Dark Matter: Canadian Astronomers Suggest It May Not Exist

[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.

 

[Michael Mozina]

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.

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

Show me where in this article it predicts any specific quantity of dark matter that is created in this BBN process? I don't see a word about thee quantity of created dark matter in most BBN definitions.

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

Precisely. :)

 

[Michael Mozina]

Here by the way is an interesting observation that was recently posted by BDOA in another thread:

https://www.physicsforums.com/showthread.php?t=195486

It seems as though WIMP annihilation theories didn't seem to jive with the recent search for high energy neutrino point sources. In fact these high energy neutrinos do not seem to track to any known point source in our immediate vicinity. That revelation is yet one more damaging piece of data for WIMP oriented dark matter theories.

http://xxx.lanl.gov/PS_cache/arxiv/pdf/0711/0711.0053v1.pdf

8.1 WIMP searches

We have performed searches for WIMP annihilations in the center of the Earth,
Sun and Galactic Center using upward through-going muons [7]. Here we
repeat the same search using upward showering muons. The cone size which
contains most of the WIMP signal is inversely proportional to the WIMP
mass. Since only high-mass WIMPs produce upward showering muons, we
perform these searches in cones only up to 5◦. Such a cone contains 90% of
the signal for a WIMP of mass 1438 GeV from the Earth and 1000 GeV from
the Sun and Galactic Center [7]. The observed data and expected background
(evaluated in the same way as in Ref. [7]) are shown in Table 2. Since, there
is no statistically significant excess in any of the search cones, we do not see
any evidence for WIMP-induced upward showering muons in our dataset.

 

[Michael Mozina]

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

Indirect detection efforts rest upon the theoretical prediction that halo WIMPs may, as they pass through the Sun, interact with solar protons and helium nuclei. Such an interaction would cause a WIMP to lose energy and become "captured" by the Sun (see Solar WIMP capture). As more and more WIMPs thermalize inside the Sun, they begin to annihilate with each other, forming a variety of particles including high-energy neutrinos.[1] These neutrinos may then travel to the Earth to be detected in one of the many neutrino telescopes, such as the Super-Kamiokande detector in Japan. The number of neutrino events detected per day at these detectors depends upon the properties of the WIMP, as well as on the mass of the Higgs boson. Similar experiments are underway to detect neutrinos from WIMP annihilations within the Earth and from within the galactic center.[2][3]

The results are in, and there were no WIMP point sources found in the earth, in the sun, or in the galactic core. When does a metaphysical theory become falsified, and how does one falsify it exactly? It seems to me that an important and key testable prediction of this theory has been falsified. There is no empirical data to support this metaphysical concept, and there may never be any empirical data to support this idea. How then can non baryonic dark matter hypothesis, and Lambda-CDM theory be any more scientifically viable than another other cosmology theory?

 

[Chronos]

Evidence favoring the existence of dark matter is abundant. It perturbs all cosmological structures and appears in gravitational lensing surveys. MOND sometimes works for structure, but is powerless to explain lensing, hence, the abiding preference for DM in the astrophysics community. It's form, however, is unknown. There could be a bestiary of 'dark' particles [my present favorite], or it could be dominated by a single entity. It is, however, devilishly difficult to detect. But, so was the neutrino for much the same reasons - the stuff does not play well with ordinary matter. Not knowing it's form does not diminish observational evidence.

 

[Michael Mozina]

Evidence favoring the existence of dark matter is abundant. It perturbs all cosmological structures and appears in gravitational lensing surveys. MOND sometimes works for structure, but is powerless to explain lensing, hence, the abiding preference for DM in the astrophysics community.

Actually this thread started by Ivan posting a link to a modified gravity theory that did seem to explain the lensing aspects of the bullet cluster data.

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

It's form, however, is unknown. There could be a bestiary of 'dark' particles [my present favorite], or it could be dominated by a single entity.

The problem may even be muddier than first believed. One "entity" that seems to be out there in the plasmas of space, that hasn't really been accounted for, are electron streams.

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

It is, however, devilishly difficult to detect. But, so was the neutrino for much the same reasons - the stuff does not play well with ordinary matter. Not knowing it's form does not diminish observational evidence.

I think my primary complaint is that one of the few actual testable "predictions" that were made with non-baryonic dark matter theories has been shot down. There are no resolved point sources of WIMP annihilation in the Super-Kamiokande detector data. This is on top of the fact that no empirical data has ever detected non-baryonic "dark matter".

Most theories would be "falsified" by such key prediction failures. DM theories however are extremely nebulous, and they are therefore utterly unfalsifiable. It's a bit like a "whack-a-mole" exercise. We can whack down some key predictions of one type of DM theory, but another DM hypothesis emerges somewhere else and nobody seems to abandon the old falsified concept that we just whacked down.

 

[Garth]

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

Show me where in this article it predicts any specific quantity of dark matter that is created in this BBN process? I don't see a word about thee quantity of created dark matter in most BBN definitions.

