Deflating Claims That ESA Craft Has Spotted Dark Matter

Yesterday, we posted news that data from the European Space Agency's XMM-Newton spacecraft had been interpreted as a possible sign of dark matter; researchers noted that a spike in X-ray emissions from two different celestial objects, the Andromeda galaxy and the Perseus galaxy cluster, matched just what they "were expecting with dark matter — that is, concentrated and intense in the center of objects and weaker and diffuse on the edges." StartsWithABang writes with a skeptical rejoinder: There seems to be a formula for this very specific extraordinary claim: point your high-energy telescope at the center of a galaxy or cluster of galaxies, discover an X-ray or gamma ray signal that you can't account for through conventional, known astrophysics, and claim you've detected dark matter! Only, these results never pan out; they've turned out either to be due to conventional sources or simply non-detections every time. There's a claim going around the news based on this paper recently that we've really done it this time, and yet that's not even physically possible, as our astrophysical constraints already rule out a particle with this property as being the dark matter!

Comments

Dark matter and the sniff test

[bradley13]

I'm just a lowly engineer, but for me "dark matter" has never passed the sniff test. It's a kludge factor thrown in to make equations balance. And a kludge factor so huge that "dark matter" is supposed to outweigh all of the observable matter in the entire universe. The only reason this doesn't sound ridiculous is because we've been hearing it for so long.

If you need a kludge factor that big, it is far more likely that the equations are wrong.

There are other possible explanations. For example, if the speed of light were a function of space and time, then the situation changes completely. All observations of the distant/ancient universe are suddenly thrown into question; the interactions within that distant/ancient universe were also different from what we see locally, today. This particular theory (variability of C) is one that crops up periodically, most recently in 2013. It is difficult to prove, but really, it's no more unlikely than the existence of huge amounts of dark matter that stubbornly refuse to interact with the known universe.

Re:Dark matter and the sniff test

[Anonymous Coward]

There's a few scenarios were evidence of dark matter has been observed. All you have to do is smash two galaxies together and the non-interacting dark matter separates from ordinary matter. The separated dark matter then causes a gravitational lensing effect, which is displaced from the ordinary/visible matter in the galaxies.

It's possible that a modified theory of gravity (e.g. MOND) could still account for the behavior, but it puts requirements on the theory that (I am told) are difficult to accomodate. Sort of like how the Higgs boson discovery at 125 GeV puts requirements on supersymmetry that are hard to accomodate--it's still possible, but much less appealing.

This particular theory (variability of C) is one that crops up periodically, most recently in 2013 [livescience.com]. It is difficult to prove, but really, it's no more unlikely than the existence of huge amounts of dark matter that stubbornly refuse to interact with the known universe.

Considering it's 100% likely that there are particles which don't interact electromagnetically or via the strong force (i.e. neutrinos), dark matter isn't a stretch at all. It's strictly required to exist in most beyond standard model theories. And since the standard model sucks at explaining some observations (e.g. the maginitude of CP violation), we have reason to believe there's more physics going on than what we can currently observe.

Re: Dark matter and the sniff test

[Anonymous Coward]

You are just a lowly engineer. You said that. Do not talk about things that are the realm of real scientists, way above your standing. Your post is just a bunch of uninformed comments by an ignoramus. Go play with your cheap machines and leave Science to the professionals. Dismissed.

Re: Dark matter and the sniff test

[Anonymous Coward]

Obvious trollbait consisting of nothing but an ad hominem and appeal to authority, but what the hey.

Anyone can do science. The idea that only professionals are capable or able to do so is elitist and belittles the scientific method.

Now, I'm not saying OP is correct - he merely stated an opinion and dredged up a couple of links to non-mainstream physics that don't have much credibility. Just like I'm stating an opinion now by saying otherwise. So none of what we've done is science or furthers it in any way.

If you really want to argue about this topic, which is incredibly difficult, go and learn about how the experiments were conducted, what results we expected and how the current models we have work. You won't need any qualifictions, but you'll probably need to put as much time and mental effort in as it would take to gain them.

If on the other hand you can come up with your own theory that explains a phenomena and can figure out some experiments capable of falsifying it that appear to validate it, then go for it - you're doing science. No swimming certificate is required. That's the beauty of reality, it doesn't care if the person interacting with it has any qualifications or not, or some otherworldy imaginary agency to justify your beliefs, it just is.

Re:Dark matter and the sniff test

[wvmarle]

I totally agree with you. Sooner or later we will find out what it is, and that 80% of matter that constitutes dark matter isn't there after all.

I always hear about dark matter when they're talking in terms of clusters of galaxies. Huge amounts of matter, immense distances. However this dark matter, four times as much as the rest of the universe, is supposed to be everywhere, have mass, but only interact through the force of gravity. However, for some reason unknown to me, the visible matter in our solar system perfectly describes how the planets orbit the sun, how the moon orbits the earth, and how hard I hit the ground when I try to fly. So where is this dark matter, all this extra gravity? Shouldn't I hit the ground a lot harder than we can explain just based on the mass of our planet?

