Physicists Resurrect an Old, Strange Dark Matter Theory

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Physicists Resurrect an Old, Strange Dark Matter Theory

Posted by Soulskill on Wednesday November 5, 2014 @05:30AM from the throwing-dark-matter-at-a-wall-and-seeing-what-sticks dept.

New submitter rossgneumann writes: Dark matter might not be nearly as exotic as most theories suggest. Instead, it could be macroscopic clumps of material formed from common particles already found within the Standard Model of particle physics. This argument comes courtesy of physicists at Case Western University (PDF). Dark matter is usually thought of in terms of exotic, so-far undiscovered particles. The leading candidates are known as weakly interacting massive particles, or WIMPs. But the Case Western theory suggests that there are no dark matter particles, at least none that exist outside of current knowledge. Instead, there are baseball-sized clumps of "regular" matter formed from unexpected combinations of Standard Model particles.

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Strange? by rwise2112 · 2014-11-05 05:32 · Score: 2

So it's strange that this matter may not be exotic?

--

"For every expert, there is an equal and opposite expert"
1. Re:Strange? by mozumder · 2014-11-05 05:36 · Score: 1
  
  Amazing that they haven't already ruled out common particles as a source of dark-matter anomalies in the galaxy rotation curves... you'd figure that would be the first suspect analyzed?
2. Re:Strange? by Anonymous Coward · 2014-11-05 05:41 · Score: 1
  
  Well, it's clearly not a strange theory, but it is unusual in that it actually attempts to find a solution assuming both the known matter and the known models of gravity. This should be relatively easy to test (compared to the other wild guesses).
3. Re:Strange? by gstoddart · 2014-11-05 05:44 · Score: 3, Insightful
  
  Or it's exotic that this matter is so strange.
  I'm afraid most of us can't really follow what physicists mean by 'exotic' or 'strange' any more.
  Does it taste minty?
  
  --
  Lost at C:>. Found at C.
4. Re:Strange? by Anonymous Coward · 2014-11-05 05:52 · Score: 5, Informative
  
  Common particles tend to absorb EMR if they're cold, or emit EMR if they're warm.
5. Re:Strange? by lgw · 2014-11-05 05:54 · Score: 5, Insightful
  
  Amazing that they haven't already ruled out common particles as a source of dark-matter anomalies in the galaxy rotation curves... you'd figure that would be the first suspect analyzed?
  You can't rule them out from galaxy rotation, that's why MACHOs were just as viable as WIMPs early on, and none of those hypotheses were particularly credible.
  But the important data is the CMBR data, which tells us, to 2 significant figures, the ratio of dark matter (does not interact with photons even at very high energy densities) to normal matter - more than 5:1 dark. It also tells us that the dark matter must be "cool" (not moving at or near the speed of light).
  At this point, any hypothesis that doesn't explain galaxy rotation and the CMBR data and the gravitational lensing from galaxy-sized objects we can't see and make some useful prediction that the current WIMP models don't is just a crackpot idea: junk science.
  
  --
  Socialism: a lie told by totalitarians and believed by fools.
6. Re:Strange? by Anonymous Coward · 2014-11-05 06:05 · Score: 3, Interesting
  
  Here's a crackpot idea for you: what if space came pre-"dimpled" at a large scale (in other words: gravity being a property of both space and mass, not just mass), and the galaxies we see are just the result of whatever loose stuff fell into the gravity wells that were already there. Then the massless lenses are simply wells that stars haven't fallen into yet.
7. Re:Strange? by Ken_g6 · 2014-11-05 06:15 · Score: 1
  
  Or maybe some of the particles include strange quarks?
  
  --
  (T>t && O(n)--) == sqrt(666)
8. Re:Strange? by Charliemopps · 2014-11-05 06:22 · Score: 2, Interesting
  
  So it's strange that this matter may not be exotic?
  It's also got the density of a neutron star and is a fluid so... Good luck
9. Re:Strange? by Anonymous Coward · 2014-11-05 06:30 · Score: 0, Troll
  
  It's like your Mom's ass?
10. Re:Strange? by Anonymous Coward · 2014-11-05 06:31 · Score: 0
  
  If you read the arixv article instead of summary and fluff, you would see some support for the fantasies; if you math and reading comprehension are actually up to the task.
11. Re:Strange? by Rinikusu · 2014-11-05 06:54 · Score: 3, Funny
  
  OOOOOO.. Quantum Buuuuuuuuuuuuuuuuuurrrrrrrrrrrrrrrrrrrrrnnnnnnnnnnnnnnnnnnnn
  
  --
  If you were me, you'd be good lookin'. - six string samurai
12. Re:Strange? by lgw · 2014-11-05 07:29 · Score: 1, Insightful
  
  And the CMBR data? Fail.
  Every problem has a simple, easy to understand, wrong answer.
  
  --
  Socialism: a lie told by totalitarians and believed by fools.
13. Re:Strange? by Anonymous Coward · 2014-11-05 07:34 · Score: 0
  
  There are some farther out ideas about dark matter being interaction with other universes, etc., that amounts to the same idea that there are just variations in gravity due something other than stuff in our universe. Regardless of what is true or not, that idea would fail according to the internet, who already view dark matter as too arbitrary of a fudge factor ("When predictions disagree with measurements, make a new theory... no, not that new theory, I don't like it, so therefore I'll say it isn't a new theory and complain on the internet").
14. Re:Strange? by Anonymous Coward · 2014-11-05 07:36 · Score: 1
  
  Its strange that the matter is largely made of Strange quarks, which are technically not exotic, even though we don't see such objects in everyday life.
15. Re:Strange? by Anonymous Coward · 2014-11-05 07:37 · Score: 0
  
  At this point, any hypothesis that doesn't explain galaxy rotation and the CMBR data and the gravitational lensing from galaxy-sized objects we can't see and make some useful prediction that the current WIMP models don't is just a crackpot idea: junk science.
  stop being an ass. just because the science isn't quite there yet doesn't mean isn't not worth pursuring.
16. Re:Strange? by lgw · 2014-11-05 07:49 · Score: 3, Insightful
  
  Sure, when it's actually done, then it's worth the attention of others. But the internet is full of easy explanations (if you ignore half the data) for just about everything in cosmology. And WIMPs mat actually be wrong. But any alternative needs to be better: this isn't politics, we can't just ignore inconvenient data.
  
  --
  Socialism: a lie told by totalitarians and believed by fools.
17. Re:Strange? by pushing-robot · 2014-11-05 08:06 · Score: 2
  
  No, the "Your-Mom" hypothesis for gravitational discrepancy in the universe has already been debated at length by many of the world's foremost astrophysicists.
  
  --
  How can I believe you when you tell me what I don't want to hear?
18. Re:Strange? by infolation · 2014-11-05 08:11 · Score: 3, Funny
  
  It's the physicist clickbait equivalent of
  
  "One strange, old trick helped me lose 165 LBs"
  
  =
  
  "Physicists Resurrect an Old, Strange Dark Matter Theory"
19. Re:Strange? by Cyberax · 2014-11-05 08:48 · Score: 5, Informative
  
  Yes, it is. We're talking about something that is close in density to neutron-star matter but can exist freely without gravitational confinement of a neutron star. This theory is indeed not new - I've studied it at university as one possible theory for the dark matter. It turns out that if stable clumps of strange matter can exist then it's possible that they form (at least) the bulk of the dark matter. But only barely.
  
  So they would look like baseball or basketball-sized spheres of matter that is even denser than neutronium. It won't be 'dark' - strange particles can interact with photons just fine. These clamps will move at 'galactic' speeds (~100 km/sec) but not at relativistic speeds. They'd be able to punch through the galactic dust clouds like a bullet through a sheet of paper and given the general density of the matter in a galaxies (i.e. 'almost perfect vacuum') the strange clumps are expected to be captured by stars in significant quantities only on the scale of tens of billions of years.
  
  Another interesting feature is their "surface tension" barrier. The strange clumps can NOT accrete normal matter, regular nuclei would simply bounce off the border between the vacuum and the strange matter. This barrier can be pierced by sufficiently energetic individual particles or by slamming into dense matter (i.e. a planet).
  
