Dark Matter: Canadian Astronomers Suggest It May Not Exist

[Ivan Seeking]

Two Canadian astronomers think there is a good reason dark matter, a mysterious substance thought to make up the bulk of matter in the universe, has never been directly detected: It doesn't exist. [continued]

http://www.space.com/scienceastronomy/071029-mm-mog-theory.html

 

[EL]

First, I doubt the Bullet cluster can be explained by modified gravity.
Second, even if so, modified gravity theories have a major problem with explaining observations on all scales. Hints of dark matter has been observed on a wide range of length scales, and while you may be able to fit one of the observations with modified gravity the same fitting won't generally work on the other scales.

 

[Michael Mozina]

First, I doubt the Bullet cluster can be explained by modified gravity.

Seeing as how I'm not a mind reader, I guess I'll have to wait to see the paper hit Arxiv before I place any bets on that one.

Second, even if so, modified gravity theories have a major problem with explaining observations on all scales. Hints of dark matter has been observed on a wide range of length scales, and while you may be able to fit one of the observations with modified gravity the same fitting won't generally work on the other scales.

Here's an earlier cosmological overview paper on this topic.

http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.0364v2.pdf

As far as I can tell it does seem to "fit" just fine. What exactly was your complaint with his overview presentation?

It seems to me that putting all your eggs in the Lambda-CDM theory (or any cosmological theory that is based on metaphysical constructs) has serious scientific drawbacks. His mathematical presentation of this modified gravity theory looks mathematically sound to me. It looks just as sound as any Lambda model I've ever looked at, and it requires a lot less faith in unseen and unproven forces of nature. I'm certainly looking forward to seeing how they explain the lensing data from the bullet cluster analysis.

 

[pixel01]

Wait and see. Anyway, I think the words by Douglas Clowe are not so strong.

 

[Chronos]

The 'Bullet Cluster' greatly constrains the nature of a universe devoid of 'Dark Matter'. Too strong to survive, IMO. Liking DM is optional. Consider how many years it took to detect' the atom.

 

[Michael Mozina]

The 'Bullet Cluster' greatly constrains the nature of a universe devoid of 'Dark Matter'. Too strong to survive, IMO. Liking DM is optional. Consider how many years it took to detect' the atom.

There is a physical difference however. In the case of the atom, we could in fact "detect" the presence of matter in controlled laboratory conditions, and we knew there were different forms of matter based on their chemical properties. The atoms could be manipulated in controlled scientific conditions. Dark matter however is not like that. Nobody knows what "dark matter" is made of, or if it even exists because it is a mathematical construct that is based upon pure observation of objects that are light years away from us, and that we could never hope to "control" in any scientific sense. There is no real "testing" that can go on because it's a mathematical hypothesis at this point in time, not a physical entity that we can play with in a lab.

The modified gravity theory is also a purely mathematical construct that is designed to explain the same pure observations of objects and events that are light years away from us. Like dark matter theory, there is no obvious way to "test" this idea in a controlled scientific experiment.

Both of these mathematical theories seem explain these distant observations, each in their own unique mathematical way. How then do we determine which theory is the "better" scientific theory?

The decision to label on theory as "better" than another is ultimately a subjective judgment call. The way I personally make that choice is for me to see how well the idea conforms to what I can observe, and how few (or how many) metaphysical entities it relies upon. For my money, the fewer the metaphysical entities it requires, the better. I'm much more open to modified gravity theory, and theories that attempt to concentrate (normal) mass along the axial plane of the galaxy, to explain distant movements, than I am open to concepts about "dark matter". I've never seen any dark matter show up in any controlled scientific lab test. I therefore have no physical evidence that it even exists in nature.

This particular modified gravity theory does not require that I put faith in a metaphysical entity, and therefore I personally find it more attractive than a 'dark matter' explanation for the same events and observations. Both ideas seem to solve the problem mathematically, but dark matter theories require that I put faith in something that nobody can demonstrate actually exists in nature.

 

[EL]

There is no real "testing" that can go on because it's a mathematical hypothesis at this point in time, not a physical entity that we can play with in a lab.

Hopefully at the LHC.

I've never seen any dark matter show up in any controlled scientific lab test.

According to the most popular dark matter models (WIMPs) you wouldn't have, since the particles have masses around and above the electroweak scale. (100 GeV-10 TeV.)

 

[pixel01]

Could it be black dwarfs, white dwarfs, planets ..anything except stars out there that we can not see then they play the role of dark matter? I think by now, scientists only observe stars and consider them matter. How about other stuff?

 

[Garth]

Could it be black dwarfs, white dwarfs, planets ..anything except stars out there that we can not see then they play the role of dark matter? I think by now, scientists only observe stars and consider them matter. How about other stuff?

The mainstream \LambdaCDM model has two types of Dark Matter, baryonic and non-baryonic DM.

The total amount of DM is about 27% of the total density, and therefore mass, of the universe. The Big Bang in the standard model can only produce about 4% of the total density as baryonic matter, mainly ordinary hydrogen and helium, (Note the visible baryonic matter, stars and nebulae, comprise only 0.3% of the total), and therefore about 23% of the total has to be some unknown non-baryonic species. Neutrinos, axions and other exotic particles have been candidates at one time or another.

There are a number of different types of observations: galaxy rotation curves, galaxy cluster dynamics, cluster gravitational lensing, large scale structure formation rates and the analysis of the CBM fluctuations, which is evidence that something is out there - but what?

Alternatively if all these observations are all to be explained by a modified theory of gravitation then that theory would have a mountain to climb, and explaining the Bullet Cluster is a particularly difficult case for such a theory.

Until the DM particle(s) have been identified in the laboratory (LHC?), their properties measured and found to be concordant with astronomical and cosmological constraints, we shall not really know what we are talking about.

For example, as another alternative, if the expansion rate of the early universe were different to that of the standard model, due to the action of some as yet unknown scalar field for example, then the amount of baryonic matter able to be produced in the BB would change and such a scenario might provide a third possibility; that all DM is in fact baryonic in nature. But then you would have to explain where it all is today and why it cannot be 'seen'!

The mainstream \LambdaCDM model is the best thing we have going, at the moment.

Garth

 

[EL]

Could it be black dwarfs, white dwarfs, planets ..anything except stars out there that we can not see then they play the role of dark matter? I think by now, scientists only observe stars and consider them matter. How about other stuff?

Big Bang Nucleosynthesis puts upper limits on the amount of baryonic (i.e. ordinary) matter in the universe. This can also be seen from observations of the CMB.
Thus, ordinaty matter can only make up a fraction of the total amount of dark matter needed. The major part must be non-baryonic.

Edit: I see Garth was faster...

 

[pixel01]

Thanks Garth and El. I can say one word by now: Wait.

 

[Chronos]

Experimental proof is the gold standard. Dark matter is not unlike neutrinos [which also took a long time to experimentally confirm], only more elusive. I am extremely confident it will be detected, but not by the LHC. It sprang, IMO, from energies far beyond the capabilities of terrestrial laboratories. There are a number of very good experiments currently underway that take different approaches. I'm confident one or more will succeed - very likely by the end of this decade. See:

http://hepwww.rl.ac.uk/UKDMC/dark_matter/other_searches.html

for examples.

 

[Michael Mozina]

Hopefully at the LHC.

Can you even describe a LHC test that might "falsify" the notion of DM?

According to the most popular dark matter models (WIMPs) you wouldn't have, since the particles have masses around and above the electroweak scale. (100 GeV-10 TeV.)

That's quite an energy range wouldn't you agree? Should we be able to be a bit more specific? It seems to me that WIMPS are but one "possible" theory related to DM, so this problem still seems to come back to the same issue.

Is there any controlled scientific LHC test that you would accept as a falsification of the existence of DM? I ask this because I know of no controlled scientific test that demonstrates that DM exists in the first place, and there is at least one other theory on the table that doesn't requires DM at all. If we can't empirically demonstrate that DM even exists in nature, and we can't falsify the idea in any controlled scientific test, and it isn't necessary to use DM to describe events in the universe, doesn't that put the concept of DM *outside* of the realm of science?

 

[Michael Mozina]

Experimental proof is the gold standard.

Controlled experimental evidence is indeed the gold standard of science. In science it is also true that the burden of proof is always on the one making the claim.

Dark matter is not unlike neutrinos [which also took a long time to experimentally confirm], only more elusive.

But there is a very significant difference between neutrino theory prior to their detection in controlled experiments and DM theory today. In the case of neutrinos, it was a series of controlled scientific tests that led us to hypothesize the existence of neutrinos. In these controlled scientific tests, we found evidence that there was a small amount of missing energy in certain known (and identified) particle decay reactions. If neutrinos did not exist to account for this missing energy, then the law of conservation of energy would have been violated. It was a known law of physics, and controlled scientific testing that led us to hypothesize the existence of neutrinos. More importantly we already knew which particle decay reactions created them, and we knew where them came from. That allowed us to create additional tests that could verify their existence.

With DM however, there are no controlled tests that demonstrate they exist, and no laws of physics that require that they exist. More importantly however, pure observation of objects that are light years away do not contain any control mechanism of any sort. There is also more than a single way to account for the lensing patterns in the Bullet Cluster data, and there is more than one way to account for the movements of galaxies, some of which do not require DM at all. We can't even be sure that DM exists based on these observation, and we have no idea where DM comes from, or how to test for it. More telling however is the fact that we have absolutely no way to falsify the concept.

I am extremely confident it will be detected, but not by the LHC. It sprang, IMO, from energies far beyond the capabilities of terrestrial laboratories. There are a number of very good experiments currently underway that take different approaches. I'm confident one or more will succeed - very likely by the end of this decade. See:

http://hepwww.rl.ac.uk/UKDMC/dark_matter/other_searches.html

for examples.

Which scientific test would falsify the DM theory? If the theory cannot be falsified, and there is no empirical evidence that DM even exists, then what makes DM theory superior (in a scientific sense) from modified gravity theory?

 

[Garth]

Just to keep the pot boiling...