Indeed there is probably something going on at large scales, where gravity doesn't work as it does on small scales. Or indeed as you suggest the speed of light is not as constant as we believe it is, and our observations are simply distorted because of that. It's going to be tricky to find all that out, as the scales involved are so huge. On the other hand, the moment scientists find out what gravity really is by looking at the tiniest bits like the Higgs boson, we may be able to understand how the universe works at large scales.

I'm looking forward to the first theories that really explain this gravity anomaly (which is what "dark matter' really is, as I understand it: seemingly too much gravity). It may throw our understanding of the universe upside down.

Re:Dark matter and the sniff test

[wvmarle]

Smashing two galaxies together is not that easy :)

The thing that bugs me most with dark matter is that it is seemingly absent on small scales (e.g. the solar system), yet somehow shows up in immense quantities on large scale. It just doesn't add up to me.

Re: Dark matter and the sniff test

[Anonymous Coward]

Psst... Nobody tell him about dark energy, that'll really set him off...

Re: Dark matter and the sniff test

[Anonymous Coward]

You're already been given one clear proven kind of "dark matter"; the neutrino. This is incredibly difficult to spot; interacts very little; is almost absent from normal ("small scale") physics and yet it's existence is clear and well evidenced. It's really not that big a stretch that there is something else.

The thing is that if there isn't someone has to come up with really clever expansions for a whole load of other stuff. This would not be nearly the first time a physicist was wrong. In fact a truly dedicated physicist should try took be wrong several times a day. However strange and contrary to instinct would rule out relativity and quantum physics; in fact most of what we know to be true about the world. You have to find something more than gut instinct to oppose this with.

Re:Dark matter and the sniff test

[Dutch Gun]

Indeed there is probably something going on at large scales, where gravity doesn't work as it does on small scales.

I've often wondered about that. It's pretty well known that classical Newtonian physics tends to break down at the quantum level. I wonder if the same thing happens at the largest scales - galaxy-sized measurements. I'd never go so far as to argue against the prevailing theory with people that study these things their entire lives, but it does make for interesting reading and/or discussion to consider some of the proposed alternatives.

Re:Dark matter and the sniff test

[Dutch Gun]

It just doesn't add up to me.

"Not adding up" was the reason dark matter was invented. ;)

Re: Dark matter and the sniff test

[Anonymous Coward]

Wrong. The "anyone can do science" concept died in the late 20th century. Modern science requires expensive equipment and funds, which are forever out of reach of any individual. The only "science" that's still doable by non-scientist is amateur astronomy and pointless rehashing of experiments already done to death some of which - especially in the realm of chemistry and "amateur rocketry" - are dangerous and ought to be banned. Leave science to professionals.

Re:Dark matter and the sniff test

[Anonymous Coward]

There are entire research groups dedicated to alternative gravity theories, but even their talks are often prefaced with the idea that dark matter does a better job of explaining the evidence in general. It would take several modifications to gravity to explain what could be explained by some dark matter theories. And for people who complain about dark matter being too arbitrary or just a fudge factor, several of the alternative gravity theories are literally fitted, arbitrary scales to just make it match the data. Yet most internet "scientists" don't seem to care in that case, because they spend so much time depending on a sniff test, going with their gut preferences instead of learning about the topic.

Re:Dark matter and the sniff test

[drinkypoo]

Yet most internet "scientists" don't seem to care in that case, because they spend so much time depending on a sniff test, going with their gut preferences instead of learning about the topic.

You can learn all there is to know about this topic and still have a difference of opinion with someone else who knows all there is to know about this topic. That's why most of us are tired of hearing about dark matter. Until you can actually show us some, shut the fuck up about it. Granted, not all scientists are claiming to have discovered dark matter every other week, but as far as anyone who doesn't necessarily believe in the stuff is concerned, it might as well be the luminiferous aether. If you can't stop some scientists from claiming to have seen the stuff every week, and you can't, then you can't stop people from speculating that they're full of shit when they're wrong every week, which they are.

Re:Dark matter and the sniff test

[wonkey_monkey]

I'm just a lowly engineer, but for me "dark matter" has never passed the sniff test.

And yet it seems like most physicists - of whom I am not one - seem to think it is the simplest explanation for what we see.

The quote in the summary sums up, for me, the somewhat churlish attitude some people adopt when faced with dark matter:

There seems to be a formula for this very specific extraordinary claim: point your high-energy telescope at the center of a galaxy or cluster of galaxies, discover an X-ray or gamma ray signal that you can't account for through conventional, known astrophysics, and claim you've detected dark matter! Only, these results never pan out;

Of course they have never panned out - so far. If one of them had panned out, we would have stopped looking. Your keys are always in the last place you look.

Photons started out their theoretical life as a kludge factor to solve the ultraviolet catastrophe (great band), and people were appalled by the idea.

Re: Dark matter and the sniff test

[Anonymous Coward]

You can still do theoretical physics without any equipment. You only have to learn some math.
Unfortunately unverified theoretical physics is about as credible as astrology.

Re:Dark matter and the sniff test

[wonkey_monkey]

Compared to the galaxy as a whole, the solar system is very dense. That would (or so something I read said) made it harder to detect because the gravity of all the regular matter in the immediate neighbourhood swamps the signal.

Re:Dark matter and the sniff test

[Anonymous Coward]

> Shouldn't I hit the ground a lot harder than we can explain just based on the mass of our planet?

