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Physicists Resurrect an Old, Strange Dark Matter Theory
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.
Common particles tend to absorb EMR if they're cold, or emit EMR if they're warm.
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.
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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]
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.
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.
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.
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