DARK MATTER : MYTH or REALITY ?

[MBoraCilek]

Many believe Dark Matter is still the biggest problem in cosmology/astrophysics.. Although we hear daily about new observations, experiments and speculations about it's possible (exotic) structure, there is no material evidence for its existence yet..What's going on, do we really need Dark Matter or should we seriously reconsider alternative theories ?
or is something really wrong about the current cosmological model ?

[Strange]

Well, to my mind, "dark matter" is a generic term for whatever turns out to cause the unexpected rotation rates seen in galaxies. It is possible (but increasingly unlikely) that it will turn out to require a modification to our understanding of gravity (e.g. MOND). But then we would need something else to explain some of the other things that are currently nicely explained by dark matter being, well, matter.

[MBoraCilek]

probably thats why I believe scientists are in a relentless effort to discover something "exotic", like a new type of particle which has not been detected yet, but hopefully (!) will be soon..In the meantime it seems that DM theory causes many problems in different areas and is questioned seriously by different researchers..for example it predicts that DM should be lumped at the centers of galaxies and that is obviously not the case, thus creating the cuspy halo problem..and many more should be on the list..I personally believe that the solution is much nearer and simpler than finding the "darkmatterino"..

[StupendousMan]

The original post in this topic questions the reality of dark matter, which is accepted by the mainstream astronomical community. Therefore, this topic ought to be moved to "Against the Mainstream".

If the poster were to ask a more specific question, then it might be appropriate for this section of the board.

[loglo]

MBoraCilek,
The need for Dark Matter has been drawn from decades of observations. Many theories were investigated, WIMPS and MACHOs came out as the favourites then observations ruled out MACHO's. Changing cosmological models won't help as that won't explain the more local effects like galaxy rotation curves. ALL alternative models to WIMPS have failed to pass muster. Feel free to knock yourself out coming up with a new one. Forgive us if we don't get too excited though.

[tnjrp]

Well, to my mind, "dark matter" is a generic term for whatever turns out to cause the unexpected rotation rates seen in galaxies

Yep, strictly speaking dark matter is a phenomenon, not the explanation. Conflating the two is a common mistake to make tho (and not just in regards to the dark matter one might add).

I would also think that dark energy is a bigger problem for cosmologists than dark matter. I'm not sure if everyone (well, expect for a few ATMers) even agrees it actually exists as of yet.

[MBoraCilek]

your views are all very important to me..thank you, and frankly speaking I would probably give the same reaction and write the same things if I were in your shoes..I just wanted to note that Dark Matter was first postulated in 1930s, if I remember correctly..that I think was a fudge solution to explain the strange behaviour in the Coma Cluster and later flat galaxy rotation curves, just as Einstein's fudge factor to defend the static universe despite his equations did not tell so (then it became the biggest blunder)..it is also correct that the mainstream thinking is based upon the existence of Dark Matter, and people like me who is skeptic about it should defend their ideas from the sidelines..to cut a long story short, cosmology is going nowhere as long as we stick to the DM theory, and 80 years is a long time..alternative theories are also nice to see, but they do not take us anywhere either..it is 2011 now, and we have the necessary tools to question a theory which has no direct observational evidence yet..everything presented as evidence is indirect and second order at best, with many contradicting phenomena..for the time being I am of course not in a position to challenge the "mainstream view" but I believe this will not last long..I intend to post a short article in the ATM section soon, which I believe will give some insight on what is wrong..with all due respect, all I am asking from everyone is "please do not forget the problem and think about it, as DM is still a problem for many of us"..

When Einstein claimed that he would solve the Gravity problem, Max Planck told him:

1) You cannot solve it, because it is too difficult.
2) Even if you solve it, nobody would believe you.

by the way, has it been solved yet ??

[antoniseb]

... it is 2011 now, and we have the necessary tools to question a theory which has no direct observational evidence yet..everything presented as evidence is indirect and second order at best, with many contradicting phenomena.. ...

Weak lensing has been an excellent direct tool for observing where and how much dark matter is present around galaxies and clusters. So far as I know nothing contradicts it. I'm looking forward to your ATM post. I will certainly have some questions about how your model explains weak-lensing observations.

[MBoraCilek]

sure Sir,
I will be pleased to answer all your questions, gravitational lensing is just one of them, following flat curves of rotation..and to everbody's surprise there will no new models, exotic concepts or complicated mathematics..no long essays, no b......t, 2-3 pages of established physics.. I would be thrilled to answer everbody when I post the article on the ATM, after legally registering it..

