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Space Science

Good bye Dark Matter, Hello General Relativity 688

Posted by Hemos
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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Good bye Dark Matter, Hello General Relativity

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  • by scsirob (246572) on Monday October 10, 2005 @10:33AM (#13756404)
    .. that Dark Doesn't Matter??
    • by spellraiser (764337) on Monday October 10, 2005 @10:47AM (#13756512) Journal
      I'm not sure. I'm still in the dark about this matter.
    • But what are the implications for light matter then?
    • by Alaren (682568) on Monday October 10, 2005 @10:56AM (#13756597)

      (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...

      • by ifwm (687373) on Monday October 10, 2005 @11:34AM (#13756914) Journal
        I've dealt with this same issue.

        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?
        • by TheRaven64 (641858) on Monday October 10, 2005 @11:44AM (#13757003) Journal
          Since when did scientists start behaving like fundies?

          When science teachers started teaching `facts' instead of the simplest hypotheses which were not disproved by any observational evidence.

          • by lgw (121541) on Monday October 10, 2005 @12:50PM (#13757558) Journal
            A valid criticism of science teachers, but not of scientists. A difference sometimes overlooked.
            • by Sialagogue (246874) <sialagogue@gma i l . c om> on Monday October 10, 2005 @01:34PM (#13757920)

              I think that overall this is a good point, but I've seen many people who make their living doing hard science who, once they open their mouths, start putting their personal credibility where it does not yet belong.

              Although I don't do it for a living, I'm dedicated to science and it's progress and I have a real love for both the process and the results. But I'm afraid that one of the biggest factors that has made science vulnerable to inroads by fundamentalists is that scientists have, of late, embrace three (admittedly hastily constructed) levels of credibility on scientific subjects:

              1) We very strongly believe this is true because it has been repeatedly verified through controlled experimentation.

              2) We very strongly believe this is true because it can be strongly inferred from existing verified data.

              3) We understand that we don't have all the facts, but we are critical thinkers for a living and our theories are worthier than your theories.

              Number 1 is where scientists should be, but in debates, articles, and various other discussions on the battle between religion a science I have seen prominent and credible scientists arguing 2 and sadly, much more often 3. I understand it, but many scientist should reign themselves in.

              Understand, I'm not saying don't fight, just that we should fight from our position of greatest strength, which is being "fundamentalist" about the scientific method. If we can teach kids, or anyone, how it works and why we're devoted to it, all the while showing by example how to be scientific in thought, then we win. There's plenty of room for religion in the world even with hard science, and there's plenty of amazement and wonder to be had in science too. I just don't want to see scientists try to expand their own role in human exploration way beyond the data.

        • by EggyToast (858951) on Monday October 10, 2005 @11:49AM (#13757058) Homepage
          Since so many have had to put up with "fundies," and the "just a theory" camp.

          The problem, as I see it, is often that those who question the theories don't have anything better to back them up -- they're just presented with skepticism or an alternative answer that has nothing to do with physics.

          Of course, I think there's more room for that in astrophysics, given the focus on math and proofs rather than testing (due to rather obvious logistics). A new mathematical proof can come out that completely changes how people view space (or, heck, an appropriate use of an old mathematical proof, as the article shows).

          But I can understand why some people would be a trifle edgy nowadays. I'm not saying that you provoked the argument, as I've dealt with scientists (heck, I live with one and hang out with her friends), but I have to ask -- when you said it was a 'mildly promising theory,' did you present an alternative opinion? One thing I learned is that scientists really dislike people saying "I don't believe that" or "I think that theory is wrong" but then don't offer what they DO believe in that's based on science. After all, that doesn't accomplish anything -- it just states a claim of belief, which isn't science.

          But I don't think I need to explain why an "accepted theory" will have people assume that it's accurate and "true" and be reluctant to drop it just at some new information or test or mathematical proof. That older theory generally has plenty of evidence to back it up -- the new theory has none. So people will look at the new theory, run through the math or tests on their own, and confirm, therefore changing the general understanding. That's how science works. The reluctance to accept just any new information without seeing a lot more proof is one of the reasons science tends to add to a base of knowledge, rather than jumping down any old path.

          • by ifwm (687373) on Monday October 10, 2005 @12:03PM (#13757169) Journal
            None of that answers my question.

            Dark Matter is far from an accepted Hypothesis, yet seemingly intelligent people defend it on the basis that it's the best thing going.

            That's just stupid. Science isn't about being right, or falling into lockstep with "accepted theories", it is about continually asking questions.

