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Dark Matter Exists 459

Posted by samzenpus
from the not-just-ordinary-matter-anymore dept.
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."
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Dark Matter Exists

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  • Dark Matters (Score:5, Informative)

    by ackthpt (218170) * on Monday August 21, 2006 @08:09PM (#15952458) Homepage Journal

    The announcement [slashdot.org] of the pending announcement [nasa.gov] regarding Dark Matter [wikipedia.org]

    "This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

    I guess he's never heard of Zaphod Beeblebrox.

    "A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."

    Also a bit of info on physorg [physorg.com]

    How does the Coalsack Nebula [seds.org] fit into this? It's dark and it's matter, right?

    • by Anonymous Coward on Monday August 21, 2006 @08:12PM (#15952470)
      Is it proof that dark matter exists that the link takes me to a blank page???
    • by gardyloo (512791)
      How does the Coalsack Nebula fit into this? It's dark and it's matter, right?

            "dark matter" I don't think it means what you think it means.
    • Re: (Score:2, Insightful)

      by Anonymous Coward
      "A universe that's dominated by dark stuff seems preposterous"

      But not as preposterous as the "Big Bang". Imagine all the matter of the universe compressed to the size of an electron. Well that is a fabulous explanation for observations. Any other ideas?
    • Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal or announced at a news conference...not on a blog shared by Mark, Claire, and Sean, whoever they may be.

      * Note that I tried to go back and confirm the names and finish reading the story so I would have something intelligent to say, but apparently the user's CPU allottment only accounts for 20% of the server's total, suggesting that there may be another form of CPU cycles t
      • Ah well, serves them right- their server melted down from the slashdotting.
      • by debilo (612116) on Monday August 21, 2006 @08:34PM (#15952578)
        Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal or announced at a news conference...not on a blog shared by Mark, Claire, and Sean, whoever they may be.

        I'm outraged -- are you really implying that we should take this proof of dark matter with a grain of salt, while there's this well-known Irish company that's using dark matter to produce free, clean and constant energy right now?
      • by rtaylor (70602)
        It's a perceived trait only. Time within the CPU in the server stops every 1/5th of a second for a duration lasting 4/5ths of a second. A 20% quota represents the full calculating capacity of the machine.

      • by wanerious (712877) on Monday August 21, 2006 @09:07PM (#15952737) Homepage
        Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal or announced at a news conference...not on a blog shared by Mark, Claire, and Sean, whoever they may be.

        They're physicists (I think Sean Carroll works in cosmology, formerly of the U. of Chicago, now at Cal Tech). It was announced, and the paper has been written. The blog, by the way, is really good.

      • Re: (Score:3, Funny)

        by mysticgoat (582871) *

        Funny, I always figured the announcement of experimental confirmation of dark matter would first be published in a scientific journal

        that thinking is SO twentieth century...

      • by Soldrinero (789891) on Monday August 21, 2006 @09:34PM (#15952872)

        I can't speak for the others, but Mark Trodden and Sean Carroll are theoretical cosmologists. I majored in astrophysics as an undergrad and read some of their papers. Also, Sean Carroll is quoted in the press release [harvard.edu] on NASA's web site.

        So these aren't just random guys talking, but professionals in the field. Also, as Sean states in his post, the result was embargoed, which means it was being kept under wraps before publication in a journal. This article and the one I mentioned above are just talking about the results that are published elsewhere. If you really want to read the journal article, it's available here [harvard.edu].

        • by radtea (464814) on Monday August 21, 2006 @11:12PM (#15953240)
          The key quote from the paper is:

          Any non-standard gravitational force that scales with baryonic mass will fail to reproduce these observations.

          This is a very nice piece of work. One observation doth not a proof make (the myth of the "crucial experiment" is, well, a myth) but if confirmed by comparable observations on similar structures it could really start to constrain inter-galactic dark matter models in ways that are much more precise than hitherto has been possible.

          The fundamental importance of this paper is less in the single observation than in the development of a new technique for probing the inter-galactic dark matter distribution directly and in detail.

          Of course, it says nothing at all about galactic dark matter.
    • Re:Dark Matters (Score:5, Informative)

      by Surt (22457) on Monday August 21, 2006 @08:22PM (#15952524) Homepage Journal
      In case your question is not meant to be humorous, the Coalsack Nebula is not 'dark' in the same sense as dark matter. It's conventional matter that is not well lit.

