Virtually all of them, the evidence for its existence is overwhelming. It's nature is still a mystery though.

There are MOND theories. These theories modify Newtonian gravity at large scales. However there are new discoveries regarding galaxies without dark matter. In such cases rotation curve indeed falls down towards X-axis as you go further from the center. If gravity is modified, it has to be universal for all galaxies. Therefore you cannot modify gravity for some galaxies and not modify for others :-) Thus the discovery of a galaxy without dark matter seems to favor the existence of dark matter in general.

Not all scientists belive in the existance of dark matter and the number of them is decreasing.

I know for example Frolich (Planck medal) , Capozziello and Moffat (MOND) for example are top scientists who do not believe that there is dark matter, but it is only due to the limited knowledge of Physics relevant to the current theories of Gravitation which are not suitable.

For example it is also very interesting the following

https://www.researchgate.net/project/Modification-of-the-laws-of-gravity-from-the-prespective-of-General-Relativity-Theory

The latest discoveries found at least one galaxy with an order or magnitude lower quantity of dark matter than others of the same "mass" and no black hole in the middle. The trajectories are well described in this case by the virial theorem.

Dark matter which is nothing but areas with lensing effect but no visible matter, might also be an additional unknown effect of gravitation, at a distance, due to the presence of a massive black hole in the center of the galaxy .

The majority of Physicists accept the dark matter hypothesis because it can be explained as a consequence of relativity theories.

Thus the fact that it is one more non detected result weaks the relativity consensus.

My 'prophecy' is that after the '''detection''' of '''gravitational waves''' from LIGO a new project will be designed and built in order to "detect" dark matter too...

Wait and you'll see it...

PS And our friend George will defend the forthcoming "detection"...

:)

@Demetris Christopoulos...

Stefano Quattrini....Biswajoy Brahmachari...

George Dishman....

Thank you...

It was more powerful the belief in dark matter than in God as I could see. Again the vice to make an HP and belive to it till counterproof. Instead of non beliving to it till any proof is found. We risk to pave Physics with unverified hp.

Actually, its existence would be established if there were experimental evidence of its existence.

Until this is accomplished, irrespective of beliefs, it remains a simple hypothesis.

@ Thierry De Mees

my dear Thierry De Mees ....it is good observation from you...from your observation the logic is what ever may be we are ignoring that should count for a less quantity of Dark matter....but we need huge amount of Dark matter ...what does it mean?

thank you....

None-because belief doesn't make sense in such a context. It's astonishing how often religious terminology is (ab)used in contexts where it doesn't make sense.

The existence of dark matter has been deduced from experiment, namely the rotation curves of galaxies-though other modifications of general relativity can't be ruled out as explanations, completely, yet.

It's its particle content that isn't known.

The CMB is the most convincing evidence for the dark mass phenomenon.

Dark matter is like a man trying to drink himself sober, and the alcoholic beverage is Einstein's theories of relativity (that are know to be wrong, see attached). God Bless, Dennis P. Allen Jr., PhD

Actually Newtonian gravity (which explains Kepler's laws, by the way-it doesn't make sense to claim that they hold only in special cases, they're equivalent to the statement that the gravitational potential decreases like 1/r) is sufficient for computing the rotation curves of galaxies: http://www.astro.cornell.edu/academics/courses/astro201/rotation_curves.htm

http://jila.colorado.edu/~pja/astr3830/lecture16.pdf

jila.colorado.edu/~pja/astr3830/lecture17.pdf

and deducing that a new form of matter is sufficient to explain them.

Disc galaxies are studied here: Article The universal rotation curve of dwarf disk galaxies

Relativistic effects aren't that important.

Not all galaxies need contain dark matter-and, in fact, there was a quite recent discovery that, at least, one doesn't: Article A galaxy lacking dark matter

This doesn't imply that dark matter doesn't exist at all, since it was never claimed that it had to be part of every galaxy, and since its effects can be detected by other methods, e.g. https://www.aanda.org/articles/aa/pdf/2016/10/aa25830-15.pdf

It does imply that certain modifications of gravity, that attempt to describe the effects of dark matter in other ways, that are, always operative, are under additional constraints.

That's something to keep in mind: The idea of dark matter may have been motivated by the rotation curves of (certain) galaxies; but that's not the only reason for studying its consequences.

@ Esa Säkkinen

my dear Esa Säkkinen ... "The CMB is the most convincing evidence for the dark mass phenomenon. ""

i am still confusing about how CMB provide convincing evidence...shall you please elaborate this?

I would say most physicists believe in the existence of dark matter. For most physicists this is far from their fields of expertise. Only a very small part of us deals with the rotation of galaxies. And we don't have any reason to distrust those who do.

There was a question how to name it. For many, hidden mass seemed a better name, but dark mass sounded more exciting, especially for journalists (the journalists are very good, polymath-ignorant).

On the other hand, very few physicist believe in the proposed models. Usually these models assume that the hidden mass interacts with the barion matter in some way stronger than gravity. The dark matter is not so dark. That's fantasy. But, it is a grant-promising matter.