            My question about dark matter has always been "Why is it more acceptable to make up a new type of matter, rather than deal with the idea that the fundamental forces may work differently than is believed?"

            Why is one SO MUCH better than the other? There is precedent for both possibilities.

            • I think the reason is that in seeking for more fundamental theories in particle physics we get theories which imply there are some particles we don't know yet. Therefore it's not too unlikely that there is a form of matter we don't know yet, and there's no known reason that it may not be enough to be relevant in large scale structures. Therefore, introducing dark matter means introducing something which we might well have to introduce anyway. Changing the law of gravitation means doing another, independent
            • by JetJaguar (1539) on Monday October 10, 2005 @12:41PM (#13757485)

              My question about dark matter has always been "Why is it more acceptable to make up a new type of matter, rather than deal with the idea that the fundamental forces may work differently than is believed?"

              Well, because there was no theoretical framework to explain the data without the use of darkmatter. Let's face it, the whole darkmatter hypothesis is extremely ad-hoc, a fudge factor added into galactic rotation calulations to make them fit to what was expected. The outcome was a predicition that darkmatter must exist.

              Now, there is nothing particularly unscientific about this. Go take a look at particle physics where all kinds of particles were predicted to exist, and as a result many particle physicists went out looking for these particles. When they were found, this confirmed the theory, when the particles were not found, they continued to look, or they revised the theory.

              The same kind of thing happened here. People have been looking for darkmatter for quite some time, however, it appears that a revision to the models used to predict galactic rotation curves *and* galactic clustering is what's needed.

              Why was the existance of darkmatter more "acceptable?" 1) Basically, because it was a prediction that fit the models. That's something that scientists like a lot, it gives the experimentalists something to really sink their teeth into. And 2) there was no way to predict that a change in the theory was needed without having already developed a theoretical framework that could explain galactic rotation curves without the need for darkmatter.

              As an astronomer, I would say that you're not wrong to ask your question, however, without having any idea of how our theory might need to be changed, it's kind of a pointless question. And in this case, it sounds like we really don't need to change our theory at all, it turns out that the range of validity of Newtonian gravity is a lot smaller than we thought.

              I think the bigger question in my mind is why hadn't someone tried to do this before now? In some sense, it's one of those things that just kind of surprises you, because all of a sudden you realize that *everyone* has been operating under the same false assumption about Newtonian gravity, and then you wonder why nobody thought to check that out.

              Of course, this all assumes that this new model using relativity is correct... It probably is, but I think it does need to under go the usual scrutiny just to be sure.

              • by mcrbids (148650) on Monday October 10, 2005 @02:57PM (#13758535) Journal
                I think the bigger question in my mind is why hadn't someone tried to do this before now?

                Science isn't truth, and it isn't fact. It's a process that, over time, results in a gradual and constant tendency towards truth.

                If you get into a debate with religious folk about "creationism" versus "evolution", one of the tactics almost invariably tried is to disprove some facet or other of evolution through some form of deductive reasoning. The basic idea is to prove that Science is somehow wrong, and then assume that creationism wins by default once that's done.

                It's easy to see the fallacy: disproving evolution (even if they can) doesn't prove creationism.

                But, scientific theory is always undergoing review and clarification. Newtonian gravity works, in limited scopes. It was revised and improved with relativity theory, which is itself being revised and improved today with multidimensional, superstring theory. It's this recursive process of deduction, testing, and review that advances science.

                We should be ecstatic! Despite our incredible efforts to find it, we've uncovered NO evidence that this has ever happened before in the multi-billion year history of the universe!

                People are stupid, and we have to acknowledge that. Our intellect barely rises above our other urges, the urge towards sex, the blindnesses caused by our tendency to suspend reason (A.K.A. "Faith") and follow the leader 'cause it's easy. And, truly fresh/new approaches to problems are rare, and hard to find. Most any "new" thought is merely an extension of a previous thought. We're creatures of habit. But, so long as we continue to try, so long as we continue to be willing to challenge our assumptions, and take the time to do so when somebody DOES come up with something new, then the process of Science progresses, and life continues to get better.

                Schools today don't teach science. They teach "facts", like "water vapor absorbs light, but absorbes blue light the least, and thus makes the sky blue". They don't ever teach the method of science, the passion of science, beyond making you recite the "gather facts, form hypothesis, test hypothesis, draw conclusion" which is only minimally how science works.