  The probability of such clump hitting the Earth is about once in every 1000 years. It'll punch through the atmosphere and explode somewhere deep in the crust or in the mantle. From the outside it'd look like a large earthquake.
20. Re:Strange? by PlusFiveTroll · 2014-11-05 09:38 · Score: 3, Interesting
  
  The issue I have with this theory is, in the 4,000,000,000 years that Earth has been around, wouldn't quite a lot of this 'matter' built up in the crust and core? Where is it at? Sinking deep in to the crust?
21. Re:Strange? by Cyberax · 2014-11-05 09:44 · Score: 5, Informative
  
  Once the surface tension barrier is breached, the clump explodes in a huge nuclear explosion. Strange matter particles then simply decay and become regular hadrons and form regular nuclei. However, it's also possible that some clumps sank to the core if the collision conditions were just right and surface tension barrier is strong enough.
22. Re:Strange? by Anonymous Coward · 2014-11-05 10:30 · Score: 1
  
  It's mathematical wankery based on exactly NOTHING.
  So why not respond with a mathematically precise criticism, instead of just listing off topics that could easily be confused for someone who just reads pop-sci garbage? As much group-think as Slashdot can have, putting actual substance in your post can bypass that easy enough. Otherwise, everyone will just assume you have no idea what you're talking about until proven otherwise.
23. Re:Strange? by Anonymous Coward · 2014-11-05 10:35 · Score: 0
  
  Doesn't sound like much of a crackpot idea. Have you considered unformulating your theory in terms of loops and springs?
24. Re:Strange? by Anonymous Coward · 2014-11-05 13:32 · Score: 0
  
  I'm needlessly cranky right now. Please just take this as positive proofreading
  
  can NOT
  "cannot"
  
  i.e.
  "e.g."
25. Re:Strange? by cazzazullu · 2014-11-06 00:53 · Score: 1
  
  Neutron-star density, as in one baseball of the stuff weights as much as 1000 Mount Everests. This stuff would fly through the Earth without too much resistance, even without slowing down too much.
  
  --
  int main(void) {while(1) fork(); return 0;}
26. Re:Strange? by painandgreed · 2014-11-06 04:49 · Score: 1
  
  Once the surface tension barrier is breached, the clump explodes in a huge nuclear explosion. Strange matter particles then simply decay and become regular hadrons and form regular nuclei. However, it's also possible that some clumps sank to the core if the collision conditions were just right and surface tension barrier is strong enough.
  In that case wouldn't we see a varying degree of dark/strange/missing versus normal matter over time and thus have more missing matter in older galaxies that were farther away and be able to test for that?
27. Re:Strange? by tehcyder · 2014-11-06 04:49 · Score: 1
  
  Not sure why this is a troll.
  If something is unfalsifiable, it may be brilliant, witty and elegant, but it's not a scientific theory: it's a good concept for a sci fi novel.
  
  --
  To have a right to do a thing is not at all the same as to be right in doing it
28. Re:Strange? by Anonymous Coward · 2014-11-06 05:24 · Score: 0
  
  Is it by any chance red?
  http://memory-beta.wikia.com/wiki/Red_matter
29. Re:Strange? by Anonymous Coward · 2014-11-06 05:53 · Score: 0
  
  The popular articles written about the ACTUAL scientific paper perhaps are not clear enough. The scientific article (found here: http://arxiv.org/abs/1410.2236) does not claim they could be common particles. They could, however, be made of large, strongly-interacting objects that are partly composed of strange quarks, but these are not typical atoms. They could also be anything else that interacts with normal matter strongly.
  To Igw and others paying attention: The point is that, observationally, dark matter doesn't have to be that "dark" in order to be a good dark matter candidate so long as it is made of very massive objects. It can interact via the strong force, electromagnetism, ... you name it. The reason why is that if these objects, whatever they are, are very massive then their number densities are very low because the total dark matter density is already fixed by observations. Consequently, their effects on the large-scale behavior of the universe (including the CMB and galaxies, as you say) are very hard to distinguish from other dark matter candidates, e.g. WIMPs, because they are effectively decoupled from the normal matter in the early universe and can easily collapse to form the halos that galaxies and clusters reside in. They also wouldn't be easily visible with telescopes because, again, their abundance by number would be quite low.
30. Re:Strange? by Anonymous Coward · 2014-11-06 07:31 · Score: 0
  
  Maybe because it doesn't actually say anything or give any details, or maybe because people see wording like "fruit loops for brains" and assume one isn't trying to contribute to an insightful conversation on the topic. Or maybe it is because absolutes like "based on exactly NOTHING" are so far from reality of the situation, that if it isn't a troll, at best it is extremely naive.
  Or that the little that was said, lumps together things that are rather different: Physicists don't treat many-worlds as a certain description of the universe, and quite frequently will spell out the difference between theory and interpretation. Holographic theory is just the idea that boundaries contain information of the interior, which applies to very real world situations and systems like electromagnetism and gets practical use, along with having testable predictions for quantum mechanics with experiments being built for now. String theory does have issues with parts not being immediately falsifiable, but the only reason to lump it in with the other two ideas is if you had the most cursory intro from pop-sci, or are just superficially judging them by their names.
31. Re:Strange? by Cyberax · 2014-11-06 09:50 · Score: 2
  
  Yes, it's one of the predictions. But since we don't see this, models are calibrated in such way as to make up for that. It's possible, barely. It's one of the reasons why this theory is unlikely - it requires too much fine-tuning to explain the observable reality.
32. Re:Strange? by RockDoctor · 2014-11-07 08:20 · Score: 1
  
  Read the section of the paper concerning detection efforts in mica. They don't see significant exposure of the specimens they examined (or which were examined in the 1990s, actually) to the particles they're looking for. They use that as one constraint on the mass of their putative particles.
  Those mica specimens go back to around 500 million years. You can go back further, but the mass constraints change because thermal effects in the rocks slowly heal older crystal dislocations, erasing the record like on an old tape. By the time you're looking at crystal defects that would have melted the crystal itself, and so erased themselves on creation. There are structures that go back this far, but they don't preserve the traces of delicate events, just violent ones.
  
  --
  Birds are not dinosaur descendants;birds are dinosaurs, for all useful meanings of "birds", "are" and "dinosaurs"
33. Re: Strange? by Anonymous Coward · 2014-11-07 09:57 · Score: 0
  
  *your
In laymen's terms... by neoritter · 2014-11-05 05:43 · Score: 3, Insightful

Excuse the oversimplification here but....
What I'm getting is, if they take a bunch of particles together in the right combination, then they no longer emit or react to photons? A) huh? B) so invisibility cloak anyone?
1. Re:In laymen's terms... by gstoddart · 2014-11-05 05:45 · Score: 1
  
  Outlook uncertain. Try again later.
  
  --
  Lost at C:>. Found at C.
2. Re:In laymen's terms... by blueshift_1 · 2014-11-05 05:45 · Score: 2
  
  B) so invisibility cloak anyone?
  
  It'd probably be more like... invisible clothes. Just let it all hang out!
3. Re:In laymen's terms... by DoofusOfDeath · 2014-11-05 05:58 · Score: 4, Funny
  
  Excuse the oversimplification here but....
  What I'm getting is, if they take a bunch of particles together in the right combination, then they no longer emit or react to photons? A) huh? B) so invisibility cloak anyone?
  I feel a car analogy is in order here.
  Lacking a physics background, I'm not the right person to make it.
  This being Slashdot, I will anyway. It's like you went to a car sales lot with 100 fully functional cars on display. You put them all into a (really) huge car compactor, and out comes a baseball-sided chunk of metal, plastic, and glass. Its brake-lights don't work.
4. Re:In laymen's terms... by Dutch+Gun · 2014-11-05 05:58 · Score: 1, Funny
  
  What are you talking about? I can clearly see those garments. Why, I'm not sure I've every seen such magnificent rainment, in fact! Such finery, of course, can only be seen by those with the most discerning of eyes, and judgement to match, I daresay.
  Surely you can see them as well, can you not?
  
  --
  Irony: Agile development has too much intertia to be abandoned now.
5. Re:In laymen's terms... by Flavianoep · 2014-11-05 06:09 · Score: 3, Interesting
  
  In laymen's terms, dark matter is a value that scientists infer from some calculations that albeit all of them correct cannot fit together. Then some scientists calculated the difference and called it dark matter, where 'dark' is a fancy word for 'nobody knows what it is'. To understand the things in the Case Western theory, which is not dark matter, consider that atoms are more than 99% vacuum, while the objects in that theory are mostly matter, not atoms. As such, they account for a large amount of matter, while not being big enough to be detectable by our astronomical instruments. They may react to photons, but most of the objects we are capable of observe in far space are really, relly huge and they are not.
  
