Fermi and dark matter

Michael Mozina rocks = dark matter idea (Question 3)

Michael Mozina said:

RC, you simply do not need any "special/exotic" kind of matter to be present in these regions. All you need is ionized and non ionized particles spread out heterogeneously. In no way is Occum going to be kind to your claim of a need for 'special' matter. All we need is 'dusty plasma", "clumpy" non ionized particles and some ordinary rocks distributed in a heterogeneous layout. There is absolutely *NO* need for 'exotic matter' to explain why some material "passes through" and why some matter interacts. The whole mainstream position is based upon the argument of "we can't figure it out, therefore exotic matter did it".

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Wrong. The whole mainstream position is based upon the argument of "we can figure out what normal matter (in various configurations) would do and this does not explain the observations. Thus it is not normal matter.".


'Dusty plasma" and "clumpy" non ionized particles will act just like the ICM plasma. This has been covered before. All particles in the ICM have a mean free path of about a lightyear. This means that a particle (ionized or not) will collide about 3 million times to pass through 1 megeparsec of the ICM (a typical galactic cluster diameter). The particle will

• Slow down.
• Heat up and emit light.

Dark matter is observed to not slow or emit light as you may know.

Rocks are a really bad idea that is easy to rule out: Michael Mozina rocks = dark matter idea (reposted since you seem to be ignoring the questions in it )

And now let's get really, really local:

First asked 13 November 2009
Astronomers have measured the distribution of matter in galactic clusters using gravitational lensing. This distribution has a massive, roughly spherical background (dark matter) with the spikes of galaxies poking out from the background.

Dark matter is present everywhere. This includes inside galaxies. This includes inside the Milky Way. This includes inside the Solar System . Thus there are experiments in labs here on Earth trying to detect dark matter with one lab reporting success (but this is contested).

We can ignore the rocks in the asteroid belt (they formed with the Solar System).


Michael Mozina:
Why have astronomers not found enormous numbers of rocks

• Passing through the Solar System?
• Floating in interstellar space?

DazzaD said:

Ahh.. thank you... beat me to it.

That is why I raised the issue.

The "existence or nonexistence of monopoles" requires Maxwell's equations to be "rewritten" just in the same way that the "existence or nonexistence" of dark matter requires the general relativity solutions to be modified to take that into account (in fact the "rewriting and redoing" for the monopoles is actually a damn sight easier with less things that can affect it, yet MM doesnt seem to be overly worried about that compared with the issue in this thread, and yet it hits at the heart of his preferred explanation).

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You might elaborate here for me a bit because your argument seems completely illogical from my perspective. I guess I'm missing something.

It seems to me that what you're doing is saying *if* x exists *then* we get to rewrite the laws of physics another way. Well.....ok.....but do you have any evidence x exists or that the laws of physics as we understand them are flawed? "Right now" we have no evidence that "laws" of physics work differently than they do, or work differently "out there somewhere" than they do right here on Earth.

Gamma rays come from discharges in the Earth's atmosphere and have been seen by Fermi. Even annihilation signatures specifically have been seen by Fermi due to discharges in the Earth's atmosphere. The discharge process is a known and "natural' source of annihilation wavelengths. The sun is also a "known and natural" source of gamma ray and specifically annihilation wavelengths. I even provided you folks with an extremely impressive (to me at least) paper with all sorts of mathematical support that demonstrates that binary stars can explain an excess of annihilation wavelengths.

As I see it there is absolutely no need whatsoever for any sort of 'exotic' matter to explain gamma rays in Fermi images. The same laws of nature apply to planets and suns in our galaxy and universe as apply to the Earth and our own sun. Binary stars might be able to produce "extra" gamma rays if we need them. There is *absolutely no need whatsoever* for any form of exotic matter to explain gamma rays in a Fermi image. We have all the math, physics and "natural sources" of gamma rays that we need to explain virtually any quantity of gamma rays from a galaxy. Occum is not going to be kind to any sort of theory that requires "exotic" variables in terms of explaining gamma rays in space. In fact Occum's razor is going to slice it and dice it and cut it to shreds. Even Alfven's "prediction" of an "ambiplasma" separating matter from antimatter isn't as "simple" to explain as what is already available to us today.

Ok, sure, 'monopoles' and unicorns may exist, "magnetic reconnection" may not be "pseudoscience* in spite of Alfven's protestations, and "dark matter' might emit gamma rays for breakfast. Anything and everything is "possible".

Empirical physics however deals with what "is known empirically" to work in a lab. There are ample empirical tools at our disposal to explain gamma rays in space that do not require any leaps of faith whatsoever. Why would we even consider *any* theory that introduces a variable (be it a monopole or dark matter) that lacks empirical support when we already have "better" empirically demonstrated options on the table, math, physics and everything?

Sure "laws" of physics might fall in the future, but then they have already stood the test of time. I'll assume the absence of monopoles and unicorns until I see them running through my backyard, or at least I see some valid empirical evidence.

I thought it prudent to point it out because we are in a dodgy position if we have argued that our "knowledge of x precludes y" if in fact precluding y was a vital step in reaching x in the first place.

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Our knowledge of natural sources of gamma rays does not preclude there from being another "possibility". It doesn't make much sense however to simply abandon what is known to work in nature in favor of an act of pure faith on the part of the "believer" in the complete absence of empirical support.

That is why scientists are actually being very open minded and sensible about allowing (possibly, until you can convince them otherwise) for the existence of dark energy and dark matter.

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There's a difference between being "open minded" and being "gullible". If I need to explain an "acceleration" of plasma, "electricity" is likely to be my first choice. If I need to explain gamma rays, "electricity" is again my first choice. If I need to explain something that I cannot explain, I don't automatically assume that the laws of physics need to change. I typically assume that I need a "better" scientific understanding of the problem and more information.

Rocks are a really bad idea that is easy to rule out: Michael Mozina rocks = dark matter idea (reposted since you seem to be ignoring the questions in it )

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I went ahead and did a calculation: how collisionless would "rocky" dark matter be?


That calculation is done for the Earth's "local" dark matter: isotropic 220 km/s orbits through a 0.3 GeV/cm^3 mean density. I gave it 5g/cm^3 density, somewhere between stone and iron.

Look at those numbers. If you built the Milky Way using Volkswagen-sized rocks as the dark matter, they'd last four thousand years between collisions; they'd be dust and plasma. Use 500 m asteroids, they'd last a million years before colliding and pulverizing. (Remember, these are 220 km/s collisions; they make Shoemaker-Levy look wimpy.) A 10^6 m planetoid could last for a gigayear---at least that survives a full Galactic orbit!---but at that point we're into the stuff that the EROS surveys have ruled out. Sub-meter-scale dust, of course, is not collisionless at all which is why it's never been even in the ballpark of viable dark matter candidates.

MM might object to these numbers all being so small: how has Earth survived for 4 Gy, he might ask, if Earthlike objects are supposedly so collision-prone? The answer is twofold: (a) dark matter is much DENSER than regular matter. The number density of actual rocks/planets/Earths is much, much lower than the number density I need to hypothesize to make them dark matter. (b) Dark matter is isotropic---it seems to orbit the Milky Way in a spherical halo, which implies orbits that intersect one another all over the place. The Earth (and most of the Galaxy's baryonic matter) is in the Galactic Disk, where intersections are much, much sparser than those in the halo.

Conclusion: rocks cannot be dark matter. Anything small would be highly collisional, and could not possibly remain "rocky" in a dense halo full of other rocks. Anything large would have been seen by EROS. The two ranges overlap generously.