    • Proof? I thought science was about skepticism. But "the results give us a high degree confidence in the accuracy of the dark matter theory" doesn't make headlines, I guess.
    • Silly Musings..... (Score:3, Interesting)

      by tempest69 (572798)
      I'm wondering how much "dark matter" is simply protons.. From what I remember from RadioIsotopes class unbound neutrons decay in about 15 minutes to a proton an neutron.. But I'm not sure what would happen to masses of stray protons in interstellar gas. The repulsion alone would prevent some coalesing activity, making it harder to form stars.. And they should be invisible, as there are no electrons to change energy states. So it should be perfectly transparent. But I dont have the the math to really fi
      • by Xeriar (456730) on Monday August 21, 2006 @08:56PM (#15952677) Homepage
        There are very few free protons or free electrons, and no free neutrons (half-life of about 15 minutes before it turns into hydrogen) - nearly all interstellar matter is composed of hydrogen and helium. Beyond which, by your theory they would be generating an absolutely massive electromagnetic charge.

        Beyond that, though, it's estimated that about half of baryonic matter is invisible for various reasons - thus, the Universe appears to be composed of 2% luminous baryonic matter, 2% invisible baryonic matter, 23% dark matter and 73% (and increasing) dark energy.
      • by wanerious (712877) on Monday August 21, 2006 @10:02PM (#15952981) Homepage
        Couple of things ---

        Zeroth, stray neutrons decay to a proton, electron, and an electron anti-neutrino. n->p+n doesn't conserve charge.

        First, "ordinary" baryonic matter like protons can only be (according to the well-verified Big Bang Nucleosynthesis) a few percent of the total mass density of the universe, and perhaps 10% of the total amount of Dark Matter. We think the dark stuff is largely, if not almost completely, non-baryonic (not made of quarks, not strongly interacting).

        Next, for any isolated mass of protons (essentially ionized H), you'd have to explain where all the electrons went, since the Universe appears to be electrically neutral on even small scales. Also, since the electric force is so overwhelmingly much stronger than gravity, any such cloud cannot be gravitationally bound and would explosively disperse. It wouldn't be perfectly transparent, since protons (being charged) have some cross-section to scatter photons just like free electrons do. In fact, the X-ray emission mentioned in the article comes from hot, ionized H.

    • Re: (Score:3, Interesting)

      by Fordiman (689627)
      "Dark Matter" is not just non-emitting matter. It's also non-interacting matter. ...

      Anybody ever think dark matter might be like Niven's 'quantum black holes'? (read "Borderland of Sol").

      The idea: a miniscule black hole formed in the high pressures during the creation of the universe. Or in supernovae. Or in some other way. The method of formation doesn't matter for this little intellectual exercise.

      They can have event horizon on the atomic or even subatomic scale; as such, they would have very dense gr
  • by Enuratique (993250) on Monday August 21, 2006 @08:12PM (#15952474)
    ...the server must have known of the impending slashdot effect and preemptively protected it's CPU from the impending meltdown
    • Full Paper (Score:5, Informative)

      by Anonymous Coward on Monday August 21, 2006 @08:21PM (#15952519)
      The full paper can be found here. From the abstract: [harvard.edu]
      We present new weak lensing observations of 1E0657558 (z = 0:296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray emitting plasma are spatially segregated. By using both wide-field ground based images and HST/ACS images of the cluster cores, we create gravitational lensing maps which show that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. 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.
      • Re:Full Paper (Score:5, Interesting)

        by The Great Pretender (975978) on Monday August 21, 2006 @09:33PM (#15952869)
        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.

        • Re: (Score:3, Insightful)

          by dhasenan (758719)
          We see a certain amount of matter in the system. We see the gravitational effects of much more than that. So we have a premise that we see everything with an appreciable mass; that is disproven by our observation of gravitational effects that differ significantly from that which we predicted via the observable matter.