No, because the gravity would cancel out here. Just like the gravity at the centre of the earth is zero because all the Earth is pulling in different directions to cancel eachother out. Hence dark matter evenly distributed all around our galaxy would be essentially undetectable. Only that closer to the centre of the galaxy than us would have an effect on us.

Re:Dark matter and the sniff test

[Charliemopps]

I'm just a lowly engineer, but for me "dark matter" has never passed the sniff test. It's a kludge factor thrown in to make equations balance. And a kludge factor so huge that "dark matter" is supposed to outweigh all of the observable matter in the entire universe. The only reason this doesn't sound ridiculous is because we've been hearing it for so long.

If you need a kludge factor that big, it is far more likely that the equations are wrong.

There are other possible explanations. For example, if the speed of light were a function of space and time, then the situation changes completely. All observations of the distant/ancient universe are suddenly thrown into question; the interactions within that distant/ancient universe were also different from what we see locally, today. This particular theory (variability of C) is one that crops up periodically, most recently in 2013. It is difficult to prove, but really, it's no more unlikely than the existence of huge amounts of dark matter that stubbornly refuse to interact with the known universe.

Yes, but Variable c would open up many, far far more dire problems than Dark Matter.

Scientists aren't suggesting that dark matter is definitely a particle. That's one guess, but it could very well be some artifact of some underlying physical reality that we just don't understand yet just like you suggest. But the speed of light isn't variable.

Re:Dark matter and the sniff test

[wvmarle]

That it is the easiest explanation, doesn't mean it's the correct explanation, or that us non-believers so to say would support one of the other theories.

To me it's indeed very much a kludge, it seems to work, but I have the strong feeling that there is something else at play. Just no idea what that something else could possibly be.

Re:Dark matter and the sniff test

[wvmarle]

Yes, yes... and I took care already not to call it "massive quantities"...

Re:Dark matter and the sniff test

[Anonymous Coward]

Engineering and computer science are the most arrogant disciplines - everything is just a special case of applied X, and if it doesn't work it must be rubbish. Apply as needed to every discipline of human knowledge. Forget the fact that theoretical physicists are typically far more intelligent than the former - usually excellent mathematicians, as well as practicing scientists who need to stay at the cutting edge of research and literature in the subject.

Re: Dark matter and the sniff test

[Anonymous Coward]

And I guess you're excluding computer science, because y'know computers are specialized pieces of equipment far out of each of the common person. Electronics too!

Anyways, most scientific equipment is grossly over priced because they only sell a few thousand per year. If there was significant interest by consumers, and consumers spent more on scientific equipment than TVs, then the prices would plummet.

Re:Dark matter and the sniff test

[Anonymous Coward]

I'm just a lowly engineer, but for me "dark matter" has never passed the sniff test. It's a kludge factor thrown in to make equations balance.

There are about 1e10 neutrinos flying through each square centimeter cross section of your body every second.
The chances of one of them interacting with your body is about once every 30 years or so.
Even our best neutrino detectors can capture only a small fraction of them every day (at best a few 100).
Given that, is it really hard to imagine there could be an even weaker interacting particle, that for current practical purposes was undetectable?

The reason we stick with dark matter as the best model, is because it seems to explain everything we observe: galactic rotation curves, distribution of clusters, Bullet Cluster like lensing, etc.
There are various models that all work well with dark matter, for example simulation of the evolution of our universe only work with 80% cold dark matter, calculations of the different ratios of atoms and isotopes also require dark matter to explain what we see today.
Everything we find seems to fit with dark matter, so what seems simpler: yet another neutrino-like particle, or some convoluted changes to our best formulas for spacetime?

Btw, the neutrino also started out as "dark matter". Experiments showed that something was carrying away momentum from other particles that could be seen. So they postulated there was an undetected particle. It took over 25 years to directly detect it.

Re: Dark matter and the sniff test

[Anonymous Coward]

Ordinary matter clumps into galaxies and stars and planets BECAUSE it interacts with light. As a diffuse uniform cloud of matter collapses under its own gravity it heats up, which provides support against further collapse. Ordinary matter can emit radiation and cool, allowing further collapse, while dark matter can't and ends up only clumping at galaxy scales. That's why we don't see effects of dark matter at solar system length scales, but why it can still dominate things at galaxy cluster scales. How radiation is critical to cooling and gravitational collapse was a well understood part of star formation theoretical astrophysics long before dark matter came up. Check out any text on star formation theory- it's very interesting stuff!

Re:Dark matter and the sniff test

[EdgePenguin]

Dark matter is NOT a kludge factor. You should not make such strident pronouncements about a subject you clearly know nothing about. The existence of dark matter is not controversial amongst astrophysicists.

The fraction of deuterium produced by primordial nucleosynthesis, and the ratio between the acoustic peaks in the CMB, both require ~83% of the mass of the universe to be something other than baryons. Given that these two indicators are from entirely separate epochs (about a hundred seconds after the big bang for the former, and hundreds of thousands of years for the latter) this is a strong result.

Re:Dark matter and the sniff test

[Baloroth]

However, for some reason unknown to me, the visible matter in our solar system perfectly describes how the planets orbit the sun, how the moon orbits the earth, and how hard I hit the ground when I try to fly. So where is this dark matter, all this extra gravity? Shouldn't I hit the ground a lot harder than we can explain just based on the mass of our planet?

