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Space NASA Science

Hubble Telescope Maps Dark Matter in 3D 174

Posted by Zonk
from the do-not-go-here dept.
dido writes "The BBC reports that the Hubble Space Telescope has been used to make a map of the dark matter distribution of the universe, providing the best evidence of the role dark matter plays in the structure and evolution of the universe. From the article: 'According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'"
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Hubble Telescope Maps Dark Matter in 3D

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  • And yet... (Score:1, Funny)

    by clifgriffin (676199)
    Pluto is still not a planet.

    *bitter*
  • by macadamia_harold (947445) on Sunday January 07, 2007 @07:10PM (#17501644) Homepage
    According to one researcher, the findings provide "beautiful confirmation" of standard theories to explain how structures in the Universe evolved over billions of years.'

    ... thereby proving god exists.
  • This is pretty cool. (Score:3, Interesting)

    by lordvalrole (886029) on Sunday January 07, 2007 @07:11PM (#17501648)
    I wonder what a 3d model of dark matter around a black hole would look like? Does it share the same properties as regular matter near a black hole?
    • by Tx (96709) on Sunday January 07, 2007 @07:17PM (#17501692) Journal
      I wonder what a 3d model of dark matter around a black hole would look like?

      Maybe I've just been around here for too long, but the parent post reads like goatse.cx meets GNAA.
    • Re: (Score:3, Informative)

      by andersa (687550)
      Black holes are too small to have any influence on the distribution of dark matter. It is a common misconception that black holes are these huge gravity monsters that suck up everything that get closer than a parsec to them.

      In reality you have to get within a few thousand kilometers of the event horizon for you to notice anything peculiar. Further away and the gravity well looks and behaves almost identical to an ordinary star.

      Black holes doesn't play any role in the distribution of cosmological dark matter
  • by Anonymous Coward
    I'm woefully ignorant on this, but is there any evidence towards the existence of dark matter, or is it something that would be necessary in order for certain theories on the composition of the universe to work?
    • by clifgriffin (676199) on Sunday January 07, 2007 @07:18PM (#17501698) Homepage
      Think of it this way. On slashdot you have a lot of posts. Some of them are good. But they can't all be good all the time. So it follows that there has to be bad posts. Lot's of them.

      That's dark matter.

      I think that should be a modifier. -1, Dark Matter

      Don't be mad that you didn't think of it...
    • by HarveyTheWonderBug (711765) on Sunday January 07, 2007 @07:40PM (#17501882)
      Yes, there is, but we do not have a clue yet of what it is made of.
      Astronomers have ways to measure the mass of objects, like galaxies, and cluster of galaxies, using a theory of the gravitation. For galaxies, the classical newtonian theory is enough: they just measure how fast the stars and the gas orbit around the galaxy, and derive directly their mass from kepler laws. For clusters of galaxies, or large structure, they use the bending of light by mass from general relativity. These measure are getting reasonably accurate. When they compare these masses to the mass they actually can see (stars, gas, etc..), they find that they can only account for 1/6 of the total mass they measure, well above all the uncertainties of the measurments. Therefore, there must be some matter (that is, something with a mass), that we cannot see (that does not interact via electromagnetism). This is the dark matter.
      For more info, there is a [wikipedia] [wikipedia.org] entry.
      • Re: (Score:3, Insightful)

        by calice (570989)

        This is what I don't get about dark matter, and this is just how I see it, and no one has ever given me a decent explanation. Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed? I am not trying to disprove dark matter, I certainly am no cosmologist, but it just seems odd that so much attention is given to dark matter, and very litt

        • by Ambitwistor (1041236) on Sunday January 07, 2007 @08:50PM (#17502524)

          Why is it that scientists think that dark matter exists simply because the observed galaxies don't conform to Newton's Laws? Wouldn't a simpler solution be to take a step back and consider that, maybe, Newton's Laws are flawed?
          You want a solution that is simple enough to explain the facts, but no simpler. Modifying the laws of gravity runs into difficulty explaining everything that dark matter can, although you can get it to explain some things (such as galactic rotation curves).

          Can someone explain to me why dark matter is the prevalent theory?
          In short, because it works and none of the alternatives people have proposed over the decades work as well. I can get into details if you want, but you should probably just start at Wikipedia.