          So, our options are to believe that some matter is disproportionately heavy than its appearance would suggest, or to believe that there's matter that we aren't seeing.
        • Re:Full Paper (Score:5, Informative)

          by NereusRen (811533) on Tuesday August 22, 2006 @12:52AM (#15953562)
          I know your post was somewhat tongue-in-cheek, but it was modded interesting, so others are probably wondering the same thing. Lets play the analogy game first...

          We know musical talent must come from either training or predisposition. We assume there are no other factors, because those two cover the reasonable possibilities. Consider this logical statement then: John Doe has no musical training, yet he is very skilled. John's musical skill cannot be explained by training, and thus proves that there exists some sort of predisposition to musical talent. It doesn't tell us (e.g.) whether it's genetic or not, but knowing for sure that it's there helps us refine our further studies.

          Now the real version. There is "more" gravity than we can account for with the combination of Baryonic (regular) matter and Einstein's theories of gravity. A LOT more. There are only two possibilities: Gravity gets stronger under certain conditions (regular matter pulls harder), or something "unseen" is pulling. Of course, both could be true, but at least one of them MUST be true to match observations. We assume there are no other explanations, because those two are broad enough to cover the entire range of reasonable possibilities.

          This experiment showed that the center of gravity of certain galaxies doesn't correspond to the center of the regular matter. In other words, the galaxy's gravity is pulling in a different direction than the normal matter would indicate. "[This] 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."
  • Starship fuel! And... if dark matter exists... then something must exist to have created the dark matter... Onward, to Vergon 6!
  • So...now that we know it exists, we'll inevitably try to figure out how to harness it. I mean, its so plentiful right? Any logic-based theories as to what technologies might be developed as a result of this? I'm really curious what scientists will be able to do with this now that they have proof its real. Yes...I'm interested in the studies that will occur and what we'll learn about this, but i'm dying to see what they'll be able to make it DO...this is an entirely new form of matter here!

    • Re: (Score:3, Interesting)

      by Vo0k (760020)
      It may be spread uniformly in the intergallactic space, meaning it's useless with density under a gram per cubic kilometer. Or it may form denser formations at distances that are useless. I mean, we're harnessing power of only one star out of a whole universe of them...
    • They claim proof that it's real, but they have no mention of proof of what it actually is. All this proves is that there is "something" there, and that it A) is not observable directly through our favourite tools (EM Emission) and B) It does exert a graviational force.

      To draw any conclusions about the potential applications of this material is pretty much impossible until we actually work out what it is.

      • "They claim proof that it's real, but they have no mention of proof of what it actually is."

        What kind of an answer would be satisfying there? It seems to me that we don't know what regular matter actually is.
    • by cryptoluddite (658517) on Monday August 21, 2006 @08:33PM (#15952576)
      I say we use it to build a dyson sphere around the entire universe. Then we can finally solve the question of whether the universe is expanding / contracting / balancing. The hard way.
  • Stargate? (Score:3, Funny)

    by WVDominick (860381) on Monday August 21, 2006 @08:16PM (#15952491) Homepage
    How does this effect the Stargate program?
  • by Anonymous Coward on Monday August 21, 2006 @08:17PM (#15952500)
    It's a big day for astrophysics.

    This Account Has Exceeded Its CPU Quota

    I think it's going to be a big day for their webmasters as well.

  • Sweet! (Score:5, Funny)

    by BigZaphod (12942) on Monday August 21, 2006 @08:18PM (#15952503) Homepage
    Now it's our turn to hide from the dark matter and wait for it to discover us! Come one everyone - pick a hiding spot and get to it! Hurry!
  • by Pike (52876) on Monday August 21, 2006 @08:22PM (#15952526) Homepage Journal
    does this mean grey matter exists as well?
    • Re: (Score:3, Funny)

      by JesseL (107722)
      It may exist, but there is very little observable evidence for it on this planet.
  • Better Links? (Score:5, Informative)

    by clang_jangle (975789) on Monday August 21, 2006 @08:23PM (#15952532) Journal
    For those who prefer here are the salient links which TF"A" (it's a blog entry) is referencing: http://chandra.harvard.edu/chronicle/0306/devil/ [harvard.edu] http://chandra.harvard.edu/press/06_releases/press _082106.html [harvard.edu]
  • by User 956 (568564) on Monday August 21, 2006 @08:27PM (#15952551) Homepage
    After much speculation, scientists now have conclusive proof of dark matter.