  --
  Linux is for people who don't mind RTFM.
6. Re:In laymen's terms... by quantaman · 2014-11-05 06:28 · Score: 2, Funny
  
  I feel a car analogy is in order here.
  Lacking a physics background, I'm not the right person to make it.
  This being Slashdot, I will anyway. It's like you went to a car sales lot with 100 fully functional cars on display. You put them all into a (really) huge car compactor, and out comes a baseball-sided chunk of metal, plastic, and glass. Its brake-lights don't work.
  I feel like a sports analogy is in order here.
  Lacking a physics background, I'm not the right person to make it
  This being Slashdot, I will anyway. It's like you have a hockey team with a bunch of good players. You then add a bunch of face-punchers who get in fights and act gritty, and out comes a dysfunction train wreck of a hockey team. They don't show up on the scoresheet.
  
  --
  I stole this Sig
7. Re:In laymen's terms... by DoofusOfDeath · 2014-11-05 06:41 · Score: 1
  
  I feel a car analogy is in order here.
  Actually, you know what? I think it sucks that Tom Magliozzi died the other day. In honor of him, my best impersonation of how he would have fielded this question:
  "How the hell would we know?"
  Losing Tom sucked. It's still the thing most on my mind.
8. Re:In laymen's terms... by Anonymous Coward · 2014-11-05 06:43 · Score: 0
  
  Oh, my, no. That would require extremely tiny atoms, and have you priced those lately? I'm not made of money. Leave me alone!
9. Re:In laymen's terms... by Anonymous Coward · 2014-11-05 08:48 · Score: 0
  
  Dyson Spheres? There are whole fleets of them floating through the galaxy.
10. Re:In laymen's terms... by Anonymous Coward · 2014-11-05 10:31 · Score: 0
  
  how many football fields is that?
11. Re:In laymen's terms... by Carnildo · 2014-11-05 10:58 · Score: 1
  
  called it dark matter, where 'dark' is a fancy word for 'nobody knows what it is'
  Actually, "dark matter" was originally called "dark" because it wasn't hot enough to emit light (the Earth, for example, would be considered "dark matter" under this definition). Dark matter was originally thought to be things like stray planets, cold gas clouds, and the like. People only started looking for exotic dark matter once they realized there wasn't enough ordinary matter to do the job.
  
  --
  "They redundantly repeated themselves over and over again incessantly without end ad infinitum" -- ibid.
12. Re:In laymen's terms... by Anonymous Coward · 2014-11-05 12:26 · Score: 0
  
  I'm so confused now! I thought the face-punchers WERE the good players. Isn't that what hockey is about?
  I'm feeling like I missed something here. How about an analogy for 5 year olds?
13. Re:In laymen's terms... by FatLittleMonkey · 2014-11-05 13:03 · Score: 2
  
  (the Earth, for example, would be considered "dark matter" under this definition)
  No, the Earth absorbs and re-emits light in a spectrum related to its temperature. Enough conventional matter would alter the observable properties of galaxies, as indeed free gas and dust does. That's how they know that there isn't enough ordinary matter to do the job: "not dark enough".
  
  --
  Science is all about firing a drunk pig out of a cannon just to see what happens.
14. Re:In laymen's terms... by Anonymous Coward · 2014-11-05 14:01 · Score: 1
  
  Ordinary dark matter wasn't really eliminated until microlensing surveys found way too few events for there to be compact, dark objects of ordinary matter, not to mention results from the CMB. Otherwise, cold ordinary matter would still be a possibility, because even though it would emit IR, it would be below detection thresholds by far and still be enough to account for things.
Physicists discover one strange theory... by Anonymous Coward · 2014-11-05 05:44 · Score: 0

...to explain dark matter. The secret OTHER scientists don't want you to know. Cut down your belly fat or something too.

Well, that's what I read the headline as, anyway.
1. Re:Physicists discover one strange theory... by Anonymous Coward · 2014-11-05 05:50 · Score: 0
  
  This one weird trick will uncover the secrets of the universe and allow you to communicate with aliens on a higher plane of existence.
Magic Matter by The+Raven · 2014-11-05 05:51 · Score: 2, Insightful

While I agree that something is odd with gravity, the certainty that many scientists seem to have that it must be an exotic particle or form we have not discovered seems misguided. It could be something exotic and new that doesn't fit with any previously discovered science... or not. Dark matter just fails Occam's Razor in my opinion.
I'm not saying it doesn't exist either... just that I think we need to be more open to alternative theories like this. I'd love to see this particular question answered in my lifetime.

--
"I will trust Google to 'do no evil' until the founders no longer run it." Hello Alphabet.
1. Re: Magic Matter by Anonymous Coward · 2014-11-05 06:51 · Score: 0
  
  You sound lahk one a dem creashunnists. Witch! Witch! It's settled science! All true Scotsmen, get yer pitchforks!
2. Re:Magic Matter by Anonymous Coward · 2014-11-05 08:13 · Score: 0
  
  There is no such thing as odd gravity. There are only scientists with odd theories.
3. Re:Magic Matter by Anonymous Coward · 2014-11-05 08:38 · Score: 0
  
  Dark Matter is a place holder that can explain an effect that we know to exist. Occam's Razor would lean more towards a new type of configuration of matter than breaking all current physics. It is one of those things that if it doesn't exist, we have much more serious fundamental problems, and in some cases, completely illogical.
4. Re:Magic Matter by Anonymous Coward · 2014-11-05 09:11 · Score: 1
  
  >Dark matter just fails Occam's Razor in my opinion.
  Glad you weren't consulted about quantum mechanics when that was being discovered, too!
5. Re:Magic Matter by Anonymous Coward · 2014-11-05 09:13 · Score: 0
  
  Nothing "fails" Occam's Razor. That's not how it works.
6. Re:Magic Matter by Anonymous Coward · 2014-11-05 10:28 · Score: 0
  
  Lets use occam's razor then, you disagree because A. you have researched the topic thoroughly and found it wrong or B. You're an idiot shooting from the hip.
  This isn't just some random crap they've decided, this is from observations. As in a lot of things that we know to work REQUIRE certain things to be true. This is called indirect observation. I can't directly observe and tell you the difference visibly from a clear acid and water, it doesn't mean acid doesn't exist, just test it. We're in the whole testing phase now, trying to figure out what's the difference between acid and water, because we know there is a difference otherwise acid wouldn't kill you when you drink it.
7. Re:Magic Matter by radtea · 2014-11-05 10:58 · Score: 5, Insightful
  
  While I agree that something is odd with gravity, the certainty that many scientists seem to have that it must be an exotic particle or form we have not discovered seems misguided. It could be something exotic and new that doesn't fit with any previously discovered science... or not. Dark matter just fails Occam's Razor in my opinion.
  I'm not sure why this was modded "Insightful" but it suggests that others share your questionable views, so I'll reply to them.
  1) Scientists are not certain that dark matter is exotic particles, which is why scientists write papers like the one under discussion here. What seems misguided to me is people who are apparently ignorant of how science--which is the discipline of publicly testing ideas by systematic observation, controlled experiment, and/or Bayesian inference--works commenting negatively on how science works. It's a bit like Creationists critiquing their own bizarre views of "evolution" while ignoring the actual theory of evolution.
  There has never been a time in the past several decades when any actual scientist has been even remotely certain about the nature of dark matter. Various ideas have been put forward, including ideas that modify gravity, and none of them have stood up to the routine tests applied to them. This has driven research toward exotic particles.
  In particular: Big Bang Nucleosynthesis puts very tight constraints on the density of baryonic matter in the universe, and it's only about 5% of the amount needed to explain the large-scale cosmological observations that imply dark matter. So it isn't like scientists are just saying, "Yay! Evidence of new particles!" Rather we are saying, "Damn, there's a problem we can't solve with baryonic matter."
  2) Occam's razor is stupid. You know, of course, that Occam himself used it to "prove" that nothing existed other than God, since to invoke other entities (matter, the Earth, shoes, cats...) to "explain" the phenomenology of experience would be to "multiply entities above necessity".
  In the cases when it works or makes sense, Occam's razor is "Bayes' Rule for Dummies". The prior plausibility of a horse being around is higher than the prior plausibility of a zebra being around. Since both horses and zebras create hoofbeats with equal probability, hearing hoofbeats increases the plausibility of the propositions "There is a horse around" and "There is zebra around" by the same factor. Since horses were more plausible before, they are more plausible after.
  That is:
  p(zebra|hoofbeats) = P(hoofbeats|zebra)*p(zebra)/P(hoofbeats)
  p(horse|hoofbeats) = P(hoofbeats|horse)*p(horse)/P(hoofbeats)
  Since P(hoofbeats|zebra) ~ P(hoofbeats|horse) and p(zebra) < p(horse) and P(hoofbeats) = P(hoofbeats), it is trivially true that p(zebra|hoofbeats) < p(horse|hoofbeats).
  No notions of "simplicity" are required.
  So: your comment is quite badly mistaken.
  