Durrer and Maartens' overview article for the dark energy issue of GRG published on today's physics ArXiv: Dark Energy and Dark Gravity

Observations provide increasingly strong evidence that the universe is accelerating. This revolutionary advance in cosmological observations confronts theoretical cosmology with a tremendous challenge, which it has so far failed to meet. Explanations of cosmic acceleration within the framework of general relativity are plagued by difficulties. General relativistic models are nearly all based on a dark energy field with fine-tuned, unnatural properties. There is a great variety of models, but all share one feature in common -- an inability to account for the gravitational properties of the vacuum energy. Speculative ideas from string theory may hold some promise, but it is fair to say that no convincing model has yet been proposed. An alternative to dark energy is that gravity itself may behave differently from general relativity on the largest scales, in such a way as to produce acceleration. The alternative approach of modified gravity (or dark gravity) provides a new angle on the problem, but also faces serious difficulties, including in all known cases severe fine-tuning and the problem of explaining why the vacuum energy does not gravitate. The lack of an adequate theoretical framework for the late-time acceleration of the universe represents a deep crisis for theory -- but also an exciting challenge for theorists. It seems likely that an entirely new paradigm is required to resolve this crisis.

Garth

 

[EL]

Can you even describe a LHC test that might "falsify" the notion of DM?

LHC could falsify many of the most popular models. If in the future energies up to ~10 TeV will be probed without finding anything, then WIMPs are in big trouble. Of course people can after that always try to build coco-models which would still avoid experimental constraints, but probably with a lot af fine-tuning (maybe even of the order needed for modified gravity theories!).
The WIMP hypothesis rests not only on its ability to explain all "dark matter"-observations (on all observed scales) and correctly account for the formation of large scale structure, but also on motivations from pure particle physics. We expect there to be new physics around the electroweak scale, and if one of these new particles turns out to be stable it automatically (if it was in thermal equilibrium in the early universe) would give a relic density of exactly the order needed to explain all dark matter. (This is the so called "WIMP miracle".)

I do not find it very unlikely that one of the expected new particles would happen to be stable. (Like e.g. the neutralino in the MSSM.) At least I find it much more likely than the curve fitting (and abandonness of the well tested GR) going on in modified gravity theories. However, that is of course a personal taste. If LHC or any direct or indirect detection experiments won't find anything within a decade, I will probably abandon my current position.

 

[EL]

and we have no idea where DM comes from, or how to test for it.

This is just wrong. See my post above.

 

[Michael Mozina]

LHC could falsify many of the most popular models. If in the future energies up to ~10 TeV will be probed without finding anything, then WIMPs are in big trouble. Of course people can after that always try to build coco-models which would still avoid experimental constraints, but probably with a lot af fine-tuning (maybe even of the order needed for modified gravity theories!).
The WIMP hypothesis rests not only on its ability to explain all "dark matter"-observations (on all observed scales) and correctly account for the formation of large scale structure, but also on motivations from pure particle physics. We expect there to be new physics around the electroweak scale, and if one of these new particles turns out to be stable it automatically (if it was in thermal equilibrium in the early universe) would give a relic density of exactly the order needed to explain all dark matter. (This is the so called "WIMP miracle".)

Try looking at this issue from a skeptics perspective for a second. These tests you describe are essentially a fishing expedition. Your (they're) "fishing" for anything in an energy range that is quite vast, and covers several orders of magnitude. That's not at all like the neutrino postulation process where we could define our theoretical numbers with some precision, and we even had identified the particle physical interactions that were the likely release point of neutrinos. Even after we cover this entire energy range, we still can't be sure about what other "whack-a-mole" versions of DM might crop up. I find it a tad disconcerting that we're hoping for a "miracle". I need some hard evidence here.

I do not find it very unlikely that one of the expected new particles would happen to be stable. (Like e.g. the neutralino in the MSSM.) At least I find it much more likely than the curve fitting (and abandonness of the well tested GR) going on in modified gravity theories.

Well, that seems like a very ironic case of finger pointing from where I sit, especially since GR has essentially been abandoned in Lambda-CDM theory as I percieve it. GR as Einstein taught GR to his students, had no dark matter component, nor any dark energy component, and it certainly had no inflation component. Even Einstein's famous addition of a constant to GR he later rejected as his greatest blunder. In Lambda-CDM theory, the GR related to known types of mass that Einstein referred to in GR only makes up about 4% of the whole picture. From my perspective Lambda-CDM theory has abandoned 96% of GR in favor of a theory that relegates the GR that Einstein described (GR related to known forms of mass) to bit player status.

However, that is of course a personal taste. If LHC or any direct or indirect detection experiments won't find anything within a decade, I will probably abandon my current position.

If I could see evidence from a controlled experiment, like beta decay reactions in the case of neutrinos, that required that we posit a theory like dark matter to uphold known laws of physics, then I might be willing to "wait and see" as you are willing to do. As it is, I simply don't see any actual physical evidence from any controlled tests that demonstrates that DM exists, or even hints that DM exists in nature.

All I've seen thus far to support the theory of DM is another mathematical theory related to what *might* be happening to objects that are light years away us and that are based on pure observations that are lacking any sort of control mechanisms. It's a bit like pointing to that same event in the sky and claiming that "something-I-never-heard-of-before" did it. From a scientific point of view, I am forced to take the skeptics approach. If the LHC comes up with any actual direct physical evidence that DM actually exists in nature, and affects objects in nature, then I"ll have to abandon my current position that DM does not exist. Skepticism is a part of the scientific method. The burden of proof in science is always on the one making the claim. If others believe that DM can affect objects at a distance, let them first show us that DM can effect objects in a lab. I'll keep an open mind on this subject, but I'll need to see some hard physical evidence that demonstrates that DM even exists before I feel any sort of confidence in the idea that DM can effect objects at a great distance.

 

[EL]

Try looking at this issue from a skeptics perspective for a second. These tests you describe are essentially a fishing expedition. Your (they're) "fishing" for anything in an energy range that is quite vast, and covers several orders of magnitude. That's not at all like the neutrino postulation process where we could define our theoretical numbers with some precision, and we even had identified the particle physical interactions that were the likely release point of neutrinos. Even after we cover this entire energy range, we still can't be sure about what other "whack-a-mole" versions of DM might crop up. I find it a tad disconcerting that we're hoping for a "miracle". I need some hard evidence here.

No, "they" are not "fishing" within that energy range. It will be covered in a systematic way.
After we have searched that energy range we will hopefully have found something. If not, WIMPs are dead to me.
I don't think you got my "miracle". I am not saying we have to wait for a "miracle" to find dark matter, but that the "miracle" is already there on theoretical grounds. The "miracle" gives us a chance of solving two problems at the same time (hierarchy problem and dark matter.)
Note that I am not saying dark matter (in the form of WIMPs) exist. Only that I find it a reasonable explanation which is much more likely than modified gravity.

Well, that seems like a very ironic case of finger pointing from where I sit, especially since GR has essentially been abandoned in Lambda-CDM theory as I percieve it. GR as Einstein taught GR to his students, had no dark matter component, nor any dark energy component, and it certainly had no inflation component. Even Einstein's famous addition of a constant to GR he later rejected as his greatest blunder. In Lambda-CDM theory, the GR related to known types of mass that Einstein referred to in GR only makes up about 4% of the whole picture. From my perspective Lambda-CDM theory has abandoned 96% of GR in favor of a theory that relegates the GR that Einstein described (GR related to known forms of mass) to bit player status.

GR is not abandoned in LCDM, and I cannot see why you are under that impression. The energy-momentum tensor is just a collection of everything that contributes to the energy density of the universe, and not just the forms of energy that happened to "be known" when Einstein forumlated his theory. To say that the inclusion of dark matter abandons GR is just as saying that the inclusion of neutrinos abandons GR.
Dark matter is just as much "matter like" as ordinary matter and should hence be included as matter in the energy-momentum tensor.
Regarding the cosmlogical constant: The cc is part of GR. The symmetries of GR allows for it and there is no reason a priori to put it to zero.
I guess you are quite alone with your perspective.

If I could see evidence from a controlled experiment, like beta decay reactions in the case of neutrinos, that required that we posit a theory like dark matter to uphold known laws of physics, then I might be willing to "wait and see" as you are willing to do. As it is, I simply don't see any actual physical evidence from any controlled tests that demonstrates that DM exists, or even hints that DM exists in nature.

The hints that DM exists in nature are plenty (galaxy dynamics, cluster dynamics, large scale formation dynamics, hiearchy problem). Each one of these scales may separately be solved by other things than WIMPs (e.g. modified gravity theory, another modified gravity theory, again another modified gravity theory, and divergence canceling physics without stable particles.), but the strength of WIMPs lies in the simultaneous solution.
As you say there are yet no laboratory experiments that demonstrate the existence of dark matter. I am not saying WIMP dark matter definitely exists, but just that it is the most reasonable explanation we have come up with.

Skepticism is a part of the scientific method. The burden of proof in science is always on the one making the claim.

And I don't think anyone claims that the existence of particle dark matter is definite.

If others believe that DM can affect objects at a distance, let them first show us that DM can effect objects in a lab.

And that is exactly what we currently are trying to do.

 

[Michael Mozina]

No, "they" are not "fishing" within that energy range. It will be covered in a systematic way.

The point here is that the search for WIMPS is unlike the search for the neutrino. In the case of the neutrino, we already had some idea of where these particles came from, and we understood the source of the particle in question. We also understood how the theorized particle tied back into particle physics.

In the case of the fabled "WIMP" particle, we have no known particle interaction source, and there is no known particle that has these properties. The is no known particle interaction that results in "missing" mass or energy that might explain where WIMPS come from. Essentially we're just dragging a huge net through a very wide energy spectrum, and hoping to find something.

After we have searched that energy range we will hopefully have found something. If not, WIMPs are dead to me.

Here's where I think a skeptical approach is warranted. If and when this search for WIMPS leads to something tangible, *then* (and only then) will WIMPS become "alive" to me. At this moment in time, I see zero evidence for WIMPS. In science, the burden of proof always falls to the one making the claim because a negative cannot ever be disproved. If and when I see tangible evidence to suggest that WIMP exist in nature, and have some effect on matter, *then* I'll be interested in studying them. At the moment however I have no evidence that WIMPS exist.