    Well, their proof is based on the detection of gravity and gravitational fields. Every real American knows that it's not "gravity", but "intelligent falling". Gravity is a myth invented by foreign scientists to make all Americans seem overweight.
  • by StupendousMan (69768) on Monday August 21, 2006 @08:30PM (#15952563) Homepage
    Astronomers observed a distant cluster of galaxies in optical light, with ordinary telescopes, and in X-ray light, with a telescope in space. This is an unusual cluster of galaxies, since there is clear evidence that one small group of galaxies are "interlopers:" members of a smaller cluster which fell into a larger one some time ago. Members of this interloping group are all bunched together at one side of the main cluster.

    The visible light image shows the galaxies within the cluster. It also shows, much fainter and much smaller, a very large number of BACKGROUND galaxies -- these are objects way, way farther away than the big cluster. As the light from these background galaxies passes through the big cluster, it is bent very slightly by the gravitational field of the cluster. This gravitational lensing distorts the shapes of the faint, little background galaxies just a bit, but with care, we can measure the effect. We learn from the lensing where the matter is in the cluster: that is, we can figure out where the stuff which produces gravitational effects is distributed. That's part one: a map of the matter within the cluster, based on gravitional lensing.

    The X-ray image shows emission from hot gas within the cluster. We have known for several decades now that large clusters of galaxies are immersed in giant clouds of very hot gas, at temperatures of millions of degrees. The gas emits copious amounts of X-rays. In most clusters, the amount of this hot gas -- its total mass -- is much larger than the amount of mass we can see in stars. That is, counting the stars in the galaxies suggests a total amount of mass-in-stars M, but computing the amount of hot gas necessary to emit all the observed X-rays yields a mass-in-hot-gas of around 10*M, ten times as much.

    On the other hand, the amount of mass derived from the gravitational lensing of background galaxies is about 10 times larger still, or about 100*M. The stuff which produces the gravitational lensing does not emit visible light, nor X-ray light, nor, as far as we can tell, any electromagnetic radiation. Therefore, we call it "dark matter". It produces a gravitational force, but that's about all we know about it. (There are additional reasons for believing that this mysterious stuff is not made up of electrons, protons and neutrons, but that's another story).

    This new result is interesting for this reason: the X-rays appear on one region of the cluster of galaxies, telling us that the bulk of the ordinary matter is RIGHT HERE. The map of total mass we can make from gravitational lensing appears in a different region of the cluster, telling us that the bulk of the dark matter is OVER THERE. It is very clear that the dark matter and ordinary matter are distributed in different places. This isn't too surprising, perhaps, if one small group of galaxies rammed into a big cluster -- the gas ram pressure might push on the ordinary hot gas in a different way than on the dark matter (which wouldn't feel any ram pressure at all, actually).

    As Martin Hardcastle pointed out to me in a Google newsgroup a few days ago (thanks, Martin!), this is certainly not the first evidence for dark matter -- we have a number of examples in which gravitational forces are larger than the amount of visible matter would suggest -- but it is the first good case in which the distribution of the dark and ordinary matters are so clearly displaced.

    • i really good comment to 100 wiseass stupid comments - pretty goood for /.

      Can you comment on whether the data support a candidate such as wimps, machos, etc ? (or am I betraying my ignorance with these acronyms
      • Re: (Score:3, Informative)

        by StupendousMan (69768)

        Can you comment on whether the data support a candidate such as wimps, machos, etc ? (or am I betraying my ignorance with these acronyms

        This data provides no evidence for the makeup of the dark matter.

        Other observations suggest that the dark matter is not Massive Compact (Halo) Objects, or MACHOs. The idea that dark matter might be composed of some sort of Weaking Interacting Massive Particle, or WIMP, is a bit out of fashion these days, but still a possibility, as far as I know.

    • Re: (Score:3, Interesting)

      by roystgnr (4015)
      We have known for several decades now that large clusters of galaxies are immersed in giant clouds of very hot gas, at temperatures of millions of degrees. The gas emits copious amounts of X-rays.