  --
  Blasphemy is a human right. Blasphemophobia kills.
8. Re:Magic Matter by paul.hatchman · 2014-11-05 16:47 · Score: 2
  
  Dark matter *is* the simplest explanation for the data. Every proposal to modify gravity introduces one or more new fields. And every time you add a new field, guess what? You are adding a new particle as well. Dark matter models not only generally fit well with observation, but also with out existing understanding of gravity. They have exactly the same downside as gravity modifying alternatives, i.e. introducing one or more new particles.
  
  Besides, I've never understood this objection. We already know about neutrinos which have mass and are weakly interacting (they only interact via the weak force and gravity) . A dark matter particle could be very similar to a neutrino, except it would not interact via the weak force and would likely be more massive.
9. Re:Magic Matter by Neil+Boekend · 2014-11-05 21:39 · Score: 1
  
  Dark matter just fails Occam's Razor in my opinion.
  If you think it's an answer then: yeah, it should.
  Dark matter is more like an open question. We don't know what causes the effects we are seeing. "The explanation with the fewest assumptions is probably the best one" doesn't really work when all the explanations require many assumptions.
  The best way to research such an open question is
  1. Think of more ways this question could be answered.
  2. Check the assumptions. Find if they are reasonable.
  3. Remove explanations that have assumptions that turn out to be wrong.
  4. goto 1
  This paper is doing 1. It may be the answer, it may not be.
  Step 2 is expensive in this case. Often even impossible.
  
  --
  Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
10. Re: Magic Matter by Anonymous Coward · 2014-11-06 00:43 · Score: 0
  
  When all you have is a particle smasher, everything looks like a particle...
11. Re:Magic Matter by The+Raven · 2014-11-06 04:49 · Score: 1
  
  There is a reason that alternatives to WIMPs are listed under Alternative Theories in Wikipedia. Claiming that the collective brainpower of most scientists has not focused on that particular theory is disingenuous.
  
  --
  "I will trust Google to 'do no evil' until the founders no longer run it." Hello Alphabet.
12. Re:Magic Matter by Anonymous Coward · 2014-11-06 05:58 · Score: 0
  
  I'm not sure exactly what you are trying to say, but just because it is labeled as alternative on Wikipedia does not mean it is studied by only a small minority of scientists. Entire research groups are dedicated to alternative gravity models, for example. But when you go to their talks, even they will admit that the alternative gravity ideas they are investigating don't appear to match data as well as missing matter models or require more fudge factors that at the moment seem too arbitrary. Like a lot of areas of research, things rarely get completely ruled out, with new observations just constraining things with upper/lower bounds, and quite a few scientists are or work with someone who is checking to see what still works within those bounds.
13. Re:Magic Matter by strikethree · 2014-11-06 17:59 · Score: 1
  
  I think you are being overly hard on the parent. What I read into his words were that by calling it "Dark Matter" we are focusing too much on the possibility that it is actually matter whereas the truth may be far more... different.
  For example, someone above proposed that space itself may be "dimpled". Another off-the-cuff proposal is that the convention of "frames of reference" is not defined properly so that the galactic curves may not be what is actually there (assuming there is actually an objective reality).
  Sure, Dark Matter is an excellent placeholder like X is an excellent placeholder in an algebraic equation; However, in algebra, we do not assume that what X actually represents will be a letter. With Dark Matter, it seems that we are assuming it will be matter... but there is zero evidence that it will be matter at all, which is why is it has the further label of dark.
  To me, the parent was insightful even if the comment did not offer any actual forward progress.
  
  --
  "Someone needs to talk to the tree of liberty about its ghoulish drinking problem." by ohnocitizen
14. Re:Magic Matter by Anonymous Coward · 2014-11-07 07:57 · Score: 0
  
  You seem to be reading something in the original post that I don't see, considering they complain it is about assuming it is "exotic particle or form we have not discovered." The post in that sense seems rather ill-informed, considering how much work has been done by scientists not assuming it is exotic (matter or otherwise), and attempts to put upper bounds on the amount of normal stuff we are not seeing. Even if saying scientists assume that it must be matter, which is not what the original post seems to say, would be wrong, as quite a few scientists continue to take other approaches with alternative gravity and observation theories. But as things stand, even those scientists often state their theories don't work as well as ones just using hard to see matter.
not likely by iggymanz · 2014-11-05 05:52 · Score: 2

we're talking about clumps of matter with a density of a hundred billion tons per cc that would collide (likely passing straight through with catastrophe on both sides) with the earth at least once a year....that would be VERY noticeable. Even moreso noticeable if the velocity was insufficient to leave the other side, we'd have a growing degenerate matter "star" in the center of our planet, which could only end badly.
1. Re:not likely by DoofusOfDeath · 2014-11-05 06:02 · Score: 1
  
  we'd have a growing degenerate matter "star" in the center of our planet
  Actually, I think Lena Dunham lives in NYC.
2. Re:not likely by gstoddart · 2014-11-05 06:05 · Score: 2
  
  we're talking about clumps of matter with a density of a hundred billion tons per cc that would collide (likely passing straight through with catastrophe on both sides) with the earth at least once a year
  Ummm ... how would we know that, and why would we expect it? I'm not disputing you, because I have no idea WTF you're saying.
  I'm saying you've just thrown out a rejection based on a conclusion I have no idea what it means or what supports it.
  Can I play too? Dark matter takes on the form of cosmic, cross-dressing clowns, who play peekaboo behind stars, steal your last beer, and pee on your rosebushes.
  
  --
  Lost at C:>. Found at C.
3. Re:not likely by iggymanz · 2014-11-05 06:08 · Score: 3, Informative
  
  I actually RTFP. They specifically mention the density, size and frequency of collision with earth of their posited dark matter candidate.
4. Re:not likely by gstoddart · 2014-11-05 06:13 · Score: 1
  
  You know, fair enough on that one ... one does see many "it can't be this because of that" just getting tossed out there on Slashdot.
  And most of us haven't got nearly enough background to assess any of that stuff.
  Physics at this level gets pretty much into voodoo and "trust us, it's complicated, but we've done the math". :-P
  But you can't disprove my cosmic, cross dressing clown theory, so I'm holding out hope. ;-)
  
  --
  Lost at C:>. Found at C.
5. Re:not likely by Anonymous Coward · 2014-11-05 06:36 · Score: 0
  
  one does see many "it can't be this because of that" just getting tossed out there on Slashdot.
  When this happens you should bookmark the post and come back in a few hours to see if there are any rebuttals from people with enough background. Right now you're just adding noise.
Lovecraftian Dark Matter by __aaclcg7560 · 2014-11-05 05:59 · Score: 3, Insightful

Wikipedia has the answer! http://en.wikipedia.org/wiki/Cthulhu
Clumps of strange quarks? by Anonymous Coward · 2014-11-05 06:02 · Score: 0

Why not simply clumps of ordinary matter? If there are n balls of radius r, then visible-light observations can only measure their cross-section c1*n*r^2. Their mass is c2*n*r^3 which you set equal to the "dark matter" mass from gravitational observations. Two equations with two unknowns, so simply solve for n and r.
um no by Charliemopps · 2014-11-05 06:14 · Score: 1, Interesting

Color me skeptical but from what I'm reading...
a form of matter that could only be formed in the early universe
It makes up 5x as much mass as ordinary mass in the universe
It's transparent to light
It's either transparent to heat or just so happens to give off almost exactly the same amount of heat as it absorbs
It has a density somewhere around the same density of a neutron star
It's not managed to devour/destroy any stars or otherwise clump together
It's a fluid
and there just so happens to be none of it on earth...
Even the studies author writes in the conclusion:

The nature of dark matter is still largely unknown. For this reason, it is prudent to
hedge our bets on what it might be
That's not exactly a ringing endorsement. It's more like "Ok, since we haven't found dark matter yet... this is way out there but hey, why not?"
1. Re:um no by Samantha+Wright · 2014-11-05 07:23 · Score: 1
  
  Hey, um... what if dark matter is just heaps of rogue planets and left-over dust and gasses from nebulae? Given that we've only recently gotten a handle on how many rogue planets there are out there, wouldn't they've been left out of our previous calculations?
  