It's because dark matter only interacts gravitationally. See, normal matter clumps up into planets and stars because it sticks to other particles, and loses energy from collisions, causing it to collapse over time into locally dense spheres (planets, stars, black holes, etc.). But dark matter doesn't: it just passes through itself (mostly: it may interact through the weak force, but only very very very rarely if so, not enough to clump up). That means it doesn't form local regions of high density. On the other hand, an object immersed in a more or less uniform sea of matter (of any kind) won't notice any gravitational effects, because it's being pulled in all directions equally (for example: you'd be weightless at the center of the Earth. Dead from the pressure/heat/lack of air, but weightless). So, we can float through a sea, even a fairly dense one, of dark matter and notice nothing at all. Now, there is an non-uniformity in this dark matter "sea": there is more on the side of us towards the center of the galaxy than there is on the other side, but that pulls the entire solar system uniformly, accelerating it in it's galactic orbit, and that effect we do in fact see.

Re:Dark matter and the sniff test

[EdgePenguin]

Although you make the common error of thinking that the only requirement for dark matter is galaxy/cluster dynamics, you have stumbled on an interesting question; why is the Milky Way dynamically dominated by dark matter but the solar system is not. Fortunately, its easily answered.

Dark matter makes up most of the mass of galaxies, including the Milky Way. One of the best bits of evidence our own galaxy has dark matter is the rate at which M31 (Andromeda) is approaching us. The expansion of the universe drives galaxies apart, so the combined mass of the local group (basically just us and M31, M33 is next in mass but its much smaller than M31) has to be enough to pull the two galaxies together such that you would see M31 at the present distance and velocity. This is called the local group timing argument, and it shows that there is much more mass than can be accounted for with visible matter in the local group. This is not the only evidence for dark matter, but it along with the milk way rotation curve makes us confident that there is substantial dark mass in our galaxy.

As to the reason you don't see much dark matter impacting on the gravity of the solar system: that comes down to geometry. dark matter is arranged in a spheroidal halo whereas most of the visible matter is in a thin disk. The dark matter halo is much less dense in our galaxy than visible matter (and especially so in our solar system as for obvious reasons its got a higher density than the galaxy as a whole) but for large enough $r$, proportionality to $r^3$ always wins out over proportionality to $r^2$, which is why dark matter dominates the outer part of the rotation curve whilst at the same time being irrelevant for the internal kinematics of our solar system.

Re:Dark matter and the sniff test

[Anonymous Coward]

However this dark matter, four times as much as the rest of the universe, is supposed to be everywhere, have mass, but only interact through the force of gravity. However, for some reason unknown to me, the visible matter in our solar system perfectly describes how the planets orbit the sun, how the moon orbits the earth, and how hard I hit the ground when I try to fly. So where is this dark matter, all this extra gravity? Shouldn't I hit the ground a lot harder than we can explain just based on the mass of our planet?

It's a good question, but you're generalizing too much. There are several things to consider:
- The 5x figure is for the proportion of DM to visible matter in the _entire_ universe (averaged).
- Because dark matter only interacts gravitationally, it will form a diffuse spheroid around the galactic core (which is also what the Bullet Cluster lensing seems to indicate). The diameter of this spheroid will be much larger than the galaxy, but gets more and more diffuse on the outside.
- The visible matter in the galaxy is in a disc, so even with 5x as much DM than visible matter, it only intersects with a small part of the disc, so there is not 5x more DM in the disc.
- There is more DM in the galactic center than on the outside (more diffuse), so again there is less DM on the outside, where we are.
- A solar system has a high average density (but still pretty low because most of it is empty) compared to the whole universe. So there will be a higher proportion of visible matter.

All this means that the DM density in the solar system is very very low. Several people did calculations and concluded that the total mass of DM in the solar system is very small, probably less than the mass of the comet Rosetta is orbiting. If you diffuse that mass throughout the whole solar system, its gravitational infuence falls below measurement error.

Re:Dark matter and the sniff test

[sconeu]

I believe that's "mass quantities".

https://www.youtube.com/watch?v=ygymejkA_CM

Re:Dark matter and the sniff test

[Anonymous Coward]

The simplest explanation may be the most likely explanation, but it isn't necessarily the correct one. You do realize that, in the recent past, physics has claimed "we've got it!" and promptly got punked, right? You know, like luminiferous aether?

Sometimes the answer isn't so obvious. If dark matter really exists, we'll find it sooner or later, but maybe it's just something nobody has thought of yet. Like how physicists threw out ad hoc theories to explain the precession of Mercury's orbit until Einstein came out of left field with general relativity. That certainly was not an intuitive, simple explanation for the phenomenon.

I'm not saying dark matter's bogus, but considering they haven't found any solid proof yet, it leaves the possibility of something less intuitive and potentially more interesting (which I don't claim to have any idea what it may be).

Re:Dark matter and the sniff test

[idji]

One of the consequences of Newton's Law of Gravity is that a spherically even distribution of matter behaves gravitationally as if it were all at the center http://en.wikipedia.org/wiki/S.... If you are INSIDE that sphere then you can IGNORE mass that is above you. Ie if you are in a hole 2000km into the earth you can ignore the outer 2000km of the earth. And so when you reach the center of the Earth you can ignore the Earth's gravity.


