same throughout the whole universe. Newton`s laws of gravity do no longer hold in non-Euclidean geometry

Salah, the curvature is something which can be detected locally. The Equivalence Principle, in the form which claims that gravity is locally equivalent to acceleration, is only an approximate rule. Tidal forces are observable locally - they are second derivatives of the metric.

No it is not George, if one or the other, the prevalent cosmological redshift of distant starlight is overwhelming empirical evidence of SPIRAL and not SCM's ongoing cosmic expansion. When it comes to fair consideration of SPIRAL you have a mental block :(

so CR is not empirical evidence of ongoing cosmic expansion, thus there is no need to hypothesize any missing dark matter.

Anti-matter was well defined before we focus observation to detect it. Nothing we knew about Dark Matter neither its construction nor its constituents. What should we observe ? Unless a theoretical description exists to visualize Dark Matter, our quest would be hopeless.

RMP: No it is not George, if one or the other, the prevalent cosmological redshift of distant starlight is overwhelming empirical evidence of SPIRAL

No Roger, your hypothesis would result in infinite redshift for every star more distant than roughly 5800 light years making them invisible, and that is all but a few thousand of the nearest stars in our galaxy. Cosmological redshift doesn't even exist within single galaxies but your model is incapable of producing anything other than (a) no redshift or (b) infinite redshift.

RMP: When it comes to fair consideration of SPIRAL you have a mental block :(

ROFL, that mental problem is called "transference", you cannot even see the blatantly obvious problem I've explained to you. Simple triangulation rules out your religious miracles.

Dark matter is certainly not a scientific theory. It is not even a hypothesis because any hypothesis must be based on reason and experimental facts. Dark matter is unreasonable because it is itself conjured from falsities, and has no experimental basis whatsoever. It is merely an irrational invention to attempt to bolster a demonstrably false theory. Here is a starting point:

Crothers, S.J., A Critical Analysis of LIGO's Recent Detection of Gravitational Waves Caused by Merging Black Holes, Hadronic Journal, n.3, Vol. 39, 2016, pp.271-302, http://vixra.org/pdf/1603.0127v4.pdf http://viXra.org/abs/1603.0127

Crothers, S.J., Relativistic Cosmology and Einstein’s ‘Gravitational Waves’, Chapter 9, Principles of ECE Theory, 2016, http://vixra.org/pdf/1611.0296v1.pdf

"Note also that the LIGO detection of gravitational waves gives direct measurements of 'luminosity distance' to black hole mergers that happened over a billion years ago, and most recently to a binary neutron star merger that happened 130 million years ago in a galaxy 130 million light years distant, NGC 4993." George Dishman

LIGO certainly did not detect black holes or gravitational waves or 'neutron stars'.

Crothers, S.J., A Critical Analysis of LIGO's Recent Detection of Gravitational Waves Caused by Merging Black Holes, Hadronic Journal, n.3, Vol. 39, 2016, pp.271-302, http://vixra.org/pdf/1603.0127v4.pdf

Cosmologists are not scientists - big bang creationism is not science.

The real crux of big bang creationism is its so-called Cosmic Microwave Background (CMB) residue. The CMB is purported to be a blackbody spectrum at a temperature of ~2.725 K. The assignment of this temperature ultimately rests upon Kirchhoff's Law of Thermal Emission and concomitant universality of Planck's equation for thermal spectra. But Kirchhoff's Law of Thermal Emission is in fact false, and, hence, Planck's equation not universal. Consequently big bang creationism is proven completely false by the physics of thermal emission, with very little by way of mathematics.

Robitaille, P.-M., Crothers, S. J., “The Theory of Heat Radiation” Revisited: A Commentary on the Validity of Kirchhoff’s Law of Thermal Emission and Max Planck’s Claim of Universality, Progress in Physics, v. 11, p.120-132, (2015), http://vixra.org/pdf/1502.0007v2.pdf

Dark matter is a purely ad hoc suggestion for why there's a big mismatch between the gravitational predictions of Einstein's general theory and observed reality. It currently has no deeper theoretical basis or founding principles. When we say that observations show that dark matter is real, what we're saying is that observations show that Einstein's general theory disagrees with physical reality in a manner that is consistently reproducible.

If we start with galaxy rotation curves, there are three main interpretations for why the galaxies hold together as well as they do.

• #1a The general theory is wrong, and nonlinearity creates a greater attraction within a galaxy for a given amount of matter
• #1b The general theory is wrong, and nonlinearity creates a weaker interaction between galaxies across intergalactic spaces than we'd expect if these spaces were simple "flat background".
• #2 The general theory is right, but there's Something Else out there.

So our main hypotheses are (#1) "GR1916 is wrong", and (#2) "Dark matter is real"

We can now assess these hypotheses for falsifiability and utility. Measurements have shown some odd behaviour for dark matter. Apparently,

• Dark matter does not clump or form independent stars. It does not stick to itself. Dark matter does not interact in any way with other dark matter, except gravitationally.
• Dark matter does not interact in any way with light, except gravitationally. It is invisible to us other than by its gravitational effect.
• Dark matter also does not show any other identifiable physical interactions at all, with anything, apart from gravitationally. It does not seem to participate in any other form of physics.
• The distribution of dark matter "shadows" that of normal matter, forming a sort of halo around it. We do not detect dark matter without normal matter being present, and the quantity of dark matter in a region seems to mirror the quantity of normal matter.

These results have been considered surprising because they do not correspond to any behaviour or principles of known matter. Hypothesis #2 "Dark matter is real" does not predict any of these results.