                Children are BORN scientists. As they explore with their hands, and their minds, the world around them, they perform hundreds of experiments a day, every day. Where do you find frogs? What bug is making that buzzing noise? What happens if you clap your hands near a grasshopper? How many blocks can I stack up before they fall over?

                So, what do we do? We lock them up in a sterile environment, where they're told not to question the teacher, and never to talk to the kids next to them. We prevent their natural curiousity, and instead, browbeat them into performing tricks like a circus animal. The apathy of the schoolchild is both detrimental and obvious.

                And after that's done, after the child's natural, scientific curiousity has been conquered, that's when we introduce the wonders of science in the most boring, unimaginably unflattering way possible, by forcing him/her to regurgitate "facts" that they'd be ridiculed to question.

                The real wonder? How does science advance at all in the face of this educational travesty?

                It's pretty obvious that scientific curiosity is built into the very fiber of humanity, or how else could still be advancing despite our incredibly expensive social efforts to prevent it?
            • by TopherC (412335) on Monday October 10, 2005 @02:35PM (#13758370)
              I wanted to suggest a couple ideas. First, dark matter is a well-favored theory because there is a lot of evidence that supports it. Galactic rotation speeds is one important piece of evidence, but I also think that gravitational lensing provides strong evidence -- which may also be explained by the GR work done in this paper. I don't know but it seems possible. I'm not an astrophysicist, and couldn't (or didn't waht to) follow all the details of the paper. Fluctuations in the cosmic microwave background is another piece of evidence for (cold) dark matter, though it gets complicated here. I don't think that the CMB directly requires dark matter, but dark matter models have been very successful here. I'm out of touch with recent CMB and cosmological accounting developments.

              Anyway, the point is that the theory of dark matter kills a lot of birds with one stone. So it's very attractive from that point of view. And there are literaly dozens of yet-untested theories that can explain dark matter as exotic particles, compact massive objects, and so on. Many of these theories have been either disproved or damaged by careful experiments, but by no means all of them. So the existence of dark matter doesn't seem all that far-fetched either.

              A second point is that a lot of this discussion has to do with scientific theories being "falsifiable", a term very much at the heart of the debate on creationism being taught in science classes. I don't think many people appreciate what the term means. Science cannot prove a theory to be true. You can only prove it to be false. Take "Newton's laws" example. It took somewhere around 250 years to prove those wrong, and relativity suffered a lot of ridicule from scientists still unwilling to let go of them.

              Well, even though there's no way to really prove a theory to be correct, a theorist still has to start somewhere -- put their faith in some basic assumptions before any progress can be made. The choice of these assumptions is mostly a matter of taste, and a little bit of cleverness -- how can you keep your set of assumptions as small and palatable as possible?

              General relativity is a really nice theory, and has stood up to a great deal of testing. It is thought to break down only on small scales far beyond our experimental reach, and there is no compelling reason to suspect its accuracy on even cosmically large distance scales. So it makes for a nice starting assumption for astrophysics. I guess the point of this paper is that some details have been forgotten about when modeling galactic rotation. It was thought that because of the small speeds involved, and weak gravitational field, that newtonian gravity (which is much easier to deal with computationally) was a perfectly good approximation. The author of this paper realized why it was not, and points this out.

              I can only imagine that, if the math is correct, this will have a huge impact on the astrophysics community. For example, they mention why newtonian gravity works so well for our solar system still, but I'm not sure any more that it would work well for cloud collapse and star formation models. If it affects these models, it will probably also affect cosmologists modeling the evolution of structure.
            • by wanerious (712877) on Monday October 10, 2005 @04:19PM (#13759095) Homepage
              Hi --- I'll give a shot at answering (I'm an astrophysicist, if that matters)

              I'm not quite sure what you mean by "Dark Matter is far from an accepted Hypothesis". It is certainly not far-fetched to imagine that there is some quantity of matter, perhaps substantial, that does not "glow" like stars do. This is why it is "dark". The original problem was one of galactic rotation curves --- matter in the outskirts of galaxies rotated around the center in a fashion exactly mimicing what it would do if there was a spherical distribution of matter extending beyond the glow of the visible disk. The hypothesis that there was just such a distribution that we cannot see is not so far-fetched. It has been admittedly difficult to identify the "conventional" bodies that could be responsible for the lion's share of such a halo. Upper limits on the numbers of brown dwarfs, Jupiter-sized objects, and small black holes have shown that no one of these are primarily responsible. Still the search continues, as it would in any good scientific theory. Any of these possibilities are seen as a simpler approach than modifying our most basic models of gravitational behavior, especially when there is no similar pattern of deviation from known laws on different scales. And, as shown by the follow-up paper in the archives, there is a real possibility that the authors have made an honest mistake.