I don't think you got my "miracle". I am not saying we have to wait for a "miracle" to find dark matter, but that the "miracle" is already there on theoretical grounds. The "miracle" gives us a chance of solving two problems at the same time (hierarchy problem and dark matter.)
Note that I am not saying dark matter (in the form of WIMPs) exist. Only that I find it a reasonable explanation which is much more likely than modified gravity.

Why? What is more "reasonable" about WIMPS it in your opinion? What makes them "better" than MACHOS for instance?

GR is not abandoned in LCDM, and I cannot see why you are under that impression. The energy-momentum tensor is just a collection of everything that contributes to the energy density of the universe, and not just the forms of energy that happened to "be known" when Einstein forumlated his theory. To say that the inclusion of dark matter abandons GR is just as saying that the inclusion of neutrinos abandons GR.

That's a bit misleading. While your point about "known" particles is valid, DM is not actually "known" to exist at this point in time. While I have no problem with you coming up with a GR theory that includes neutrinos because they are "known" to exist, I would have a problem with you inserting invisible things into GR theories. That part about "known" particles is a valid point in your argument, but DM is not "known" to actually exist.

I see absolutely no scientific validity for including inflation, and dark forces in GR since they have not been shown to exist in nature, and are not "known" to exist in nature. It would be like me handing you a completely new theory related to a half dozen invisible forces that you've never heard of before, and then tying it loosely back to a variation of Einstein's GR theory. Suppose I did all that and started relegating normal matter and normal GR to a 5% role in the process. You wouldn't let me claim that my invisible forces are "known" to exist. They don't exist as far as anyone "knows" from controlled experimentation.

Dark matter is just as much "matter like" as ordinary matter and should hence be included as matter in the energy-momentum tensor.

This is a claim that you simply cannot backup with results from controlled scientific experiments. In other words you simply "assume" that dark matter exists, and that it is like normal matter in that respect. However, you cannot show that it is so in a controlled scientific experiment. You simply have *faith* that DM exists, and that it has properties that are similar to normal mass. You can't backup that claim via science, it's something I simply have to accept (on faith) as part of your theory. Unfortunately I don't accept that DM exists, let alone that it has similar gravitational properties without some tangible evidence of these claims from controlled scientific experimentation.

If your search for WIMPS leads to some tangible evidence that WIMPS exist, and it can be shown that they act like normal matter as it relates to the forces of gravity, *then* your statement is no longer a statement of faith, but rather it will become a statement of fact. Until then however, it's purely an act of faith on your part to even make that claim.

Regarding the cosmlogical constant: The cc is part of GR. The symmetries of GR allows for it and there is no reason a priori to put it to zero.
I guess you are quite alone with your perspective.

GR (from a mathematical point of view) does indeed allow us to insert a constant. Einstein did it himself and then called it his greatest blunder. The fact we can do it, doesn't mean we "should" do so. Just because I can do it, does not mean I can claim that my half dozen new theorized invisible forces can be inserted into GR. I can't slap unknown forces of nature to GR and then claim that I'm still basing my theory on GR. The fact you *can* add a constant to GR doesn't mean you *should* do so, or that it's correct. Einstein regretted adding a constant to GR in fact.

The hints that DM exists in nature are plenty (galaxy dynamics, cluster dynamics, large scale formation dynamics, hiearchy problem).

But MOND theories and modified gravity theories explain these events too. Neither of these options require DM to explain such observations. That fact that there is "missing mass" observed in some distant observation is not an automatic guarantee that this "missing mass" requires WIMPS. For all you know that missing mass is in the form of MACHOS, or something far more mundane than WIMPS or axions.

Each one of these scales may separately be solved by other things than WIMPs (e.g. modified gravity theory, another modified gravity theory, again another modified gravity theory, and divergence canceling physics without stable particles.), but the strength of WIMPs lies in the simultaneous solution.

It seems to me that this is a subjective judgment call, not a scientific statement of fact.

As you say there are yet no laboratory experiments that demonstrate the existence of dark matter. I am not saying WIMP dark matter definitely exists, but just that it is the most reasonable explanation we have come up with.

It evidently is very "reasonable" from your current perspective. From my EU perspective however, it's like me claiming that this "missing mass" was in the form of invisible potatoes, and that I believe that my theory about invisible potatoes is "reasonable". I don't know how to define "reasonable" when it relates to a particle (or in this case several metaphysical constructs) that has never been shown to exist in nature.

And I don't think anyone claims that the existence of particle dark matter is definite.

In science however, the burden of proof always falls the person who is making the claim. If you believe that DM can have an effect on normal matter, then it is up to you to demonstrate this claim. If you cannot demonstrate that claim in controlled experiments, then it can only be considered an act of faith, not a scientific solution. A lot of people seem to have "faith' that DM exists. I simply do not share that faith. I take a more skeptical approach to science. I expect to see evidence that something exists in nature before I simply *assume* that it exists and has an effect on distant objects.

And that is exactly what we currently are trying to do.

If and when WIMPS or axions, or Macho's are shown to exist, then your theory becomes less of an act of faith, and more of a statement of fact. At the moment however, I can only describe your search for DM (particularly WIMPS) as an act of faith. Science requires leaps of faith at times, if only faith in the idea so that the new idea can be tested. I'm not suggesting we should eliminate faith from science, but I can't personally put much faith in the notion of DM when there are other viable scientific theories to explain these observations that do not require DM. If however DM can be shown to exist in controlled scientific experiments, *then* I'll become a lot more interested in the idea.

 

[EL]

M.M., you are making a straw-man. Don't try to insinuate I am claiming that WIMPs exist. All I am saying is that there are good hints for its existence.

What is more "reasonable" about WIMPS it in your opinion? What makes them "better" than MACHOS for instance?

BBN (and CMB data) put an upper limit on the number of baryons. MACHOS are baryonic dark matter, and hence cannot make up all the dark matter needed. Moreover, the formation of large scale structures does not work as well.

That's a bit misleading. While your point about "known" particles is valid, DM is not actually "known" to exist at this point in time. While I have no problem with you coming up with a GR theory that includes neutrinos because they are "known" to exist, I would have a problem with you inserting invisible things into GR theories. That part about "known" particles is a valid point in your argument, but DM is not "known" to actually exist.

I really cannot see how you even can see a problem with invoking dark matter in the energy-momentum tensor? What is wrong with postulating a WIMP candidate (of which we of course know the equation of state and can hence plug into the energy-momentum tensor) and then use GR to calculate its consequences? I simply cannot see where you find a problem with this?

In other words you simply "assume" that dark matter exists, and that it is like normal matter in that respect.

Yes, we assume e.g. a WIMP model. The model tells us it has the same properties as ordinary matter (i.e. the same equation of state). Then we use GR. Again, where is the problem?

GR (from a mathematical point of view) does indeed allow us to insert a constant. Einstein did it himself and then called it his greatest blunder. The fact we can do it, doesn't mean we "should" do so.

Yes, GR includes a cosmological constant term. Wheter or not it should be put to zero is up to experiments to decide.

But MOND theories and modified gravity theories explain these events too.

MOND theories have problems explaining all scales at the same time. (Also, they of course provide no solution to the hierarchy problem.)

It evidently is very "reasonable" from your current perspective. From my EU perspective however, it's like me claiming that this "missing mass" was in the form of invisible potatoes, and that I believe that my theory about invisible potatoes is "reasonable".

Then you need to do some reading.
Go on and calculate the relic density and structure formation scenario for your potatoes. Also make sure they can explain the astronomical observations on all scales, and that they are not already excluded by existing experiments. Please also motivate their existence by something totally unrelated to dark matter. (I guess the hierarchy problem won't work here though...)

 

[Michael Mozina]

M.M., you are making a straw-man. Don't try to insinuate I am claiming that WIMPs exist. All I am saying is that there are good hints for its existence.

While I have no problem with you suggesting that there are "good hints" for the existence of 'missing mass', we cannot even be certain of what form that missing mass might take. While I have no real problem with a MACHO oriented explanation for "missing mass", or even a neutrino oriented explanation for 'missing mass' (now that we know that neutrinos have mass), I do have a very huge problem with assuming that this missing mass is in the form of a WIMP. I have a problem with that idea because as far as I know, WIMPS do not exist in nature. That is an extraordinary claim. It would be akin to me jumping to the conclusion that that an object we saw in the sky together, that neither one of us could happen to identity at that moment, is "probably" from another planet. I'll grant you that there seems to be mass that we cannot easily identify, but I have no evidence that this missing mass exists in WIMPS through any controlled scientific test. If and when you find controlled scientific evidence of WIMPS, and can show me tangible properties of WIMPS based on these controlled tests, then I'll be happy to let you suggest that WIMPS might do the trick as it comes to explaining that missing mass problem, and those galaxy rotation patterns.

It seems to me that most of the presumed "dark matter" theories show that the missing mass is found around the outer edge of the galaxy. IMO that is much more easily explained in terms of a MACHOS (that act like a large asteroid belt) than being due to any sort of subatomic particle. It seems to me that a subatomic particle would be more apt to follow the typical mass bodies of a galaxy, since they would presumably be created in, and released from these normal mass particles.

BBN (and CMB data) put an upper limit on the number of baryons.

Well, BBN really puts no upper limit on the number of baryons. The bigger the BANG, the more the baryons. It does put an upper limit on heavy atoms. Even the BBN stage of BB theory however has a serious "problem" in the first second or so of the process. As electrons, protons and neutrons, and other forms of mass began to form, the forces of gravity should have pulled the whole thing back together again in an instant. Without relying upon a metaphysical construct from the start (Guth's theorized inflation field), the whole BBN process would preclude expansion from ever occurring.

Even more interesting is the fact that the CMB data actually shows that there is a "hole" in the universe that should not even exist according to the inflation theory. Form the very first instant, the BANG theory relies upon unproven forces of nature, and these theorized forces of nature have already failed some key observational tests.

MACHOS are baryonic dark matter, and hence cannot make up all the dark matter needed. Moreover, the formation of large scale structures does not work as well.