  --
  Bio questions? Ask me to start a Q&A journal. Computer analogies available for most topics!
2. Re:um no by Crashmarik · 2014-11-05 07:31 · Score: 1
  
  Sure it's a tough list but it's no worse than what people keep trying to come up with
  http://phys.org/news157292373....
  Here we have physicists creating a new class of particle with an in principle undetectable fifth long range force as well
3. Re:um no by oh_my_080980980 · 2014-11-05 07:52 · Score: 1
  
  Wow more dumb-asses commenting on something they know nothing about.
4. Re:um no by wonkey_monkey · 2014-11-05 07:56 · Score: 1
  
  I think the standard objection to that idea is that there'd have to be so many/much of them/it that we'd have seen them by now.
  
  --
  systemd is Roko's Basilisk.
5. Re:um no by Agent0013 · 2014-11-05 08:22 · Score: 1
  
  And it clumps together forming the scaffolding for the galaxies, but it also somehow separates out to only show up as a halo around the outer edge of the galaxies. I was just watching this video yesterday to understand what they think this stuff is and many of the things she says contradict themselves. https://www.youtube.com/watch?...
  Plus, nowhere do they ever say they account for time dilation in the galactic rotation speed. If gravity is more intense in the center of the galaxies, then time there will be slower. Which will appear as the outer edge of the galaxy rotating faster than it should. Time is moving faster for the matter there, so it moves further from our viewpoint. Our most accurate clock shows a difference from moving the clock from the floor to putting it up on the wall, I think there would be somewhat more of a difference when you move towards the center of a galaxy.
  She also says how it passes through when two galaxies collide without interacting, but in some cases it collides and stays in the middle while the galaxies pass through and are on opposite sides. It seems to be some magical stuff that can do whatever the physicist wants it to do at the moment.
  
  --
  
  -- ssoorrrryy,, dduupplleexx sswwiittcchh oonn.. -Quote found on actual fortune cookie.
6. Re:um no by tnk1 · 2014-11-05 08:28 · Score: 5, Informative
  
  There was always an assumption that rogue or orphaned planets could contribute. Cross referencing against observations and known theories yielded a contribution that exists, but is far too small. These are what they are refering to as MACHOs.
  There needs to be *a lot* of whatever is causing the discrepancies, and that much "normal" matter would probably be easily measured as the effect that the mysterious matter has is significant enough to require an equivalent mass to something like 20-30% of the mass of the universe. It would be difficult to believe we could be off on our observations by that much.
  Cold Dark Matter: http://en.wikipedia.org/wiki/C...
  MACHOs or Massive Compact Halo Objects are large, condensed objects such as black holes, neutron stars, white dwarfs, very faint stars, or non-luminous objects like planets. The search for these consists of using gravitational lensing to see the effect of these objects on background galaxies. Most experts believe that the constraints from those searches rule out MACHOs as a viable dark matter candidate.[5][6][7][8][9][10]
  Also:
  http://en.wikipedia.org/wiki/D...
  Studies of big bang nucleosynthesis and gravitational lensing have convinced most scientists[10][80][81][82][83][84] that MACHOs of any type cannot be more than a small fraction of the total dark matter.[8][80] Black holes of nearly any mass are ruled out as a primary dark matter constituent by a variety of searches and constraints.[80][82] According to A. Peter: "...the only really plausible dark-matter candidates are new particles."[81]
7. Re:um no by Anonymous Coward · 2014-11-05 09:06 · Score: 0
  
  That list is what we already know about Dark Matter that is a bare minimum to explain what we're seeing.There are some assumptions being made, like Dark Matter actually being matter, but it's a pretty safe bet. We all know Murphy's law will make sure this isn't true.
8. Re:um no by Anonymous Coward · 2014-11-05 10:33 · Score: 0
  
  That's not how time works, and you just showed you probably weren't the target market but not understanding that time is relative. A car can move at 55mph and I can see that from a stand still without saying they've slowed down.
9. Re:um no by radtea · 2014-11-05 10:40 · Score: 1
  
  That's not exactly a ringing endorsement. It's more like "Ok, since we haven't found dark matter yet... this is way out there but hey, why not?"
  The interesting bit of the paper is pointing out that observational limits excluding Standard Model-ish dark matter are incomplete. This is significant, as the new physics required to make stable "macros" of the kind discussed (nuclear-dense objects in the range of a few hundred grams to around the mass of the Earth, with a gap in the middle) is quite a bit less substantial than that required for physics beyond the Standard Model.
  It it not-inconceivable that the strong force could have some weird metastable minimum for objects on this scale, and not being able to rule out such objects by observation is a problem, so we really should spend a bit of time closing those gaps.
  
  --
  Blasphemy is a human right. Blasphemophobia kills.
10. Re:um no by Chalnoth · 2014-11-05 10:48 · Score: 2
  
  Before the CMB was emitted, the entire universe was an extremely smoothly-distributed ionized plasma. There were no galaxies or stars or planets: just a smooth plasma whose temperature varied from place to place by about one part in 100,000. We can see an image of the universe when this plasma cooled to the point it became a gas. This image shows a very clear signature of dark matter (in fact, it's the most sensitive detection of dark matter density that exists).
  This proposal has the same sort of problem: how would you produce such extremely dense objects when the matter was distributed so evenly?
11. Re:um no by mbone · 2014-11-05 10:50 · Score: 2
  
  We would have seen them via gravitational microlensing. This provides a graph of the limits on dark matter, and the planetary mass range is excluded.
  Also, planets (unlike condensed dark matter) would not evade the Big Bang Nucleosynthesis limits on baryonic matter, which rule this out for any mass range.
12. Re:um no by amaurea · 2014-11-05 12:15 · Score: 4, Interesting
  
  To follow up, I'd like to point out plot 2 in the article under discussion (go on, have a look. Opening a PDF isn't that painful). It is a plot of part of the parameter space for dark matter particle candiates, with weakly interacting, relatively light particles in the lower left corner and strongly interacting very heavy particles in the top right corner. MACHOs live to the right in this plot, and WIMPs near and below the bottom. The interesting thing about the plot is that it shows all the regions that have been excluded, color coded by how they were excluded. MACHO territory is basically completely excluded by microlensing. That doesn't mean that MACHOs don't exist - they definitely do (the earth basically qualifies, since it's compact and doesn't shine), but there can't be anywhere enough of them for their gravity to be important.
  If you make the MACHOs smaller so that they aren't as good at lensing, you have to compensate by having more of them to get enough gravity, so microlensing can exclude a pretty wide parameter range. But if things get too light the lensing effect gets too small for us to detect, ending the microlensing exlusion range at a particle mass of about 10^24 g, about 1/10000 of the Earth's mass. But if they get a bit smaller, then can then be detected using lensing interferometry (=nanolensing), and for even lighter objects, by their imprints on crystals found in deep mines that act as natural particle detectors.
  Anyway, I encourage everybody to read the paper: It details all the different techniques used to exclude models. The paper is really quite the opposite of what the [rant]typical Slashdotter anti-science prejudice[/rant] is. It's not somebody pulling some hypothesis out of thin air and then not bothering to test it. As the plot shows, this is really a case of eliminating slice after slice of the model space, with 75% of the area in the figure already being excluded.
13. Re:um no by amaurea · 2014-11-05 12:28 · Score: 4, Interesting
  
  I was very suspicious when I saw the vixra.org link, but you've actually found a non-crackpot vixra article (if a very short one)! I guess it goes to show that one shouldn't be too quick to judge something by its company.
  (Some context for other readers. arxiv.org is where all scientific papers in the fields of astronomy, particle physics and related fields are posted and read by working scientists. In these fields it has in practice supplanted traditional journals - on still submits articles to them, but nobody actually reads them, since articles appear on arxiv much earlier, and arxiv is free to everybody and much more convenient than dozens of scattered journals. But not everybody can post on arxiv. One must either be part of an academic institution or be endorsed by somebody who is. vixra was formed as a completely open alternative where anybody could post. But it quickly drowned in a deluge of crackpots. I've sampled it at several points (mostly the astronomy section), and did not succeed in finding a single remotely worthwhile paper in several pages of listing in any of the attempts. Hence my surprise this time.)
14. Re:um no by amaurea · 2014-11-05 13:32 · Score: 2
  
  How likely do you think it is that scientists haven't thought of clumping of dark matter or gravitational time dilation in galaxies? It sounds like you really believe that all dem stoopid scientists and their entire field of research have missed your "novel" and "revolutionary" points. I think usually when it seems that way, the natural thing to do is to assume that you've misunderstood something, at least until you've properly researched the issue.
  