        • I have often mentioned my disbelief in common astronomical theories to my fellow students at the Niels Bohr Institute here in Copenhagen, and not once have I been meet with an attitude like the one you describe. (For instance I don't believe such a thing as a GR-black hole actually exists..)

          In my oppinion your fellow students are seriously lacking in their scientifical education if they are unable to accept that alternative theories should be considered seriously but critically.

          Perhaps with quantum mechan

          • "because QM is true and that's just the way it is.. "

            I find this funny because I too see this a lot. It must come from trying to teach the subject. When pressed, however, I've had people fall back to "OK, it could all be wrong, but *you* have to proposed a better quantum theory of measurement first". So I think even Quantum(tm) alternatives may be considered seriously but critically, it's just that you have to propose a very broad replacement theory, beyond what could easily be expressed in English.

            On th
          • by pregister (443318) on Monday October 10, 2005 @01:02PM (#13757656)
            In my experience, undergraduate science students, at least in the US, are usually of the belief that they are being taught "facts". Maybe in an introductory class more emphasis is placed on the unknowns, but as they move into their specialties all but the most controversial or speculative ideas are presented as facts.

            Generally as they move into graduate studies there is more emphasis on the quest for knowledge as opposed to the memorizing and understanding of facts.

            As one of my professors said my first year of graduate school, "You're graduate students now...you're allowed to have opinions."

            IMO, all science degrees should include a class in Philosophy of Science. Most undergraduate students I've talked to about this idea say something along the lines of "Philosophy has nothing to do with science."

            -pete
        • by jkabbe (631234) on Monday October 10, 2005 @12:24PM (#13757363)
          My favorite quote on this general issue comes from Carl Sagan in one of the Cosmos shows:

          Talking about early observations of Venus...

          "Observation: Couldn't see a thing.
          Conclusion: DINOSAURS!!!"

          That scientific methodology has not left us, I am afraid to say.
      • by whm (67844) on Monday October 10, 2005 @12:00PM (#13757150)
        Which just goes to show you--once a scientific "fact" has been established, our attachment to it becomes as dogmatic as any theological notion...

        Perhaps for some people, but not for the overall scientific community. This article being the most obvious example. And I need not note the difficulty one would encounter trying to debunk a theological notion...

      • by mcc (14761) <amcclure@purdue.edu> on Monday October 10, 2005 @01:54PM (#13758069) Homepage
        I've been suggesting for years that "dark matter" is an unnecessary idea which only exists as a transitional kludge until we can uncover some more fundamental error in the theory of gravity, like planetary epicycles or what not. I have made this suggestion both on the internet and in person to some people I hang around with from my college's physics department.

        While generally people have not agreed with me, I have never encountered what I would call "dogmatic" resistence; I never felt that people were upset at my suggestion or disrespected my opinion that this was a possibility.

        Perhaps the reason why you have met with poor results expressing the same idea have more to do with the way in which you expressed the idea?

        I find a lot of people seem to believe that if people disagree with them, it is automatically because of dogmatic resistence. Not necessarily, maybe it's just because you've not made your case very well, or because there are other factors to the discussion you aren't considering (for example, that asking a physicist to abandon the idea of dark matter would-- in the absence of a better explanation for anomolies in gravitational theory-- effectively require them to accept the idea that the galaxy is the wrong shape for no reason whatsoever).
  • As usual... (Score:4, Insightful)

    by lax-goalie (730970) on Monday October 10, 2005 @10:34AM (#13756415)
    ...the simplest solution turns out to be the best.
    • Re:As usual... (Score:4, Insightful)

      by GoofyBoy (44399) on Monday October 10, 2005 @10:42AM (#13756470) Journal
      Um.. define "the best"?

      The "Truth"?

      The "most elegent"?

      The "one that majority of scientists can most willingly accept"?

      The "one that my mind can most willingly accept"?
    • Re:As usual... (Score:3, Interesting)

      by lawpoop (604919)
      This has always struck me as an anthropocentric, 'faith-based' element in modern physics. Why should the universe be simple and elegant? Because it's 'beautiful'? Because we don't like doing hard math problems?