Reality Check said:

Wrong. The whole mainstream position is based upon the argument of "we can figure out what normal matter (in various configurations) would do and this does not explain the observations. Thus it is not normal matter.".

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No RC, you *DID NOT* figure it out, so you stuffed the gaps of your own ignorance with an "exotic" form of "dark matter"! You didn't even *TRY* to figure it out before LEAPING to the conclusion that your plasma body is homogeneously distributed, 99% ionized, and without any form of "clumpy" matter at all! You aren't open to any criticism. You aren't listening to reason either. Nobody is claiming *ALL* the matter is made of rocks or MACHOS. That is your own pathetic strawman RC. The plasmas of the ICM are "heterogeneous", "dusty" and include normal material objects galore of every shape and size. When you add them all together, some of them "pass through", some of them "slam together" and all it combined adds up to the total mass we're looking for. As long as you resist *ANY* sort of alternative explanation for matter that "passes through" the collision process, you only make yourself look bad IMO.

Never once did you even offer me a source for your 99% ionization claim. Not once did you offer me a legitimate "bone" in terms of "giving an inch". Pretty much everyone else in this conversation has been more open to alternative than you. Why is that? Are you so afraid of questioning your own beliefs that you can't consider alternatives?

ben m said:

I went ahead and did a calculation: how collisionless would "rocky" dark matter be?

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Woah! I never claimed even a majority of the missing mass was found in "rocks". That might account for a small portion of the mass whereas the heterogeneous layout of "dusty plasma" may be responsible for the vast majority of the matter that "passes through" the collision. I have no idea where all the "missing mass" is located, but I also have no evidence whatsoever from these lensing studies that any of that missing mass is found in any form of exotic matter. Frankly I am *A LOT* more worried about your "assumptions* about ionization rates and the overall layout of material than I'm worried about rocks.

Michael Mozina said:

Woah! I never claimed even a majority of the missing mass was found in "rocks". That might account for a small portion of the mass whereas the heterogeneous layout of "dusty plasma" may be responsible for the vast majority of the matter that "passes through" the collision. I have no idea where all the "missing mass" is located, but I also have no evidence whatsoever from these lensing studies that any of that missing mass is found in any form of exotic matter. Frankly I am *A LOT* more worried about your "assumptions* about ionization rates and the overall layout of material than I'm worried about rocks.

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I just showed you that dust doesn't pass through. The mean free flight time of sub-meter dust, IF there's enough of it to make up the dark matter halo, is measured in years---look at the early entries of the table. It orbits a short distance and then it collides. The collisions (a) make it NOT neutral dust anymore, they make it a hot plasma which is trivially visible in both absorbtion and emission. (The mean collision kinetic energy is over 200 eV per nucleon, far above ionization energies.) The collisions (b) remove material from halo orbits and drop it into non-intersecting disk orbits. Dark matter is not in the disk, it's in the halo.

Don't like my assumptions? Propose your own. Can you find *any* configuration of dust, rocks, and planets which can peacefully fill the Galactic halo for more than a gigayear or so?

Michael Mozina said:

I have no idea where all the "missing mass" is located, but I also have no evidence whatsoever from these lensing studies that any of that missing mass is found in any form of exotic matter

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This is a problem. You're not willing to think very hard about what it would mean for the missing mass to be regular matter, but you want to assume that it will work out somehow. Why? Because you intuit that such a working-out must be more plausible than the 70-year-old 70s-vintage idea that there must be particles beyond the Standard Model.

You do have to think about it a little bit. Dust---even ice-cold neutral dust with no IR emissions---is still a light absorber. The Milky Way's halo is not opaque---there are not even substantial opaque spots in it (whereas there are in the disk, due to real dust: http://apod.nasa.gov/apod/ap041219.html) Where, MM, are your denser dust clouds hiding?

Do you have some dust/rocks configuration in mind---anything at all---that you think looks like the actual Milky Way halo?

• Not opaque
• Not glowing
• Dynamically long-lived despite the intersecting nature of halo orbits[/I]
• total mass of ~1 trillion solar masses?
• No more than 8% of the mass in Moon-sized or larger bodies

Michael Mozina said:

No RC, you *DID NOT* figure it out, so you stuffed the gaps of your own ignorance with an "exotic" form of "dark matter"!

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No MM , you *DID NOT* figure it out, so you stuffed the gaps of your own ignorance with an "exotic" form of "normal matter"!

I *DID NOT* figure it out is right. I am not an astronomer. Thus I have to rely on what actual astronomers state. As far as I can tell, the consensus in the scientific community is that the Bullet Cluster, MACS J0025.4-1222 and Abell 520 obervations deomstarte that most of the ICM is not normal matter.

Michael Mozina said:

You didn't even *TRY* to figure it out before LEAPING to the conclusion that your plasma body is homogeneously distributed, 99% ionized, and without any form of "clumpy" matter at all!

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I did *TRY* to figure it using my general knowledge of physics.

• I never claimed that the ICM is homogeneously distributed.
• I never claimed that the ICM is exactly 99% ionized. I stated that 99% could be the mostly ionized part of the ICM as in:

  In astronomy, the intracluster medium (or ICM) is the superheated gas present at the center of a galaxy cluster. This plasma is heated to temperatures of between roughly 10 and 100 megakelvins and consists mainly of ionised hydrogen and helium, containing most of the baryonic material in the cluster. The ICM strongly emits X-ray radiation.

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• By definition the ICM is without any form of "clumpy" matter at all. It is a plasma consisting of gas.

I know that intracluster space contains stars.
I know that intracluster space will contain rocks and "clumpy" matter from the intracluster stellar systems and possibly pulled out of galaxies.

Michael Mozina said:

You aren't open to any criticism. You aren't listening to reason either. Nobody is claiming *ALL* the matter is made of rocks or MACHOS. That is your own pathetic strawman RC. The plasmas of the ICM are "heterogeneous", "dusty" and include normal material objects galore of every shape and size.

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I know that you are not claiming that.
You are still displaying your ignorance that the ICM by definition is a plasma.

The "normal material objects galore of every shape and size" are not part of the ICM. They are in intracluster space that includes:

• The ICM.
• Intracluster stars.
• Intracluster rocks.
• Intracluster dust.
• etc.

Michael Mozina said:

When you add them all together, some of them "pass through", some of them "slam together" and all it combined adds up to the total mass we're looking for. As long as you resist *ANY* sort of alternative explanation for matter that "passes through" the collision process, you only make yourself look bad IMO.

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Any "lumpy stuff" will pass though. I know that. You know that.

What you cannot grasp is that all of the plasma that is the ICM in the colliding clusters in the observations of the Bullet Cluster, etc. has collided, heated up, formed shock waves and slowed down. This is what normal, electromagnetically interacting particles do whether ionized or not. So all of the normal matter in the ICM is in the central blob - except for the few stray atoms from the ICM that somehow managed to avoid millions of collisions.

That leaves your intracluster "lumpy stuff" to form the outlying blue blobs.
These blobs are 40 times more massive than the galaxies in the clusters. These blobs are 6 times more massive than the ICM in the clusters.
The issue is not the existence of "lumpy stuff" We know that there are intracluster stars and they are "lumpy stuff".

The issue is: Is there enough of this "lumpy stuff" to account for the mass in the blue blobs?

We can rule out most "lumpy stuff" to leave rocks and black holes and the questions that you are ignoring.

Astronomers have already ruled out MACHOs (one form of "lumpy stuff" according to MM) as a significant part of dark matter. They can be at most 8% of the dark matter in a galaxy.