If you now apply this to Dark Matter and ASSUME that the Dark Matter in our part of the galaxy is evenly distributed then its gravitation effect upon is is effectively zero (or insignificant in terms of the Sun's effect on us). That is why we are unlikely to be able to measure local Dark Matter's effect on us, it is better to look outside of a Galaxy where it is less "spherical" or comparable to baryonic matter's influence
Also, since the baryonic matter INSIDE our solar system has MANY ORDERS OF MAGNITUDE of density higher than the Dark Matter INSIDE our solar system, Dark Matter is completely irrelevant for the orbits of solar planets, moons, etc..

Re:Dark matter and the sniff test

[Anonymous Coward]

"dark matter does a better job of explaining the evidence in general"

What are the actual constraints on the properties of "dark matter". If they are weak enough then it is not very impressive that the idea can be used to fit the data.

Re:Dark matter and the sniff test

[budgenator]

However, for some reason unknown to me, the visible matter in our solar system perfectly describes how the planets orbit the sun, how the moon orbits the earth, and how hard I hit the ground when I try to fly. So where is this dark matter, all this extra gravity? Shouldn't I hit the ground a lot harder than we can explain just based on the mass of our planet?

I assume that because this so called dark matter, if it really exists, is pretty homogeneous at scales of planetary systems so all of the gravitational pulls at infinitely different angles just cancels out.

Re: Dark matter and the sniff test

[EdgePenguin]

I never said there was no other evidence for dark matter. The ratio of deuterium and the acoustic peaks of the CMB require most of the mass in the universe to be non baryonic. I simply stated the evidence that this non baryonic matter makes up most of the MW-M31 system. Your strident arrogance, coupled with your immense ignorance of the subject matter, would make a wiser person stay quiet.

Re: Dark matter and the sniff test

[EdgePenguin]

Stop. Really. You are embarrassing yourself. That is EXACTLY what you meant. You said I thought "the equations were off in two regards", so clearly you didn't know about any of the other evidence of dark matter. Now you are back-pedalling as you slowly realise you are not even vaguely qualified to be in this conversation.

Re: Dark matter and the sniff test

[Anonymous Coward]

How am I backpedaling? A reasonable interpretation of your statement is that you find those two pieces of evidence sufficiently convincing to accept the dark matter hypothesis. You are correct that I really have no idea what the extent of the evidence is pro/con regarding dark matter, so as a heuristic I make preliminary judgements regarding its validity based on the statements of the supporters of the hypothesis. I have found them to be consistently overconfident given the extreme claims they are making. This is valid behaviour on my part.

Re: Dark matter and the sniff test

[EdgePenguin]

The claims are "extreme" because you don't like them, and the confidence of astrophysicists in this matter is a consequence of the overwhelming weight of evidence.

You have decided to take a position on a subject you are completely ignorant of, and that contrary positions to this are "extreme" and thus must be treated as fringe nuttery. Essentially, you think that your ad hoc guesses should be treated like the null hypothesis. You can try and dress it up in as much intellectual sounding language as you like, but you are being absolutely moronic and I'm done with you.

Re:Dark matter and the sniff test

[WillKemp]

[......] dark matter is arranged in a spheroidal halo whereas most of the visible matter is in a thin disk.

That sounds unlikely. How did it happen?

Re: Dark matter and the sniff test

[WillKemp]

Yeah, too right. If it wasn't for the meddling of a lowly patent clerk, we wouldn't be in this mess in the first place!

Re: Dark matter and the sniff test

[Anonymous Coward]

"This is not the only evidence for dark matter, but it along with the milk way rotation curve makes us confident that there is substantial dark mass in our galaxy." ...
"the overwhelming weight of evidence"

Re:Dark matter and the sniff test

[Anonymous Coward]

I mean sure there *could* be such a thing, it is much more plausible the equations are just wrong though.

You do realize that dark matter is an acknowledgement that the current theories are wrong and is a new theory to try to fix it right? It isn't any more or less of a new theory than other alternatives, but people try to act otherwise to support their gut feelings. Also your comment highlights one of the area that alternative gravity equations tend to fail, being able to explain only one short coming at a time, in a way often incomparable with other alternatives (you can't just pile up the effects) and with plenty of arbitrary factors to fit the data.

Re:Dark matter and the sniff test

[Anonymous Coward]

That it is the easiest explanation, doesn't mean it's the correct explanation, or that us non-believers so to say would support one of the other theories.

This is true of every single theory in science, yet this reasoning is often used to selectively endorse people's preferred theories all the time as if it is specifically applies on in certain cases.

Re: Dark matter and the sniff test

[EdgePenguin]

Another good question. Gas can lose energy because it interacts with other radiation and matter, but dark matter cannot. The total angular momentum of the system must always be conserved, and a disk is the lowest energy configuration that does this. Both dark matter and gas start off in the spheroidal arrangement, and then the gas the cools to form a disk.

Re: Dark matter and the sniff test

[WillKemp]

Leave science to professionals.