I don't see the correlation here between baryonic dark matter, and any notion that it "cannot" makeup all the dark matter needed. As far as I know from tangible science, that's the only kind of "dark mass" that you have to work with. There isn't any other form of "dark matter" that I am aware of based on controlled scientific tests.

I really cannot see how you even can see a problem with invoking dark matter in the energy-momentum tensor?

I don't actually have any problem with you invoking MACHOS in the energy-momentum tensor. I have a huge problem with you invoking unproved forms of matter and energy into the energy-momentum tensor however, just as you would have a problem with me invoking non-baryonic invisible potatoes in the energy-momentum tensor. If I cannot provide you with strong evidence of non-baryonic invisible potatoes from controlled scientific experimentation, then I have no business trying to stuff them into a GR based math formula.

What is wrong with postulating a WIMP candidate (of which we of course know the equation of state and can hence plug into the energy-momentum tensor) and then use GR to calculate its consequences? I simply cannot see where you find a problem with this?

But you don't even know the actual energy state of a WIMP, or even if it exists yet. You have a very vague idea here that involves many orders of magnitude of an energy state, and nothing in the way of tangible, physical, empirical evidence to show that it actually exists in nature. You can postulate it's existence if you like, but then you are obligated to show that it actually exists before you point at distant events and claim that WIMPS did it.

Yes, we assume e.g. a WIMP model. The model tells us it has the same properties as ordinary matter (i.e. the same equation of state). Then we use GR. Again, where is the problem?

The problem is that you have never demonstrated that WIMPS physically exist in reality. You don't have any empirical evidence that WIMPS even exist, and no known form of mass acts like a WIMP. That's the problem.

Yes, GR includes a cosmological constant term. Wheter or not it should be put to zero is up to experiments to decide.

"Pure" GR (GR without metaphysical constructs), does not require any sort of 'constant' to describe the gravitation attraction of the energy-momentum tensor. It works fine with real mass made of real particles to describe the gravitational attraction properties of matter. If there are other forces of nature acting on objects of mass, those forces of nature probably have "properties" that are based on the specific type of energy involved, and GR would not be necessary to describe these forces. GR is great for describing the attraction force of mass objects. There is no evidence that GR *should* be used to try to describe all the external forces of nature that act on mass as one big gargantuan math formula. If the external influences on matter are EM oriented, perhaps Alfven's MHD theories would be better suited when it comes to doing the math.

There's a bigger problem however. The math we have done with Lambda-CDM theory turns out to have a gaping hole in it, despite a nearly homogeneous prediction of inflation.

I can see why Einstein called the introduction of this constant as his greatest blunder, because even if there are external forces of nature acting on mass bodies, these forces will have mathematical properties that are directly related to the force involved, that are not necessarily even related to the gravitational component. IMO the Lambda-CDM theory isn't "pure" GR. It's a loosely GR oriented theory with a liberal dose of metaphysics mixed in, it's about 96% metaphysics in fact.

MOND theories have problems explaining all scales at the same time. (Also, they of course provide no solution to the hierarchy problem.)

MOND theorists, and modified gravity theorists seem to disagree with you. WIMP theories have serious problems explaining all time scales at the same time as well, particularly that first serious problem about showing that they actually exist in nature.

Then you need to do some reading.
Go on and calculate the relic density and structure formation scenario for your potatoes. Also make sure they can explain the astronomical observations on all scales, and that they are not already excluded by existing experiments. Please also motivate their existence by something totally unrelated to dark matter. (I guess the hierarchy problem won't work here though...)

I think you're taking my statements a bit too literally here. I don't actually have any faith in invisible potatoes, or WIMPS or axions, or anything 'invisible' to physics here on earth. As I suggested earlier, if and when you can show me evidence that WIMPS actually exist in nature, and you can demonstrate their influence on photons and protons and neutrons and electrons in controlled scientific tests, then I'll be happy to entertain WIMP theories. Until then, I will consider WIMP theories to be pretty "wimpy, wimpy, wimpy". :) Sorry, I just couldn't resist.

I absolutely have no philosophical problem with you inserting baryonic mass (MACHOS) into GR theories. It's only when you attempt to insert unproven entities into GR that I get uncomfortable. Extraordinary claims require extraordinary evidence. If you claim that non-baryonic forms of mass exists, the onus of responsibility to demonstrate your claim falls to you. That is how science has always worked, and I'm not asking for the moon here. As long as you keep inserting things like DE, (non baryonic) DM and inflation into GR, I'm going to require that you demonstrate that these things actually exist in nature. I will willingly let you toss MACHOS or neutrino mass into GR and mix them liberally. I will however require additional empirical evidence of any other form of "dark matter" that you might attempt to toss into GR. It seems like this is a very fair and reasonable request on my part since it SOP for all areas of science, not simply astronomy.

 

[eep]

What about direct-detection experiments like CDMS and Liquid Xenon? Both are finally becoming sensitive enough to probe the heart of parameter space where WIMPs are thought to exist. If nothing is seen within 5 to 10 years then that will raise some serious questions, but I think for now we need to sit and wait.

If someone comes up with a modified gravity theory which can explain what we're seeing, that doesn't make it right.

 

[EL]

M.M., this is getting silly. You are still making a straw-man. You still do not seem to get the difference beween a hypothesis and a fact. (WIMP dark matter is a hypothesis, not a claimed fact.) And please, try to shorten the posts. I do not find time to answer all of your comments, but I'll do a few.

It seems to me that most of the presumed "dark matter" theories show that the missing mass is found around the outer edge of the galaxy. IMO that is much more easily explained in terms of a MACHOS (that act like a large asteroid belt) than being due to any sort of subatomic particle.

As I said, MACHOs are baryonic. Baryons cannot make up more than a fraction of the dark matter needed (due to constraints from BBN).

It seems to me that a subatomic particle would be more apt to follow the typical mass bodies of a galaxy, since they would presumably be created in, and released from these normal mass particles.

You have a lack of knowledge here. The WIMPs (if they exist) were created at the big bang. That is why one talks about the "relic density". Furthermore, huge super computer simulations (e.g. the "Millenium simulation") have simulated the universe's structure formation including WIMPs. The resulting distributions agree very well with the observations we make. In fact, simulations without (cold) dark matter fails to reproduce the observed structures. Your impression that the dark matter gets distributed in the same way as baryonic matter is simply false.

Well, BBN really puts no upper limit on the number of baryons.

Yes it does. I don't have the energy to go into this. All I will say is that the scientific community agrees with me.

I don't actually have any problem with you invoking MACHOS in the energy-momentum tensor. I have a huge problem with you invoking unproved forms of matter and energy into the energy-momentum tensor however, just as you would have a problem with me invoking non-baryonic invisible potatoes in the energy-momentum tensor.

No, I have no problem with you invoking potatoes into the energy-momentum tensor, why would I? Your arguing about what is allowed in the energy-momentum tensor and not appears very strange to me.

But you don't even know the actual energy state of a WIMP, or even if it exists yet. You have a very vague idea here that involves many orders of magnitude of an energy state, and nothing in the way of tangible, physical, empirical evidence to show that it actually exists in nature.

Argh, what i do is to postulate a WIMP and calculate its consequencies. I know its equation of state perfectly (its just the same as for matter, simply because it is matter, i.e. pressure=0. If I would postulate a very light particle it would have the same equation of state as radiation: pressure=density/3)

The problem is that you have never demonstrated that WIMPS physically exist in reality.

No, that is not a problem since I postulate a model for a dark matter particle. Of course that doesn't prove the particle exists, but it doesn't stop me from calculating its properties.

If there are other forces of nature acting on objects of mass, those forces of nature probably have "properties" that are based on the specific type of energy involved, and GR would not be necessary to describe these forces.

WIMPs have mass (by construction). Hence it interacts gravitationally.

IMO the Lambda-CDM theory isn't "pure" GR. It's a loosely GR oriented theory with a liberal dose of metaphysics mixed in, it's about 96% metaphysics in fact.

First, you certainly belong to a minority then.
Second, even if you somehow refuse to allow the cosmological constant in "pure" GR, what does this have to do with dark matter? Dark matter can still be invoked in "pure" GR.

If you claim that non-baryonic forms of mass exists

In fact I know it exists: neutrinos, electrons, positrons. I don't know wheter WIMPs exists, and I have never claimed so either. Stop insinuating that.

I will willingly let you toss MACHOS or neutrino mass into GR

If I follow your reasoning, how could you put in MACHOs when you don't no if they exist?

(Edit: Actually, I think my last question goes right to the heart of this discussion. Please focus on that one.)

 

[Michael Mozina]

What about direct-detection experiments like CDMS and Liquid Xenon? Both are finally becoming sensitive enough to probe the heart of parameter space where WIMPs are thought to exist. If nothing is seen within 5 to 10 years then that will raise some serious questions, but I think for now we need to sit and wait.

If someone comes up with a modified gravity theory which can explain what we're seeing, that doesn't make it right.

But the reverse is also true. Just because non-baryonic dark matter theories can explain what we're seeing, that doesn't mean non-baryonic dark matter exists in nature. It's a hypothesis, that may or may not be true.

All I'm suggesting is that astronomers seem very convinced that the can tell us what was occurring 13.7 billion years ago. I'm far less convinced that we have all the 'big picture" details correct, and I therefore entertain a much larger range of theories as it relates to cosmology.

 

[eep]

But the reverse is also true. Just because non-baryonic dark matter theories can explain what we're seeing, that doesn't mean non-baryonic dark matter exists in nature. It's a hypothesis, that may or may not be true.

All I'm suggesting is that astronomers seem very convinced that the can tell us what was occurring 13.7 billion years ago. I'm far less convinced that we have all the 'big picture" details correct, and I therefore entertain a much larger range of theories as it relates to cosmology.

Of course, that only makes sense. Everyone should be comfortable with the possibility that dark matter may not exist. There's not much point in arguing over it thought - the modified gravity people need to come up with predictions we can test, and the dark matter folks need to wait and hope one of these direct-detection experiments gets a hit.

 

[Michael Mozina]

You still do not seem to get the difference beween a hypothesis and a fact.