  And it clumps together forming the scaffolding for the galaxies, but it also somehow separates out to only show up as a halo around the outer edge of the galaxies.
  Have you thought about why our galaxy is the size it is? Gravity is definitely pulling inwards, so why doesn't it just collapse? The answer is velocity and angular momentum. The stars are all in free fall, but they keep missing the center of the galaxy because of their tangential velocity. Even if you start with very low angular velocity, as something collapses its angular velocity grows (just like figure skaters rotate faster when pulling in their arms). And to form galaxy-size objects you already have to get rid of a lot of angular momentum, and the way you do that is through pressure and friction. They baryonic gas that makes up the raw materials for the galaxy has some of this, and is therefore better at collapsing to small objects than dark matter is. This isn't just a handwavy argument - when you put dark matter and baryons into detailed physical simulations and let them run from a start state corresponding to our pictures of the primordial universe, you actually end up with galaxies embedded in dark matter halos.
  
  Plus, nowhere do they ever say they account for time dilation in the galactic rotation speed. If gravity is more intense in the center of the galaxies, then time there will be slower. Which will appear as the outer edge of the galaxy rotating faster than it should. Time is moving faster for the matter there, so it moves further from our viewpoint. Our most accurate clock shows a difference from moving the clock from the floor to putting it up on the wall, I think there would be somewhat more of a difference when you move towards the center of a galaxy.
  The Schwartzchild radius of our galaxy (counting the visible matter) is 0.0003 light years. 1 light year away, the gravitational time dilation would be a tiny 0.015% compared to the outside of the galaxy. At 1% of the radius of the galaxy it would be 3e-7. At our position it would be 5e-9. So if you ignored it, you would still be 99.9999% correct about velocities in almost all the galaxy, and only do slightly worse at the core. So why can we measure this effect on earth? Because we have ridiculously accurate clocks.
  
  She also says how it passes through when two galaxies collide without interacting, but in some cases it collides and stays in the middle while the galaxies pass through and are on opposite sides.
  No it doesn't. You seem to be talking about the explanation of the Bullet Cluster here. The bullet cluster (like any galaxy cluster) is believed to consist of three components: Stars (which we can observe directly), diffuse gas (which we can observe directly) and dark matter (which does not emit light). Stars are compact and practically never hit each other. When two galaxy clusters collide, none of the stars hit each other due to the enormous distances between each individual star, so the stellar part of all the galaxies pass straight through each other as if nothing happened. But the stars aren't the main component of the galaxies. There is much more diffuse gas (the same kind of stuff stars are made of, but not yet collapsed to form stars). This gas has a pressure, and fee
15. Re:um no by PPH · 2014-11-05 14:38 · Score: 1
  
  It appears that Mount Stupid may be made entirely of Dark Matter.
  
  --
  Have gnu, will travel.
16. Re:um no by CauseBy · 2014-11-05 18:19 · Score: 1
  
  "It's transparent to light"
  Came here to say this. It's dark matter because it doesn't seem to emit or block light. Baseball-sized clumps of whatever would block light. We'd know it was there because we couldn't see the stars behind it.
  I didn't read the article. Maybe they explained that bit.
17. Re:um no by Anonymous Coward · 2014-11-06 02:25 · Score: 0
  
  There are still theories and ideas for dark matter that interact with light or emit light, but do so too weakly to be observed by telescopes. Some particle detector searches for dark matter candidates are specifically built on this principle. Searches for things blocking stars were limited to about things more massive than the moon currently, so if some weird, very small thing existed, it would have gone unnoticed in that sense.
18. Re:um no by Agent0013 · 2014-11-06 02:48 · Score: 1
  
  Ok, I went back and looked at what she was saying about the Coma galaxy cluster again. The dark matter was in the center, but the galaxies did not collide like I thought she was saying. They are just swirling around each other.
  
  This isn't just a handwavy argument - when you put dark matter and baryons into detailed physical simulations
  You do realize they decide what dark matter must do, then put it into the simulation that way. Of course it will act in the exact way they said it should. That is quite obvious. The question is whether there is actually matter or something else causing these observations.
  It seems like you know something about the math used to find the time dilation caused by gravity. How are you calculating this? What does the Schwartzchild radius have to do with it?
  The other thing I don't quite get is how they think they know the amount of matter there is in the galaxies. Plenty of scientists talk about how hard it is to find brown dwarfs. We can't even find all the earth impacting asteroids in our solar system, much less the small ones out there just floating about. How can they be so sure they have an accurate count for the amount of mass when they are just trying to count the visible stuff.
  The other thing that seems like it does not make sense is the way they say the dark matter just streams right through the earth. If it has gravity, and reacts to gravity, then why does it not react to the earth's gravity or even the gravity of the sun. Shouldn't the dark matter clump up in a ball in the center of the sun making the mass of the sun greater? First they say it feel gravity, then they say it doesn't.
  You also act like this is known stuff. You do realize that nobody knows what is going on and dark matter is just a place holder for the lack of knowledge about what is happening at large scales in the universe, don't you?
  
  --
  
  -- ssoorrrryy,, dduupplleexx sswwiittcchh oonn.. -Quote found on actual fortune cookie.
19. Re:um no by amaurea · 2014-11-06 05:31 · Score: 1
  Ok, I went back and looked at what she was saying about the Coma galaxy cluster again. The dark matter was in the center, but the galaxies did not collide like I thought she was saying. They are just swirling around each other.
  Oh, it was about the Coma cluster, not the Bullet Cluster. I apologize for confusing you with an unrelated discussion. The Coma cluster evidence is based on the velocity dispersion of the galaxies in the cluster, not separation of components like the Bullet Cluster is. The argument here is that the galaxies move too quickly compared to the gravity produced by the stars, so if there isn't some extra matter the cluster would blow apart (the Coma cluster is not unique in that way, the same thing is observed in every cluster). The argument is not as clear cut here as in the Bullet Cluster, since small modifications of the law of gravity can explain it as well as dark matter can. Modified gravity without dark matter fails for the Bullet Cluster though.
  
  You do realize they decide what dark matter must do, then put it into the simulation that way. Of course it will act in the exact way they said it should. That is quite obvious.
  Nobody is claiming that simulations in themselves constitute empirical evidence. Simulations are used as a step in the hypotetico-deductive method to work out the consequences of a hypothesis. It goes like this: We propose that we have some dark matter with a few simple properties (interacts only via gravity, initially distributed homogeneously, 5 times more of it than baryons). We then run that through a simulation to see what the world would look like if things really were like that. Then we compare the simulation to observations to see how well they match. If all the different observables match well, we consider the hypothesis to be strengthened. If they don't match at all, it would be weakened. One then repeats this for lots of different hypotheses to see which ones work best. Lots of things might seem like good ideas while they're at the handwavy stage, but turn out not to work when actually implemented in detail. That's where simulations help you.
  
  The question is whether there is actually matter or something else causing these observations.
  That is indeed the question, and there are (and have been) lots of different alternatives.
  