The problem is that we've seen that shit before - it's called religion. Only a small clique of superior beings can actually know god's mind - and everyone else must just shut up and listen. If you can't explain this stuff in ways that non scientists can understand, then (a) you're not worth your wages, and (b) nobody's going to believe you.

Re: Dark matter and the sniff test

[WillKemp]

So does that mean dark matter is effectively a cloud of gas and its particles are constantly in rapid motion, but constrained in a spheroid by gravity? Or am i completely failing to grasp how it works?

Re:Dark matter and the sniff test

[WillKemp]

[......] theoretical physicists are typically far more intelligent than [engineers and computer scientists]

That depends on your definition of intelligence. But, whatever it is, all the intelligence in the world is worthless without the ability to communicate its products clearly in a way that lesser mortals can understand. Theoretical physicists, as a whole, do a very poor job of that.

Re: Dark matter and the sniff test

[EdgePenguin]

Thats right. Spheroidal systems in astrophysics are generally held up against gravity by such random motions, whereas flattened systems tend towards being help up by ordered rotation.

Re:Dark matter and the sniff test

[Anonymous Coward]

The fraction of deuterium produced by primordial nucleosynthesis, and the ratio between the acoustic peaks in the CMB, both require ~83% of the mass of the universe to be something other than baryons

Why shouldn't we read this as: "Our equations are off by 83%."?

Re:Dark matter and the sniff test

[EdgePenguin]

Because the equations aren't "off" at all. They precisely predict the mass density of the universe and the baryon density of the universe from observations. The difference between these two values is very well established. Read the results papers from Planck and WMAP.

Re: Dark matter and the sniff test

[Rich0]

Don't waste your time arguing with trolls. It is a bit like somebody spending all day arguing that there are lots of things that could make a pendulum behave the way it does besides the earth turning.

Since the whole point of dark matter is attempting to account for phenomena which have no other explanation, it is entirely possible that all of physics is off the mark. However, to just dismiss the entire matter because any ONE specific issue is somewhat circumstantial is to miss the overall picture. There is certainly a lot of evidence that established theories are wrong, and there are a lot of independent constraints on what is going on.

Re: Dark matter and the sniff test

[Anonymous Coward]

If you can't explain this stuff in ways that non scientists can understand, then (a) you're not worth your wages, and (b) nobody's going to believe you.

I agree with this in general, but the problem in situations like this, is there are a crap ton of laymen level explanations on the topics, from astrophycist's blogs to a few popsci books that actually get detailed, to public talks to astrophysicists actually answering questions online forums. But when someone bitches and moans about modern science when making statements that show they haven't even read something at the level of a Wikipedia article on the subject, then they should leave it to professionals. It is not so much of professionals being superior beings, but that difficult, far from trivial problems and subjects are not a domain for lazy and superficial people.

Re:Dark matter and the sniff test

[Anonymous Coward]

You can learn all there is to know about this topic and still have a difference of opinion with someone else who knows all there is to know about this topic

And the problem is that such a situation is irrelevant to 99% of the armchair statements on the internet, that make mistakes or wrong claims about the subjects at hand that they would not made if they even took the effort to read Wikipedia or sit in a public lecture on the topic. There are plenty of people with massive backgrounds in the subject who are critical of various theories, and no one shouts them down when they express themselves in a way that actually reflects that knowledge. Regardless of who is write or wrong, people will be called out for basing their arguments on stupid reasons and for being overly confident on something that they were actually not just ignorant, but lazy with.

Re:Dark matter and the sniff test

[Anonymous Coward]

Exactly, "dark matter" does not exist, never has existed and never will exist. It just "sounds cool", its a media darling, like heartbleed.

Re:Dark matter and the sniff test

[Agent0013]

The very gasses that the say separated out from the galaxies have the ability to cause the bending of light also. It is just like refraction through a medium like glass, but there is no solid boundary that it passes through. Instead it has a varying index of refraction which leads to the very same bending of light that has been attributed to the dark matter that they keep saying is there. The bullet cluster isn't quite the nail in the coffin that the news will put it out as.

To me it sounds like a little circular reasoning. Physicists were looking for an aether and couldn't find one. Einstein comes along and explains that one isn't needed because of relativity. He first adds then removes the cosmological constant. We find things expanding too much so add the cosmological constant back in by the process of dark energy which supposedly involves vacuum energy of the aether, so we have added that back in also. And now we need dark matter to fix gravity also. So the need to get rid of the aether has led us around to putting it back in. Perhaps we went astray someplace back then and are heading off in the wrong direction.

I'm not trying to say I know more than the people working on this. I find it interesting either way though. But I have seen examples of scientists following the wrong trail for a while before it gets figured out. We are just starting to understand that the whole fat makes you fat thing was bad science and isn't really true. And we are all told the pyramids are tombs when no mummys have ever been found in one. No frescas or writing of the person buried there either like in all the other tombs of that time. Some guy in the past makes some claim and everyone buys it for quite a long time before it gets figured out that we took a wrong turn back then.

Re:Dark matter and the sniff test

[david_thornley]

Gasses do indeed have mass, and can cause gravitational lensing. However, we can detect them through other means, and there just isn't enough mass there by a long shot. In any case, the Bullet Cluster is an example of lensing happening where there is little or no gas. Gravitational lensing without matter we can detect does strongly suggest matter we can't detect.

