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Good bye Dark Matter, Hello General Relativity
Posted by
Hemos
on Mon Oct 10, 2005 09:30 AM
from the all-einstein-quotes-you-know-are-wrong dept.
from the all-einstein-quotes-you-know-are-wrong dept.
dr. loser writes "The CERN newsletter reports that a new paper by scientists at the University of Victoria has demonstrated that one of the prime observational justifications for the existence of dark matter can be explained without any dark matter at all, by a proper use of general relativity! What does this imply for cosmology and particle physics, both of which have been worrying about other aspects of dark matter?"
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So does that mean... (Score:5, Funny)
Well it clearly matters to some people... (Score:5, Insightful)
(No pun intended)
I think this is a great article.
See my comment here [slashdot.org] where I wonder if maybe we're getting way too excited about dark matter without having any material reason (other than "this is the only explanation that fits our current expectations of gravity") to believe it actually exists.
Based on the moderation that followed, I would say that "some people" don't like it when popular theories get questioned. Which just goes to show you--once a scientific "fact" has been established, our attachment to it becomes as dogmatic as any theological notion...
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Re:Well it clearly matters to some people... (Score:5, Insightful)
There seems to be, as you put it, a "dogmatic" belief, often from undergrads (I'm guessing), that their now current understanding of physics is "right", and that any questioning of dark matter is an excuse to call the qestioner ignorant.
I've asked numerous times why I should think dark matter is anything other than a mildly promising theory.
The responses questioning my intelligence, calling me names, and generally being assholes outnumber the cogent replies 3 to 1.
Since when did scientists start behaving like fundies?
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From the Abstract (Score:5, Interesting)
That's really interesting. It makes sense to model a galaxy as a fluid on a very large scale. After all, gravity is a relatively weak force. I haven't gone through the paper, but if their math is right, since the assumption is relatively benign, this seems like it would be experimentally verified.
Since the model assumes that a galaxy is a fluid (on a large scale), the model would predict fluid-like phenomena. What I wonder is if there is a galactic analogue to solitary waves. How would these manifest? (A friend wrote his thesis on solitons)
Recent Sci Am article treats waves in galaxies (Score:5, Informative)
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That sound you heard... (Score:5, Funny)
And then refuted virtually instantaneously... (Score:5, Interesting)
Re:And then refuted virtually instantaneously... (Score:5, Interesting)
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Re:Be careful of the source (Score:5, Insightful)
I noticed you were referring to an article on arXiv.org.
Err... you do realize that the "we don't need dark matter" is also on arxiv.org, and lists itself as only submitted?
Plus, it's submitted to ApJ, but is not following the ApJ citation standard. Not that that really means anything, but it does tell you that the authors still have some i-crossing and t-dotting to do.
-Rob
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What, no Gaffer Tape? (Score:5, Funny)
Every teccie knows that the universe is held together by gaffer tape, and the only problem has been to find the link between gaffer tape and dark matter.
If relativity does away with dark matter, well fine, but the cosmologists are missing the key issue here. All this means is that now we have to find the link between relativity and gaffer tape.
Tentative results (Score:5, Insightful)
What does this imply for cosmology and particle physics, both of which have been worrying about other aspects of dark matter?
The case for dark matter has been built for several decades. There is a mountain of evidence that needs an alternative explanation. I would call these new results tentative at best.
Re:Tentative results (Score:5, Insightful)
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WYSIWYG universe (Score:5, Insightful)
This may also be a cautionary tale about the use of linear models (Newtonian gravity) versus nonlinear ones -- interactions among masses distort the solution. If one assumes the wrong things and gets an answer that doesn't fit the observations, perhaps its time to change the assumptions, not add unseen dark matter, epicycles, etc.
"What does this imply....?" (Score:5, Funny)
Einstein has once again, Powned modern physicists. (Score:5, Funny)
Hell, even Hawking has never shaken up the ideas of science and physics to anything near the degree Einstein has.