          Or perhaps why something like MOND is always ignored?
          MOND isn't ignored. Go to the astro-ph arXiv or the Smithsonian/NASA ADS Abstracts and search for MOND papers. You'll find them, along with criticisms of MOND. Here [preposterousuniverse.com] is a nice but somewhat outdated set of slides on how well MOND fares against the evidence, and a more recent [cosmicvariance.com] blog post by the same author discussing newer evidence that tightens the screws on MOND even further.

          As I said, I don't know what is right, but it just seems like a hack-job to me.
          I don't know why all the hate for dark matter. Screwing around with the laws of gravity isn't any more elegant, and there are plenty of plausible candidate particles for dark matter lying around in various extensions to the Standard Model.
          • I don't know why all the hate for dark matter.

            Some skepticism is certainly in order. Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed. The fact that a better theory of gravity hasn't been produced doesn't mean that the current one is correct.

            There are pretty st

            • Since we currently have no way of independently confirming the existence of dark matter, we also have no way of distinguishing between two possible cases: one case is that dark matter corresponds to some real, physical material; the other is that the theory of gravity we're using is flawed.

              No one has actually succeeded in producing a modified gravity theory that can mimic the effects of dark matter. It is not true a priori that this can be done; there are a lot of constraints on both the possibilities for dark matter and the possibilities for a gravitational theory, and they don't necessarily intersect.

              There are pretty strong parallels between dark matter and the infamous epicycles.

              Dark matter is not like epicycles. Epicycles are essentially a Fourier expansion of any orbital motion, and as such, they are totally non-predictive and unfalsifiable. Dark matter theories

              • by alienmole (15522)

                This is false. If you take any one phenomenon, such as galactic rotation curves, you can explain it by postulating a particular distribution and type of dark matter. But there's no reason why that same distribution and type should also account for other, independent phenomena -- which it does. We can't get "whatever result we want" by fudging the dark matter distribution. If we fudge it one way, it can disagree with other observations. The fact that it doesn't is the reason why dark matter has become a mai

        • Re: (Score:3, Insightful)

          It's not completely true that MOND does not get any attention, there are very regularly publications in refereed journals about it, to prove it, disprove it, or try to make it better. Here is the problem as I see it:
          1. The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.
          2. MOND had some success in explaining various observational puzzles, but has also some problems with o
          • Re: (Score:3, Insightful)

            by NotZed (19455)
            # The current accepted theory of gravitation, general relativity, works extremely well: it's predictive power has so far never be successfully challenged. Many have tried, noone has succeeded.

            You mean, apart from the fact that you need to create 90+ percent more matter in the universe than what is visible to prevent galaxies from flying apart?

            i.e. without dark matter (and dark energy), gravity doesn't predict much.

        • Personally I think the simplest solution is that dark matter is made up of neutrinos. Although I don't know whether that would be possible or not.
          • Re: (Score:3, Informative)

            by Ambitwistor (1041236)
            No. Neutrinos aren't massive enough to be (most of the) dark matter. See here [princeton.edu] for a brief but more detailed discussion.
        • These clever chaps have done just that.

          They actually mapped it.

          On 3D!

          If it was a hack, it would be one of the cleverest, more accurate hacks in the history of science.

      • Re: (Score:2, Interesting)

        by Anonymous Coward
        Yes, there is, but we do not have a clue yet of what it is made of.
        Well, most of science has yet to agree what it is, but Randy Mills has a pretty solid theory backed by observations. [blacklightpower.com]

        Mainstream says the 10% of the universe that is observable is 90% hyrogen, 9% helium, and 1% everything else. Mills says that the 90% unobservable universe is a lower-state hydrogen atom that he calls a "hydrino". The Mills theory explains the answers to some very old scientific questions, such as 'what happens to a phot
    • by pln2bz (449850) * on Sunday January 07, 2007 @11:30PM (#17503870)
      The real story of how we ended up with dark matter is not widely understood or accepted.