      I'm not against it, but it seems to be taken on faith that the universe should be simple and elegant. So far the track record is pretty good, but that doesn't mean that it's a scientific belief. Don't get me wrong, I'm not against a simple-and-elegant universe; I just haven't heard any scientific ex
      • Re:As usual... (Score:3, Insightful)

        by Surazal (729)
        In physics, the simpler answers tend to be the correct ones. Note that General Relativity is far more complex than Newtonian physics, though it's universally accepted that the former is the correct theiry. Newtonian physics is regarded as a reasonable approximation most times. It's why it's still taught in schools (you don't need to take relativity into account when measuring the momentum of a car going down the freeway, for example).
    • Re: As usual... (Score:4, Interesting)

      by Black Parrot (19622) on Monday October 10, 2005 @10:57AM (#13756604)
      > ...the simplest solution turns out to be the best.

      Surely GR & QM are better than the super-simple Newtonian/Euclidian model that went before.
    • by lgw (121541) on Monday October 10, 2005 @11:03AM (#13756645) Journal
      As any engineer knows: every problem has a simple, easy to understand, wrong answer.
  • Damn.. (Score:4, Funny)

    by Druox (911165) on Monday October 10, 2005 @10:35AM (#13756425)
    Geeze science, make up your mind - Think of the poor sci-fi writers for those made-for-tv movies! Have you considered THEM before publishing research findings??
  • From the Abstract (Score:5, Interesting)

    by poopdeville (841677) on Monday October 10, 2005 @10:38AM (#13756440)
    A galaxy is modeled as a stationary axially symmetric pressure-free fluid in general relativity. For the weak gravitational fields under consideration, the field equations and the equations of motion ultimately lead to one linear and one nonlinear equation relating the angular velocity to the fluid density.

    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)

  • by OakDragon (885217) on Monday October 10, 2005 @10:38AM (#13756441) Journal
    ...was physicists around the world collectively slapping their foreheads.
  • Dark Matter... (Score:4, Insightful)

    by crymeph0 (682581) on Monday October 10, 2005 @10:44AM (#13756488)
    Always smelled like aether/ether [wikipedia.org] to me anyway.
    • Re:Dark Matter... (Score:3, Insightful)

      by booch (4157)
      Yes. The whole idea of dark matter was a kludge to explain why they weren't seeing what they expected. I always figured that they were interpretting things incorrectly, or measuring incorrectly. For one thing, it's mainly based on how much ordinary matter we expect in "empty space", or the space between stars. Recent discoveries suggest that there may be a lot more matter in the Oort cloud [wikipedia.org] than we originally thought. (Although still pretty small, compared to the sun -- but I think we're still under-estimati
  • by Anonymous Coward on Monday October 10, 2005 @10:45AM (#13756498)
    The great thing about the speed of communication these days is that whenever a moronic story hits the web, it can be refuted immediately. See, in this case, Singular disk of matter in the Cooperstock and Tieu galaxy model [arxiv.org], which says:
    Recently a new model of galactic gravitational field, based on ordinary General Relativity, has been proposed by Cooperstock and Tieu in which no exotic dark matter is needed to fit the observed rotation curve to a reasonable ordinary matter distribution. We argue that in this model the gravitational field is generated not only by the galaxy matter, but by a thin, singular disk as well. The model should therefore be considered unphysical.
    • I noticed you were referring to an article on arXiv.org [crookedtimber.org]. While it may certainly be true, these articles have not been peer reviewed by a scientific journal. Also note that this author appears to have only the single article on the site (which may or may not mean anything - draw your own conclusions).

      I think arXiv.org is a great idea - a way for physicists to communicate ideas informally before going through the hassle of getting them published. It's still best to take it all with a grain of salt, as p
      • by rknop (240417) on Monday October 10, 2005 @11:15AM (#13756748) Homepage

        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

    • by Chuckstar (799005) on Monday October 10, 2005 @11:27AM (#13756857)
      I read the article and I fail to see how this criticism holds water. The article under discussion proposes a thin disk of non-luminous (as opposed to "Dark") matter on the same plane as the galaxy, in roughly the same distribution as the luminous matter. Such a disk could be made of dust or other particles, would be an order of magnitude smaller than the proposed Dark Matter, and would potentially be difficult to observe. One wonders whether the refuting author finds Dark Matter more or less "physical" than a thin disk of real matter.
  • by lheal (86013) <lheal1999@@@yahoo...com> on Monday October 10, 2005 @10:45AM (#13756501) Journal
    I always thought "dark matter" was a kind of special pleading, an appeal to magic in the face of the unknown.

