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.

Comments

In laymen's terms...

[neoritter]

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?

Re:Strange?

[gstoddart]

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?

Magic Matter

[The Raven]

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.

Re:Magic Matter

[radtea]

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.

Re:Strange?

[lgw]

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.

Lovecraftian Dark Matter

[__aaclcg7560]

Wikipedia has the answer! http://en.wikipedia.org/wiki/Cthulhu

Re:Strange?

[lgw]

And the CMBR data? Fail.

Every problem has a simple, easy to understand, wrong answer.

Re:Strange?

[lgw]

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.