      Some time ago, a man named Hannes Alfven, who is today considered the father of plasma physics, founded the field of magnetohydrodynamics, which astrophysicists have been using to model plasma in the universe for several decades now. This field treats plasma as a fluid and assumes that currents cannot flow through the plasma because it treats plasma as an ideal conductor with no resistance. This is actually not *anything* like the way that plasma operates in the real world, and since plasma represents 99%+ of all observable matter within the universe, this massively incorrect assumption yields absurd results in astrophysics today. Plasma is in fact electrically conductive and its electrical properties interact with its mechanical motions, and vice-versa. If you've ever seen a novelty plasma globe, then you intuitively know that plasma is not like a fluid. You can tell by looking closely at a plasma globe that the plasma creates filaments and these filaments pair up and twist around one another. These twisting currents are called Birkeland Currents. As the current flow increases through them, they pinch together with increasing force and this pinching action can actually condense matter into a ball. This is a big deal because there is no good reason to believe that molecules will gravitationally collapse from a diffuse collection of matter in space; in fact, gases obviously expand in a vacuum. Contrary to the more popular beliefs propagated in astrophysics and the media today, the z-pinch effect is likely actually how planets and stars form. Astrophysicists don't understand this because of their earlier assumptions regarding plasma being a fluid with no currents. But we can see strong evidence of Birkeland Currents and Z-Pinches happening through our telescopes.

      The thing is, astrophysicists will see what they want to see through the telescope. All observations today are interpreted through mainstream concepts like stellar evolution and Big Bang theory. When an anomaly pops up, it can be a very simple matter to propose a "patch" for the theory to keep it going. Astrophysicists will invoke collisions, black holes, gravitational lensing or malformed electrical theory in order to explain away anomalies. But you will notice that anomalies are discovered nearly every week these days (especially with stellar evolution), and this is a problem because things like collisions should not actually be happening as often as they are being invoked to dismiss the anomalies.

      When Hannes Alfven received his nobel prize for plasma physics in the 70's, he recused himself from the field that he created (MHD) and warned astrophysicists to abandon it, and that the path they were taking would eventually dead-end. But they completely ignored him and continue to do so. So, now we have mysterious forces tugging on matter throughout the universe that we can't see. This is what we call dark matter. Dark energy is supposed to be matter that can gravitationally repel. Electrical forces can accomplish both of these feats without any mysterious matter. All you have to do is drop the earlier incorrect assumptions about plasma and accept that extremely diffuse plasma flows can and do exist. You will notice over time that the dark matter studies will reveal some details that correspond with the properties of electricity over plasma. For this particular article, it was noticed that the structure of the dark matter was in places filamentary. Filamentary structures are far easier to generate with electricity than with gravity. It was also mentioned that dark matter can exist in the absence of physical matter. This is to be expected with plasma because plasma can consist of just electrons and ions, or it can also be coexisting with or collecting dust.

      Some brave scientists and electrical engineers called Electric Universe Theorists are working on understanding the universe in terms of real plasma physics -- which makes p
  • Enlighten me (Score:4, Interesting)

    by Original Replica (908688) on Sunday January 07, 2007 @07:16PM (#17501684) Journal
    To those /.ers that know more of physics than I do, is Dark Matter supposed to be some actual particle, or is it a kind of natural gravitational topography? Everything I read ( quick google search/old copy of "Elegant Universe") about it seems to be rather vague and mysterious.
    • Re:Enlighten me (Score:5, Informative)

      by ceoyoyo (59147) on Sunday January 07, 2007 @07:36PM (#17501846)
      Nobody knows.

      Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

      The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet. That's not as far fetched as it sounds -- neutrinos are just such a particle. They have mass so they interact gravitationally but they interact with ordinary matter extremely weakly in all other ways. Massive neutrinos were also candidates to explain some of the dark matter for a while, but I believe once their actual mass was measured it was too little to explain more than a bit of the dark matter.
      • Re:Enlighten me (Score:5, Informative)

        by Dachannien (617929) on Sunday January 07, 2007 @08:02PM (#17502098)
        Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes, that intersect our own universe's brane, resulting in a gravitational distortion that becomes huge at cosmological scales. A similar concept is used to explain why the gravity exhibited by real matter in our own universe has a strength many orders of magnitude smaller than the other forces - most of the gravitons leave our universe's brane, while the mediating particles of other forces (gluons, photons, etc.) are constrained to move within the brane.