Actually I do understand that difference. I'm just not convinced that mainstream astronomy understands that difference. I'm always hearing astronomers talk about metaphysical constructs as though we are certain that they exist, and that's the way things happened in some distant past. I keep hearing things like "The universe is about 13.7 billion light years old, plus or minus a few billion years." The only way that could possibly be true is *if* all the various metaphysical hypothetical entities of Lambda-CDM theory pan out. If even one of them does not exist in nature (particularly inflation), that age estimate will be completely meaningless. It is not "fact" that there was ever a "big bang". It is not "fact" that DE and non-baryonic DM exist, or that inflation ever existed in nature. I tend to ruffle a lot of feathers when I say that in public, but it's certainly true that Lambda-CDM theory is not fact, nor is the age of the universe "fact", nor is the notion that there was a "big bang', a factual statement. These are all "theories", or as you said "hypothesis" that may or may not be fact. The "fact" is that inflation has not be demonstrated, and that DE has not been demonstrated, and that non-baryonic forms of DM have not been demonstrated. Lambda-CDM is but one theory among many competing theories. Those are the facts.

(WIMP dark matter is a hypothesis, not a claimed fact.) And please, try to shorten the posts. I do not find time to answer all of your comments, but I'll do a few.

I'll try to focus on the specific issues, and the specific areas of my concern. We seem to agree that non-baryonic forms of matter of all sorts are "hypothetical" entities, and we cannot be sure that such things even exist in nature.

As I said, MACHOs are baryonic. Baryons cannot make up more than a fraction of the dark matter needed (due to constraints from BBN).

Here is where we seem to take different paths. From my perspective, if it is true that baryons cannot make up more than a fraction of the dark matter needed to make your theory work correctly, then IMO it is time for you to scrap (or at least devalue the importance of) your gravity centric theory. There are only certain forms of "matter" that we can be sure actually exists in nature, and you don't have any evidence of any non-baryonic forms of matter.

You have a lack of knowledge here. The WIMPs (if they exist) were created at the big bang. That is why one talks about the "relic density"

Well, ok, if you say so. I stand corrected. From my perspective however, that is like me claiming that something you never heard of before was created in the big bang. I will grant you that this is in fact the theory behind WIMPS, but from my vantage point that is a "hypothesis" that has no empirical support. I am skeptical of any theory that begins with an unproven premise related to a hypothetical entity. It's like me "assuming" that something else was created in a bang (like invisible potatoes) and yet offering you absolutely no scientific evidence to support my claim that invisible potatoes exist in reality.

Furthermore, huge super computer simulations (e.g. the "Millenium simulation") have simulated the universe's structure formation including WIMPs. The resulting distributions agree very well with the observations we make. In fact, simulations without (cold) dark matter fails to reproduce the observed structures. Your impression that the dark matter gets distributed in the same way as baryonic matter is simply false.

Well, the basic problem from my perspective is that you have no empirical evidence that WIMPS exists in reality, so from my way of looking at your theory, it has a big "flaw" in it. You also have no empirical evidence showing how a WIMP does or does not interact with matter, so any computer simulations will be based on ad-hoc "properties" that you have assigned to the particle in your computer code. I have absolutely no way to verify any of this based on physics or physics experiments. If you had empirical evidence that demonstrated that WIMPS existed, and you could show how they interacted with normal matter, then your computer code would be based on known laws of physics. Since that is not the case with non-baryonic forms of matter, these are metaphysical simulations that are based on unsupportable properties about a theoretical form of matter. I would have to assume the simulations were done correctly, but that the "properties" that were assigned to the theoretical property were completely "made up". They cannot be based on empirical evidence that shows how these particles physically interact with baryonic matter based on controlled experimentation.

No, I have no problem with you invoking potatoes into the energy-momentum tensor, why would I? Your arguing about what is allowed in the energy-momentum tensor and not appears very strange to me.

I think this is really the heart and soul of our disagreement. It represents the fork in the road where we seem to part company. I don't have any problem at all with you putting "known" physical entities into GR theories. Adding neutrinos and MACHOS to GR are absolutely and completely fine by me because I know for a fact that these items exist in nature. I do however have a huge problem with stuffing *unproven* entities into a GR formula. My invisible potatoes form of mass is a "foul" and it is unacceptable, because I can't demonstrate that invisible potatoes exist in nature. It is therefore invalid for me to put these items into a GR formula *without* ever demonstrating that they actually exist in nature. It doesn't matter whether or not my invisible potato theory matches some distant observation, I still need to verify that invisible potatoes exist in nature and have some effect on nature in controlled experiments.

It seems equally strange to me that you would allow things to be "slapped on" to GR theory without expecting some kind of empirical evidence that such things even exist in nature. From my perspective, that's like expecting you to accept my invisible potato theory at face value because invisible potatoes *might* exist, and they might come in all sizes, from macroscopic sizes, to subatomic sizes. My invisible potato variation of GR theory is not actually GR theory any longer. It's a purely metaphysical extension of GR theory.

Argh, what i do is to postulate a WIMP and calculate its consequencies. I know its equation of state perfectly (its just the same as for matter, simply because it is matter, i.e. pressure=0. If I would postulate a very light particle it would have the same equation of state as radiation: pressure=density/3)

And likewise, both my "large" (big potato) and my "tiny" (subatomic) variation of invisible potato theory follows the equation state of matter just perfectly, simply because it is "matter", i.e. pressure=0.

I'm afraid that my slapping unproven properties onto my invisible potato theory isn't making my potato theory any more believable simply by virtue of me adding "properties" (that I can't actually verify) to my potatoes. You can't stop me from calculating it's properties, but that doesn't mean you are obligated to accept my invisible potato theory. I might tell you that invisible potatoes have mass by construction, but then this "construction' of mine is purely hypothetical, and completely arbitrary.

First, you certainly belong to a minority then.

That is irrelevant from my perspective by the way.

Second, even if you somehow refuse to allow the cosmological constant in "pure" GR, what does this have to do with dark matter? Dark matter can still be invoked in "pure" GR.

MACHOS can certainly be invoked in pure GR, and neutrinos can be invoked in pure GR, because we have "physics" (real physics) to fall back on as it relates to verifying the "properties" of these *known* forms of mass. Invisible potatoes cannot be invoked in pure GR, because there is no real "physics" to verify anything I might claim about invisible potatoes. If I tell you that they pass through normal matter, you can't verify it via physics. It is a purely metaphysical construct. I can't invoke invisible potatoes in pure GR without turning that variation of GR into a metaphysical variation of GR.

In fact I know it exists: neutrinos, electrons, positrons. I don't know wheter WIMPs exists, and I have never claimed so either. Stop insinuating that.

I'm not insinuating anything, and please don't take our conversation personally. I'm simply pointing out that all theories have "limits" and "flaws". Lambda-CDM theory is no different. It relies upon unproved metaphysical constructs. That's all I'm insinuating.

If I follow your reasoning, how could you put in MACHOs when you don't no if they exist?

We can toss in as much baryonic matter (in any form) into a GR theory as we please, because any form of baryonic matter has "testable" properties. If we add these kinds of things to GR theory, we are not making any "extraordinary" claims. We know that baryonic matter exist in nature. It is only if we make the "extraordinary" claim that some new form of matter exists (invisible potatoes), and is responsible for these observations, that we take on an additional burden of proof. We take on this burden of proof by virtue of postulating a new (unevidenced) form of matter. My "beef" is that you are attempting to explain a distant event with an unproven metaphysical construct (WIMPS), not that you are proposing the existence of "missing mass" in some distant observation.

We know that planets exist in nature. We are therefore welcome to explain that missing mass with planets and planetary materials. We know that asteroids exist in nature. We are therefore welcome to explain that missing mass with asteroids. We don't know that WIMPS or invisible potatoes exist in nature, so it is not acceptable for us to use such things to explain distant observations. If an when we have evidence that WIMPS actually exist in nature *then* I will have no problem with you suggesting that this missing mass is in the form of non-baryonic matter. There is an extra burden of proof on our theory if we wish to attribute distant events on an unproven form of matter. We must also prove that such forms of matter actually exist and that they interact with baryonic matter exactly as we specified.

 

[Michael Mozina]

Of course, that only makes sense. Everyone should be comfortable with the possibility that dark matter may not exist. There's not much point in arguing over it thought - the modified gravity people need to come up with predictions we can test,

But that works both ways. What controlled scientific test shows that non-baryonic forms of mass exist in nature? When a theory fails a key "prediction" as Lambda-CDM failed to predict the non-homogeneous nature of our universe, what then should we do with Lambba-CDM theory, particularly the inflation hypothesis of Lambda-CDM theory? Guth proposed inflation to "solve a monopole problem" as he perceived it, and to explain the homogeneous layout of the physical universe. We now know that the universe is not homogeneous in layout and nobody can demonstrate that monopoles exist, or that inflation solved a "missing monopole problem".

and the dark matter folks need to wait and hope one of these direct-detection experiments gets a hit.

Well, hope does spring eternal, but IMO it's a poor substitute for hard empirical evidence. If and when I see someone demonstrate the existence of non-baryonic forms of mass, I'll be quite happy to entertain non-baryonic form of matter in GR theory. Of course I will still need to see some evidence that "dark energy" causes "space" (whatever that is) to expand, and that inflation actually exists before I'll buy into those aspects of the Lambda-CDM theory. I'm not imposing any special requirements on any particular theory, but I will require that each and every theory meet basic scientific requirements. One of those requirements is that extraordinary claims always require extraordinary evidence. So far I see lots of extraordinary claims in Lambda-CDM theory (DE, DM, inflation), and very little in the way of supporting evidence. That is not to say that non-baryonic forms of mass *cannot* exist, it's just that I do have any evidence that the *do* exist. That is also true of DE and inflation. I can't disprove a negative, so the burden of proof must fall to the individual that makes the claim. If someone makes the extraordinary claim that non-baryonic forms of mass exists, they will need to support that statement with solid empirical evidence. That is SOP (standard operating procedure) for all branches of science.