Intracluster space contains the ICM. It also contains intracluster stars, planetary nebulae and globular clusters that are likely to have been removed from galaxies by gravitational forces. These visible intracluster objects emit 10-20% of the stellar light. Being charitable this is 20% of the mass of a galaxy.

So far we have "lumpy stuff" giving 0.28 of a galaxy per visible galaxy - only 39 galaxies to go!

Maybe "lumpy stuff" is dust? But Far-Infrared Emission from Intracluster Dust in Abell Clusters has measured no dust in 5 clusters and a low inferred dust mass in another.

That leaves the other candidates that MM has mentioned for "lumpy stuff": rocks and black holes.

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• Michael Mozina rocks = dark matter idea
• Michael Mozina rocks = dark matter idea (Question 3)

I would like to point out, for clarity, that RC is citing constraints on the dark matter in galaxy clusters and I am citing constraints on the dark matter in galaxies themselves.

Personally, I chose to use the Milky Way halo only because I work in the field and have more of the relevant numbers at my fingertips. The same general calculations (opacity or lack thereof, collision rate, etc.) can of course be done for the galaxy cluster dark matter.

Reality Check said:

What you cannot grasp is that all of the plasma that is the ICM in the colliding clusters in the observations of the Bullet Cluster, etc. has collided, heated up, formed shock waves and slowed down. This is what normal, electromagnetically interacting particles do whether ionized or not. So all of the normal matter in the ICM is in the central blob - except for the few stray atoms from the ICM that somehow managed to avoid millions of collisions.

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A correction: The Wikipedia article on the intracluster medium states that the mean free path of the ICM particles is "roughly 10¹⁶ m, or about one lightyear". But a light year is 9.461×10^15 m. Thus 10¹⁶ m is nearly 10.57 light years. Thus the above particles would be experience hundreds of thousands of collisions.

ETA
Since the article got the conversion from meters to light years wrong, I went looking for a better source of information. I found a couple of PDFs that look more trustworthy:
The Intracluster Medium
Gas Dynamics in Clusters of Galaxies
and give an actual equation: Mean free path = 23 kpc (T/10⁸)² (n/10^-3 cm^-3)^-1
Thus a typical ICM particle has a mean free path of 23 kpc. This is 1% of the usual scale of galactic clusters (~2 Mpc) or 2% if we keep with the 1 Mpc scale that I have been using based on the Bullet Cluster observation. That implies to me that the dark matter blobs could include as much as 2% from the ICM plasma. In other words the contribution from the ICM is insignificant.

In fact even if all of the ICM ended up in the dark matter blobs (it does not!), the contribution would still be minor. Someone would still have to find ~33 galaxies worth (for each visible galaxy) of "lumpy stuff" to make up the observed mass in the dark matter blobs.

Reality Check said:

A correction: The Wikipedia article on the intracluster medium states that the mean free path of the ICM particles is "roughly 10¹⁶ m, or about one lightyear". But a light year is 9.461×10^15 m. Thus 10¹⁶ m is nearly 10.57 light years. Thus the above particles would be experience hundreds of thousands of collisions.

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Check your math---10^16 meters is 1.057 light years. Same conclusion, though.

Michael Mozina said:

You might elaborate here for me a bit because your argument seems completely illogical from my perspective. I guess I'm missing something.

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Ok. I will have a go.

My point is that you seem to insist on having "something in your hand" before you are willing to believe it and that you insist that the "current laws" are enough to explain the effects, or at least we shouldnt be looking to expand on those laws and theories just yet.

But...

You may have been misinformed about these "laws and theories".

Maxwell's equations, as you may have seen them and been taught them, are in fact a "bodge job" if you will to fit the observation that at THAT time magnetic monopoles were not seen to obviously exist in abundance.

The simple fact is that if you accept that they are an excellent description of "all things magnetic and electric" then you have to accept that in their proper form they allow for the magnetic monopoles, in fact some might say even demand them.

For instance, if just a single monopole exists, and you trust that Maxwell's equations are valid, then ALL electric charges MUST be quantised. Which they are.

My point is that just arbitrarily throwing away monopoles seems to be doing the same thing that you criticise other people for when they refuse to throw away, say dark energy.

One might oversimplify the problem and say that the cosmological constant, which again is something that can be added to the equations describing general relativity (but which wasn't originally because it didn't seem to fit what they observer or what they wanted to observer back then) can "explain" why dark energy may exist.

For me the two situations are analogous.

With your favoured theory heavily based on electromagnetism you outright refuse to entertain the possibility of a magnetic monopole which is a perfectly valid predication of a theory that is amazingly successful in so many other ways. I find it hard to justify such picking and choosing. One might be crass and say that "absence of evidence is not evidence of absence ".

I brought it to your attention in the hope that you might begin to understand why cosmologists are willing to entertain such seemingly strange ideas as dark energy, precisely because they are so rooted in what is actually really going on.

If we were to go round using the simplified set of equations for electromagnetism that you see in undergraduate courses you would achieve an awful lot in physics but you would never understand the concept and problem of magnetic monopoles.

Similarly for general relativity. And particle physics. And the structure and evolution of stars. etcetc.

I just think that were we to fall into that rut we would never really have been willing to entertain ideas such as special relativity.

Ok, sure, 'monopoles' and unicorns may exist, "magnetic reconnection" may not be "pseudoscience* in spite of Alfven's protestations, and "dark matter' might emit gamma rays for breakfast. Anything and everything is "possible".


Sure "laws" of physics might fall in the future, but then they have already stood the test of time. I'll assume the absence of monopoles and unicorns until I see them running through my backyard, or at least I see some valid empirical evidence.

Michael Mozina said:

There's a difference between being "open minded" and being "gullible". If I need to explain an "acceleration" of plasma, "electricity" is likely to be my first choice. If I need to explain gamma rays, "electricity" is again my first choice. If I need to explain something that I cannot explain, I don't automatically assume that the laws of physics need to change.

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There is indeed a difference. But the key thing is, do you truly think that cosmologists as a whole are being gullible in this case?

What I tried to explain above is that cosmologists first line of attack is NOT to change the laws of physics, that is exactly what I am arguing against! Yet I think you may have misunderstood or I may have misrepresented myself.

Michael Mozina said:

I typically assume that I need a "better" scientific understanding of the problem and more information.

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That is an excellent soundbite but it means nothing in a practical sense.

If we are completely unable to explain away an effect using all known physics, and if the experimental evidence says that no matter what version of this theory you use you cannot account for the whole effect, we are left with the dramatic but necessary conclusion that we need a serious rethink.

I thank RC and others in this thread for patiently pointing out the issue raised originally and I apologise for this sidetrack.

I too would like to see a detailed response to RC's last few posts as he seems to raise a few simple but interesting questions about the nature of the matter within the ICM.

DazzaD I have to say you are a welcome addition to the forum, having followed these threads since BAC and the BiG Bang thread this is common to many many many of these threads in SMT.

MM carries the whole 'empirical' testing to a whole new level and then engages in special pleading when it comes to nutrinos, mesons and Yukawa particles, but then so did BAC.

Now MM has learned from the experience here, the posts are a little more careful in their construction.

But the data do not matter, it is the ideas and rather obsessive. Good luck, I have engaged in the same topic and have about twenty others.

DazzaD said:

Ok. I will have a go.

My point is that you seem to insist on having "something in your hand" before you are willing to believe it and that you insist that the "current laws" are enough to explain the effects, or at least we shouldnt be looking to expand on those laws and theories just yet.

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Well, technically I will require some sort of "empirical support" to actually "believe" that something exists in nature. That does not mean that I will not entertain 'possibilities' which lack empirical support at the moment.

