[Dragon]

You're an idiot. There is no grand unified theory of everything yet; Dark matter is needed to explain the observations we can make with telescopes; there is no known link between it and what is happening in quantum physics at the moment.

The first part was uncalled for (the first part of my post was said jokingly, but it seems that it went over your head). As for the second part, I'm planning to look for it. As for the third part, I hope to find it along the way.

[The E]

No, it didn't "go over my head". It just bypassed the "oh look a joke" part of my brain and went straight to the "oh my god how could anyone say something this stupid while at the same time claiming to study this stuff" part.

[Dragon]

So it went over half of your head. And the smiley should've tipped you off. I admit though, it wasn't the funniest joke in the world (I couldn't tell the funniest one, because I quit learning German) [/obligatory python reference]

[z64555]

If there's anything fishy in the physics that will let us remove dark matter from our models, it's the way gravity behaves at long distances.

Such as gravity lensing?

[General Battuta]

If there's anything fishy in the physics that will let us remove dark matter from our models, it's the way gravity behaves at long distances.

Such as gravity lensing?

No, gravitational lensing is a well-understood phenomenon that proceeds naturally from the predictions of GR.

[The E]

It's more about how gravity acts on a galactic and intergalactic scale.

[z64555]

So the approximation of zeroing the gravity force as the distance between acting object increases, isn't upheld in some cases?

[General Battuta]

Not quite that simple. You can read about alternative proposals to the Lambda-CDM model here, but none of them has yet panned out as well as dark matter in terms of predictions.

[Dragon]

Some (long) time ago, I've read a very interesting article about a theory that attempted to explain dark matter by irregularities in the "structure" of space. It did violate the Copernican Principle (IIRC, a "denser" area of space between the observed target and the Earth would make the target seem heavier), but considering that some irregularities were needed for the universe as we know it to form, it seemed quite logical.

Note, I might have mixed up some details, unfortunately I can't find this article, and I've read it a long time ago.

[Bobboau]

here is a funny idea, what if dark matter is a phenomenon that dissipated recently over the whole universe roughly at the same time. we can only see the effect in the local group because they are the only things close enough to be within the visible bubble.

[watsisname]

A fun idea, though as I understand it we see the evidence of dark/missing matter throughout, not just outside our local group.  Even our own galaxy rotates too fast for the visible/known amount of material it contains.

[Bobboau]

I was going by the title of the thread.

[Mongoose]

I know that dark matter is (at least currently) the best explanation for what we've observed, but my heart really really wants one of those other theories to pan out in the end, because the whole thing feels for all the world like "luminiferous aether" come back to haunt us.

[Astronomiya]

A fun idea, though as I understand it we see the evidence of dark/missing matter throughout, not just outside our local group.  Even our own galaxy rotates too fast for the visible/known amount of material it contains.

Yes, this is true.  The paper that prompted this latest flurry of press purported to show that there is essentially no dark matter in the solar neighborhood, and, by extension, essentially none at our distance from the Milky Way's center.  However, said paper is on shaky ground and at least to my mind is probably wrong.  Other, previous studies seem to contradict it anyway, since we know (not to good precision, but I think at least at the factor of two level*) that the Milky Way's mass is some 10¹² M_sun or so, far too much to be accounted for by the baryonic mass we see.

*Yes, this is what passes for good precision in a lot of astronomy.  We're getting better, honest!

[watsisname]

Speaking of which, you mentioned earlier that a slight flaring of the galactic disk would pretty much render their models moot.  But what is flaring, exactly?  Is that similar to a central bulge?

[Cyborg17]

Speaking of which, you mentioned earlier that a slight flaring of the galactic disk would pretty much render their models moot.  But what is flaring, exactly?  Is that similar to a central bulge?

+1

[z64555]

Flaring means the outside ring of the disk is thicker than the "usual" disk, which tapers down to like a knife edge. (Or so I think)

[Astronomiya]

Flaring is the opposite of tapering; so, instead of the disk tapering off to zero thickness as you move away from the center, it gets thicker instead.  Just from common sense reasons, it can't flare very much, if it does.  If it does at all, though, their model fails badly.  Check Fig. 5 in their paper; if dh/dR is as little as 0.3 (this means that if you go 1 kpc further out, the disk effectively thickens by 300 pc), all of a sudden their results are quite consistent with a lot of dark matter being present.  They dismiss the possibility of flaring of the thick disk by saying that if it was all that big, it would have been detected conclusively by now.  I don't think that is at all a safe assumption in this case.

[watsisname]

Ah, like the shape of protoplanetary and accretion disks, that makes sense.

Did some searching on the topic, found some articles stating that there is flaring of our dust and gas disk, (and it is warped, as well!) but I'm having a hard time finding actual numerical constraints on the flaring.


Edit:  Found this.
Three models were compared with data from the near-infrared DENIS survey.  First model is a flat disk, second is a warped disk, and third is both warped and flaring.  The best fit is for the third model, seen on page 233.  Mathy details:

For galactocentric radii R > R_warp, the mid-disc is shifted perpendicular to the plane by a value
z_warp = z_ccos(θ - θ_max).

The warp has its maximum amplitude z_c towards θ_max, and this amplitude increases linearly as z_c = γ_warp(R - R_warp).

As in Gyuk et al. (1999), we model the flaring of the discs by increasing the scale heights by a factor k_flare, beyond a galactocentric radius R_flare, with
k_flare = 1 + γ_flare(R - R_flare).

etc

Apparently this warping/flaring is driven by interactions/collisions with satellite galaxies and the dark matter halo.  Crazy!