[Jerry]

Weak lensing has been an excellent direct tool for observing where and how much dark matter is present around galaxies and clusters. So far as I know nothing contradicts it. I'm looking forward to your ATM post. I will certainly have some questions about how your model explains weak-lensing observations.

Weak lensing is pretty good evidence glaxies and clusters bend light more than anticipated, based upon the observed matter and current theory. The evidence from the bullet cluster is consistent with dark matter demonstrating inertial properties.

Since we haven't found evidence of anything other that gravitational forces in 'dark matter' physics; the phenomenon falls outside of the general rule of cause-and-effect that are consistent with our local experience. In other words, it is a mystery.

A paper last week worth footnoting on this topic:

arXiv:1101.5155

A Cosmic Coincidence: The Power-Law Galaxy Correlation Function

...We assume that galaxies reside within dark matter halos and subhalos and use a semi-analytic substructure evolution model to study subhalo populations within host halos...
...we do show that the physics responsible for setting the galaxy content of halos do not care about the conditions needed to achieve a power law xi(r) and these conditions are met only in a narrow mass and redshift range. We conclude that the power-law nature of xi(r) for Lstar and fainter galaxy samples at low redshift is a cosmic coincidence.

Power-law red shift relationships always make me nervous; more especially so when it is demonstrated that the rule only applies to the most local features. If a local trend does not show persistence to deeper redshifts, the trend should be a suspected selection effect: Not the whole picture.

[Tensor]

your views are all very important to me..thank you, and frankly speaking I would probably give the same reaction and write the same things if I were in your shoes..I just wanted to note that Dark Matter was first postulated in 1930s, if I remember correctly..that I think was a fudge solution to explain the strange behaviour in the Coma Cluster and later flat galaxy rotation curves, ...

Actually, using the definition as matter that only seems to interact gravitationally, dark matter was first postulated c1828 by M Alexis Bouvard of France and T J Hussey of England (who was first is not known, but both of them discussed it by letters to each other in 1828).

Their dark matter was described as another planet. It was a fudge factor for Newton's gravitational law to explain the motion of Uranus. At the time, it couldn't be seen (or more properly, wasn't recognized) as interacting electromagnetically, only gravitationally. Of course, that dark matter turned out to be Neptune. But how were they to know that 18 years before it was verified as interacting electromagnetically (recognized by observation using light)?

[Ken G]

And along similar lines, one could also say that neutrinos represent another successful search for dark matter, though the "dark" matter wasn't detected by its gravity, but rather its energy. Certain nuclear reactions did not appear to conserve energy, so either conservation of energy was wrong, or there was some exotic matter carrying the energy away. Pauli went with the latter hypothesis, and the rest is history. So dark-matter type hypotheses have scored stunning victories in the past. No doubt they've also gone defunct in some cases. However, the claim that dark matter is "holding back" cosmology is quite clearly at odds with the facts. Cosmology is a rapidly advancing field, to the point that now we have the phrase "precision cosmology" (a phrase considered to be an oxymoron just a few short decades ago), and the dark matter hypothesis is an important contributor to these recent advances.

In fact, the whole rejection of dark matter is beginning to remind me of the rejection of natural selection as the engine of evolution. I'm not saying there is the same agenda behind the rejection, it's just that the claim is made that natural selection is a dead end that doesn't work, when in fact everything that we understand about evolution requires an understanding of natural selection. Same for cosmology-- it is probably true that by this point, with all the observational information we have at our disposal, much of what we understand about the history of the universe stems from understanding the attributes of dark matter. More and more, it is impossible to say much of anything that is true on large scales without using the language of dark matter.

[Strange]

I like the neutrino analogy as well.

In fact, the whole rejection of dark matter is beginning to remind me of the rejection of natural selection as the engine of evolution.

There seems to be a similar emotional investment. I don't understand the motivation but there are people who seem to be very worked up about scientists "making stuff up to make their models work" rather than doing "proper science" (whatever that is supposed to mean). And there are some people who seem to claim it is all some sort of left-wing and/or atheist conspiracy. Just odd.

[Jerry]

It is a matter of weight: There has been a seven decade long search for a carrier for dark matter, and most of the usual suspects (planets, dust, ions, neutral gas, neutrinos and attracter beams) have been eliminated. At some point, the original assumption about how gravity should behave should become suspect.