Your second paragraph seems a bit incoherent, and ignores the fact that dark matter and dark energy are different things. We know there's dark matter already, since neutrinos qualify. Dark energy seems to this amateur somewhat more nebulous a concept, but the luminiferous aether has nothing to do with it. Nor did we drop it because of relativity. You seem to be confusing Michelson-Morley as an inspiration for relativity with some relevance of relativity to the aether idea. Michelson-Morley simply failed to detect and aether drift, suggesting that either we are the center of the Universe or light has a constant speed, the latter being a key factor in special relativity.

Dark matter doesn't fix gravity. It's an elegant and economical way to explain some gravitational effects we don't understand, and fits in with some particle physics stuff that I don't understand. Dark matter as a way of explaining galactic rotation curves is something like the discoveries of the outer planets from unexplained anomalies in their orbits. It's a way of explaining gravitational lensing when, as far as we can tell, there is nothing to create the gravitational field. Fiddling with gravitational theory to explain all the gravitational effects seems to me much like fiddling with it to explain the orbit of Saturn rather than hypothesizing a planet called Uranus.

Re:Dark matter and the sniff test

[david_thornley]

Until you can actually show us some

I'm going to ask for a definition of "show" here. By definition, dark matter is invisible, since it doesn't interact electromagnetically. What would constitute "showing" to you?

Dark matter isn't an idea that comes and goes each week. The theory has been around for a while, and scientists are currently attempting to discover what its other properties might be, and how else to detect it. Nobody is discovering or failing to discover dark matter itself.

Re: Dark matter and the sniff test

[beastofburdon]

I agree fully with your post. In fact there are many areas of science where the theory has become a religion and anything that contradicts the theory is derided as being "not scientific" or immediately "discredited" without any test of the data or new theory.
Even worse there is the medical field where the outcome of many studies is based solely on who is paying for it. Most of them being conducted in secret and the results only ever being published if the study supports the interests of the funders.

The current state of science is a disgrace!

Re:Dark matter and the sniff test

[Anonymous Coward]

Instead it has a varying index of refraction which leads to the very same bending of light that has been attributed to the dark matter that they keep saying is there.

All known gases, and especially plasmas, have a frequency dependent index of refraction. Gravitational lensing is independent of frequency.

Spammy submitter is spammy

[Anonymous Coward]

Moreso for spamming unreadable crap.

there isn't any dark matter!

[Anonymous Coward]

Dwarf exoplanets are out there. You just haven't discovered them yet. You want to find your missing matter? Look to Pluto!

This is post-modern science...

[Anonymous Coward]

...There seems to be a formula for this very specific extraordinary claim: point your high-energy telescope at the center of a galaxy or cluster of galaxies, discover an X-ray or gamma ray signal that you can't account for through conventional, known astrophysics, and claim you've detected dark matter! ...

It's similar to 'Climate Science'. Pick a thermometer, note a temperature rise that you can't account for, and claim that it must be humans that did it.

Only then you have to make up more stories when the temperature rise goes away again...

Re:This is post-modern science...

[Anonymous Coward]

This just in : Scientists have determined the cause of bad weather. Gaia is angry! Buy an electric car to appease her. In unrelated news, stay tuned during the following commercial advertising for electric cars.

Kinda like the Gamma Bogon?

[Anonymous Coward]

And magnetic monopoles, when I was younger. I spent a fascinating class arguing with an MIT physics professor. His claim that "they must exist becase it makes Maxwell's Equations more electant and symmetrical" was like the the mathematics professor's claim that probabilities always being positive meant something subtle about how the universe works, and wasn't an artifact of how we chose to *)describe* probability.

I loved a great deal of both their teachings, but sometimes very smart people get very silly.

Do We Need Dark Matter?

[AbsoluteXyro]

As I understand it, dark matter is our best guess at explaining an observation of mass via gravitational lensing and other effects where there is not enough visible matter to account for it. What I never see mentioned, and perhaps there's a good reason for this unbeknownst to me, is the possibility that this phenomenon exists independent from any matter, just as we do observe it. It seems to suggest that without matter space time would be flat across the entire universe. Why isn't it possible that space time is inherently imperfect, with it's own curvatures independent of mass? I've never seen this question asked, or answered. Maybe I've been looking in the wrong places, though. Can someone enlighten me?

Re:Do We Need Dark Matter?

[Greyfox]

Sure, dark matter is just a question mark, really. We're observing something that doesn't fit in with our understanding of how gravity works. We have not observed what's causing it, but based on how we observe gravity working, we're building a model of properties this unknown effect must have. At the point we're at with our understanding of it, we may as well have called it "magic." That would be a much more honest name for the level of understanding we have of it. But it's awfully hard to get a research grant for a space telescope to go looking for magic.

It's starting to feel like supersymmetry, though, where each successive observation seems to provide evidence against the hypothesis. There just hasn't been a particularly compelling competing hypothesis to explain what we're seeing.

People tend to think of science as absolute because it's kind of taught that way in school. We go over everything we have a solid understanding of and people don't get exposed to the edges where we're still trying to understand things very often. But there are really still a lot of things we don't understand about the world and universe we live in, and watching the scientific method at work can be confusing if you haven't been exposed to it a lot. I think scientists feel compelled to talk about these things as if they understand them more than they do, because, again, it's very hard to get a research grant to find the thing that you think has to be there but you don't know exactly what it is.