If however I am asked to "rank" or "judge" these various ideas, any "empirically viable" solution is going to be a "better" option than one that is based upon pure speculation about what *might* exist in nature.

In some instances that may not be possible. In other words, there may be no "natural" explanation based on empirical physics. The neutrino is an excellent example. There simply was no known particle, at that energy state, to explain "missing energy' from "controlled experiments". That kind of scenario does tend to suggest that there is "something new" to discover. Without "natural" options to choose from, a "new" idea makes a lot of sense.

In other cases, such as gamma rays seen in Fermi images, there are ample "natural" sources of gamma rays and other 'natural' solutions to this problem. There is no need to introduce another variable to explain gamma rays from our galaxy in any quantity. Occum's razor arguments now apply to this issue, unlike the neutrino scenario. I no longer need anything 'new' to explain what we observe. There could be multiple 'natural" solutions that I will have to choose from, all of which might be viable. In that case I may have to 'choose between competing empirical solutions'. All such options will necessarily be 'more scientifically attractive" than any options that rely upon 'acts of faith' in a "new" thing.

It's not as though I failed to provide you folks with a natural alternative, or failed to provide you with a "quantified" as well as a "qualified" explanation. I did provide you with a "natural" solution to this "mystery". There is no need to introduce "dark matter" to explain gamma rays in our galaxy. It is an absolutely unnecessary and unsupported assertion. No amount of math is going to "fix" the basic problem. Since there is no need to introduce a "new" variable, and there is no empirical support allowing me to validate the math, it's a nearly completely useless theory IMO. It has no empirical support whatsoever, whereas "electrical discharges" are well empirically supported. I simply see no need whatsoever for any non empirical theory at this point in time because there is a way to explain these observations without introducing any new variable. Occum's razor now applies to this argument.

As I said, there may be cases where there are no valid solutions to the problem using known forces of nature. In this case however, discharges and suns (binary ones as well) are able to 'explain' what we observe. In such scenarios, I have a much tougher time "believing" something else is required, or that something "unknown to mankind" is responsible for these emissions.

In the case of "monopoles", they too are "unnecessary". Electrical engineering is highly advanced to the point of being able to create these computers we're using right now. It works in the lab. Maxwell's equations have been able to "explain" everything we've observed "better than" any other option. *If* someone comes up with a scenario that requires them to exist, and can demonstrate they do exist, then I have a logical reason to "believe" in them. In the absence of such information, I will typically choose to "lack belief" in them. It's nothing personal. It's pure physics.

With your favoured theory heavily based on electromagnetism you outright refuse to entertain the possibility of a magnetic monopole which is a perfectly valid predication of a theory that is amazingly successful in so many other ways. I find it hard to justify such picking and choosing. One might be crass and say that "absence of evidence is not evidence of absence ".

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My "bias" in that case is based upon "empirical physics". That "bias" can be overcome at any point in time by additional evidence. It's not 'set in stone', it's simply rooted in a bias toward empirical physics. That isn't "unusual" in most scenario, particularly when a "natural' solutions is available.

I brought it to your attention in the hope that you might begin to understand why cosmologists are willing to entertain such seemingly strange ideas as dark energy, precisely because they are so rooted in what is actually really going on.

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I can understand them "entertaining" various ideas. In this particular case however, there's no need whatsoever to do that, and no empirical support whatsoever.

There is indeed a difference. But the key thing is, do you truly think that cosmologists as a whole are being gullible in this case?

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Yes, in the case of the Fermi images I certainly do. In fact I would say that their own "anti EU bias" is likely to be the "cause" of that gullibility. It's more like "stubborn gullibility". They don't *want* to accept an "electrical" solution to that observation. They therefore "make up" a half dozen unsupported assertions and expect me to buy the idea. I find that sad and frankly very frustrating.

What I tried to explain above is that cosmologists first line of attack is NOT to change the laws of physics, that is exactly what I am arguing against! Yet I think you may have misunderstood or I may have misrepresented myself.

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Like DD, I'm very happy that you opted to join this conversation. I've appreciated your input and your attitude. You've been highly logical, scientifically oriented, and completely professional. You need however to keep in mind however that I have a very *long* history with some of these folks, spanning many boards over many years. I've seen them in action on many occasions. I've seen their biases, and I've been victimized by those irrational biases.

*IF* their 'first line of attack' was skewed toward empirical physics, they would simply accept that there is a valid "explanation" for these Fermi images and DM is not responsible for those gamma rays. There bias however favors "dark" stuff, and "inflation" and they have a very strong *against* all things with an EU flavor. That is a deadly combo in my experience. They literally reject empirical physics only because they don't "like" that kind of empirical physics. In this case they reject a solution based upon pure empirical physics in favor of a "dark" solution that requires "faith" in their belief system. That is utterly absurd IMO, but I see it happen over and over and over and over again. IMO it's rooted in their dislike of EU/PC theory. Unfortunately for them we live inside an electric universe.

If we are completely unable to explain away an effect using all known physics, and if the experimental evidence says that no matter what version of this theory you use you cannot account for the whole effect, we are left with the dramatic but necessary conclusion that we need a serious rethink.

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Whereas you might have an argument in terms of that lensing data, your argument points out the flaw in the mainstream position and attitude. There *IS* a "natural' explanation for gamma rays in Fermi images. The only reason they don't "like" that solution is that it favors EU theory and does nothing whatsoever to support their beliefs. The launched Fermi with the intent of "finding dark matter". IMO they now see 'evidence' for dark matter in everything they see, regardless of whether or not there are viable empirical solutions to the problem. They are going out of their way to misrepresent and mistreat "science" now only because it doesn't jive with their preconceived intent.

It think it is time to create a new thread.

We seem to be engaged in two different conversations at this point. This thread was specifically intended to discuss the topic of Fermi and whether "dark matter" has anything to do with gamma radiation.

There is also a larger debate taking place about the very existence of "any kind" of exotic matter based on any type of observation, including lensing data. I'm of the impression that this "larger" debate should take place in different thread, and this thread should stay focused on the Fermi data specifically.

IMO I have offered you a valid scientific 'explanation' for the gamma radiation. Discharges in the Earth's atmosphere generate gamma rays every day. Fermi has even seen annihilation wavelengths from such discharges. Our own sun can be clearly observed in the Fermi images. Binary star studies suggest that excess gamma radiation near the core of our own galaxy can be the result of binary star populations. There are "natural" explanations form what we observe in Fermi images, and no sort of exotic matter is necessary to explain these images.

I think I'd like to respond to Ben and RC in a new thread. You'll need to be patient with me today, I do have some work to finish before I can enjoy my weekend.

Michael Mozina said:

There is also a larger debate taking place about the very existence of "any kind" of exotic matter based on any type of observation, including lensing data. I'm of the impression that this "larger" debate should take place in different thread, and this thread should stay focused on the Fermi data specifically.

Click to expand...

It's entirely relevant, when discussing whether Fermi is sensitive or insensitive to a particular dark-matter hypothesis, to establish that everyone knows what the dark matter hypothesis is.

If you want to continue discussing the Fermi data, can you allow for the sake of argument that the hypothesis in question, "dark matter is made of heavy WIMPs with a nonzero annihilation cross section to photons", is NOT RULED OUT BY ANY OTHER DATA, nor by Occam's Razor, nor by particle physics. If you'll accept that, we can discuss the Fermi sensitivity to that hypothesis.

ben m said:

It's entirely relevant, when discussing whether Fermi is sensitive or insensitive to a particular dark-matter hypothesis, to establish that everyone knows what the dark matter hypothesis is.

Click to expand...

Agreed.