How long has he been dead? And he's STILL stirring up trouble!
Personally, I think his statue in Washington DC needs to be bigger. He's done far more for this country and the world at large than most of the people with bigger statues. It's just not fair!
Still uses dark matter (Score:5, Interesting)
The poster title is misleading, the paper still leaves a place for dark matter, but on very smaller amounts and far from the halo. So, this matter could easily be barionic (paper's conclusion).
What is really interesting is that the third galaxy didn't fit the model as well as the others. It may be because of the inacuracy of the calculations (is the inacuracy measurable? The paper should have said that) or because there is something different on this one, maybe a smaller concentration of dark matter near the center.
Dark matter still needed in cosmology (Score:5, Informative)
Re:And in 10 years... (Score:5, Funny)
Maybe.
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Re:And in 10 years... (Score:5, Insightful)
Science never has been definite. The defining characteristic of science is that it accepts that all solutions to problems are tenative, and that some piece of information might turn up in the future that will cause us to doubt what we now believe. Intellectual process can't happen without replacing wrong old ideas with better new ones.
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Re:Neat (Score:5, Insightful)
Note that this is the LaTeX source files for the paper, not source code. What would you do with a GPL scientific paper -- change some things and put your own name on it?
Anyway. I'm surprised it took so long for anyone to do this. Is the an obvious approach, especially if the alternative to postulate entirely new classes of matter. We lesser scientists tend to carry an inferiority complex over the supposed genius of physicists, but I wonder if we've maybe given them too much credit.
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Re:Neat (Score:5, Informative)
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My question: (Score:5, Interesting)
If gravity has no "speed" then the advisories against instantaneous communication are violated as a change in the relative position of mass A to mass B would instantly be signaled even across the galaxies.
If gravity does have a speed then wouldn't this "dark matter" be explained as all of the extra grativational "signals" making their way through the universe?
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Re:As usual... (Score:5, Funny)
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Re:No magic pixie dust after all (Score:5, Informative)
The neutrino, when originally discovered, was discovered because something was missing. Particle collisions were seemingly violating the conservation of energy and momentum. Postulating the existence of an unknown, massless or nearly massless particle that interacted only weakly solved that problem.
Only later was the neutrino discovered.
Unanswered questions, very specific unanswered questions (we need *something* to do *this*) often do lead to new discoveries in science.
I'm not saying that dark matter necessarily has to exist, but the galaxy and cluster gravitational dispersion evidence were strong indicators that there had to be more gravity there. Postuatling that we weren't seeing all the mass was a very reasonable postulate. Now there are lots of other reasons (e.g. CMB, large scale structure evolution) to suspect it's there. And, possibly, in the next decade, we will finally identify the dark matter particle in the lab. We'll see.
-Rob
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Re:New discoveries lead to new theories (Score:5, Interesting)
Black holes are, well, dark... so all the 'dark' matter is concentrated in localized places, namely the center of the galaxies.
Black holes at the center of galaxies have masses of 10^6 to 10^9 times the mass of the Sun. (Our Galaxy's black hole is towards the smaller side of that range.
Large galaxies themselves have masses of 10^11 to 10^12 times the mass of the Sun.
The black holes at the centers of galaxies, as far as just gravity is concerned, are dynamically unimportant to the outer parts of the galaxies.
Plus, the problem is more than that. It's not just that we don't have enough matter to explain the rotation curves of galaxies or the velocity dispersion of galaxy clusters, it's not in the right place. As you get farther from the center of the galaxy, you need more and more matter compared to what we see. Adding more matter right at the center wouldn't help that, even if the black holes were big enough (which they aren't).
(The black holes may be dynamically important to the evolution of galaxy structure for other more complicated reasons-- the generation of energy in their accretion disks can create jets and such that may limit the growth of galaxies-- but that's a separate issue from expalining the rotation curves we see in spiral galaxies.)
-Rob
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