        See also http://en.wikipedia.org/wiki/Brane_cosmology [wikipedia.org] .
        • by ceoyoyo (59147)
          Yeah, I find that one of the more interesting theories since it would give us our only way of detecting what's on adjacent branes. Whatever it turns out to be, dark matter and dark energy seem to be some of the most interesting anomalies going today. Maybe one day I'll get my faster than light yacht.
        • by glwtta (532858) on Sunday January 07, 2007 @10:04PM (#17503214) Homepage
          Some string theorists believe dark matter may be gravitons, emitted by matter on adjacent branes

          Yeah, but string theorists make theoretical physicists look like scientists :)
        • Re: (Score:3, Funny)

          by Khyber (864651)
          Brrrrrraaaaannnneeesssss *shambles around aimlessly*
        • This is actually made a much less tenable theory by the latest gravitational lensing result involving colliding galaxies. Presumably matter on an adjacent brane would interact with itself other than gravitationally, but it's clear from the lensing that the dark matter didn't interact with itself other than gravitationally.

          Perhaps the laws of physics are different on the other brane, but it still seems odd that the two bunches of matter would pass right through eachother.

          Well, there could be two adjacent

          • This is actually made a much less tenable theory by the latest gravitational lensing result involving colliding galaxies. Presumably matter on an adjacent brane would interact with itself other than gravitationally, but it's clear from the lensing that the dark matter didn't interact with itself other than gravitationally.

            Perhaps the laws of physics are different on the other brane, but it still seems odd that the two bunches of matter would pass right through each other.

            Well, there could be two adjacent br

      • The rest seems to be something that interacts only gravitationally... it might be a particle we haven't discovered yet.

        It is possible that most of the dark matter needed by current theories to explain the universe we see doesn't really exist, and that our understanding of gravity is wrong. The TeVeS theory, developed from MOND, may be able to explain the universe without requiring that most of it be made of dark matter and dark energy. See Gravity's dark side [physicsweb.org]. Also mentioned in a previous Slashdot stor [slashdot.org]
        • by ceoyoyo (59147)
          It is possible, but observations seem to be making it less and less likely. It doesn't explain these Hubble observations very well, and it doesn't explain the colliding galaxies observation.

          Even without those, as you said, modifying gravity might explain most of the observations. That still leaves some others, that we'd need something else to explain. Even the modified gravity researchers are saying ou still need some dark matter to make everything work.

          So, Occam's razor -- which is the simplest explanat
      • Re:Enlighten me (Score:5, Informative)

        by radtea (464814) on Sunday January 07, 2007 @10:24PM (#17503364)
        Some portion of it could be ordinary matter that's simply non-luminous, but I think there are observations that limit that to a small proportion.

        Big Bang nucleosynthesis limits the amount of baryonic (that is, "normal") matter to a relatively small fraction of the total observed mass of the universe. The basic idea is that we know how big the universe was when protons and neutrons (collectively known as nucleons) were being formed--at some point the cosmic fireball cooled off to the point where quarks were no longer free, so they condensed into nucleons. We also know that the lifetime of a free neutron is about 15 minutes, so there was only about an hour for nuclei more complex than hydrogen to form.

        So, if the universe was VERY dense in the hour or so after nucleon formation then every single proton would have run into a neutron or two and there would be almost no plain old hydrogen in the universe--everything would be helium and deuterium. On the other hand, if the the universe were extremely diffuse during that single hour there would be hardly any helium--only the few percent made by stellar fusion and supernova in the past ten billion years. As it is, we are pretty sure based on observations and theory that about 20% of the helium in the universe was formed in the Big Bang. That, plus some more problematic numbers from deuterium and lithium and helium-3, give us a very good estimate of the total baryonic mass in the universe.

        The visible mass is quite a bit smaller than the total baryonic mass, and there is some reason to believe that the flat rotation curves of spiral galaxies are due to baryonic dark matter, although it would have to be in the form of small clumps of matter like comets or dead stars or something to not do any significant scattering of light.

        Dark matter on larger scales is completely unrelated to galactic dark matter--the use of the single term "dark matter" for these totally unrelated problems is unfortunate and confusing, as I point out every time this topic comes up on /.

        The observation reported here, like the colliding galactic clusters observation reported a month or so ago, is amongst our first clear view of extra-galactic dark matter, which is too copious to be explained as normal baryonic matter.