Hi

There are so many scientists that "believe" in dark matter. I think is not just a matter of believe or not believe. Scientists are not just "believers". The idea of dark matter was based originally, on the past, on the standard version of the Virial Theorem and today our present conception of dark matter is based on its generalized version. Scientists have a huge collection of data and open questions involving our present knowledge of the content and dynamical evolution of the Universe. Dark energy and dark matter represent possible explanations for some of those open questions. Unless a better explanation appears.

The answer depends upon what you mean by "dark matter". If you mean something that we know is there as a result of its gravitational effects, its existence is certain, and any self-respecting student of galaxies or cosmology must accept its existence. On the other hand, if you mean something that is in no way similar to any kind of matter known to exist, the answer is not as clear. Most cosmologists have accepted the existence of what I would call "Strange Dark Matter", but I doubt there is any way to do an accurate poll to find out the actual number of people involved. For a thorough discussion of why we can be certain that something called Dark Matter must exist, but the more uncertain matter of just what Dark Matter is, refer to my page about Dark Matter In Galaxies, at http://cseligman.com/text/galaxies/dark.htm

Hi Courtney

There are many candidates for dark matter. In particular, dark matter particles may interact with the four forces nature: the strong, the weak, the electromagnetic, and the gravitational forces. As for instance: WIMPs - weakly interacting massive particles, which have been subject to extensive research beyond the Standard Model; axions, low-mass, slow-moving particles, which may decay into a pair of photons; MACHOs,.massive astrophysical compact halo objects; Kaluza-Klein particles, linked to a "fifth dimension"; gravitinos , a superpartner of the photino (supersymmetric particles); and so on. As we can see many candidates. Up to now we do not have a more definitive explanation of this problem.

@Thierry De Mees

My dear Thierry De Mees, forget about spiral disc or galaxy, shall we discuss about gravity in between two galaxies?

Do we require dark matter in this condition also?

@Thierry De Mees

My dear Thierry De Mees...thank you...

Throughout history, scientists have given names to then partly understood processes simply to be able to think about them, that for a time induced the conclusion that the name corresponded to a physically existing substance.

The most striking example is that of phlogiston, that was the name used for a time to describe what was thought to be a "substance" contained in bodies that explained why some bodies could burn or oxidize. The phlogiston "substance" passed away when knowledge was sufficiently advanced for the elements to be identified and the function of oxygen in combustion and oxidation was understood.

My view is that "dark matter " and "dark energy" may simply be modern day's "phlogistons" possibly due to the fact that the virial theorem could be grounded on insufficient experimental evidence or possibly some flat out invalid premise.

@André Michaud...

My dear André Michaud, yep it is true ...

Hi s h s hussainsha

• "How many scientists or physicists do believe in existence of Dark matter? ":
• It is a good thing that people do not treat this question literally, and they talk about whether they personally believe or not in dark matter :-). In my opinion, the better question would be: Do you like or not the idea of dark matter? To this question I would answer that I definitely do not like it!:-)

@Jerzy Hanckowiak

My dear Jerzy Hanckowiak, thank you for correcting my question...

Any how you understood question in your way and also give answer...but we feel very happy if you have given answer with a logic reason....because we are here to learn ...

Thank you....

It suffices to calculate the velocity profile produced by any given mass distribution and compare the measured profile with that. Any deviation implies that there is more mass-since gravity doesn't cancel out, it's always attractive. Nothing more is needed.

Dear Thierry

I have to agree in part with you. I do not have this discrepancy information of the order of 4.5 between the predictions of the original formulation of Virial's theorem and its generalized form. I do not see also that the theorem applies to spherical objects. As I see, the theorem, in its non-geometric version, applies to punctual objects and to particles whose motions are random and isotropic, which makes the theorem even more limited.

The Virial theorem is a result of the studies of Clausius in thermodynamics. He used originally with other type of potentials.

Hi Thierry

I agree that the virial theorem does not take into account many "unvirialised" aspects of the gravitational interaction involving galaxies, clusters of galaxies and so on. No doubt that these aspects not taken into account in the virial theorem may change our perspective about the need for dark matter. I read your paper. Interesting work. I am not still convinced about the 4.5 factor. Anyway, let's see.

@Cesar Zen Vasconcellos..

My dear Cesar Zen Vasconcellos, it's good encouragement from you to Thierry...

Hi s h s hussainsha

Thanks. He is right regarding these unvirialised aspects.

I would hope that there are no scientists that "believe" in "dark matter" as if it were an article of "faith". Dark matter was introduced as a patch to fix an otherwise inexplicable departure from the expected in the rotation of the outer parts of galaxies. It is a hypothesis and evidence for it or something like it seems to be mounting but hard-core proof remains elusive. Until there is a testable "theory of dark matter" the question of dark matter remains open. Neither "belief" nor "denial" are appropriate in the ongoing inquiry but simply the evidence pro and con.

@Dwight Hoxie

My dear Dwight Hoxie, thank you...

Preprint Dark Matter Might Reside in Extra Physical Dimensions

"Extra physical dimensions" is internally contradictory concept due to the fact that dimensions are property of presentation not physical phenomena.

First you have to find out the interaction mechanism and then you can see how many dimensions it demands to present it.