Wait Just a Second

[Anonymous Coward]

Time and time again when the subject GLobal (not) Warming comes up all we hear from the would be Slashdot PhDs is "Peer Review! Peer Review!"

But somehow now it's just fine to dump all over the findings of a group of scientists...real scientists, with degrees and shit, not just a Slashdot handle and low UID) and not a mention of peer review in sight.

Fucking hypocrites, the lot of you.

Science

[Livius]

Dark matter is a hypothesis. So far it fits the data, but new data may force modification or even rejection of the hypothesis. The reason it's an exciting area of research is exactly because physicist acknowledge that its an imperfect hypothesis.

All science works this way. The luminiferous aether hypothesis was not foolish or worthless - it was valuable science because when tested its limitations led to new insights. And while the materials science metaphor was eventually judged inappropriate, if "empty" space can have an energy density or a geometry, it may yet turn out that something about the basic idea of a luminiferous aether could be true.

Re:Science

[esperto]

Actually, from what I recall, dark matter, and dark energy, are just place holders for stuff that generate effects that we can measure but yet do not have an explanation for, we have a few hypotesis, some more likely than others, but no proof for any of those yet.
Basically we KNOW that our models are incomplete and that are stuff out there causing galaxies to rotate at a different speed than it supposed to be just by visible matter and that are other stuff making shit fly appart faster, but we don't have an actual clue of what they are.

Check out this unusual pattern of gamma rays!

[RevWaldo]

~ What do you think professor? Does it prove the existence of dark matter?

~ This? Oh, bless your heart, no, my young assistant. This is just chatter from some ancient interstellar civilization. Trade negotiations if I'm not mistaken.

~ Gosh, you're right, professor, I should have realized that myself.

~ Yes, completely useless I'm afraid. Fear not, we'll find the evidence someday.

.

Re:I'm also an engineer

[EdgePenguin]

You do not have a better theory. You have a hypothesis, posted on a webpage. This is timecube territory, sorry. Why is it that engineers make such laughably bad attempts to second guess scientists? And why do they insist on bothering actual scientists with mass emails about their crazy ideas?

Dark Matter is not a tweak to gravity

[EdgePenguin]

A lot of engineers and computer programmers seem to think that dark matter is just a fudge to make rotation curves fit, and that they being smarter than astrophysicists can see through this obvious error. This is profoundly irritating

Dark matter is required to explain the ratio of elements produced during big bang nucleosynthesis, the acoustic peaks of the cosmic microwave background, gravitational lensing, cluster dynamics, the Local Group timing and finally, yes, rotation curves. In the last application (which is bizarrely considered to be the only place dark matter is invoked), the most popular alternative hypothesis MOND, which has no theoretical basis and exists purely to fit rotation curve data, doesn't actually do that well on modern rotation curves.

You cannot offering any critical comment on dark matter that won't make you sound like a terminal case of Dunning-Kruger to an astrophysicist unless you understand all of the things I mentioned above.

Re:Dark Matter is not a tweak to gravity

[WillKemp]

Shoulda been first post!

Re:Dark Matter is not a tweak to gravity

[x_t0ken_407]

Perfect description of what goes on. Thanks for saving me the time on my rant, lol.

Re:Dark Matter is not a tweak to gravity

[Anonymous Coward]

Bullshit. Half of the things you mention only have very weak evidence. Besides, there are other explanations that I have not published yet, related to quantum mechanics, that explain dark matter. Turns out dark matter is a result of L2-norm conservation.

If it's not dark matter...

[Anonymous Coward]

Maybe it's luminiferous aether? Or phlogiston?

Re:I'm also an engineer

[Anonymous Coward]

And why do they insist on bothering actual scientists with mass emails about their crazy ideas?

Huh? I'm not doing any such thing. Besides, most physicists are closed tighter than a drum. Who would waste their time talking to them. The more "sciencey" the more closed-minded. Sheldrake has it right.

Re:I'm also an engineer

[EdgePenguin]

Yes, we are all Educated Stupid and thats why we don't believe in Timecube!

Question

[Anonymous Coward]

Does George W. Bush receive 10 rectal hydrations each day?

No.

20.

haha

Did Dick Cheney's gay daughter turn him on to the pleasures of rectal hydration?

Yes.

Haha

Re:I'm also an engineer

[Anonymous Coward]

(Different AC): As a physicist having actually tried to engage the previous poster about their theory, they felling into the typical crackpot habit of not actually wanting to discuss their or mainstream theories at all, but instead wasting a lot of time discussing perceived problems with scientist, education, and modern philosophy of science. Baiting someone with one topic and then never going into any detail might work for the local evening news, but wears thin quickly.

Given the globe is warming

[Anonymous Coward]

Your "Global not warming" indicates you are not capable of determining who is being hypocritical here.

Ah, more historical ignorance....

[Anonymous Coward]

By "lowly patent clerk" you mean someone who had already been considered for a professorship at a university, right?

I guess you'd also describe Feynman as "A lowly bongo player", yes?