    • At first, maybe. When the speed at which galaxies rotate wasn't as expected, one legetimate proposal is that there's enough "dark matter" to make up the difference. After all, astronomy is inherently limited to what we can "see", and matter like dust clouds that obscure what we can see. The universe could be full of matter that doesn't interact much with light, and we'd only find out about it when we started measuring large-scale gravitic effects. Not really an appeal to magic, more of a "this makes the
    • by rknop (240417) on Monday October 10, 2005 @11:12AM (#13756719) Homepage
      So was the neutrino.

      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
  • by Morgaine (4316) on Monday October 10, 2005 @10:48AM (#13756523)
    TFA is just plain silly.

    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)

    by amightywind (691887) on Monday October 10, 2005 @10:49AM (#13756533) Journal

    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.

  • Interesting (Score:3, Insightful)

    by andrewman327 (635952) on Monday October 10, 2005 @10:49AM (#13756538) Homepage Journal
    I wonder if some scientists might already be so invested in theories of dark matter that they will refuse to accept this position.
  • WYSIWYG universe (Score:5, Insightful)

    by G4from128k (686170) on Monday October 10, 2005 @10:52AM (#13756555)
    Perhaps it is a WYSIWYG universe, we just don't understand how to properly see what we see.

    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.

  • by promatrax161 (913597) on Monday October 10, 2005 @10:55AM (#13756584)
    ...is going to become the major worry. Data from supernovae distance measurements indicate that the Universe has been expanding for some time already. That means that there has to exist a sort of anti-gravity (called dark energy by astrophysicists). Now, that is hard to explain by conventional means (although it is possible), and may involve either a "beyond Einstein" type of theory (e.g., an improved general relativity) or some exotic form of energy (or both). So, although general relativity alone might account for the rotational curves of galaxies, it does not account for the large-scale properties of the universe.
  • by ben0207 (845105) <ben DOT burton AT gmail DOT com> on Monday October 10, 2005 @10:56AM (#13756590) Homepage
    It means my physics paper is proper fucked, for one.
  • by doublem (118724) on Monday October 10, 2005 @10:56AM (#13756592) Homepage Journal
    How many of us have done as much?

    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!
  • by marcosdumay (620877) <marcosdumay@gmSTRAWail.com minus berry> on Monday October 10, 2005 @10:58AM (#13756606) Homepage Journal

    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.

  • by Henriok (6762) on Monday October 10, 2005 @10:59AM (#13756615)
    Really?! I'm interessted in astronomy and physics at a hobbyist level, and have always assumed that the simulations of gravity and galaxy formation was done with relativistic mathematics. Instead they have used approximations using newtonian theories? WTF? No wonder they came out wrong!

    I can live with newtonian approximations on a solar system level, but doing cosmology on the scale of galaxies, the age of the universe it self and so forth they really should have used the sharpest tool in the tool box.

    If I had the knowledge and the machine power to do simulations my self I would've done so, but I don't so I trusted the astronomers. They really shuldn't have taken the shortcuts, escpecially after their scientific profgress went boink and they started devicing exotic new models just to cover up their seemingly faulty theories! Shouldn't they have done a simmulation without the approximations just to evaluate how good their approximations was?

    I'm dissapointed!
    • As another poster (here [slashdot.org])has already pointed out, other physicists have since worked through the algebra of this paper and found it lacking.

      I'm told there is a mistake in the general relativistic metric used in the paper. Basically, a small error left them modeling the wrong situation. The situation they actually studied was one with an axially symmetric cloud of self-gravitating gas (the galaxy) AND a thin, heavy disk. The thin, heavy disk screws things up and produces the effect they observe.
  • by Weaselmancer (533834) on Monday October 10, 2005 @11:05AM (#13756655)

    What does this imply for cosmology and particle physics, both of which have been worrying about other aspects of dark matter?

    I think it implies that we can stop chasing for something that probably doesn't exist, and get about the business of finding out what's really going on out there.

    Maybe it's just me, but the first time I heard about dark matter and how it "must be out there" because it makes the calculations add up nicely...first thing I thought of was the ether. For a long time we needed an ether to explain radio waves, light propogation, etc. Turns out the truth of the matter is something totally other. And it's a far more facinating other, IMHO.

    I'm guessing that hundreds of years from now, physics students will be reading about dark matter and chuckling. Same way we do today when we read about the luminiferous ether [wikipedia.org].

    • "Maybe it's just me, but the first time I heard about dark matter and how it "must be out there" because it makes the calculations add up nicely...first thing I thought of was the ether."