      Do we know yet what keeps that gas at million-degree temperatures? Maybe I'm naive, but I'd expect radiation (especially X-Rays!) to cool the gas, and I can't think of any mechanisms that would heat it back up that quickly.
      • Good question! (Score:3, Informative)

        by xiox (66483)
        That's a good question - this is termed the "cooling flow problem". We expect to see lots of gas cooling in relaxed clusters (not the colliding one discussed here) as the gas is dense in the central regions. However there's a lack of evidence of cool gas, so most people think something is heating it (although there are many solutions possible http://uk.arxiv.org/abs/astro-ph/0010509 [arxiv.org]). The ideal candidate is the central supermassive black hole (AGN), however it is difficult to understand how this process wor
  • by suitepotato (863945) on Monday August 21, 2006 @08:32PM (#15952569)
    ...just supposition. After reading all this, all I see is that dark matter, which cannot be observed by any means other than gravitational effects on other non-dark-matter matter and seems suspiciously absent from everyday experience and experiment here on Earth, must exist because we think we see mass and energy behaving in a way that goes with our theories, yet we've seen it behave that way before and it is only in recent times we've decided that something is wrong with physics and we need dark matter.

    Can anyone say aether? I knew you'd try...

    We have next to zero understanding of the quantum vacuum, and don't know for certain if everything should pop in and out there including not only electrons and photons, but antiprotons and neutral pi mesons and everything else too. We do know it exists from many many Earth-side experiments and reams of dead trees covered in equations. We don't know how the potential fields exist which give rise to the fields we know, we don't know how any of them link in all ways to the nuclear fields which we also don't understand too well but we have loads of equations and experiments for those.

    So we invent something, call it "dark matter", and look for anything we can then say matches our thought experiments and we can forgo all the careful Earth-side experiments. We just sort of treat the absence of any dark matter here or anywhere near here as one of those Hitchhiker's Guide SEPs.

    More science-by-supposition and proof-by-spectacle. Show me the proof. Show me why dark matter has to exist. Prove it out with careful calculation and application to everything across the board. We've set off fifty megaton nukes for crying out loud without a single sign of anything amiss that would suggest we have a giant hole in physics requiring dark matter. We've done experiments on electromagnetic fundamentals, nuclear forces, and so on and along the way, we didn't hear of a need to invent dark matter.

    But some people look at the cosmos and decide that despite not truly understanding the whole picture of physics at every scale yet, we can claim that dark matter exists and here's proof. Where in the Nine Hells does this stuff fit with the physics theories they alread promulgate as accepted science to be taught in universities?

    It looks like modern aether, and it looks as though anyone buying it will be upset when someone working right along on the regular investigations into quantum physics and spacetime and so on puts it together and says, "oh, here's why that galaxy moves that way. We didn't need dark matter after all..."
    • by HappyEngineer (888000) * on Monday August 21, 2006 @08:57PM (#15952679) Homepage
      I didn't understand it until I watched the video.

      Essentially it goes like this. They see a collision and make an assumption about what it was that collided.

      Then, they looked over the area and determined where the mass is right now (from our point of view).

      If the assumption about what collided is correct then the result should have been a mass of hot gas that is distributed like you'd expect if a ball of hot gas collided with another ball of hot gas.

      Dark matter supposedly only interacts by gravity. Normal matter interacts by gravity plus nuclear and electromagnetic forces. That means that in a collision, normal matter collides with other normal matter while dark matter is merely slowed down and pulled by gravity.

      The mass distribution that they observed matched up with the mass distribution implied by the dark matter theory. It can't be accounted for with just normal matter.

      The parts of the theory that would need to hold up:
      - the assumed initial configuration of the matter before collision.
      - the current mass distribution that they observed.
      - the calculation about how the collision should behave if it's all normal matter.
      - the calculation about how the collision should behave if it's part dark matter.

      If those parts hold up then it's a pretty striking discovery.
      • Re: (Score:3, Interesting)

        by fimbulvetr (598306)
        We say dark matter, but we don't really mean dark _matter_ right? I mean, this isn't just a lot of peanut butter and jelly sandwiches floating in space? It's just an intangile. Other than having a lot of gravity at this point, it's pretty much undefined.

        So what if it's a ripple/tight spot in spacetime? How could we tell?