  Dark matter
  
  MACHOs: Compact dark objects made of normal matter. For example, planets, brown dwarfs, cold neutron stars and white dwarfs, black holes, etc. These don't emit much light, and are hence dark matter. The Earth is an example of one of these. They definitely exist, the question is if there are enough of them to provide the needed gravity. This used to be the most popular hypothesis, but it has fallen out of favor for two main reasons. Firstly, while these objects are hard to find individually, if they are around in the needed quantity they would cause large amounts of gravitational microlensing, which we are getting quite good at measuring. We do not observe anywhere near enough microlensing events for there to be that many MACHOs out there. Secondly, all the baryonic matter the MACHOs are made from messes up the production of deuterium, helium-3 and helium-4 during Big Bang Nucleosynthesis. There is no doubt that a considerable amount of MACHOs exist, but very probably not enough of them.
  Diffuse gas: There could also be a lot of mass in diffuse gas that's not part of stars. This gas can be quite hard to observe, and we didn't use to be very good at seeing it. And after our instruments got better, it turned out that there was in fact several times more mass in this diffuse gas than mass in stars. However, we are now
20. Re:um no by Agent0013 · 2014-11-06 06:18 · Score: 1
  
  Thanks for all of the info. I read up on this stuff, but it is nice to have someone who understands it better put things into another way to look at it that makes things a little easier to understand.
  Your point about gravity being a conservative force where the object speeds up the same amount that it slows down when leaving makes sense. I should have thought of that as I do know that objects in space aren't just captured in orbit without making some sort of changes to their velocity. This then makes me wonder how the dark matter ever gathered together in the first place with the galaxies.
  The exact GR you speak of sounds interesting. Is that related to calculating the gravity in the galaxy more accurately than treating it as all the mass being in the center? Because the matter at the edge of the spiral is getting pulled by all the other matter around. And with it moving toward some of the mass and away from some other mass, it could be seeing some sort of gravity red-shift that causes a further speed up (I am thinking of the speed of gravity and the searched for gravity waves). I don't quite see how that would hold the elliptical galaxies together in the same fashion as they are all moving pretty randomly as I understand it.
  And thinking about the idea of dark energy, after watching some videos on these subjects, makes me wonder if the big bang isn't just a mis-interpretation of the expansion due to this dark energy phenomenon. There is the cosmic microwave background radiation that supposedly comes from the early big bang. But if there was another place that could come from. . . I guess it still leads to a smaller universe in the distant past and you don't quite get around it leading back to a point in space. Unless new matter is created somewhere in between the current matter. Then you could have expansion indefinitely where it didn't start at one point or one time.
  The universe is a pretty interesting place. From the quantum scale where totally weird things take place, to the cosmic scale where unexplained things are observed. I just hope we find some answers to this stuff because it sure would suck to stay in the dark for the rest of my life. And it seems like dark matter and dark energy should be two aspects of one think somehow. Like if we really understood how gravity worked, perhaps quantum gravity, they would both be explained there.
  Again, thanks for the time you have given posting your very informative text.
  
  --
  
  -- ssoorrrryy,, dduupplleexx sswwiittcchh oonn.. -Quote found on actual fortune cookie.
21. Re:um no by Anonymous Coward · 2014-11-06 07:03 · Score: 0
  
  You do realize they decide what dark matter must do, then put it into the simulation that way.
  
  The vast majority of time in physics, "simulation" refers to just a method of numerically solving equations, especially partial differential equations. Short of an implementation bug, there is not really any distinction to be made between complaining someone uses simulations from someone uses math in general to describe systems in physics. And like with other systems in physics, you don't just plug the results into a simulation, you plug in the basic equations you think describes the system and initial conditions. If you knew those equations would give the exact answer you wanted, you wouldn't even do the simulation in the first place, as the whole point of such numeric work is to see what the equations do in a given situation. At that point, it is like any other aspect of science, where you propose an idea, and if it turns out to make a prediction that contradicts observations, you have to change something.
  
  Of course it will act in the exact way they said it should. That is quite obvious.
  So no, this isn't true, especially not obviously so. Rarely is a system simple enough that you can just look at it and know what the results will be, and if it is, then it would be published as analytic/theory work, not as computational. And when it comes to trying finding numeric solutions to non-trivial test problems, across many fields of physics, computation has shown problems. The question then becomes where the mistake is, and how much needs to be changed, especially if it works in some situations, but not others.
22. Re:um no by amaurea · 2014-11-07 02:10 · Score: 1
  
  The exact GR you speak of sounds interesting. Is that related to calculating the gravity in the galaxy more accurately than treating it as all the mass being in the center?
  No, it's a bit more subtle than that. The problem is that General Relativity is non-linear. In Newtonian gravity, which is linear, you can just add up the gravitational influence from each source to get the total force. This is not strictly true in GR. But we know that GR reduces to Newtonian gravity in the weak field limit, and the gravitational field is weak (in the technical sense) in the overwhelming majority of the galaxy (everywhere except very close to black holes), so it makes sense that those few small regions shouldn't mess things up. A closely related problem is what's called the averaging problem: If you compute the metric based on a lumpy mass distribution and then take a spatial average of it, that's not necessarily the same as taking the spatial average of a lump matter distribution and then computing its metric. (Sorry, that's probably too technical and poorly explained)
  There is a way to take all of this properly into account, called numerical relativity. It is extremely computationally intensive, and currently not feasible to do for simulations of galaxies (or the universe). But it may be possible in a few years, so we might know if this really is a problem or not in the relatively near future. Currently a set of small-scale investigations have been done. They are inconclusive, but it seems like one needs pretty contrived matter distributions to get any noticeable effect.
  
  I don't quite see how that would hold the elliptical galaxies together in the same fashion as they are all moving pretty randomly as I understand it.
  Elliptical galaxies are indeed different from disk galaxies in how they are held up. Disk galaxies are held up by coherent angular momentum. Elliptical galaxies are held up by velocity instead. Velocities are typically much more radial than in a disk galaxy, and stars move a bit like the "hole through the center of the earth" example I described earlier - falling in towards the central region, sweeping past it and then heading out again. The galaxy doesn't collapse because its hard to get rid of those velocities without any stars colliding. But there is a very weak form of friction available called dynamical friction that slowly redistributes the kinetic energy between stars.
  
  I guess it still leads to a smaller universe in the distant past and you don't quite get around it leading back to a point in space. Unless new matter is created somewhere in between the current matter. Then you could have expansion indefinitely where it didn't start at one point or one time.
  What you are describing here is called the steady state theory. It has an eternally expanding universe that nevertheless always looked qualitatively the same because new matter was continuously created to compensate for the dilution from the expansion. It was quite popular in the early 20th century. It does predict the presence of background radiation, just like the Big Bang does, but it fails at the details: The radiation would not be expected to follow a black-body spectrum, nor would one expect it to be as cold as 2.7 K. It does not correctly predict the pattern of waves we observe to be imprinted on it, and it incorrectly predicts it to be unpolarized. It also cannot explain the chemical abundances in the universe (why is there so much hydrogen and so much helium, etc.). And it predicts that galaxies far-away should look qualitatively the same as galaxies nearby, while we actually observe them to look quite different, being smaller and messier, as one would expect from galaxies which are just in the presence of forming.
here's an analogy by slashmydots · 2014-11-05 06:23 · Score: 0, Redundant

Oh look, a floating object in the sky. Logically, it must be:
1. a UFO driven by aliens
2. one of the millions of things we have flying around in the air these days

Oh look, all matter with light bouncing off it doesn't account for all the gravity we experience. It must be: 1. magical made up matter that hasn't been proven to exist
2. regular matter without light or other radiation bouncing off of it in a detectable amount.

Aren't scientists supposed to be smart? Then again, what gets hour long specials and their own show on the History Channel: people using sticks to move large blocks to build the pyramids or aliens building the pyramids. More Ancient Aliens right after the break!
1. Re:here's an analogy by ledow · 2014-11-05 07:03 · Score: 2
  
  That's not what dark matter is.
  If dark matter existed in normal form, the gravity associated with it would be vastly distorting the universe as we know it.
  Pretty much, we know that dark matter can't be normal - as you would consider it - matter. All other theories as to what it might be are just as unproven and have just as many holes.
WIMP by Anonymous Coward · 2014-11-05 06:30 · Score: 0

I remember WIMP as Windows Intel Microsoft Platform
Just too few to see by grimJester · 2014-11-05 06:33 · Score: 2

Nothing like an invisibility cloak. If I understand the paper correctly they're just heavy enough that there are few enough that we haven't seen them.
"Baseball-sized" by PPH · 2014-11-05 06:33 · Score: 2

Glad they didn't say "football-sized" or we'd have to go down that whole units thread yet again.

--
Have gnu, will travel.
1. Re:"Baseball-sized" by Anonymous Coward · 2014-11-05 07:55 · Score: 0
  
  Baseball sized clumps of intergalactic matter are known as the perfect weapon in an all-out spaceball war across the galaxy. Spacesnow fortress after spacesnow fortress have been succumbed under the penetrating power of expertly aimed hail of spaceballs.
2. Re:"Baseball-sized" by Rob+Riggs · 2014-11-05 09:24 · Score: 1
  
  Baseball sized? No, no no,no. I have a much more plausible theory: the Universe is just god's Croquet course.
  