 

[Count Iblis]

DAMA/NaI experiment has very likely detected dark matter

 

[EL]

We know that planets exist in nature. We are therefore welcome to explain that missing mass with planets and planetary materials. We know that asteroids exist in nature. We are therefore welcome to explain that missing mass with asteroids. We don't know that WIMPS or invisible potatoes exist in nature, so it is not acceptable for us to use such things to explain distant observations.

The point is that it has been shown that baryonic matter cannot explain what we observe. Neither can the non-baryonic matter we know of. Then we have in principle two alternatives:
1) There is matter of some form not contained in the Standard Model out there.
2) There is only Standard Model matter, and it's the laws of gravity which need to be altered.
We then need to make hypothesis' in both cases. Either we cook up some new form of matter, plug it into the existing equations, and see if it can explain the observations. Or we cook up some new laws of gravity, calculate the predictions, and see if it can explain the data.
First of all, when it comes to matching the observed data, the attempts with some forms of matter (WIMPs) are quite successfull, while the attempts with altering the laws of gravity have big problems.
Secondly, WIMPs have good theoretical motivations from particle physics, while modified gravity theories are mearly curve fitting.
This is why I (and most professionals) favors dark matter particles over modified gravity. (With that I am not saying WIMPs exists, only that it looks much more promising than any modified gravity theory.)

 

[Michael Mozina]

DAMA/NaI experiment has very likely detected dark matter

I've skimmed through about 65 pages of "theory" thus far, and I didn't see a single mention of a control mechanism of any sort. Can someone start by cluing me in as to the page number that relates to the control mechanism(s) that they used?

 

[EL]

DAMA/NaI experiment has very likely detected dark matter

The DAMA claim is highly controversial. No other experiment have been able to confirm their claimed signal. Also, the DAMA colaboration refuse to make their data publicly available. The general opinion is that the DAMA results are highly uncertain and should not be used as a claim for detection of dark matter.

 

[Count Iblis]

The DAMA claim is highly controversial. No other experiment have been able to confirm their claimed signal. Also, the DAMA colaboration refuse to make their data publicly available. The general opinion is that the DAMA results are highly uncertain and should not be used as a claim for detection of dark matter.

None of the other experiments use the same methods. There is room to explain both the positive results of DAMA and the negative results of CDMS and other searches. Only if one assumes that DM is a neutralino can one say that the other searches have excluded DAMA (but even in that case there is still a small window for light WIMPS, as P Gondolo and G Gelmini have pointed out).

Now, I don't agree with the sentiments raised by Michael Mozina in this thread, but the very common attitude that "other searches have ruled out DAMA", even though they are still compatible is an example of theory ruling out an experimental result, the theory being the favored neutralino WIMP candidate.

Of course, the DAMA results need to be confirmed by independent searches. However, it is entirely possible that the current searches won't detect dark matter, as the DAMA team have pointed out in their recent articles, as their signal rejection methods to separate nuclear recoil signals from other signals may throw away signals from DM that interact in different ways.

 

[Michael Mozina]

The point is that it has been shown that baryonic matter cannot explain what we observe.

While I'm am sure that you (in very good faith) believe that this statement is true, I do not believe that you can scientifically demonstrate it to be true. EU theory can explain galaxy rotation patterns without dark matter. MOND and modified gravity theories do so as well. Other than the known particles of particle physics, I don't have any evidence that other forms of matter exist. It's therefore not even logical to me to *assume* that there are absolutely no other ways to explain this seeming amount of "missing mass" without resorting to unproven forms of matter. For all I know, our current technology is simply 'primitive' when it comes to identifying various forms of standard matter at a distance, including electrons that flow though the plasmas of space/time. Before I can accept your statement as fact, I must know with great confidence that no other possible options remain, and I simply don't feel that all other theories can be disregarded so quickly.

Neither can the non-baryonic matter we know of. Then we have in principle two alternatives:
1) There is matter of some form not contained in the Standard Model out there.

There are plenty of such theories out there by the way.
http://archives.cnn.com/2002/TECH/space/07/23/sun.iron/index.html

2) There is only Standard Model matter, and it's the laws of gravity which need to be altered.

That seems like a reasonable possibility to me considering the scale of the distances in question, and our inability to verify that our laws of gravity (as we understand them) apply to all cosmological distances and densities.

We then need to make hypothesis' in both cases. Either we cook up some new form of matter, plug it into the existing equations, and see if it can explain the observations. Or we cook up some new laws of gravity, calculate the predictions, and see if it can explain the data.

We can also explore EU theories related to electron flows through the arms of the galaxies and through the solar systems. We can explore a lot of possible options here.

First of all, when it comes to matching the observed data, the attempts with some forms of matter (WIMPs) are quite successfull, while the attempts with altering the laws of gravity have big problems.

This seems like a subjective judgment all to me. WIMPS have big problems with detection and verification too. The concept of suggesting that one theory has a "big problem" seems to have a very subjective component.

Secondly, WIMPs have good theoretical motivations from particle physics, while modified gravity theories are mearly curve fitting.

IMO the whole notion of dark matter, particularly the non-baryonic forms of dark matter, dark energy and inflation are merely curve fitting exercises as well IMO. We can't figure out the fast spin rate of stars near the edges of galaxies, so liberally curve fit in some 'dark matter' to make it work. We can't figure out the acceleration of our universe, so we sprinkle in a lot of "dark energy". We need some way to explain homogeneous mass layouts, and to explain why matter didn't implode the moment in formed? Toss in some inflation! It's just a different way of curve fitting from my perspective.

This is why I (and most professionals) favors dark matter particles over modified gravity. (With that I am not saying WIMPs exists, only that it looks much more promising than any modified gravity theory.)

The problem here I think is partly related to age. I'm old enough to remember BB theories that predated DE and inflation. In my day, "dark matter" meant nothing more than "matter we cannot identify with our primitive technology" and generally related to MACHO types of "structures". As I see it, the whole BB theory has become more and more stuffed full of curve fitting metaphysical forces and unproven forms of matter. Lambda-CDM theory is nothing like the BB theories I was exposed to as a child. The notion therefore that WIMP theories are "promising" seems again to be a very subjective judgment call. I can't prove that you're wrong about the existence of WIMPS, but then you can't prove that you're right either. I tend to favor a skeptical approach to science, where the burden of proof falls to the one making the claim. IMO you can't provide any controlled experimental evidence to suggest that WIMPS exist, and I don't know how you would even attempt to put a control mechanism on a WIMP experiment because you don't seem to think that they originate in other forms of matter, but they are a relic of an event that you could never hope to duplicate in controlled conditions. I can't disprove a negative, and I can't even think of decent way to test your concept scientifically using controlled experiments. You must therefore provide evidence that WIMPS exist. So far I haven't see any empirical evidence that WIMPS exist. I therefore can't find anything scientifically superior about a theory that relies heavily upon such forms of mass.

 

[EL]

There is room to explain both the positive results of DAMA and the negative results of CDMS and other searches.

You are right in that there's still some models left to explore before the DAMA result is "ruled out". (I just said no other experiment have been able to confirm the signal.)
I think much of the scepticism agains DAMA stems from the "non-public" policy for their data. What do you think of this problem?

 

[Michael Mozina]

You are right in that there's still some models left to explore before the DAMA result is "ruled out". (I just said no other experiment have been able to confirm the signal.)
I think much of the scepticism agains DAMA stems from the "non-public" policy for their data. What do you think of this problem?

http://news-service.stanford.edu/news/2000/march1/darkmatter-31.html

What caused the recoil events? The likeliest explanation is that a handful of ordinary neutrons seeped into the underground apparatus and collided with the detectors, just as CDMS scientists predicted.

"Our neutron identification comes from a statistical argument," explains Cabrera.

He says that, on four separate occasions, recoil events were recorded by more than one germanium detector at the same time. According to statistical models, what probably happened is that a single neutron bounced off one detector then collided with another one sitting a few inches away.

But WIMPs rarely interact with anything, so if a WIMP made contact with the first detector, the odds of it colliding with a second one nearby are infinitesimally small.

...

According to Cabrera, DAMA's results "were statistically incompatible with the CDMS findings."

Based on DAMA's model, he says, the expected number of WIMPs in the CDMS experiment should have been 24. That's three times more than the maximum number of WIMPs that could possibly have been detected at Stanford, according to a statistical analysis by CDMS.

It seems to me that these were the two most damaging pieces of evidence against the DAMA results. The lack of public access to the data, only makes their claim more suspicious, particularly since their method should have yielded a significantly higher number of hits with the CDMS detector.

I'm also having a hard time with the whole premise of this concept. We have to accept the DAMA theory about the speed of a dark matter 'sea' to even believe that there should be a seasonal influence. The other main complaint I read suggested that the ambient temperature itself my have been responsible for these seasonal differences.

 

[EL]

M.M., if you don't shorten your posts I will not find the time to continue answering. (You seem just to repeat the same words over and over again, please focus on what you find most important.)
WIMPs are not curve fitting, since every specific WIMP model is motivated by particle physics arguments. The structures of WIMP models (e.g. the Minimal Supersymmetric Standard Model) are not cooked up in order to fit the cosmological observations. (As is the case for MOND.)
When you write EU, do you mean Electric Universe or whatever it is called? That is a crackpot theory, right?
Your link about the "iron sun" is also "crackpot alert". (And I do not get what it had to do with matter not contained in the standard model.)
When I wrote "The point is that it has been shown that baryonic matter cannot explain what we observe", I of course ment "The point is that it has been shown that baryonic matter, together with the ordinary known laws of physics, cannot explain what we observe."
Once again, please shorten your answers.

Edit: Just to clearify, this was a respons to your post #34.

 

[Count Iblis]

You are right in that there's still some models left to explore before the DAMA result is "ruled out". (I just said no other experiment have been able to confirm the signal.)
I think much of the scepticism agains DAMA stems from the "non-public" policy for their data. What do you think of this problem?

I think they should have made it public. They already have published models in which the detected effect is not due to nuclear recoils. The criticism of their experiment was that they cannot distinguish between nuclear and electron recoils and it is commonly assumed that WIMPS will produce nuclear recoils while the electronic effects are noise. So, I can't see why they won't make the data public now that this issue isn't so relevant anymore.