        I imagine it like the universe being a mostly inflated balloon. Everything inside is the universe. All of the super massive things (Black holes, etc) are so large, they cause outward bulges
    • by Harmonious Botch (921977) on Monday August 21, 2006 @09:36PM (#15952879) Homepage Journal
      Remember Vulcan, the planet with an orbit inside of Mercury? It was PROVEN to exist in the late 1800s. The calculations showed that Mercury's orbit required a smaller planet to make Mercury's orbit precess as it did. People even went looking for it with the finest telescopes of the day. And they saw it.
      Then some smart aleck who worked in a patent office came along and showed that space is warped and that Mercury's orbit fits perfectly. Vulcan disappeared, never to be seen again.

      Vulcan had more data in favor of its existence back then than dark matter does now. Pardon me, but I'm as skeptical as parent.
    • by The Master Control P (655590) <ejkeever&nerdshack,com> on Monday August 21, 2006 @10:25PM (#15953064)
      Show me why dark matter has to exist.
      Executive summary of TFPP (The Fucking Physics Paper):
      Step 1: Observe galaxy cluster 1E0657-558 through the Magellan optical telescope, note positions of lensed galaxies.
      Step 2: Observe galaxy cluster 1E0657-558 through the Chandra X-Ray observatory, note positions of colliding gas.
      Step 3: Using statistics and vector calculus, compute where the centers of mass causing the lensing are.
      Step 4: Note that the computed center of mass (green contours) doesn't match the position of the gas which composes ~90% of the cluster's visible mass (false-color smear), as shown on page 2 [arxiv.org].

      Conclusion: Something that we can't see comprises ~90% of 1E0657-558's mass. This something emits no EM radiation, no particle radiation, and thus does not interact with the normal matter in the cluster via electromagnetism or the nuclear forces. It's only measurable property is it's mass, hence "Dark Matter".

      We've set off fifty megaton nukes for crying out loud without a single sign of anything amiss that would suggest we have a giant hole in physics requiring dark matter. We've done experiments on electromagnetic fundamentals, nuclear forces, and so on and along the way, we didn't hear of a need to invent dark matter.
      Why should a divergent nuclear chain reaction reveal or be affected by the presence of something that doesn't interact by the strong, weak, or EM forces? Dark matter doesn't come up when experimenting with forces that don't affect it.

      But some people look at the cosmos and decide that despite not truly understanding the whole picture of physics at every scale yet, we can claim that dark matter exists and here's proof. Where in the Nine Hells does this stuff fit with the physics theories they already promulgate as accepted science to be taught in universities?
      Physics is nothing more than a way to model the universe and it's contents. Would you have exclaimed suprise at Einstein's use of wave-particle duality to explain the photoelectric effect because we didn't understand phyisics at the atomic scale circa 1900? The photoelectric effect, the quantum theory of the atom, black holes, and now Dark Matter are the things we use to make "known physics" jibe with observed reality. The whole reason Dark Matter is proposed because the current model of gravity acting on visible mass doesn't fit observations.
  • Age of the Universe? (Score:3, Interesting)

    by Kaenneth (82978) on Monday August 21, 2006 @08:35PM (#15952584) Homepage Journal
    I had read that if the universe were infinite that the sky would be blindingly white from all the old light from old stars, which is one of the reasons that a Big Bang (or other creation) was assumed to have happened.

    But if there are dark clouds that can absorb the light, could there be stars further than 13ish billion light years away, that are simply obscured?
    • olbers paradox (Score:3, Interesting)

      that the night sky is not the temp of the suns surface is called olbers paradox http://jersey.uoregon.edu/~imamura/123/lecture-5/o lbers.html [uoregon.edu].
      I believe the resoluiton of this paradox is one of hte outstanding successes of the expanding universe idea discoverd by hubble
    • Re: (Score:3, Informative)

      by wanerious (712877)
      This was an early objection to the paradox, but was later shown to be irrelevant since any gas blocking the light from distant stars would eventually heat up (by conservation of energy) to the average temperature of those distant stars and would glow itself.
  • by 10100111001 (931992) on Monday August 21, 2006 @08:37PM (#15952602)
    This Account Has Exceeded Its CPU Quota