If you want to continue discussing the Fermi data, can you allow for the sake of argument that the hypothesis in question,

Click to expand...

For the sake of argument....

"dark matter is made of heavy WIMPs

Click to expand...

This will be considered "Claim A" and B. Wimps exist. They are "dark".

The next assumption/claim is that WIMPS (assuming the are found) are 'long lived'. We'll call that "Claim/Assumption C"

with a nonzero annihilation cross section to photons",

Click to expand...

We'll call that "Claim D".

There's a "Claim E" coming that relates to where the WIMPS are presumably located/concentrated, but that will depend on which gamma rays in particular you are attempting to attribute to these hypothetical particles.

is NOT RULED OUT BY ANY OTHER DATA,

Click to expand...

I agree.

nor by Occam's Razor,

Click to expand...

I disagree. I handed you a perfectly logical "explanation' for gamma rays, and an excess of gamma rays near and around the core that require no 'hypothetical' entities.

nor by particle physics.

Click to expand...

Ok, as long as you agree that WIMPS are a 'theoretical' particle from a 'non standard' branch of particle physics theory. They are not a part of standard theory, and no SUSY particle (or other theoretical particle) has been confirmed to exist. It's not "ruled out' in terms of SUSY theory, but it is not included in standard particle physic theory.

If you'll accept that, we can discuss the Fermi sensitivity to that hypothesis.

Click to expand...

Well, for purposes of the discussion I can agree to pretty much all your assertions with the exception of the Occum's razor debate. That will become important as we review the various claims of your hypothesis, all of which must be 'true' for your theory to work.

You're not catching on to this "hypothesis" thing. The hypothesis is that WIMPs explain the mainstream, gravity-based dark matter observations. That includes their being stable, their being weakly-interacting, and their being where the dark matter is (halos, clusters, galaxy centers) with substructure ("clumpiness" or "cuspiness" are terms of art here) only as allowed by mainstream galaxy formation theory.

That---the whole thing---is the "dark matter is WIMPs" hypothesis.

Let's establish that, can we?

AFTER THAT we can make an additional hypothesis: if WIMPs are out there AND their mass is in range Y and they have a photon-annihilation channel with cross section X then Fermi would see Z. But let's get to that hypothesis/prediction pair after you've understood the prerequisite, please.

And all of that is still totally different from the reverse question: "given that Fermi saw W, what hypotheses are favored?" That is a data-analysis problem and an interesting one, but it's predicated on understanding the hypotheses---which you still don't. Start at the beginning.

ben m said:

You're not catching on to this "hypothesis" thing. The hypothesis is that WIMPs explain the mainstream, gravity-based dark matter observations. That includes their being stable, their being weakly-interacting, and their being where the dark matter is (halos, clusters, galaxy centers) with substructure ("clumpiness" or "cuspiness" are terms of art here) only as allowed by mainstream galaxy formation theory.

Click to expand...

By "catching on", you mean I'm supposed to simply agree with everyone as one "complete package", inseparable, with exactly all the various "properties" you claim, including distribution which "just so happens" to coincide with the binary star populations near the core?

What you're suggesting here Ben includes all the following "assumptions" that are all part of your package 'hypothesis".

A new form of matter exists beyond the "standard" particle physics theory.
This new particle is "long lived" and doesn't deteriorate in say a millisecond.
It only interacts with other matter in the specific way that you claim at the "weak" level of particle physics. It "decay's" in some way that releases both an electron and a positron at whatever rate you evidently are allowed to "postdict" from whatever observation you're claiming they relate to now and into the future.

That---the whole thing---is the "dark matter is WIMPs" hypothesis.

Click to expand...

Just out of curiosity, are you allowed to tinker with any of those variables for any particular observation? In other words, can you assume a different decay rate for various types of observations?

Let's establish that, can we?

AFTER THAT we can make an additional hypothesis: if WIMPs are out there AND their mass is in range Y and they have a photon-annihilation channel with cross section X then Fermi would see Z. But let's get to that hypothesis/prediction pair after you've understood the prerequisite, please.

Click to expand...

It seems as though your "prerequisite" is that I accept a host of "assumed properties", and then you still intend to tinker around with the quantity, location, and that "photon-annihilation channel with a cross section x" variable. Do I understand your 'prerequisite" correctly? Am I allowed to challenge any of the those assumptions independently, or does that simply detract from your argument in a way you find personally offensive for some reason?

And all of that is still totally different from the reverse question: "given that Fermi saw W, what hypotheses are favored?" That is a data-analysis problem and an interesting one, but it's predicated on understanding the hypotheses---which you still don't. Start at the beginning.

Click to expand...

As I see it Ben, "starting at the beginning" means I look for a valid empirical way to "explain" whatever it is I observe. If and only if I can't do that will I typically entertain "exotic" concepts. In this particular case I have shown you evidence that the excess gamma rays we're looking for can be explained by an excess of binary stars in the core, and the shape of that core and gamma ray excess just so happens to align itself pretty well with where we believe such stars are located. Fermi has already confirmed that it can see "stars", including our own, and even annihilation signatures at rate x from planetary discharges. If planets, suns and binary suns can explain what we observe, why do we need an 'exotic' alternative again?

DazzaD said:

You may have been misinformed about these "laws and theories".

Maxwell's equations, as you may have seen them and been taught them, are in fact a "bodge job" if you will to fit the observation that at THAT time magnetic monopoles were not seen to obviously exist in abundance.

Click to expand...

Was Newtonian mechanics a 'bodge job' too once GR became popular?

Hypothetically speaking perhaps (assuming we find monopoles in the future), sure, maybe it's a "bodge job" to lack belief in monopoles. In practical application in the lab however, it's works quite well. In reality it's hardly a "bodge job" to correctly describe and accurately "predict" events in nature. So far those equations correctly describe nature, including the fact that nature does not seem to include any monopoles. I can't spend my life worrying about "what if" scenarios that might invalidate some part of my "empirically oriented belief system", I can only concern myself with the here and now and apply what I know (empirically) here and now to the topic at hand, in this case gamma rays seen in Fermi images.

It just so happens that nature does a wonderful job of emitting gamma rays via discharges on Earth and it produces them in the atmosphere of our own sun. We observe annihilation processes here on our own planet in the Fermi equipment. We observe them from our own sun in the Fermi equipment too. It's therefore not much of a "leap of faith" for me to believe that binary stars emit these same gamma rays in greater quantity due to their unique interactions. Nothing proposed in the explanation I offered you requires the existence of anything new "exotic'. It's a "simple" and elegant solution to explain those gamma rays.

We can take such an understanding now and apply such an understanding to distant galaxies as well and learn something about them from what we've learned from our own galaxy.

If however you (collectively speaking) wish to promote an alternative explanation, should it not be able to compete empirically with another empirical alternative? I mean sooner or later we may have to 'grade' these various proposals and "empirical qualification' has to count for something. When and where is it appropriate to apply Occum's razor if not to this specific scenario? If empirical physics can explain what we observe, why wouldn't it be considered a "superior" theory to one that is based on hypothetical entities a half dozen hypothetical "properties", none of which enjoy empirical support?

Michael Mozina said:

What you're suggesting here Ben includes all the following "assumptions" that are all part of your package 'hypothesis".

A new form of matter exists beyond the "standard" particle physics theory.
This new particle is "long lived" and doesn't deteriorate in say a millisecond.
It only interacts with other matter in the specific way that you claim at the "weak" level of particle physics. It "decay's" in some way that releases both an electron and a positron at whatever rate you evidently are allowed to "postdict" from whatever observation you're claiming they relate to now and into the future.

Click to expand...