  --
  the growth in cynicism and rebellion has not been without cause
3. Re:"Baseball-sized" by PlusFiveTroll · 2014-11-05 09:44 · Score: 1
  
  Douglas Adams was right all along.
4. Re:"Baseball-sized" by canadiannomad · 2014-11-05 10:07 · Score: 1
  
  Ape #1: Dear me. What are these things coming out of her nose?
  Dark Helmet: Hey, hey, hey. Watch my Helmet.
  Ape #2: Spaceballs.
  Ape #1: Oh, shit. There goes the planet.
  
  --
  Hmm, the humour and sarcasm seem to have been be lost on you.
5. Re:"Baseball-sized" by Anonymous Coward · 2014-11-05 12:57 · Score: 0
  
  They didn't say that because the objects aren't football sized. In fact they are baseballs, not just baseball sized.
  All the great baseball stars of the past (Ted Williams, Babe Ruth, Joe DiMaggio, etc.) actually hit some balls into orbit. Collectively they form Baseball Dark Matter (BDM Theory). All those baseballs have a uniform gravitational field that alters the rotational dynamics of galaxies.
  You heard it here first!
1 weird theory! by AdamThor · 2014-11-05 06:50 · Score: 1

Now you can understand dark matter with this 1 weird theory!

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-- "Oh. This guy again."
Nice paper by Anonymous Coward · 2014-11-05 06:51 · Score: 0

Regardless of whether you buy what is being sold the tour of constraints is enlightening.
Strange dark matter? by mi · 2014-11-05 06:54 · Score: 1

Physicists Resurrect an Old, Strange Dark Matter
Sounds scatological...
"Old" you say? Eeeww....

--
In Soviet Washington the swamp drains you.
Galactic Oort-type cloud by ITRambo · 2014-11-05 06:57 · Score: 2

Does this imply that there might be an Oort-style cloud, or bubble-like sphere, on the galactic edges made of small clumped matter, the total mass of which is many times that of the observable galaxy?
1. Re:Galactic Oort-type cloud by mbone · 2014-11-05 10:45 · Score: 1
  
  No. The dark matter is in a Halo (not quite spherical), which extends out from (roughly) maybe 2000 light years to 100,000.
  It has to be more or less uniform to give the disk it's more or less flat rotation curve. If it was all on the edge, the mass inside wouldn't really feel it, and that wouldn't work.
Old News by Anonymous Coward · 2014-11-05 07:01 · Score: 0

The 'leftover cosmic goop theory' has been common knowledge for years.
WD-40 and an orange are your best bets.
the reason you can't find that mass by swschrad · 2014-11-05 07:03 · Score: 0

is that it's in boxes behind stuff. this is a theory that all these PhDs, going college to college to advanced study for a decade or so, should sign on to in a flash. I'll take my Nobel in person, thanks.

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if this is supposed to be a new economy, how come they still want my old fashioned money?
LOL ... w00t? by gstoddart · 2014-11-05 07:42 · Score: 0

Old, strange, and dark ... I think my wife would say that describes me fairly accurately. :-P

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Lost at C:>. Found at C.
It isn't a "fun" theory by smchris · 2014-11-05 07:47 · Score: 1

Hitting a baseball-sized clump of matter in interstellar space at 200,000 km/hour could take the fun out of space travel.
1. Re:It isn't a "fun" theory by sexconker · 2014-11-05 08:07 · Score: 1
  
  Space Dandy did it. Be more original.
Sorry you feel that way. by publiclurker · 2014-11-05 08:32 · Score: 0

But there is no way to dumb it down any further so that you could even begin to comprehend any of this.
cross section - mass ratio limits by mbone · 2014-11-05 08:58 · Score: 4, Informative

The various limits on dark matter actually limit the ratio of the scattering cross section and the mass of whatever is making up the dark matter (this obviously does not apply to MOND type theories, which are different).
So, there are two ways to have a more-or-less non-interacting dark matter - have a small mass, and a very, very small cross section (as in WIMPs), or have a large mass, and a high density (as in quark matter DM theories). The large mass means that the scattering cross section can be more or less anything, and, specifically, can be what you would expect for regular matter.
Lord Nibbler is responsible for Dark Matter by Anonymous Coward · 2014-11-05 09:15 · Score: 0

Someone left the can of snouts out for him.
Real Reason Dark Matter Can't Be Seen... by pubwvj · 2014-11-05 10:25 · Score: 0

Real Reason Dark Matter Can't Be Seen: The reason scientist can't find Dark Matter is that they're not looking in the right place. As soon as they look at it then it is not dark matter but normal matter. This is because the Universe is very much like a game simulation in the computer where it only displays what you are looking at, not the things you're not looking at. This selective display saves computational resources allowing a higher, more realistic frame rate. Although the objects aren't displayed they still have to be accounted for in terms of gravitational and other force calculations because they are there. In the real Universe there are many people all looking in many directions, much like a multiuser game, so many more different places are being displayed. Yet, still not all of the Universe has observers at the same time because there just aren't enough people looking or, as the case often is, they're looking at the same think like the Kardashians or a soccer game rather than the dark matter they meant to be looking at. The result is that even with the trillions of trillions of trillions of observers in the Universe not all parts of the Universe are being observed at any given moment. These unobserved portions are simply not displayed. That's where the Dark Matter is. If you look really quickly you might... oops, you looked and it got displayed so now it's no longer Dark Matter... And that is why the scientists can't see Dark Matter.
jealous bro? by Anonymous Coward · 2014-11-05 11:51 · Score: 0

Surprise, surprise, trashdot retards modded me troll.
Shit like the "many worlds" "theory", the fucking "everything is actually a hologram" "theory", and pretty much all of string theory prove my point.
It's mathematical wankery based on exactly NOTHING.
Sound like you're jealous because you don't have the brain power to even begin to understand it.
Correction: 0.02 light years by amaurea · 2014-11-05 13:40 · Score: 1

The stellar mass of the milky way is about 64 billion solar masses, giving a Schwartzchild radius of 0.02 light years. The time dilations should therefore be corrected to 1% at 1 light year, 2e-5 at 1% of the galaxy's radius and 3e-7 at our radius. It does not change the conclusion noticeably..
Libertarian? by Anonymous Coward · 2014-11-05 13:45 · Score: 0

Let me guess you also vote Libertarian and think they're different from Republicans.
1. Re:Libertarian? by Anonymous Coward · 2014-11-06 07:22 · Score: 0
  
  You probably vote for Democrats and think they're different from Republicans.
Or it could be, by Anonymous Coward · 2014-11-05 16:10 · Score: 0

you know, subtle flaws in their mathematical analysis. Sometimes reality is the most obvious, simple solution, you know? Nah, COULDN'T be THAT, you know?
statistics? by m.alessandrini · 2014-11-05 18:32 · Score: 1

But everything that's "strange" in physics cannot form the most part of the matter in the universe, isn't it? I'd bet more on our physics not having discovered everything yet, i.e. relativity, 3-dimensional space... could only be a temporary step in our evolution.
I'm from the future by Anonymous Coward · 2014-11-05 23:09 · Score: 0

Dark energy, which is distributed relative evenly in space, is in fact time. Think about that for a moment. How is this related to dark matter? Well..
Our Universe is a larger version of a galactic jet by Anonymous Coward · 2014-11-08 02:53 · Score: 0

Aether has mass. Aether physically occupies three dimensional space. Aether is physically displaced by the particles of matter which exist in it and move through it.
The Milky Way's halo is not a clump of stuff anchored to the Milky Way. The Milky Way is moving through and displacing the aether.
The Milky Way's halo is the state of displacement of the aether.
The Milky Way's halo is the deformation of spacetime.
What is referred to geometrically as the deformation of spacetime physically exists in nature as the state of displacement of the aether.
A moving particle has an associated aether displacement wave. In a double slit experiment the particle travels through a single slit and the associated wave in the aether passes through both.
Q. Why is the particle always detected traveling through a single slit in a double slit experiment?
A. The particle always travels through a single slit. It is the associated wave in the aether which passes through both.
What ripples when galaxy clusters collide is what waves in a double slit experiment; the aether.
Einstein's gravitational wave is de Broglie's wave of wave-particle duality; both are waves in the aether.
Aether displaced by matter relates general relativity and quantum mechanics.