Perhaps they are waiting for confirmation from DAMA/Libra...

 

[eep]

Well, hope does spring eternal, but IMO it's a poor substitute for hard empirical evidence. If and when I see someone demonstrate the existence of non-baryonic forms of mass, I'll be quite happy to entertain non-baryonic form of matter in GR theory. Of course I will still need to see some evidence that "dark energy" causes "space" (whatever that is) to expand, and that inflation actually exists before I'll buy into those aspects of the Lambda-CDM theory. I'm not imposing any special requirements on any particular theory, but I will require that each and every theory meet basic scientific requirements. One of those requirements is that extraordinary claims always require extraordinary evidence. So far I see lots of extraordinary claims in Lambda-CDM theory (DE, DM, inflation), and very little in the way of supporting evidence. That is not to say that non-baryonic forms of mass *cannot* exist, it's just that I do have any evidence that the *do* exist. That is also true of DE and inflation. I can't disprove a negative, so the burden of proof must fall to the individual that makes the claim. If someone makes the extraordinary claim that non-baryonic forms of mass exists, they will need to support that statement with solid empirical evidence. That is SOP (standard operating procedure) for all branches of science.

The whole point of doing a direct-detection experiment for dark matter is to get the empirical evidence that it does exist. Are you saying that nobody should be looking for dark matter because nobody has found it before?

 

[Count Iblis]

http://news-service.stanford.edu/news/2000/march1/darkmatter-31.html



It seems to me that these were the two most damaging pieces of evidence against the DAMA results. The lack of public access to the data, only makes their claim more suspicious, particularly since their method should have yielded a significantly higher number of hits with the CDMS detector.

I'm also having a hard time with the whole premise of this concept. We have to accept the DAMA theory about the speed of a dark matter 'sea' to even believe that there should be a seasonal influence. The other main complaint I read suggested that the ambient temperature itself my have been responsible for these seasonal differences.

Emmmm, you are now talking just like the people who you have a problem with

The higher number of hits is only relevant for the neutralino-like models. The DAMA experiment is more model independent, as it also sensitive to other DM candidates that would not produce a signal in the CDMS detector.

The "speed of the DM sea" is a pretty robust model independent thing. One can think of extra features in here like DM strams, but basically, the Earth does revolve around the Sun, and that is bound to produce an annual modulation. Thing is that only DAMA has the sensitivity to see the annual modulation. All the other experiments need to be able to separate individual DM recoil events from background events. But that's only possible if you know that DM will produce nuclear recoils, which you actually do not know for sure.

The DAMA experiment does not depend on the experimentor being able to tell what is a recoil due to DM and what is not. You just detect the annual modulation. If you make sure that there is no annual modulation in the noise, the annual modulation you see is due to DM.

 

[Michael Mozina]

M.M., if you don't shorten your posts I will not find the time to continue answering. (You seem just to repeat the same words over and over again, please focus on what you find most important.)

Well, I guess I must be enjoying the conversation to be this long winded. :)

WIMPs are not curve fitting, since every specific WIMP model is motivated by particle physics arguments. The structures of WIMP models (e.g. the Minimal Supersymmetric Standard Model) are not cooked up in order to fit the cosmological observations. (As is the case for MOND.)

That whole last DAMA paper was based on the theory of "dark matter". The WIMP model is simply "cooked up" to find a way to explain a cosmological phenomenon. In fact the whole basis of their "testing method" (if you can call a test with no control method a test method) is based on cosmology theory. It's certainly a curve fitting hypothesis by those same standards.

When you write EU, do you mean Electric Universe or whatever it is called? That is a crackpot theory, right?

No, definitely not. Not unless you consider Hannes Alfven, a winner of the Nobel prize for MHD theory a "crackpot". Kristian Birkeland was certainly not a crackpot either. I'm not sure I even understand what you feel constitutes "crackpot" theory since none of Alfven's theories had any mention of metaphysical entities. IMO that puts EU theory head and shoulders above Lambda-CDM theories.

Your link about the "iron sun" is also "crackpot alert". (And I do not get what it had to do with matter not contained in the standard model.)

The standard model assumes that plasmas inside suns do no mass separate to any great degree. Instead, it assumes that plasmas stay pretty much mixed, even though magnetic fields and gravity wells are known to cause mass separation in plasmas here on earth. If you remove that single assumption from standard theory it's possible to explain "missing mass" in a variety of different ways, including the notion that sun's are not mostly made of hydrogen and helium, but rather they are mostly made of iron and nickel.

There was in fact a very interesting article that came out today that talked about the electrical properties of x-ray emissions and the over abundance of metals in the x-ray spectrum.

http://www.sciencedaily.com/releases/2007/11/071102152248.htm

I personally find it rather disconcerting that you would label EU theory/Plasma cosmology theory from a Nobel prize winning scientist a "crackpot" theory, yet think nothing about the fact that you willingly accept a theory of the universe that evokes at least three metaphysical forces to work correctly. I find that truly fascinating behavior in fact. What makes something a "crackpot" theory exactly? What makes WIMP theory superior to an iron sun theory when it comes to explaining "missing mass" in objects that are light years away from us?

 

[Michael Mozina]

Emmmm, you are now talking just like the people who you have a problem with

The higher number of hits is only relevant for the neutralino-like models. The DAMA experiment is more model independent, as it also sensitive to other DM candidates that would not produce a signal in the CDMS detector.

The "speed of the DM sea" is a pretty robust model independent thing. One can think of extra features in here like DM strams, but basically, the Earth does revolve around the Sun, and that is bound to produce an annual modulation. Thing is that only DAMA has the sensitivity to see the annual modulation. All the other experiments need to be able to separate individual DM recoil events from background events. But that's only possible if you know that DM will produce nuclear recoils, which you actually do not know for sure.

The DAMA experiment does not depend on the experimentor being able to tell what is a recoil due to DM and what is not. You just detect the annual modulation. If you make sure that there is no annual modulation in the noise, the annual modulation you see is due to DM.

That is somewhat of a circular argument IMO. The authors *assumed* that we traverse a "sea" of "dark matter", they don't assume for instance that dark matter simply moves around the galaxy with the rest of the matter in the galaxy as most theories suggest. I don't even see how the dark matter models actually predict this movement behavior of dark matter in the first place. It seems like a bold faced assumption to begin with. They then suggest that we should see some annual modulation in the data due to their model. That's more or less a self serving prediction isn't it?

Beyond that, there are "problems" with their interpretation. What are the odds that a WIMP struck multiple detectors in the same events on four different occasions? According to Stanford, the model that the DAMA folks propose 'should have' resulted in 3 times the number of hits that they recorded, and even Stanford's model predicted a few miscellaneous "hits" that are related to neutron events and would not be related to WIMPS. The main problem with this method of trying to demonstrate the existence of WIMPS is that we really have no "control" mechanism. In the neutrino experiments, we could put our detector next to a nuclear reactor and switch the reactor on and off to see the effect it has on our controlled scientific experiment. In this case you can't turn on or off the WIMP "generator" (for lack of better term), and you're attempting to chalk up any variation in hits to a single source that may or may not exist. I admit that this "theory" is an interesting attempt to physically demonstrate the existence of WIMPS, but it's based on pure observation, not controlled experimentation. I can't even think of a logical way to "control" any WIMP experiment.

 

[Michael Mozina]

The whole point of doing a direct-detection experiment for dark matter is to get the empirical evidence that it does exist. Are you saying that nobody should be looking for dark matter because nobody has found it before?

Of course not. I would have had no trouble accepting neutrino experiments even before we'd observed their effect on matter in controlled tests. The difference however is that they could in fact "control" the flow of neutrinos in the first scientific neutrino experiments by turning on and off the nuclear reactor that they used to emit neutrinos. Since WIMPS are presumed to be a relic of the BB, what control mechanism is even possible to verify that a "hit" is due to what we think it's due to (WIMPS), rather than some other influence that we didn't consider (neutrons or cosmic rays, or some other factor)?

 

[EL]

The WIMP model is simply "cooked up" to find a way to explain a cosmological phenomenon.

No. WIMP models (like supersymmetry, kk-theory, etc) are motivated by particle physics and fundamental physics ideas. With that I mean that there are reasons completely separated from cosmology for some kind (or kinds) of WIMPs to exist.
I find many of the non-cosmological motivations for the existence of some kind (or kinds) of WIMP particles quite reasonable.
Wouldn't you also say it is quite likely, based on particle physics arguments, we will find some new particles around the electroweak scale?
All it takes then is that one of the particles happens to be stable (at least on cosmological time scales) and only interacts through the weak force, in order to be a good dark matter candidate (since such a particle automatically provides a relic density of the order needed to explain the dark matter). Note that any stable particle leaves a relic density (which can be calculated). It is just that WIMPs happen to leave a relic density of the right order to explain the dark matter. (The so called "WIMP miracle".)
And yes, we do not know wheter such particles exist or not, but if they do they could explain the dark matter.

 

[Count Iblis]

Dark Matter in Many Forms

Jonathan L. Rosner
(Submitted on 7 Sep 2005 (v1), last revised 1 Nov 2005 (this version, v3))
Abstract: Since ordinary matter constitutes about 4% of the closure density of the Universe while dark matter constitutes about six times as much, it is urged that searches for dark matter consider that it may exist in several forms. Implications for detection and hadron and e^{+}+ e^{-} colliders are discussed.

 

[Michael Mozina]

No. WIMP models (like supersymmetry, kk-theory, etc) are motivated by particle physics and fundamental physics ideas.

How can they possibly be motivated by fundamental physics ideas when you don't even believe that WIMPS are created from atoms, or anything to do with atoms? While you might be using some aspect of particle physics theory to support the idea, the entire purpose of theorizing WIMPS is to explain why your mass oriented cosmology theory doesn't work right. There is no pressing need within the realm of particle physics for a WIMP particle to exist. Unlike the neutrino, where the motivation for proposing neutrinos was based on controlled particle physics experiments, the whole reason for proposing WIMPS was to 'explain' dark matter. It's not as though any particular particle interaction we observe requires that WIMPS exist.