    I haven't yet read this article due to it being slashdotted, but I'm sure it is at least as credible as the story about the new source of free energy from magnets and as accurate as the one that says goldfish are smarter than dolphins.
  • by saboola (655522) on Monday August 21, 2006 @08:55PM (#15952669)
    George Bush hates dark matter
  • MOND (Score:4, Insightful)

    by MasterPlaid (731392) on Monday August 21, 2006 @08:59PM (#15952692)
    From the title - "This result doesn't rule out alternate gravity theories like MOND". Actually, this directly rules out MOND. That's a big part of the point of the experiment.The idea is that the mass in these clusters doesn't come from the obvious sources of visible matter (the gas), as it would in a MOND or normal gravity scenario, but rather from the invisible (i.e., dark) matter.
  • "To be published..." (Score:5, Interesting)

    by posterlogo (943853) on Monday August 21, 2006 @09:55PM (#15952953)

    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.

  • by fahrbot-bot (874524) on Monday August 21, 2006 @10:23PM (#15953053)
    A steaming pile of Dark Matter was found on the sidewalk and traced back to Nibbler's [wikipedia.org] litterbox. Bad Nibbler!
  • by Spellunk (777915) on Monday August 21, 2006 @10:29PM (#15953077)
    Did anyone else notice the amazing quality of TFA? I actually understand more about dark matter from that article than from anything else I have read on the subject to date. This makes me less grumpy about all the money I felt was "wasted" on telescopes vs. planetary exploration.
    • Re: (Score:3, Interesting)

      by olclops (591840)
      Yes! Finally someone noticed. I was thrilled with the writing of that blog entry, which is why I chose to submit that rather than a more "official" write-up (also, none of the big publications had picked the story up when I submitted it yet. On the other hand, a real publication would have been able to handle the server load. Oh well). But my original summary even said something about how well written the blog entry was, but the editor cut that part.
  • by constantnormal (512494) on Monday August 21, 2006 @11:34PM (#15953320)
    ... 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 [google.com]) 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 [newscientist.com]", 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).

    • Re: (Score:3, Informative)

      by khallow (566160)

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

      The prediction was that mass distribution wouldn't match baryonic mass distribution because the non-baryonic part only interacts with itself gravitationally. Hence, there would be far more diffusion of non-baryonic component than the baryon component in the collision described in the article. The article claims that they indeed observed a mass distribution derived from the study of grav

  • by evilviper (135110) on Tuesday August 22, 2006 @12:22AM (#15953472) Journal
    Dark Matter Exists [cosmicvariance.com]
    Sean at 11:52 am, August 21st, 2006

    The great accomplishment of late-twentieth-century cosmology was putting together a complete inventory of the universe [uchicago.edu]. We can tell a story that fits all the known data, in which ordinary matter (every particle ever detected in any experiment) constitutes only about 5% of the energy of the universe, with 25% being dark matter and 70% being dark energy. The challenge for early-twentyfirst-century cosmology will actually be to understand the nature of these mysterious dark components. A beautiful new result [harvard.edu] illuminating (if you will) the dark matter in galaxy cluster 1E 0657-56 is an important step in this direction. (Heres the press release [harvard.edu], and an article in the Chandra Chronicles [harvard.edu].)

    A prerequisite to understanding the dark sector is to make sure we are on the right track. Can we be sure that we havent been fooled into believing in dark matter and dark energy? After all, we only infer their existence from detecting their gravitational fields; stronger-than-expected gravity in galaxies and clusters leads us to posit dark matter, while the acceleration of the universe (and the overall geometry of space) leads us to posit dark energy. Could it perhaps be that gravity is modified on the enormous distance scales characteristic of these phenomena? Einsteins general theory of relativity does a great job of accounting for the behavior of gravity in the Solar System and astrophysical systems like the binary pulsar, but might it be breaking down over larger distances?

    A departure from general relativity on very large scales isnt what one would expect on general principles. In most physical theories that we know and love, modifications are expected to arise on small scales (higher energies), while larger scales should behave themselves. But, we have to keep an open mind in principle, its absolutely possible that gravity could be modified [blogspot.com], and its worth taking seriously.