        The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark matter would never be slowed down by anything, and so would never form clumps on any scale.

        So it is probable that extra-galactic dark matter is pretty exotic, or that something was sufficiently different in the early universe to make gravity sufficiently dissipative to form the observed clumps. Either way, the flood of observations using these new microlensing techniques is going to start killing off theories in droves--at least those theories that make actual predictions.
        • by ceoyoyo (59147)
          Good explanation. Thank you.
        • Re: (Score:3, Interesting)

          by TMB (70166)
          Just one minor quibble:

          The problem that cold dark matter theorists have to deal with is that the extra-galactic dark matter can't just interact gravitationally, because gravity is too weak a force to produce structures in the short time the universe has been around. To clump in the manner observed, extra-galactic dark matter has to have some mechanism for losing energy. Otherwise two pieces of dark matter (or a piece of dark matter and a peice of ordinary matter) would just pass through each other. The dark

        • Galactic dark matter has a problem called MOND. If we don't agree with MOND on the galactic scale then we need to obtain MOND from our theories of formation of dark matter, because MOND agrees very well with the observed galactic data, even predicting the very low dark matter and the very high dark matter ratios obtained for the different galaxies, which this report calls problematic.
          See http://www.astro.umd.edu/~ssm/mond/ [umd.edu] for further information on MOND.
    • by a.d.trick (894813)
      I'm not an expert on physics but AFAIK I don't think anyone knows much at all about dark matter. It seems to me like it's just a poor excuse for why the observed facts don't fit our lovely theories.

      Damned facts, always getting in the way.
      • Re: (Score:3, Insightful)

        by TapeCutter (624760)
        Close, dark matter is the "hack" we use to make our theories fit our obervations. If we had not observed "something" we would not need to invent the name "dark matter" to label it.

        I fail to see how it is a "poor excuse" for anything, it's mearly a description of something we don't fully undersatnd but can indirectly observe and therfore label. Maybe our elegant theories will need to change to account for future observation but right now our notion of what we label as "dark matter" explains the observed a
    • Re:Enlighten me (Score:4, Informative)

      by Anonymous Coward on Sunday January 07, 2007 @08:00PM (#17502086)
      The general belief is that it is an actual particle. There are other competing theories such as MOdified Newtonian Dynamics which have slight corrections to our current laws of gravity, but more and more evidence is ruling out the simplest of these models and it's pretty clear that at least some of the dark matter is actually particles. Another thing people thought dark matter could be was normal matter which doesn't produce light, things like planets and failed stars. However, extensive astronomical searches for these objects (called MACHO's) using both the fact that they should occassionally block our view of stars and their potential to cause gravitational lensing have turned up nothing. This basically leaves some sort of new particle as the dark matter canidate. The current theory is that this particle only interacts via the weak nuclear and gravitational forces. It Is is called a WIMP (weakly interacting massive particle). There are a bunch of different models of what this particle is. Basically nearly every theory of physics beyond our current Standard Model has some sort of particle that it's proponents hold up as a dark matter canidate.

      There are a wide variety of dark matter searches being conducted which directly search for the particle. The general idea is to see their interaction through the recoil of an atom when one strikes the atom's nucleus. This is very difficult. The most common current technique is searching for the "sound" a dark matter particle interacting with cryogenically cooled germanium crystals produces.
    • Really, the evidence for "dark matter" has been made through its effects - it bends light, and makes galaxies spin at a different rate than what we're currently observing. Scientists have inferred its existance from its effects. Not a really bad practice, but as the other posts around here indicate, we've got a long way to figuring out what the hell is really going on.
    • by elrous0 (869638) *
      "Dark Matter" always struck me as a kind of dodge. We discover that the universe doesn't have enough mass to account for the current pet theories in physics, and so rather than question the theories themselves, we invent a mysterious new "dark matter" that we can't actually see (but which MUST be there because the theories can't POSSIBLY just be wrong).

      It strikes me as a wishful-thinking fiction more than a testable, observable phenomenon.

      -Eric

  • by ars (79600) <assd2NO@SPAMdsgml.com> on Sunday January 07, 2007 @07:24PM (#17501750) Homepage
    "beautiful confirmation" of standard theories?????

    What standard theories? Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows. There is a very nice (and complete!) standard model of physics, and dark matter holds no place.