However, hypothesis #1, "GR1916 is wrong" predicts all of these results. If there's no such thing as dark matter, and GR simply has bad classical equations for field theory, then we end up with all these behaviours.

In terms of scientific predictive power, the hypothesis that "GR is wrong" has successfully predicted every qualitative aspect of dark matter that we've found so far, while "Dark matter is real" has predicted not much more than the consistency of the mismatch between GR and reality (which we also get with the "GR is wrong" hypothesis).

Hypothesis #1 is also not obviously falsifiable, while hypothesis #2 is. #2 requires that we will never find any aspect of dark matter that cannot be modelled as a smooth continuous gravitational field correction to existing GR – we will never find any properties of dark matter other than a gravitational field, and we will never find that field in the absence of conventional matter.

If dark matter remains indistinguishable from a field effect associated with conventional matter, Occam's razor suggests that we should probably treat it as a field effect associated with conventional matter.

As scientists, we know that #2 makes predictions that so far have a 100% success rate, while #1 makes no obvious predictions, #2 is falsifiable while #1 doesn't seem to be, and #2 is more efficient in that it generates these behaviours from known matter rather than inventing radical new types of matter with exotic properties.

So "GR is wrong" is objectively the more correct scientific interpretation of the evidence, and as scientists, it should be our default interpretation.

Eric Baird

The galactic dynamics, the CMB anisotropies and the gravitational lensing do not agree with the observations. Either an additional component of mysterious unseen nonbaryonic matter (Dark Matter) is needed-to bridge the gap between theory and observations-or, the theory of gravity should be modified. The large structure spacetime is no longer flat. Hence the laws valid at flat space (Virial theorem ) fail to be valid at non-Euclidean spacetime. Gravity is geometry. The first natural step is to modify the underlie geometry itself. We prove the spacetime is hyperbolic. We modify the equation of motion in the updated hyperbolic geometry that fits the data and predicts the observed flat rotation curve without invoking Dark Matter. Thus, the hyperbolic structure of the spacetime, not dark matter, accounts for the current anomalies in the observations.

https://www.researchgate.net/publication/322490801_The_Hyperbolic_Universe_Does_Not_Need_Dark_Matter

Salah: Thanks! A nice paper! :)

I think a lot more attention should be directed at these sorts of geometrical approaches.

Unfortunately, the research dynamics seem to be biased towards "particle" descriptions:

If one invents a new hypothetical particle (with a fun name) to explain dark matter, then lots of journalists will write articles about it, and experimenters will cite the paper as potentially important in the hope of getting research funding to carry out tests ... which might give them five or ten years of gainful employment before the experimental results turn out to be negative or inconclusive.

But if one finds a way of explaining the same effects without inventing new forms of matter, then even though the idea might represent better science, it may have a smaller natural constituency with an incentive to cite, promote and recommend the idea. A more efficient idea can be less successful in the marketplace because its efficiency generates fewer financial/career/publicity opportunities for other researchers.

Dear Salah,

I quickly went through your paper and I have to say it is very interesting!!!!

As far as I've understood, your model, in the short-range, reduces to the Schwarzschild metric of GR.

Very recently also Capozziello wrote a paper on modified Einstein equations to account for the Dark Matter, but it seems it has some issues. Here there is a very good argument, a quality change which is the indication of the overall structure which is not a generic non linearity, but it is Hyperbolic.

How many galaxies did you test with your model? Did you go through the Tully-Fisher observations?

Could it be possible that the Hyperbolic nature is due to the gravitational energy which is not accounted locally by GR but, according to GR, to satisfy the conservation laws for isolated systems, most of it should be far outside the disc of the galaxy where the space is supposed to be flat (Minkowskian)? In other words, there is a neglected degree of freedom where gravitational energy should fit and the EEP is definitely singled out!!!

Not being an expert I have this feeling that It may be the case that dark matter will be the modern version of phlogiston and caloric which were explaining combustion and heat until oxygen and atoms were discovered.

The only reason is that there is no place for new matter in standard model.

First the Gravitational energy has to be reinstated locally to make gravitation work consistently with the other interactions. GR misses a big chunck

" I think, Dark Matter hypotheses is too flexible to be falsifiable !"

Not really. We have numbers giving the amount of dark matter. We can get these numbers from different sources. If they do not agree, then dark matter is falsified. Up to now, agreement of all the numbers within the experimental error has been achieved.

K. Kassner

-Simeon Bird, one of the physicists at Johns Hopkins says : “When you don't know what something is, you have to consider everything". But even nondetections constitute progress, in that they reveal to us what the dark matter is not!!! Does this make sense, to rule out what is not dark matter? Potato is not dark matter and tomato also is not dark matter …etc indefinitely.

KK: " Not really. We have numbers giving the amount of dark matter. We can get these numbers from different sources. If they do not agree, then dark matter is falsified. "

... or, they could announce that they'd now discovered that there were two different types of dark matter.

Dm is an extensible hypothesis that's retrospectively fitted to the data, with no real predictions. We might expect the measured distribution to not vary wildly from situation to situation, or from day to day, but even the absence of wild variations isn't a "given", it's an observation. The competing "field theory" explanation might suggest that perhaps the strength of the galaxy-curve anomaly should increase with time, as galaxies move further away from each other, so that more distant, older galaxies should show more traditional gravitational behaviour than nearer ones. But even if that's verified, dm proponents could counter that all it means is that the quantity of dm is steadily increasing over time. And since they haven't committed to what dm actually is, they can get away with auxiliary hypotheses like this as to how dm is supposed to behave, as new data comes in.