BBN is not about the creation of DM, it is about the nucleosynthesis of baryonic matter.

Non-baryonic DM, if it exists, would have been produced at an earlier stage, which is unknown at present as non-baryonic DM is undiscovered and unknown at present.

So your statement

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.

is incorrect.

A MOND theorist would conclude "Ordinary matter constitutes about 4% of the closure density of the Universe" as well.

To change the 4% closure density of baryonic matter and arrive at the correct amount of helium, you have to change the R(t) of the universe during those first three minutes.

This might be possible if a form of DE was dominant then, however that would change the other trace element abundances.

Garth

 

[eep]

This is on top of the fact that no empirical data has ever detected non-baryonic "dark matter".

Most theories would be "falsified" by such key prediction failures. DM theories however are extremely nebulous, and they are therefore utterly unfalsifiable. It's a bit like a "whack-a-mole" exercise. We can whack down some key predictions of one type of DM theory, but another DM hypothesis emerges somewhere else and nobody seems to abandon the old falsified concept that we just whacked down.

I don't see why you would expect to have seen empirical evidence of direct detection of non-baryonic "dark matter". CDMS and presumably Liquid Xenon are *just now* starting to get enough detector mass to perform a search in the heart of the WIMP parameter space. It's foolish to stop looking for something before you look where you expect to find it.

 

[Michael Mozina]

BBN is not about the creation of DM, it is about the nucleosynthesis of baryonic matter.

That was my whole point. The smiley at the end of my post was specifically intended to point out that BBN has nothing to do with dark anything.

Non-baryonic DM, if it exists, would have been produced at an earlier stage, which is unknown at present as non-baryonic DM is undiscovered and unknown at present.

It's a little odd (fishy actually) from my perspective that you believe that DM is something like 10 times more abundant that normal matter, it's larger than a proton, yet it's not even mentioned once in BBN? How come?

There's a core problem here form the very start. Baryonic and even non-baryonic forms of mass would have caused the whole mass body to collapse in on itself in the first few seconds. These calculations then cannot be directly related to testable physics without introducing a metaphysical force of nature to explain why the whole thing wouldn't implode during the BBN event. If you intend to toss inflation into that mix, where are those calculations? Where is your empirical evidence that inflation is a real force of nature and has some effect on controlled test of this nucleosynthesis of mass process?

So your statement is incorrect.

A MOND theorist would conclude "Ordinary matter constitutes about 4% of the closure density of the Universe" as well.

I don't believe that your 4% "ordinary" matter number is accurate, because that is all that BBN predicts. 100% of the matter that comes out of BBN theory is directly related to baryonic matter. To be honest however, I haven't really sat down to figure out the density of baryonic mass in a MOND theory probably because I'm not that attached to MOND theory. Do you have a published and peer reviewed reference that verifies that statement about a 4% figure?

To change the 4% closure density of baryonic matter and arrive at the correct amount of helium, you have to change the R(t) of the universe during those first three minutes.

Those first three minutes should have been pretty uneventful based on standard GR theory. The mass density of the singularity would have been enormous. Nothing should have escaped that gravitational well. It's is only when you begin by slapping inflation theories into this mix that any sort of "density' calculation might be possible. How did you arrive at an energy density of baryonic matter based on *standard* (non-metaphysical) physics without the whole thing imploding in the first second?

This might be possible if a form of DE was dominant then, however that would change the other trace element abundances.

Garth

Well Garth, I suppose anything is possible. I've never seen any evidence for DE either, so IMO that's just another gap filler to prop up an otherwise failed gravitational theory. GR theory as Einstein practiced it, and taught it, was really a theory about the *attraction* force of matter. Einstein himself regretted ever trying to "complicate" a GR theory of attraction with a constant. He called that introduction of a constant his greatest blunder. GR works perfectly to describe gravitational attraction. Any external force of nature that moves physical bodies would likely take on properties that are directly related to that specific force of nature, not that mass body. There is no indication that an attractive force of nature has anything at all to do with acceleration. EM fields can describe an acceleration processes in plasma bodies without resorting to any sort of metaphysics. IMO DE is just as "out there" in metaphysicsville as DM theory, perhaps even more so.

When I took physics classes in college, we talked about various forces on objects and the effect that these forces of nature had on objects. I never once heard any of professors claim that: "There was no direct force involved in that acceleration process between two objects, the space between the objects is simply expanding and accelerating". While pure expansion can be achieved by "coasting", some physical force would be required to cause the objects to accelerate away from one another and some physical force would need to keep them from attracting one another and causing the expansion rate to decrease over time.

You would have been laughed out of class for claiming that there was no actual force that relates to GR, and thereby limits the speed of objects to light speed, the "space (however that relates to real physics) between" the objects simply expands at unbelievable speeds! You would have flunked any test on such a topic had you attempted to use that kind of explanation to describe the acceleration of objects.