    I should qualify, I'm talking about theroes of non-baryonic dark matter [wikipedia.org] and even worse dark energy [wikipedia.org].

    Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

    Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge.
    • by ars (79600)
      I shouldn't have used the phrase "is fitting facts to the data", please ignore it, I misstyped. Pretend the sentence just ended in a ?
    • by ceoyoyo (59147) on Sunday January 07, 2007 @07:47PM (#17501958)
      Isn't that exactly what they did? They measured mass distributions through gravitational lensing and noted the places where there was more apparent mass then there should be. You can theorize that gravity works strangely at large scales, and inconsistently too, since they found clumps, but the simplest explanation that matches the observations is that there is something with mass that we can't see. It might be normal matter, but the fact that there's an enormous amount of it and it somehow avoids rubbing together and getting hot like all the other matter we know of is problematic. When galaxies collide it also seems to just keep on going while the normal matter slows down when it hits something going the other direction. Given those two observations (dark and appears not to interact other than gravitationally), a subatomic particle isn't so bad an explanation. It's not so far fetched either -- we know of other particles that have those properties. They're called neutrinos.
    • by HarveyTheWonderBug (711765) on Sunday January 07, 2007 @07:52PM (#17501988)
      "beautiful confirmation" of standard theories?????
      Yes indeed. The standard paradigm for the evolution of the Universe is the widely accepted lambda-CDM model, or Cold Dark Matter with a cosmological constant (or dark energy). The recent results of WMAP, of the high-z supernovae, all point toward a set of cosmological parameters where the energy density of the universe is made of:
      • 70% of dark energy
      • 30% of matter
        • out which, stars, gas, neutrino are making at most 5%
        • so we are left with 25% of dark matter
      So yes, dark matter is widely accepted. It's not satisfying because we have no clue about what it is (it clearly does not interact electromagnetically), but we can feel its gravitational pull. Coming up with a good theory on its nature is one of the hardest challenges in modern astrophysics.
      • Re: (Score:2, Insightful)

        by yusing (216625)
        70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations??

        I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment.

        Explaining the universe is hard. But saying stuff like "it's real", even implying that it is ... when there's not even a working theory about it yet ... is dangerous to the craft. When people get religious about stuff like string theory, it endangers science.
        • 70% of the universe is made of some theoretical "substance" that hasn't shown up in several decades of particle physics observations??

          Why should it, if it's weakly interacting and massive? (Which are precisely the properties it needs to explain the astrophysical observations, by the way.)

          I smell a Thomas Kuhn moment in the making. Or at least, a phlogiston moment.

          The difference is that dark matter keeps on passing new and independent observational tests.

          • Oops, you were referring to dark energy, not dark matter. Dark energy may not be a "substance" at all; the best current explanation of dark energy (the cosmological constant) is a modification of the laws of gravity, not a new kind of particle.
    • But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.

      You do realize that science is 'just' fitting theoretical models to data, do you? And that, while a model survives by being able to fit more types of data, it usually starts by fitting one or a handful?

      Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anythi
      • by sholden (12227)
        It's pretty clear the phrase that was meant to be typed was "making shit up".

        Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess, the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect, can't do experiments on, doesn't exist locally, and is completely different from the universe we do obse
        • Re: (Score:3, Informative)

          by Ambitwistor (1041236)

          Because galaxies don't rotate the way our current theory of gravity says they should, because gravitational lensing isn't working the way our current theory of gravity says it should, because of a bynch of other thing I guess,

          You act as if having a bunch of observational evidence for dark matter is unimportant.

          the accepted solution it to declare that 95% of the universe is made of stuff we can't directly detect,

          Would dark matter be more palatable to you if it only made up 5% of the universe? Why does it suddenly become more implausible if it makes up most of the universe. It's because it makes up most of the universe that we can even tell it's there.

          can't do experiments on,

          That remains to be seen; we may be able to create such particles in accelerators, and we may also be able to detect them in the Sun, in cosmic ray experiments, etc.

          That being sai

    • by Ambitwistor (1041236) on Sunday January 07, 2007 @08:22PM (#17502282)

      What standard theories?
      The standard theories of large-scale structure formation in the early universe, which is mediated by non-baryonic dark matter.