      And Plank thought the same about that quantum physics he invented. He even spent a great part of his life working against quantum physics, and here we are, using computers...

      Some times, a completely weard theory that just fits the data is right, there is why people take them seriously.

  • by ebcdic (39948) on Monday October 10, 2005 @11:05AM (#13756658)
    Before this paper, it seemed that the rotation of galaxies was inconsistent with the amount of visible matter.

    Now it is consistent. But is it consistent with the visible matter plus any significant amount of dark matter? That is, does the GR calculation show that there can't be much if any dark matter?
  • by darteaga (806257) <darteaga@@@ya...com> on Monday October 10, 2005 @11:05AM (#13756662)
    Even if the article was correct, and dark matter was not needed to explain rotation curves in galaxies, dark matter [wikipedia.org] is still needed to explain the acceleration of the universe [wikipedia.org], its large scale structure [wikipedia.org] and the primordial anisotropies in the cosmic microwave background [wikipedia.org].
  • by mindpixel (154865) on Monday October 10, 2005 @11:20AM (#13756789) Homepage Journal
    I worked for years drving the VLT in Chile...MOND was a very hot anti-dark matter theory in that control room...

    http://en.wikipedia.org/wiki/Modified_Newtonian_dy namics [wikipedia.org]
  • by ajs318 (655362) <sd_resp2 AT earthshod DOT co DOT uk> on Monday October 10, 2005 @11:22AM (#13756813)
    Science began by making apparently unrelated observations, and later filled in the gaps to create unifying theories. Nature's apparent horror of a vacuum, and a whole lot of other phenomena, are explained by the pressure in a fluid acting equally in all directions. Many phenomena suddenly made sense when it was discovered that matter attracts other matter.

    Now, we still have a few gaps, including that small things appear not to behave the same way as big things. No doubt, if we can quantify the differences* -- or explain why that would be impossible -- we can take a stab at a single Grand Unifying Theory which would underpin all of Physics.

    It's also possible that there could be another possible set of laws of physics which would be mutually consistent, even consistent with the G.U.T., just contrary to all our observations. If there existed a parallel universe which obeyed this set of laws, one of four things could happen:
    1. It would collapse to a single point in our space
    2. A single point of space in that universe would be bigger than the whole of this universe
    3. It would exist for only a brief instant of our time
    4. A single instant of time in that universe would last longer than the lifetime of our universe
    Of course, it's also possible {but extremely unlikely} that there is no Grand Unifying Theory, just a supreme being with a sick sense of humour who keeps changing the rules slightly every time we get close to discovering what they are .....

    * Canonical example of difference between quantum and classical phenomena: Why can't a chair just spontaneously shift position? My own take is that quantum wave functions do exist in large systems, but "quantum" phenomena are not generally observed because the waves are not coherent {just as you don't see interference fringes where the light from two candles falls on the same surface}.
    • Canonical example of difference between quantum and classical phenomena: Why can't a chair just spontaneously shift position?

      It can and does, all the time.

      Consider the chair as a fundamental particle. It can be described in terms of its mass, as a particle, or of its wavelength, as a wave. How far you can expect tunneling in a chair can be observed is a function of its wavelength, and for an object as massive as a chair its wavelength is terribly terribly small...
  • by adminispheroid (554101) on Monday October 10, 2005 @11:37AM (#13756940)
    Seems like somewhere in the translation from this preprint to the popular press, this turned into "no dark matter after all." Let me put this in context.

    There are two problems in astrophysics in which dark matter is invoked as a possible explanation. One is the "galaxy problem": galactic rotation curves imply a distribution of matter different that you would infer from looking at the luminous matter. The other is the "cosmological problem": observation of redshift vs. distance, and of the cosmic microwave background, and other similar measurements imply a total mass density in the Universe different from what you would infer from looking at the luminous matter. Each of these problems can be explained with dark matter (e.g. some kind of extremely massive particles that only participate in the weak interaction, not yet observed). Sadly, the properties of the dark matter needed to solve these two problems are not necessarily the same.

    This paper claims to eliminate the need for dark matter to solve the galaxy problem, but does not address the cosmology problem.

  • by Anonymous Coward on Monday October 10, 2005 @12:23PM (#13757361)
    I'm not in this field anymore, but I spent 4-5 years in quantum gravity, black hole astrophysics, and inflationary cosmology. Summarizing my reactions to other comments in this thread:

    First, I will say that I have not gone through this new paper in detail. I'm skeptical at a gut level that their results seem to depend on general relativity, because GR should not be relevant on the scale of galactic rotation curves: there is good reason why all the calculations ignore GR. It makes me think that there is a flaw in their calculation, and indeed another poster referred to a potential rebuttal of their GR analysis.