With that I mean that there are reasons completely separated from cosmology for some kind (or kinds) of WIMPs to exist.

There is no particle physics interaction that requires or necessitates that a WIMP particles exist. No identified particle interaction is known to create "WIMPS". The whole motivation for proposing WIMPS was to explain a perceive amount of "missing mass" based on a very specific cosmology theory, not modified gravity theory for instance.

I find many of the non-cosmological motivations for the existence of some kind (or kinds) of WIMP particles quite reasonable.

What non cosmological motivation seems reasonable to you?

Wouldn't you also say it is quite likely, based on particle physics arguments, we will find some new particles around the electroweak scale?

I don't know. I can't say. It's certainly possible. It might even be probable. That is not to say that even if we find a new subatomic particle that it will have anything at all to do with "WIMPS". My fear here is that you are intentionally opening up a huge door so that you can drive a Mack truck through any sort of subatomic particle "finding" they might observe. You don't know from the outset if any new finding in particle physics will be related to WIMPS, but your theory is so vague and so undefined, that you might be able to "pounce" on nearly anything. For all I know these new subatomic interactions will be temporary and unstable and revert back to a more stable particle that we have already identified in a matter of milliseconds, or hours.

All it takes then is that one of the particles happens to be stable (at least on cosmological time scales)

That is certainly a key requirement. How will you know if it's "stable"?

and only interacts through the weak force, in order to be a good dark matter candidate (since such a particle automatically provides a relic density of the order needed to explain the dark matter). Note that any stable particle leaves a relic density (which can be calculated). It is just that WIMPs happen to leave a relic density of the right order to explain the dark matter. (The so called "WIMP miracle".)
And yes, we do not know wheter such particles exist or not, but if they do they could explain the dark matter.

The key point here is that Modified Gravity theory and MOND theories don't even require that DM exists at all. While anything remains "possible", what separates physics from metaphysics is empirical evidence. I see no compelling empirical evidence that WIMPS exist in nature. At present, Lambda-CDM theory relies upon no less than three different forms of metaphysics. It is therefore quite difficult for me to accept that this is the "best" cosmology theory available, or that it should be the only cosmology theory that is taught to astronomy students in college. IMO MOND theories, and EU theories (Birkland's/Alfven's work) deserve equal consideration.

 

[Michael Mozina]

Dark Matter in Many Forms

Well, let's look at the assumptions they begin with.

1. INTRODUCTION
Ordinary matter constitutes about 4% of the closure density of the Universe,

That is only true according to Lambda-CDM theory. If you don't subscribe to Lambda-CDM theory, (for instance you're a MOND theorist) this statement is false.

while dark matter is responsible for about five times as much: d = (23 ± 4)% [1, 2]. Ordinary matter exists in several stable forms: p, n (when incorporated into nuclei), e−, and three flavors of neutrinos.

No argument there.

(The lifetimes of the two heavier mass eigenstates probably exceed the age of the Universe.)

That is highly unlikely based on current neutrino theory. Current theories suggest that neutrinos "oscillate" from one eigenstate to another just in the distance from the sun to the earth. There is nothing in these experiments that suggest that lifetimes of eigenstates are measured in billions of years. This is simply a false statement based on current neutrino theory. Even neutrons have a half life of less than 15 minutes before they decay into to protons and electrons and neutrinos.

We could expect dark matter to exhibit at least as much variety [3].

Pure speculation.

2. STABLE OBSERVED MATTER
To describe the variety of stable forms of ordinary matter, I begin with the simplest grand unified theory

There is no agree upon grand unified theory. This whole paper is based on pure speculation, and pure conjecture, and it has several obvious errors in just the first page.

 

[EL]

M.M., please try not to repeat the same arguments many times in the same reply. The posts are getting so long.

How can they possibly be motivated by fundamental physics ideas when you don't even believe that WIMPS are created from atoms, or anything to do with atoms?

If WIMPs exist they can be created by colliding standard model particles in accelerators, thus they have "something to do with atoms". That is, WIMPs interact with standard model particles.

While you might be using some aspect of particle physics theory to support the idea, the entire purpose of theorizing WIMPS is to explain why your mass oriented cosmology theory doesn't work right.

I think you are under the impression that WIMPs is some kind of fuzzy particles which properties we just make up in order to fit the cosmological data.
WIMPs is a class of particles, namely consisting of those which are Weakly Interacting (i.e. interacts only through the weak force, just like neutrinos) and massive Massive (~1TeV) Particles.
To this class belongs for example the neutralino.
The neutralino exists in the MSSM (Minimal Supersymmetric Standard Model). As you probably know, supersymmetry is an important concept within theoretical physics and is motivated by a number of plausible theoretical arguments. One reasons for supersymmetry to show up at the electroweak scale is because it solves the "hierarchy problem" (i.e. it cancels the quadratically divergent Higgs mass corrections).
The purpose of "theorizing" the neutralino (in the first place) hence lies on the fundamental physics level. Then it happens that, if it exists, it can also explain the dark matter. Thus, two totally unrelated problems could be solved by the existence of weak scale supersymmetry.
If we just would cook up the properties of new particle just in order to fit the cosmological data, that would on the other hand be curve fitting.

That is not to say that even if we find a new subatomic particle that it will have anything at all to do with "WIMPS".

If we in accelerators find a Massive Particle which is Weakly Interacting it is by definition a WIMP. Wheter that WIMP really makes up the dark matter we have to confirm with direct detection (such as CDMS) and/or indirect detection experiments (such as GLAST).

That is certainly a key requirement. How will you know if it's "stable"?

By measuring its properties in experiments.

The key point here is that Modified Gravity theory and MOND theories don't even require that DM exists at all.

No, but instead of invoking new particles, they invoke new parameters in the equations describing gravity.
For the first, these parameters are invoked just in order to fit the cosmological observations.
Secondly, MOND theories have turned out less successfull then WIMPs when it comes to explaining dark matter on all scales.

 

[Garth]

Well, let's look at the assumptions they begin with.

1. INTRODUCTION
Ordinary matter constitutes about 4% of the closure density of the Universe,

That is only true according to Lambda-CDM theory. If you don't subscribe to Lambda-CDM theory, (for instance you're a MOND theorist) this statement is false.

Incorrect.

The conclusion that ordinary matter constitutes about 4% of the closure density of the Universe is derived from the standard BBN processes taking place in a universe that expands according to GR when it is dominated by radiation.

In that case p = \frac{1}{3} \rho c^2 and the scale factor is given by R(t) \propto t^\frac{1}{2}.

This sets the limit on the time for nucleosynthesis to continue.

Dark Matter and Dark Energy have nothing to do with it.

Garth

 

[Michael Mozina]

I think you are under the impression that WIMPs is some kind of fuzzy particles which properties we just make up in order to fit the cosmological data.

No, I think they were a handy hypothetical particle, related to a *non* standard particle physics theory, that was quickly stuffed into the gaps of an otherwise failed gravity centric theory of the universe.

http://en.wikipedia.org/wiki/Neutralino

WIMPS and neutralinos are "hypothetical" particles from a non standard and still very controversial branch of particle physics theory.

WIMPs is a class of particles, namely consisting of those which are Weakly Interacting (i.e. interacts only through the weak force, just like neutrinos) and massive Massive (~1TeV) Particles.

But you don't know if "sparticles" even exist in nature. They are hypothetical particles from a non standard branch of particle physics theory. It's a bit like me grabbing MOND concepts and stuffing them liberally into an otherwise failed particle physics theory and claiming that these two otherwise failed ideas support one another.

To this class belongs for example the neutralino.
The neutralino exists in the MSSM (Minimal Supersymmetric Standard Model).

But the neutralino does not exist in reality as far as we know.

As you probably know, supersymmetry is an important concept within theoretical physics and is motivated by a number of plausible theoretical arguments.

And to date it is not supported by any *empirical* data.

One reasons for supersymmetry to show up at the electroweak scale is because it solves the "hierarchy problem" (i.e. it cancels the quadratically divergent Higgs mass corrections).
The purpose of "theorizing" the neutralino (in the first place) hence lies on the fundamental physics level.

It lies in a *non standard* fundamental "metaphysical" construct. Physics requires empirical support. Metaphysics does not. WIMPS have no empirical support. There is no physical, empirical evidence that WIMPS or axions or neutralinos exist in nature.

Then it happens that, if it exists, it can also explain the dark matter. Thus, two totally unrelated problems could be solved by the existence of weak scale supersymmetry.
If we just would cook up the properties of new particle just in order to fit the cosmological data, that would on the other hand be curve fitting.

It seems to me you are simply curve fitting your gravity model with a metaphysical entity that has never been shown to exist in nature. I hear and understand your basic argument EL, but I think you're trying to split hairs here. MOND theory does nothing that you are not also doing. You are simply attempting to somehow justify your "dark matter" curve fitting exercise based on a hypothetical entity from a non-standard, and non-proven particle physics theory. It's a very weak argument unless and until that particle physics theory you're trying to peddle has empirical support. Since there is no empirical support of WIMPS, it's simply "gap filler" or "curve fitting filler" for an otherwise failed gravity theory.

If we in accelerators find a Massive Particle which is Weakly Interacting it is by definition a WIMP. Wheter that WIMP really makes up the dark matter we have to confirm with direct detection (such as CDMS) and/or indirect detection experiments (such as GLAST).

Thus far, there is absolutely no confirmation of these metaphysical bad boys from any controlled tests that we've conducted thus far.

No, but instead of invoking new particles, they invoke new parameters in the equations describing gravity.

So which is "better" from a scientific perspective and why do you feel it is "better"?

For the first, these parameters are invoked just in order to fit the cosmological observations.

That is the only reason that dark matter was postulated in the first place as well. The amount of hypothetical dark matter is a postdicted number based on distant observation, it is not a predicted number based on particle physics theory.

Secondly, MOND theories have turned out less successfull then WIMPs when it comes to explaining dark matter on all scales.

The concept of "less successful" is rather subjective IMO. MOND theories have been moderately successful and they require no faith in metaphysical particles. They are newer theories, and thus they haven't had the same effort put into them as "dark matter' theories have enjoyed.