    Furthermore, it would be really cool. Personally, I would prefer to explain cosmological dynamics using modified gravity instead of dark matter and dark energy, just because it would tell us something qualitatively different about how physics works. (And Vera Rubin agrees [newscientistspace.com].) We would all love to out-Einstein Einstein by coming up with a better theory of gravity. But our job isnt to express preferences, its to suggest hypotheses and then go out and test them.

    The problem is, how do you test an idea as vague as modifying general relativity? You can imagine testing specific proposals for how gravity should be modified, like Milgroms MOND [wikipedia.org], but in more general terms we might worry that any observations could be explained by some modification of gravity.

    But its not quite so bad there are reasonable features that any respectable modification of general relativity ought to have. Specifically, we expect that the gravitational force should point in the direction of its source, not off at some bizarrely skewed angle. So if we imagine doing away with dark matter, we can safely predict that gravity always be pointing in the direction of the ordinary matter. Thats interesting but not immediately helpful, since its natural to expect that the ordinary matter and dark matter cluster in the same locations; even if there is dark matter, its no surprise to find the gravitational field pointing toward the visible matter as well.

    What we really want is to ta

  • this stinks (Score:3, Interesting)

    by drDugan (219551) * on Tuesday August 22, 2006 @02:54AM (#15953885) Homepage
    it reeks of PR. ... the kind of PR that happens when people are REALLY trying to get others accept a point that is hard to accept.

    I've been following the "dark" story on and off since I stopped studying physics seriously after college. The MOND system makes a whole lot of sense. My non-professional-physicist read on the MOND / DARK controversy is that several of the alternate theories (like MOND) that remove the need for dark matter are fairly convincing. Dark matter is not convincing at all - not testable, not observable, and reminds me a lot of Santa Claus. Somebody brought the presents, right? The problem is that a vast majority of cosmologists are all so far down the dark matter band wagon that if dark matter goes away... lots of careers will be lost. Destroyed. These professionals who trade solely in reputation and intellectual-ism will have their rug pulled right out from under them.

    A much more plausible explanation is that some people are trying really hard to amp up the PR. Sort of like what happens when you need a distraction from a big debate, so you get all the airline travelers to throw away liquids. Anyone who tells you they have proof for something that by definition can not be observed is selling PR. For those of you who believe it without question, I've got a bridge I'll sell you.

    After taking about 30 minutes and reading no less than 6 heavily biased PR pieces... I say this stinks. It's certainly not science - (yet).

    • Re:this stinks (Score:4, Informative)

      by UtucXul (658400) on Tuesday August 22, 2006 @10:48AM (#15955409) Homepage
      My non-professional-physicist read on the MOND / DARK controversy is that several of the alternate theories (like MOND) that remove the need for dark matter are fairly convincing. Dark matter is not convincing at all - not testable, not observable, and reminds me a lot of Santa Claus.
      You have to remember, MOND requires adding a new, arbitrary, constant (and in the covarient version, TeVeS, a minimum of 3 new constants). So it isn't clear if MOND or dark matter does betterr from an Occam's Razor type of arguement.
      But, MOND and the related theories DO NOT remove the need for dark matter (or dark energy). MOND does away with dark matter on galazy scales, but clusters still require dark matter to match observations (for the record, I do simulations of galazy clusters).
      A much more plausible explanation is that some people are trying really hard to amp up the PR. Sort of like what happens when you need a distraction from a big debate, so you get all the airline travelers to throw away liquids. Anyone who tells you they have proof for something that by definition can not be observed is selling PR. For those of you who believe it without question, I've got a bridge I'll sell you.
      There really is no big conspirency. Lots of astronomers are not comfortable with dark matter or dark energy. But they aren't trying to fake their way into making other believe it. At the moment, dark matter fits the data very well (without breaking relativity and other well tested physics). I've been to lots of talks and seen lots of papers where people take the idea of modified gravity seriously. Unfortunately, it is hard to come up with a modified theory of gravity that explains the data without getting something else well tested wrong. It doesn't mean it can't be done.
      • Re: (Score:3, Insightful)

        by HuguesT (84078)
        My own argument against MOND and suchlike gravity mods is that they are totally ad-hoc. Modifying gravity is nice, but to be convincing it would be better to come up with beliveable first principles from which such a modified theory would emerge, rather than adding random free parameters with no basis in reality.

Them as has, gets.

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