    Second, as yet another poster mentioned, galactic rotation curves are just ONE evidence for dark matter. We have evidence from the aforementioned stellar orbits in galaxies, plus the motions of satellite dwarf galaxies, gravitational lensing, measurements of galactic gas temperatures (depends on the local gravitational neighborhood), anisotropies in the CMBR, the rate and structure of large-scale cosmological structure formation, etc.

    (There are also a bunch of theoretical reasons to believe that dark matter particles could exist purely on the basis of particle physics, even if you ignore the astrophysical evidence; see axions, supersymmetry, etc.)

    It's not surprising to come up with an alternative that can explain ONE of these phenomena. In fact, there is already another alternative that can also explain galactic rotation curves: MOND (MOdified Newtonian Dynamics), an alterating of Newton's laws of gravity. (There is a relativistic extension by Bekenstein, although it's currently even more ad hoc than dark matter appears to be.)

    The problem is coming up with explanations for ALL of these phenomena. Dark matter is the only theory that has been able to do so, and it's not for lack of trying. Contrary to popular Slashdot groupthink, scientists are not in love with coming up with the most absurd and exotic possibilities they can. Most astronomers hated dark matter. For decades. I even know one who only came around to it a few years ago. It's simply that dark matter works, and everything else people tried to propose in its place didn't. As Carl Sagan said, "No physicist started out impatient with commensense notions, eager to replace them with some mathematical abstraction... Instead, they began, as we all do, with comfortable, standard, commonplace notions. The trouble is that Nature does not comply."

    Now, this is not to say that dark matter is the end-all, unassailable dogma. It's possible there are alternatives, including modifications to gravity. I like to compare it to the discovery of Neptune and the perihelion precession of Mercury. People say that it's ad hoc to postulate unseen matter to explain gravitational anomalies. But that's precisely what led to the discovery of Neptune: its gravitational effects on Uranus. On the other hand, you can't always get away with postulating unseen matter: when Mecury's orbit wasn't behaving right, people tried inventing an unseen planet ("Vulcan"), but it turned out that general relativity was the answer, modifying the laws of gravity. Either can be right a priori.

    In the dark matter case, it was once true that the evidence in its favor was strong and there were a number of competing theories, but now there is a lot more evidence, and higher standards for theories, and dark matter is pretty much all that's left. People should and do continue trying to come up with alternatives, but as of now, dark matter is still the best game in town. Far from claims of ad-hockery and epicycles, dark matter is actually a robust physical theory: most theories of dark matter have already been falsified because they make such specific predictions about what we should see. It's only a very specific type, quantity, and distribution of dark matter that can work. That's the hallmark of a good theory, not unfalsifiable wish-fulfillment.

    Finally: this is a
  • by tenzig_112 (213387) on Monday October 10, 2005 @03:01PM (#13758568) Homepage
    hot off the wires:

    VICTORIA, BRITISH COLUMBIA- When astrophysicists first ran calculations on the observed rotational speeds of nearby galaxies in the 1970's, they ran into a bit of a problem when the numbers didn't add up. According to the familiar laws of Newtonian mechanics, these meta bodies should be much heavier than the number of solar objects would imply. This gap led to one of the most controversial inferences in modern science, that
    the universe contains a massive amount of non-radiating "dark matter" hidden among the stars. For decades scientists were satisfied with this notion. Lectures were delivered, textbooks were printed, and tenure was granted.


    A new paper from the University of Victoria, however, casts doubt on all of this. It argues that the whole notion "dark mattter" may be the byproduct of a miscalculation [someone forgot to carry the six] and demonstrates how a proper application of Einstein's principles of general relativity can fully account for a galaxy's rotation and mass without considering this unobserved dark matter. Such contrary ideas often run into resistance, but this theory has engendered far more scientific vitriol than anyone expected.


    In fact, when researchers arrived to deliver the paper at a conference last weekend, they were met by an angry mob of civil rights protesters headed by Julian Bond of the NAACP.


    "It's fairly clear what's going on here," said Bond through a bullhorn. "Just because it's dark they're saying it doesn't count. I, for one, will not stand for this sort of disenfranchisement. We demand that CERN count all the matter."



    OK, not really. Just thoght it would be fun.

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