The observations of dark matter mean that we know a lot of its properties. This means that we can make hypotheses about what would have those properties. The hypotheses can then be tested by further observations. This is a basic part of the scientific method.

As Ben said dark matter has a a set of observed properties. The list below is quoted from Ethan Siegel's blog article What is Dark Matter?

1. It isn't in dense clumps. Not faint, dark stars, not planets, not basketballs, and not gas and dust. We've already gone over that it can't be normal matter, but it also can't form structures the same way that normal matter does.
2. It doesn't interact with itself. Yes, it interacts gravitationally, but that's not what I mean. It doesn't feel the strong nuclear force, it doesn't feel the electromagnetic force, and if it feels the weak force, it feels it even more weakly than neutrinos do! (And you need about a light year of lead to stop your typical neutrino.) As a result of this, dark matter is incredibly fluffy and diffuse, which means even in our Solar System, by the heart of our galaxy, dark matter's effects are negligibly unobservable.
3. These dark halos form very early. This is very important. Looking back as far as we can see, we find that these diffuse collapsed structures have been around for pretty much the entire history of the Universe. This tells us that the dark matter is cold, or that its kinetic energy has pretty much always been much, much less than its mass. This rules out every single standard model particle that we know of from being dark matter, since the stable ones are relatively light and are all produced hot.

Click to expand...

I will add point 3 to the list of problems with your "lumpy stuff" idea (even though "lumpy stuff" is ruled out by point 1).

Ethan Siegel goes on to list three candidates that meet the crteria for dark matter:

1. WIMPs
2. Cold massive particles like axions
3. Something even more exotic.

An additional hypothesis is that the WIMPs either

• decay with a long lifetime or
• annihilate.

IMO: This is a reasonable hypothesis beacuse we know of particles that decay with various lifetimes and there is no reason to suppose that WIMPs do not have anti-particles or are their own anti-particles, e.g. the neutralino found in SUSY theories.

If this additional hypothesis is correct then dark matter will emit gamma rays that can be detected. The detection of these gamma rays shows that if we eliminate all known sources of gamma rays then the gamma rays are from an unknown source of gamma rays. That unknown source may be dark matter.

Michael Mozina said:

Was Newtonian mechanics a 'bodge job' too once GR became popular?

Click to expand...

No...

but then I am not seriously suggesting that because Newtonian mechanics has served us so well for hundreds of years we shouldnt ever look for an alternative explanation to that experimental stuff we see, that we should be seeking ways, forever and a day, to try and explain that stuff using just Newtonian mechanics.

This is exactly my point.

Michael Mozina said:

When and where is it appropriate to apply Occum's razor if not to this specific scenario? If empirical physics can explain what we observe, why wouldn't it be considered a "superior" theory to one that is based on hypothetical entities a half dozen hypothetical "properties", none of which enjoy empirical support?

Click to expand...

Can I just point out that Occam's razor is not a "rule" in science.

In any case, it should only be used to make a judgement when "all other things are equal".

In this case plasma cosmology and the mainstream explanation (say a variant of lambda-cdm) are NOT equal. Not by a long shot.



Please note, that in pretty much all my posts I am talking generally, I am NOT specifically referring to the Fermi results on gamma rays and their possible explanation as possibly being evidence of a possible dark matter distribution.

DazzaD said:

Can I just point out that Occam's razor is not a "rule" in science.

Click to expand...

Well, let me ask you a "philosophical" question then about "science". When is it appropriate to choose/favor a solution that is based upon pure empirical physics vs a pure act of faith?

IMO this Fermi thread is pretty much a "classic" example of this specific bias playing out at the microscopic level of cosmology:

In this case plasma cosmology and the mainstream explanation (say a variant of lambda-cdm) are NOT equal. Not by a long shot.

Click to expand...

When you choose "equal", how exactly do we "compare" theories? IMO even if we put "qualification" on an equal footing with "quantification', there's no logical way to claim that exotic forms of "dark matter" had anything to do with gamma rays that have been seen in Fermi images, or cosmology in general.

In fact the mainstream seems to be going out of their collective way to *NOT* mention the fact that "electrical discharges" are the likely source of the bulk of these emissions. Instead we're seeing a "leap of faith" into a pure theoretical construct related to 'dark matter', and no mention of the fact that planets and suns are the most likely 'source' of these emissions. It's not even logical IMO.

In any case, it should only be used to make a judgement when "all other things are equal".

Click to expand...

Well, they aren't even "equal" yet. I've provided a mathematically supported paper that links these gamma ray excesses that have been attributed to "dark matter" in some papers to "binary stars". Which is a more "logical' solution here?

Even if quantification only counts as say a single point, I've handed you a 'slam dunk' that includes mathematical explanations as well visual (in Fermi images) verification of the fact that planets and suns are "known sources" of gamma rays. It's therefore no "leap of faith' for me to believe that binary stars are 'brighter' and "scattering happens" in a dusty core filled with binary stars.

"Dark matter" isn't even an option because it's purely a mathematical construct. There's no empirical physics whatsoever behind it. It only gets one point for quantification, and no point for qualification. They aren't even "equal" theories yet, it's 2 to 1 in favor of 'discharges".

If you ask me then is "dark matter" a more viable "explanation" than "electrical discharge', my answer is clearly no, certainly no in *this particularly* instance. In this specific instance "electricity in the atmospheres of bodies in space did it" enjoys both mathematical quantification and empirical qualification.

"Dark matter did it" theory will forever remain a "second rate" theory IMO until and unless it ever gains some sort of empirical support. Until that time, it will only ever be able to receive one point of a possible two points on the "qualification/quantification" scales of science.

IMO that is not unlike your monopole example. If and when they can be shown to exist, then it's worth considering them. In the mean time I'm not beholden to explain 'why' they don't exist in nature.

Reality Check said:

The observations of dark matter mean that we know a lot of its properties.

Click to expand...

No you don't. You're making up those properties as you go, just like the "dark matter annihilates to produce gamma rays" claim.

Michael Mozina said:

No you don't. You're making up those properties as you go, just like the "dark matter annihilates to produce gamma rays" claim.

Click to expand...

It is not like "dark matter annihilates to produce gamma rays" claim. That is a hypothesis that may explain a couple of observations (the Fermi haze and the spectrum of gamma radiation).


The observations of dark matter give us its properties:

1. It isn't in dense clumps.
2. It doesn't interact with itself..
3. These dark halos form very early.

These observations of the properties of dark matter allow use to construct hypotheses about what is it. Note the order: Observations -> properties -> hypotheses.

Michael Mozina said:

By "catching on", you mean I'm supposed to simply agree with everyone as one "complete package", inseparable, with exactly all the various "properties" you claim

Click to expand...

If you want to discuss Fermi, then YES---you need to accept that this, this package I describe, is what we call the WIMP hypothesis. You must accept that definition of the hypothesis before you can even know what Fermi is on about. Moreover, to avoid more retreads, I think you should for the sake of discussion allow that this hypothesis is not otherwise ruled out.

If you want to say "that hypothesis is nonsense from the start", then there's no point discussing Fermi at all---in which case I think you need another thread.

including distribution which "just so happens" to coincide with the binary star populations near the core?

Click to expand...

What? Who said anything about that? The Milky Way core is the place where we have the least detailed knowledge of the DM density. Halos and cluster cores are the places where we have the most detailed knowledge. None of this has anything to do with binaries.

Michael Mozina said:

...snip...
In this particular case I have shown you evidence that the excess gamma rays we're looking for can be explained by an excess of binary stars in the core, and the shape of that core and gamma ray excess just so happens to align itself pretty well with where we believe such stars are located.

Click to expand...