Look at it from a chemists prospective: Homeopathy uses the assumption that if you divide a substance into small enough pieces, you can separate out the physical part from the spiritual part, and present a patient with a pure, spiritual cure. To do this, the founder of homopathy performed 300 dilutions - (taking one part out of thirty three hundred times.) So in a way, homopathy is true: 30^300 is much larger than avacados number, so not one atom of the original material remains: only the curative properties of the infinitely divisible spirit.

If I am a chemist, how much can I concentrate, or dilute dark matter? What is the smallest particle, how will it screw up my chemical or nuclear reaction? How does it differ in my laboratory from spirit? Zero precision here: I can't use dark matter or study it, therefore I have to wonder if it really exists; or if the behavior we witness at great distances is due to a misunderstanding of fundamental forces.

Another 'dark matter-like' theory persisted a century ago in spite of two decades of shrinking parameter space: aether. Scientists in 1910 who still accepted the aether theory assigned little or no weight to Michealson's experiment. Dark matter searches are proving just as elusive.

[Ivan Viehoff]

It is a matter of weight: There has been a seven decade long search for a carrier for dark matter, and most of the usual suspects (planets, dust, ions, neutral gas, neutrinos and attracter beams) have been eliminated. At some point, the original assumption about how gravity should behave should become suspect.

This has been studied. The dynamic behaviour of galaxies is sufficiently diverse that we cannot make a reformulation of gravity to explain it. This can be explained by a cloud of dark matter, because these dark matter clouds can be diverse in a way that explains the diversity of observations.

Matter that won't interact very much with the stuff we know about is a big nuisance to detect, identify and quantify. But, as neutrinos demonstrate, it doesn't mean it doesn't exist.

[Boratssister]

Is not a blackhole dark matter?

[Strange]

Is not a blackhole dark matter?

In the general sense that it is dark, yes. But in the sense of "dark matter" as the material that appears to make up most of the mass of galaxies, no.

[icarus5]

dark matter white matter -->why not space that change state?diffrent kind of space with connection to the evolution of any surface of space--remark-->just personal opinion..

icarus5

[Hornblower]

dark matter white matter -->why not space that change state?diffrent kind of space with connection to the evolution of any surface of space--remark-->just personal opinion..

icarus5

Let's say personal conjecture. You have not shown us enough intelligible material for us to form any opinion of it.

[icarus5]

hornbloer ,that why i had say this is my personal opinion..or personal conjecture,if you like this at this way - that fine with me,but even then if people will thinks there are other way to look at the universe 'this will be more then enough..

icarus5

[Boratssister]

In the general sense that it is dark, yes. But in the sense of "dark matter" as the material that appears to make up most of the mass of galaxies, no.

have blackholes been ruled out? they have the mass,they just need the numbers. how could we tell if there was more blackholes than stars. could we detect sirius if it was a blackhole?

[pzkpfw]

hornbloer ,that why i had say this is my personal opinion..or personal conjecture,if you like this at this way - that fine with me,but even then if people will thinks there are other way to look at the universe 'this will be more then enough..

icarus5

It's difficult, because this whole thread almost begs for it, and the line between {question} and {suggestion-in-the-form-of-a-question} can get blurry, but please don't put personal conjecture into threads where mainstream science is being discussed. In other words, if you wish to prose an alternative answer to some problem of science, please do it in the ATM ("Against the Mainstream" sub-forum). Please note that that forum has some rules of its' own. Thanks.

(This advice might apply to a few members herein...)

[Hlafordlaes]

In fact, the whole rejection of dark matter is beginning to remind me of the rejection of natural selection as the engine of evolution. I'm not saying there is the same agenda behind the rejection, it's just that the claim is made that natural selection is a dead end that doesn't work, when in fact everything that we understand about evolution requires an understanding of natural selection. Same for cosmology-- it is probably true that by this point, with all the observational information we have at our disposal, much of what we understand about the history of the universe stems from understanding the attributes of dark matter. More and more, it is impossible to say much of anything that is true on large scales without using the language of dark matter.

Aren't we still speaking of observed gravitational effects and a posited yet still-undetected cause? That is, how proven is it that non-baryonic matter with no EM interaction exists? I am under the impression dark matter is still a logical deduction awaiting experimental confirmation. Not challenging, just eager to hear the proof!

And, if feeling generous, you might touch on dark energy. It sometimes sounds like a property of space in the absence of matter and energy, like a rampaging step-child born of spacetime and now bereft of content, an exploding nothingness. (Not proposing; just a confession of ignorance.)

[Strange]

have blackholes been ruled out? they have the mass,they just need the numbers. how could we tell if there was more blackholes than stars. could we detect sirius if it was a blackhole?

