Dark Matter Exists

olclops writes "It's a big day for astrophysics. After much speculation, scientists now have conclusive proof of dark matter. This result doesn't rule out alternate gravity theories like MOND, but it does mean those theories will have to account for exotic forms of dark matter."

Comments

Re:Full Paper

[The Great Pretender]

Now hold on a second, I'm not an astrophysist, I'm a chemist, but let me apply a little scientific reasoning to your last sentance An 8 sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen

How exactlty does demonstrating that something cannot explain a phenomina prove that a counter argument is proven? That's like saying the spontaniuos combustion of my dog cannot be proven with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen.

"To be published..."

[posterlogo]

From the NASA press release: "These results are being published in an upcoming issue of The Astrophysical Journal Letters."

Two points. First, journals really hate it when press releases are made prior to the publication date. Second, this journal has an "impact factor" of ~5-6, compared to Nature, or Science, which have impact factors of ~25. Why are they publishing in some obscure journal if this is really the rock-solid proof that they claim it is?? Makes me wonder.

As I understand the process ...

[constantnormal]

... this would constitute a confirmation if a prior prediction was made, and the observed results match the prediction.

This appears to be no more a confirmation for dark matter than when the Michelson-Morley experiment (in 1881) "confirmed" the existence of ether. In the immediate aftermath of the Michelson-Morley experiment, theoreticians generated lots of mathematical "proofs" (e.g., The Ether of Space, Sir Oliver Lodge, Harper & Bros, 1909) that showed how a boundary layer in the ether surrounding the Earth accounted for the observed results. A series of subsequent refinements of the Michelson-Morley experiment showed that the speed of light was truly independent of direction, and Einstein's theories, which did not require the existence of ether, provided a better fit for the observed results than was a boundary layer in the ether.

Over time, the Michelson-Morley experiment was recognized to have disproved the existence of ether -- but it wasn't that way initially.

Alternative explanations include "quantum critical phase transitions", and I'm sure that there are other possibilities, that a series of observations of similar cosmological events will provide the range of data needed to select the hypothesis that best describes the observations.

Being able to fudge one theory to fit a single observation falls quite a bit short of a "conclusive proof". Maybe dark matter does exist, but it's going to take a lot more observations for it to be convincing to me.

How precisely does dark matter permit the expansion of the universe to be defined, and how precisely does the observed phenomenon fit those numbers?

Wake me up when someone has a quantum mechanical model that tells how quarks are bound together in dark matter, or when someone manages to tap into dark energy (which is supposedly all around us).

So what's new, then?

[Moraelin]

So what's new then? All along the whole case for "dark matter" was that galaxies -- _all_ galaxies -- rotate strangely like a rigid body, except right near the centre. According to newtonian mechanics the stars in a galaxy should behave basically like the planets in our solar system: the farther from the centre you get, the slower they move. But in a galaxy stuff moves like that only near the centre, and then it's like gravity changed gradually from 1/(R*R) to 1/R, and the stars rotate at an almost constant angular velocity around the centre.

So from there it's that either:

1. there's a metric buttload of matter we can't observe other than through gravity, in some weird distribution all through the galaxy's disc, or 2

2. we accept that gravity isn't working like we think it does

(Or my favourite: 3. galaxies are just a rotating texture there, so _of_ _course_ they rotate like a rigid. Noone would be dumb enough to simulate the individual stars just to give us a pretty sky in this MMO we call RL ;)

And somehow the favourite is 1, for no obvious reason than that noone wants to modify gravity theories. It's as if Galileo, upon discovering that a stone dropped from the mast doesn't lag behind the ship, would then proceed to invent some "dark wind" that pushes the stone along with the ship. Since existing wind obviously isn't strong enough to push the stone that hard, it's got to be some dark wind in there too. Just, you know, for the sake of not contradicting the existing Aristotelian system.

Anyway, all along we knew that it can't be conventional matter, because we already had plenty of galaxies in various states of illumination and they all behave the same.

So exactly how does the new one help there? It seems to me like it still can't offer conclusive proof that 1 is true and 2 is false, because it would _still_ be equally well explained by 2. What this "solves" is at most a sub-distinction inside 1, once we're dead-set on believing 1 instead of 2. It says basically that if we already decided it's 1, then, yep, it's definitely not baryon matter (rocks, gases, protons, etc), but some weird matter that interacts only with gravity.