Can you give the citations to your source for these statements?
I cannot find them in the thread.

As far as I can see:

• All stars emit gamma rays.
• Fermi detects the gamma rays from the Sun because the Sun is close to us.
• Fermi does not detect the gamma rays from normal stars including normal binary stars because they are far from us, i.e. the intensity of gamma rays is too low to detect.
  For example I can see no mention of Alpha Centauri (a binary star) being a strong gamma ray source.
• If a binary star system involves strong magnetic fields, e.g. one of the pair is a neutron star then it could be a source of gamma rays.
  However I suspect that it will be a point source of gamma rays that can be distinguished from the gamma ray background.

The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze subtracts the 3-month Fermi point source catalog as well as the LMC, SMC, Orion-Barnard’s Loop, and NGC 5090.

This question seems to have been forgotten.

First asked 5 November 2009:

The answer to Can Micheal Mozina answer a simple question? post about colliding blobs is not how astronomers confirmed that the Bullet Cluster, MACS J0025.4-1222 and Abell 520 contain matter that does not interacting electromagnetically like normal matter. The distribution of the dark and visible matter in the clusters was a big clue. The scientific confirmation though is that computer simulations of colliding blobs containing a mixture of normal, gaseous matter and matter that only has gravitational friction show the same properties as in my post:

• The dark matter goes straight through the normal matter.
• The normal matter collides, slows down and heats up.
• As the collision progresses the dark matter emerges from the cluster (the outlying blobs seen in the Bullet Cluster).
• As more time passes the dark matter reverses direction and heads back into the cluster. MACS J0025.4-1222 is just entering this stage while Abell 520 is well into this stage.

See Dark Matter Part 3.5: When Clusters Collide!

Michael Mozina: What is wrong with the computer simulations?

P.S. One result of the computer simulations is the prediction that under the right conditions dark matter will from a ring around the cluster.
Here is a news article (since you like these) about a ring of dark matter:
NASA finds further proof of dark matter
(I really dislike that "proof" word - it should be "evidence").

Now we have four observations or dark matter that agree with it not interacting electromagnetically like normal matter!

Reality Check said:

Can you give the citations to your source for these statements?
I cannot find them in the thread.

Click to expand...

http://www.internationalskeptics.com/forums/showpost.php?p=5294456&postcount=359
http://www.nature.com/nature/journal/v451/n7175/abs/nature06490.html

As far as I can see:

• All stars emit gamma rays.
• Fermi detects the gamma rays from the Sun because the Sun is close to us.
• Fermi does not detect the gamma rays from normal stars including normal binary stars because they are far from us, i.e. the intensity of gamma rays is too low to detect.

Click to expand...

• 
  
  Er, you're now telling me that not just "some" of the gamma rays (the excess) comes from dark matter, but *all* of it? Could you point me to a paper that attributes "all" the gamma rays to "dark matter" rather than simply an "excess" of them?

Michael Mozina rocks = dark matter idea (Questions 4 and 5)

And now back to the galactic clusters!

First asked 16 November 2009
Astronomers have measured the distribution of matter in galactic clusters using gravitational lensing. This distribution has a massive, roughly spherical background (dark matter) with the spikes of galaxies poking out from the background.

IMO: "Lumpy stuff" (rocks and black holes) will not be moving fast. They will especially will not exceed the escape velocity of galaxies. If the "lumpy stuff" formed in intracluster space then it will have roughly the velocity of the cluster. If the "lumpy stuff" formed in the galaxies then there is the problem of extracting it from the galaxies. Collisions can explain the observed intracluster objects such as stars but not enough "lumpy stuff" to match the mass of dark matter.

Galaxies in a galactic cluster move. They will act like vacuum cleaners and collect "lumpy stuff". This means that as time passes the balance between galaxies will shift - galaxies will get heavier and the amount of dark matter will reduce. If enough time passes galaxies will become heavier than the "lumpy stuff" in between them.

Michael Mozina:

Why have astronomers not found seen that galaxies become less dense with increasing distance from us?
Why is the "lumpy stuff" in intracluster space so much of the mass of the cluster when there has been ~13 billion years for the galaxies to vacuum up the "lumpy stuff"?

I started the other thread for you. Feel free to stop hijacking this thread now and please keep this thread "on topic". Got any evidence that "dark matter" emits gamma rays?

Michael Mozina said:

http://www.internationalskeptics.com/forums/showpost.php?p=5294456&postcount=359
http://www.nature.com/nature/journal/v451/n7175/abs/nature06490.html

Er, you're now telling me that not just "some" of the gamma rays (the excess) comes from dark matter, but *all* of it? Could you point me to a paper that attributes "all" the gamma rays to "dark matter" rather than simply an "excess" of them?

Click to expand...

Er, No.
I am saying that the excess cannot come from "binary stars" you have been stating. You do not supply a qualifier so it looks like you are referring to any binary star system. I assumed you meant normal binary stars which is obviously wrong.

The paper states that there are X-ray binaries whose distribution fits the the distribution of gamma rays. The abstract concludes:

Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter.

Click to expand...

So they are stating what has been explained to you many times:
Dark matter might or might not be an explanation for the Fermi data after all of the known sources of gamma rays (including this one) are removed (the Fermi haze).
IOW: Removing the known sources of gamma radiation from the Fermi data leaves the unknown sources, one of which could be dark matter.

No one is stating that dark matter is the explanation for the Fermi haze.

The other paper does what scientists do all the time - it takes an observation and sees if there is a hypothesis to fit it. In this case the observation is the shape of the spectrum of gamma rays from the Fermi data and the hypothesis is that it is caused by dark matter. This leads to a testable, falsifiable prediction that if dark matter is the cause of the spectrum then it must have certain properties. There are ongoing controlled, empirical experiments in labs here on Earth that may confirm or falsify this hypothesis.

Michael Mozina said:

I started the other thread for you. Feel free to stop hijacking this thread now and please keep this thread "on topic". Got any evidence that "dark matter" emits gamma rays?

Click to expand...

OK, so for the purpose of discussion, the dark matter we are looking for is in particular some as-yet-undiscovered stable massive particle.

Various specific hypotheses for the identity of the particle include, by necessity, gamma ray emission in pair annihilation reactions. The details are 100% standard particle physics: just like the hypothesis of the top quark obviously required that it decay into bottom quarks, the hypothesis of the Higgs obviously requires it to decay to the heaviest available particle, and so on. Examples of gamma-predicting hypotheses include SUSY dark matter and Kaluza-Klein dark matter. Each such hypothesis makes a specific prediction about the gamma ray spectrum.

Other hypotheses predict NO gamma ray emission. Examples include axion dark matter and some forms of sterile neutrino dark matter.

Let's see, what do scientists do when they have a hypothesis that predicts something observable? They try to make the observation and see if it confirms or excludes the hypothesis. FERMI is currently making observations. It has ruled out several hypotheses so far. If it sees a convincing SUSY-like or KK-like signal it might help confirm one of those hypotheses, obviously after lots of followup work. It can't say anything about axions, because the axion hypothesis do not predict gamma rays.

In other words, MM, your question is a bizarre one to which you ought to have known the answer. Fermi is looking for (among other things) new things, things we haven't seen before. No, we haven't seen those things before---that's why we have to look before knowing if they are there.

Michael Mozina said:

I started the other thread for you. Feel free to stop hijacking this thread now and please keep this thread "on topic".

Click to expand...

This thread has not been hijacked.
Your argument is that dark matter cannot emit gamma rays. Your evidence for this is an idea that it is "lumpy stuff". Refuting this idea is easy and should be (has been) done in this thread.