      Dark matter does not exist, as least not as far as anyone (except astronomers with good imaginations) knows.
      Wow, that's a compelling counterargument. However, it neglects the decades worth of observational evidence in favor of dark matter in the form of galactic rotation curves, the motions of satellite dwarf galaxies, gravitational lensing, measurements of galactic gas temperatures (which depend on the local gravitational neighborhood), anisotropies in the CMBR, the rate and structure of large-scale cosmological structure formation, etc.

      There is a very nice (and complete!) standard model of physics, and dark matter holds no place.
      Actually, one of the leading dark matter candidates is the axion, which was introduced into the Standard Model to resolve the strong-CP problem. However, the astronomical evidence indicates that the Standard Model of particle physics is most likely not complete, and that at least one new weakly-interacting massive particle is needed.

      Regular matter, that is simply dark - i.e. cold, and not emiting light, does not bother me. But making up particles no one has ever seen just because you don't understand what you are seing is fitting facts to the data.
      There is nothing wrong with "making up particles no one has ever seen" in order to explain discrepancies in either theory or observation. It's rather the point of science, to frame new hypotheses. Historically, see the prediction of the positron, on the basis of theoretical consistency between quantum mechanics and relativity, or the prediction of the neutrino, on the basis of apparent non-conservation of energy.

      Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature. If you don't understand something, say so, don't invent plausable explanations that have nothing supporting them except your lack of knowledge.
      Dark matter is a plausible explanation precisely because it is supported so well by numerous disparate observations. There are other ways one can attempt to explain various discrepant observations (e.g., by modifying the laws of gravity), but dark matter is far and away the most successful, as it passes all known independent tests. There's no reason why an ad-hoc patch designed to explain galactic rotation curves should also end up explaining, say, cosmological expansion, or large-scale structure. And it's silly to claim that we cannot measure anything: we can measure the gravitational effects of dark matter.

      Sure, everyone would love it if we could detect dark matter particles directly — and if they interact non-gravitationally, we hopefully will someday. But what's silly is to claim that we have little reason to believe that dark matter particles exist.
    • It misses one of the four fundamental forces of nature. You know, an unimportant little thing we call "gravity." Naturally, if there's a particle that only interacts gravitationally, it would also have to be missing from the standard model.

      There's also the unresolved matter of actually observing a little particle that is in the Standard Model called the Higgs boson.

      Trust me, the standard model is really really good, but it's far from complete.
    • by Carmelbuck (921788) on Sunday January 07, 2007 @09:02PM (#17502630)
      Every time an article regarding dark matter is posted on Slashdot, there are nonsense "fudge factor!!1!" postings like the above. And every time, like-thinking idiots mod them up as "Insightful" or "Interesting". And every time, I suspect, people like me get the urge to go through and respond to every single one, but have to limit ourselves.

      So let's start at the beginning, shall we? Galaxy rotation curves indicate that there is more mass in galaxies than would be inferred from the luminous matter. How do we know that it's not clouds of cold gas? Because that's ruled out by 21cm observations and by studying the absorption spectra of extragalactic objects. How do know that it's not clouds of hot gas? Becasue that's ruled out by UV and X-ray observations. How do we know that it's not brown dwarfs and black holes? Because that's ruled out by microlensing surveys.

      Now, studies of galaxy dispersion velocities in clusters indicates that there's more mass in galaxy clusters than than would be inferred from the galaxies themselves, plus the intracluster medium which is observed in the X-ray. This is verified to high accuracy (i.e., the estimates of the total cluster mass are in close agreement) by hydrostatic X-ray mass measurements and by weak lensing observations. How do we know that it's not clouds of cold gas? Because that couldn't coexist with the hot gas, and because the dark matter spatial distributions are clearly different from the gas distributions. How do we know that it's not clouds of hot gas? See "intracluster medium" above. How do we know that it's not brown dwarfs and black holes? Because there's no mechanism for moving large numbers of objects out of the galaxies into the ICM (there are some intracluster stars, yes, but relatively very few--and the number of those gives us hints as to the number of non-luminous objects similarly ejected). How do we know that it's not neutrinos? Because neutrinos are experimentally shown to be too light and too fast, and cosmological constraints show that too few would have been produced in the Big Bang.