I am fairly sure they have. Black holes do not emit radiation but they do tend to be surrounded by infalling matter, which does. They may also be detectable by gravitational lensing. There has been some discussion about it here before. I think the conclusion was that if there were enough to account for dark matter, they should have been seen.

[loglo]

Black holes fall under the category of MACHOs, which have been largely ruled out as responsible for DM.

[Boratssister]

I am fairly sure they have. Black holes do not emit radiation but they do tend to be surrounded by infalling matter, which does. They may also be detectable by gravitational lensing. There has been some discussion about it here before. I think the conclusion was that if there were enough to account for dark matter, they should have been seen.

I suppose blackholes were the first suspects! Silly me.

[Grashtel]

That is, how proven is it that non-baryonic matter with no EM interaction exists?

The existence of neutrinos was pretty well proven last I checked and it satisfies those criteria. On the other hand IIRC neutrinos aren't a good candidate for dark matter though, but they at least show that it is possible to have the very low detectability that whatever makes up dark matter needs.

[Ken G]

Aren't we still speaking of observed gravitational effects and a posited yet still-undetected cause? That is, how proven is it that non-baryonic matter with no EM interaction exists? I am under the impression dark matter is still a logical deduction awaiting experimental confirmation.

Dark matter as an actual substance with certain constraints on its attributes (not very precise constraints, mind you) is still required to understand almost anything in cosmology. So it's not just a "placekeeper" for whatever solves the problem, it is an actual model that is still rather vague. What is needed to pin down what this stuff is is some kind of independent detection, no question that is needed and currently lacking. And we might get surprised-- maybe there is no such actual stuff, and maybe natural selection is not the engine of evolution. All we know at the moment is we cannot make any sense out of a wide array of cosmological observations without the language of dark matter, just as we cannot make any sense out of a wide array of evolutionary observations without the language of natural selection.

And, if feeling generous, you might touch on dark energy.

Dark energy is not quite as well substantiated as dark matter, but it is getting more and more so all the time. Its attributes are even less well constrained than dark matter, because its affects on the acceleration of the expansion are only barely constrained. However, it now represents the lion's share of the active agents in the current motions of the universe on the largest scales. With its inclusion, people now talk about "precision cosmology" which involves both dark matter and dark energy, and more and more this is being taken seriously in wide astronomy circles. Maybe it's premature, time will tell, but it is becoming more and more accepted because it is the only current model that achieves broad consistency. Remember, the goal of a "best model" is not to assert what is true, for that can never be proven, it is to serve as a basis for the working hypotheses that will guide the future directions of astronomy research. That's all science ever does.

It sometimes sounds like a property of space in the absence of matter and energy, like a rampaging step-child born of spacetime and now bereft of content, an exploding nothingness. (Not proposing; just a confession of ignorance.)

That's as good a description of it as any, we really just don't have a particularly useful model of it at the moment. And the prospects for getting such a model are not as good as dark matter-- dark matter might be independently detected tomorrow, for all I know (because there already exist many fairly specific hypotheses about what it might be and how to find it), but I don't see anything but an empirical "equation of state" of dark energy being determined any time soon. Particle physics is nowhere close to a model for it.

[Hlafordlaes]

The existence of neutrinos was pretty well proven last I checked and it satisfies those criteria. On the other hand IIRC neutrinos aren't a good candidate for dark matter though, but they at least show that it is possible to have the very low detectability that whatever makes up dark matter needs.

I didn't do my due diligence to check the 'net before saying "non-baryonic" and so am rightly called to task. Nice point that neutrinos demonstrate the feasibility of other low-detectable particles.

[Hlafordlaes]

Dark matter as an actual substance with certain constraints on its attributes (not very precise constraints, mind you) is still required to understand almost anything in cosmology. So it's not just a "placekeeper" for whatever solves the problem...

Thanks, that answers my question.

... people now talk about "precision cosmology"

Heady times indeed! It seems there are enough telescopes and instruments up or going up soon that some fairly substantial breakthroughs are in store. Nice time for astronomer-types!

Remember, the goal of a "best model" is not to assert what is true, for that can never be proven, it is to serve as a basis for the working hypotheses that will guide the future directions of astronomy research. That's all science ever does.

Yes, this is now an SKC for me (standard KenG caveat). I am, however, still adapting to this renewed distance between what I thought was reality, and whatever reality may be. And there I was coming to BAUT to try to close the gap... sheesh!