Unfortunately, the standard collisionless CDM has problems . It is helpful to remember that the notion that the DM must be non-baryonic is not a direct observational result, but rather the result of plugging observations into the standard model. Those observations are telling us that either the DM is non-baryonic or the standard model needs adjustment. Both options must be kept open.

Not yet. Certainly the coupling of visible and dark matter suggests the proposed non-baryonic candidates may not have the right properties.

Ditto

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982

Could it be something else? Such as "frame dragging." I recall that a test by NASA has proven that locally in earth orbit (no dark matter near the earth) that "frame dragging" does indeed occur. I'm unsure if the fabric of space itself is being moved.

But you would need a whole lot of gravity to move the space fabric itself, something on the order of a planet shows a small drag. How big would it be for gee a whole galaxy?

Now could we move a region of space (and everything in that region) faster than the speed of light? Special relativity does not preclude this idea.

If the amount of frame dragging is what is predicted by general relativity (and the recent experimental results are in agreement with that), then no. The frame dragging cannot account for what we see. It's possible, of course, that general relativity is wrong at large scales, but so far there's no solid evidence of that, and attempts to explain the rotation curves with a modified theory of gravity have not worked so well.

Hum,
Well yeah, we can tweak the physical laws so that the constants are not, er, constant.
Gravity could vary, or the speed of light increase with time, etc.
That could be possible.
But they bring their own problems. And the knock on effect will basically affect all the science of the last century.

A prospect that not a lot of ppl would want, especially QED.

If we were to assume the standard theory was incomplete (which it is anyway) and that dark matter did not exist. How would you tweak the standard theory to account for the large scale structure so that they match up with observation?

(that tweak would also hopefully also explain away the need for a halo around galaxies yet leave the fine structure or deuterium levels within the bounds observed today)

Is it not just easier to say that most of the universe is similar to our own local bit of the universe and just create something called `dark matter`?

We did something similar when we invented the `neutrino`, a particle that had to exist to account for observations, yet at the time was thought to be impossible of ever being detected due to its properties.
I’m sure there were people back then who would have proposed that it did not exist and it was better to modify the fundamental laws (which seems silly now with hind sight – though at the time it was a possibility).

I partly agree, but the main question is not what to call it, but if the assumption that our "local" theories are applicable to galaxy rotations is correct. We have only scratched the surface in our own backyard, until we understand what is going on here there is enough reason to doubt that we can make these sweeping assumptions on dark matter (the main one being that it must exist).
About the neutrino analogy, it is true that sometimes a particle or object is postulated long before it is discovered, but in this case it has taken way too long imo, plus additional observations indicate that any dark matter candidate needs to be "coupled" to luminous matter in progressively exotic ways.

Cheers.

I completely agree with this statement.Since Einstein is declared sacred and no discussion seems to be possible about the "Big Bang" there have been all kinds of unproven assumptions to make the facts fit the theory.

Hi all this is my first on this new combined forum. The above quote is from a similiar Thread to this. I think the main point i was trying to make was that there is perhaps an angular dependance to gravity when it is being frame dragged. Similiar to the pattern seen around a drain hole. Add to this the effect of the stars themselves i.e. they once gathered in an arm will have a mutual gravitational effect: which will enhance the angular dependance. Intuitivilly i doubt that if the idea of frame dragging can have an angualar dependance then i doubt that it would be observable in the current results about the earth's frame dragging.

There's a paper here http://xxx.lanl.gov/abs/astro-ph/0507619 that says they used general relativity to explain galaxy rotation curves without needing dark matter. It's from astro-ph, so I guess it's not woo woo and has too much math in it to be woo woo. Did anybody know about this paper? Had any errors been found in it or is it the unfounding of dark matter?

It's worth taking a look. Hard to believe that under "the weak gravitational fields under consideration" (quote from the abstract) that general relativity would make that much of a difference, though. If their (Cooperstock and Tieu, University of Victoria, with some recognition from the Gravity Research Foundation) calculations are correct, maybe the original ones (that showed a dark matter halo) are wrong.

Astro-ph does not require any peer review, it's just a place for people to post their own papers, sometimes before they've even been submitted to a regular journal. I've seen articles on astro-ph that were simple rebuttals to articles posted there by other researchers. Appearance on astro-ph signifies nothing.

I wouldn't go that far. They won't let you post on astro-ph if you try putting too many articles on there that haven't been through peer review. This particular article was submitted to ApJ and will probably be updated once it has been accepted. Most of the articles on astro-ph have been accepted for publication in a journal or conference proceedings.

Although - I do think its becoming more common for researchers to submit their papers to astro-ph before they've been accepted by a journal.

__________________
"The scientist who asks the right question reconnoiters a new patch of the unknown, and may, with luck, bring it within the constricted but expanding boundaries of the known."

~Timothy Ferris (The Red Limit) 1982