Ever since Guth's inflation theory became 'all the rage' in astronomy, it has become more and more acceptable to stuff metaphysics into math formulas. Prior to Guth's metaphysical inflation theory, metaphysics was frowned upon. IMO it should still be frowned upon. I have no faith in inflation, I think Guth made it up in his imagination. I also have no faith in DE or DM, and I'm certainly not alone in that skepticism of the growing reliance upon metaphysics in modern astronomy:

http://cosmologystatement.org/

I think that the older generation tends to be a bit more skeptical about these types of theoretical approaches to science. Plasma physics branches of science tend to be far more interesting to me, and far more useful IMO because the ideas that come from these branches of science can be tested in controlled conditions. I've never seen anyone come up with a 'controlled' non-baryonic matter test. I've never seen anyone come up with a controlled DE test. I've never seen anyone come up with a controlled inflation test. These are all mathematical constructs that do not seem to have any relationship to anything that actually exists in nature.

 

[Michael Mozina]

I don't see why you would expect to have seen empirical evidence of direct detection of non-baryonic "dark matter".

I expect to see empirical evidence of every claim eep. That's what separates science from pure faith.

CDMS and presumably Liquid Xenon are *just now* starting to get enough detector mass to perform a search in the heart of the WIMP parameter space. It's foolish to stop looking for something before you look where you expect to find it.

While I absolutely agree with you that it would be foolish for us to stop looking for something before we look where we expect to find it, but we have already looked for it and we didn't find it.

http://xxx.lanl.gov/PS_cache/arxiv/pdf/0711/0711.0053v1.pdf

8.1 WIMP searches

We have performed searches for WIMP annihilations in the center of the Earth,
Sun and Galactic Center using upward through-going muons [7]. Here we
repeat the same search using upward showering muons. The cone size which
contains most of the WIMP signal is inversely proportional to the WIMP
mass. Since only high-mass WIMPs produce upward showering muons, we
perform these searches in cones only up to 5◦. Such a cone contains 90% of
the signal for a WIMP of mass 1438 GeV from the Earth and 1000 GeV from
the Sun and Galactic Center [7]. The observed data and expected background
(evaluated in the same way as in Ref. [7]) are shown in Table 2. Since, there
is no statistically significant excess in any of the search cones, we do not see
any evidence for WIMP-induced upward showering muons in our dataset.

They didn't find any point sources in the high energy neutrino data. What do we do now? How long do we keep looking for something that may not even exist? Why am I personally obligated to put faith in WIMP theory when it has already failed at least one critical observationally oriented "test", and there is no empirical evidence to support SUSY particle theory in general? I guess that is the real dilemma for me. I simply can't find it in me to put faith in any idea that sounds remarkably like 'dogma' and lacks empirical support. The skeptic in me just cringes.

 

[EL]

M.M., our discussion is leading nowhere. It seems you cannot differ between a suggestion (hypothesis) and a claim. As soon as anyone suggests that WIMPs may solve the dark matter problem you say something in line with: "How can you suggest that when we don't know that they exist". Once again, no one claims that WIMPs is the solution. WIMPs is a suggestion, just like MOND is. What we are discussing here is which one we find being the best suggestion.

I'll try to do a (last) summary:

There are astronomical observations which cannot be explained by known physics (GR + Standard Model).

There are two suggestions that (at least at first sight) makes some sense:
* Adding more parameters to our model of matter (i.e. extending the Standard Model)
or
* Adding more parameters to our model of gravity (i.e. extending General Relativity)

At this stage both attempts are on pretty equal footing. We could just try a number of ad hoc particle models, or a number of ad hoc MOND models, just with the intention of fitting the cosmological data. However, if we cannot find any other reasons for those extensions, they are both pretty much curve fitting.

Now, there are hints completely unrelated to cosmology whispering about the need to extend the Standard Model, namely the so called "hierarchy problem". In order to solve this "hierarchy problem" there need to exist new particles with certain properties not far above the electroweak scale. Now, by a coincidence, it turns out the kind of model needed for the solution of the hiearchy problem, also provides a good dark matter candidate. (I.e. when doing the calculations one sees that this particle automatically would leave a relic density of the order needed to explain the dark matter.)

Even if you do not agree with that such a "unification" is a good motivation for WIMPs (although I actually cannot see how one don't find such a "unification" appealing), that does not mean that WIMPs are less motivated than MOND; instead they are simply back on the same footing (i.e. more or less just a curve fitting).

Let's for a while pretend that WIMPs were not motivated by any particle physics arguments. How could we then determine wheter WIMPs or MOND is the best attempt?
Well, we simply have to construct models of both kind and try to fit the cosmological data.
As it has turned out, WIMPs are much more succesfull in fitting the data than MOND.
So, even if based only on its "curve fitting ability", WIMPs defeats MOND.

Add to that the "unification" argument and the WIMPs gets an even bigger lead.

With this I am not saying that WIMPs is the solution. I am neither saying that modified gravity cannot be the solution. All I am saying is that I find WIMPs a much more promising solution than modified gravity. (So don't try to make any more straw-men out of this.)