If your argument is that dark matter may emit gamma rays then this thread is over. That is what everyone has been saying. In that case we can take the "lumpy stuff" rebuttal to the other thread.

Which is it MM?

Michael Mozina said:

Got any evidence that "dark matter" emits gamma rays?

Click to expand...

Yes

• The unknown sources for the Fermi haze which include dark matter.
• The fit to the Fermi gamma ray spectrum from the hypothesis that dark matter emits gamma rays.

Is it strong evidence? - no.
The first observation might be explained by something other than dark matter.
The second hypothesis needs independent confirmation.

RC, MM, you aren't even talking about the same gamma rays.

The gamma ray excess seen by EGRET at the galactic center was (specifically) 511 keV gammas, the energy that you expect from positron annihilations. This specific energy line---and no other---appeared to come 50% from the galactic center and 50% from a cluster of LMXBs. This rules out those specific dark matter models which predicted very large 511 keV fluxes.

The Fermi telescope is searching for gamma rays between 30,000 keV and 300,000,000 keV. This has nothing to do with the LMXB positrons. This range is sensitive to totally different dark matter models, and contaminated by totally different backgrounds. In fact, the places you'll see attempts to use dark matter to explain Fermi data are (AFAIK) always focusing on the highest-energy end of this range.

ben m said:

OK, so for the purpose of discussion, the dark matter we are looking for is in particular some as-yet-undiscovered stable massive particle.

Click to expand...

So let us agree that the "base" hypothesis "assumes":

1. A new massive particle exists.
2. It only weakly interacts with other forms of matter.
3. It is "long lived"

Are these all the assumptions of the "base hypothesis', or does it also include a given decay rate?

Various specific hypotheses for the identity of the particle include, by necessity, gamma ray emission in pair annihilation reactions.

Click to expand...

Um, I don't quite accept that "necessity" concept. Is it a "necessity" that a WIMP decay at some specified rate under some specific condition? Is the gamma ray emission process also part of the "basket of goodies" that I have to accept or is that part open to challenge?

The details are 100% standard particle physics: just like the hypothesis of the top quark obviously required that it decay into bottom quarks, the hypothesis of the Higgs obviously requires it to decay to the heaviest available particle, and so on. Examples of gamma-predicting hypotheses include SUSY dark matter and Kaluza-Klein dark matter. Each such hypothesis makes a specific prediction about the gamma ray spectrum.

Click to expand...

So you're taking this number from some part of SUSY theory rather than "winging it"? How can I "verify" or falsify that number?

Other hypotheses predict NO gamma ray emission. Examples include axion dark matter and some forms of sterile neutrino dark matter.

Click to expand...

Ok. "Note to self: This isn't the only possible "exotic particle" that might explain "missing mass". " Got it.

Let's see, what do scientists do when they have a hypothesis that predicts something observable? They try to make the observation and see if it confirms or excludes the hypothesis. FERMI is currently making observations. It has ruled out several hypotheses so far.

Click to expand...

Did it rule out that binary star study somehow?

If it sees a convincing SUSY-like or KK-like signal it might help confirm one of those hypotheses, obviously after lots of followup work. It can't say anything about axions, because the axion hypothesis do not predict gamma rays.

In other words, MM, your question is a bizarre one to which you ought to have known the answer. Fermi is looking for (among other things) new things, things we haven't seen before. No, we haven't seen those things before---that's why we have to look before knowing if they are there.

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The problem from my skeptical perspective Ben is that you're "looking" to stuff the gaps of ignorance related to any gamma radiation with "dark matter" with unverified "properties" galore. Even if I give you one or two of them to start with, the whole thing requires the existence of something new whereas the solution I provided you earlier does not. Same question to you then: When is it appropriate to choose/favor a "simpler" theory over one that requires multiple unverified things to be true?

How exactly are you getting these positrons out of the "dark matter" in a way that is visible to us here on Earth? In other words, an "annihilation' at the core of a sun isn't going to do us much good. These decay/ e+ e- process have to occur somewhere "visible" to us here on Earth.

ben m said:

RC, MM, you aren't even talking about the same gamma rays.

The gamma ray excess seen by EGRET at the galactic center was (specifically) 511 keV gammas, the energy that you expect from positron annihilations. This specific energy line---and no other---appeared to come 50% from the galactic center and 50% from a cluster of LMXBs. This rules out those specific dark matter models which predicted very large 511 keV fluxes.

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Such signature have a known source.

http://www.sciencenews.org/view/generic/id/49288/title/Signature_of_antimatter_detected_in_lightning

The Fermi telescope is searching for gamma rays between 30,000 keV and 300,000,000 keV. This has nothing to do with the LMXB positrons. This range is sensitive to totally different dark matter models, and contaminated by totally different backgrounds. In fact, the places you'll see attempts to use dark matter to explain Fermi data are (AFAIK) always focusing on the highest-energy end of this range.

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So how exactly are you proposing that these wavelengths are in any way related to "dark matter"???

Michael Mozina said:

Such signature have a known source.

http://www.sciencenews.org/view/generic/id/49288/title/Signature_of_antimatter_detected_in_lightning

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Yes, this is called a "background". We know that the Sun, LMXBs, etc., produce these low energy gamma rays. If the dark matter emits low-energy gamma rays, it will be difficult to conclusively observe because we'll have to convince ourselves that Observation X cannot be just background. This may be difficult or impossible. We are trying.

This process is called "science".

So how exactly are you proposing that these wavelengths are in any way related to "dark matter"???

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Listen: the hypothesis that dark matter is made of SUSY LSPs includes everything we know about the SUSY LSP hypothesis---including things we learn about it from, e.g., collider data and electroweak theory. One aspect of this hypothesis is that the LSP annihilation products include > 50 GeV gamma rays. Understand? That's a prediction of the SUSY LSP hypothesis for what the dark matter is made of.

The data does not yet support or refute this hypothesis.

Michael Mozina said:

Um, I don't quite accept that "necessity" concept. Is it a "necessity" that a WIMP decay at some specified rate under some specific condition? Is the gamma ray emission process also part of the "basket of goodies" that I have to accept or is that part open to challenge?

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Please reread the post. The hypothesis tells you the particle properties. In the SUSY hypothesis, one of the properties is "coannhihilation to gamma rays" (NOT decay!), like it or not. This comes from the same sort of particle theory calculations that tells Large Hadron Collider physicists that the "Higgs hypothesis" automatically includes Higgs decay to heavy pairs, or that tells neutrino physicists that the "Majorana neutrino hypothesis" automatically includes neutrinoless double-beta decay of the 76Ge nucleus.

So you're taking this number from some part of SUSY theory rather than "winging it"? How can I "verify" or falsify that number?

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Yes, we're taking these claims from particular SUSY theories; there's a wide range of theories, which Jungman, Kamionkowski and Griest http://arxiv.org/abs/arXiv:hep-ph/9506380 surveyed appropriately. For a particular experiment, you have to ask what particular theories they were or were not sensitive to.

Ok. "Note to self: This isn't the only possible "exotic particle" that might explain "missing mass". " Got it.

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Good, now you understand. A given observation can only test the theories that predict something related to that observable. Fermi can only possibly test SUSY and Kaluza-Klein dark matter. ADMX can only possibly test axion dark matter. EROS could only possibly have tested MACHO-type dark matter.

Michael Mozina said:

Did it rule out that binary star study somehow?

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What, the 511 keV/LMXB association? To first order this is a totally different question than anything Fermi deals with. On the other hand: state a specific hypothesis for the origin of the 511 keV line and I'll tell you whether Fermi can say anything about that hypothesis.