      Now, studies of cosmological structure formation indicate that the size and number of galaxy clusters in the universe are not consistent with what would be expected given an all-baryonic universe. How do we know that...er...well, that's that. Cold collisionless dark matter is required to make the simulations work.

      How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above. The MOND people cheerfully acknowledge this, even if their advocates on Slashdot don't.

      Look, the history of physics is replete with things whose existence was inferred long before they could be directly observed--neutrinos, quarks, atoms themselves, and much, much more. It's simply asinine to suggest that "we haven't directly measured it" means "it doesn't exist". Heck, we only really "see" subatomic particles because of the photons given off when they interact with one thing or another--"seeing" dark matter via measurements of its gravitational effects is hardly less direct.

      And we'll just ignore the nonsensical "fitting facts to the data". The bottom line is, there are multiple, independent lines of evidence that dark matter exists, and that it is non-baryonic. Uninformed posters on Slashdot can pat themselves on the back for their intelligence as much as they want, but they're only fooling themselves.

      • mod parent up !
        • Seconded.
          • by NeoSkink (737843)
            Indeed! Carmelbuck covered the reasons Dark Matter is part of the standard cosmological model very well. His comment really should be the highest moded, not the above uninformed "Dark Matter is just made up!" rants.
      • I'd also add; Even if (and that's a pretty big if) the theory of dark matter is wrong and there's a better answer, if it's the closest model we have to reality it's still worth using. Newton was slightly wrong about gravity, and we still use his model in situations where relativity has negligible impact.
      • by anandsr (148302)
        "How do we know that modified gravity isn't the answer? See multiple independent lines of evidence above. There are no theories of modified gravity that come even close to explaining all of the above."

        True. Nothing can really provide better answers than saying god does everything. Fact is that Dark Matter and Dark Energy are not falsifiable theories. They can only be proven true, by finding the so called dark matter, but cannot be proven false by any means.

        The best Dark Matter theories require 2 parameters
        • by fm6 (162816)
          They can only be proven true, by finding the so called dark matter, but cannot be proven false by any means.
          You're saying that there are no crucial experiments [uchicago.edu] relating to dark matter and never can be. That's a big claim, and one you're going to have to justify.
    • by fermion (181285)
      On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model. The æther is shown not to exist and we have a more robust theory for the propagation of light. I suspect that the same will be true dark matter, and it will lead to a more robust theory of gravity.

      That said, as the universe is explored in more detail, we increasingly see that the standard model is robust but has some issues, in the same way that mor

      • Re: (Score:2, Informative)

        by Ambitwistor (1041236)

        On one level, I consider dark matter to have the same credibility as the æther. An interesting concept, but largely created as hack to the model.

        Aether theories didn't make any predictions that correctly explained any new observations. Dark matter does.

        Certain unexplained acceleration in the cosmos has renwed interest in the Einstein cosmological constant, which if it exists, renews the presence of the æther, albeit in a different form.

        The cosmological constant is a modification of the laws of gravitation, not anything like what was historically referred to as the aether.

        Dismissing a concept simply because it is a mathematical hack is a mistake. In reality we use mathematics because it is a precise language that will often lead us to an unobserved reality.

        This point is well taken. However,

        Recall that special relativity is based on Einstein's assertion that equations should be symmetric.

        That wasn't Einstein's motivation for introducing special relativity. (On the other hand, the complete form of Maxwell's equations of electromagnetism were based on Maxwell's assertion that the equations should be symmetric.)

      • by yusing (216625)
        Dismissing a concept simply because it is a mathematical hack is a mistake.

        But talking about hypotheses as if they were solidly established theoretical constructs, dovetailing with the framework of well-established physics, does, IMHO, a disservice to science. For one thing, it tends to make it hard to see alternatives by freezing an attitude and blinkering the imagination needed to see alternatives. For another, it tends to make some laymen skeptical about *any* claims of science.

        IIW, a hypothesis repeated
    • by radtea (464814)
      Scientists often discuss new theories, etc, and in that context dark matter has it's place, but to claim it exists - as this story does - without being able to actually measure anything is quite silly and premature.

      The whole point of these observations is that they are an entirely new probe of extra-galactic dark matter, and they are consistent with dynamical estimates of extra-galactic dark matter distributions.

      Ergo, they consistute compelling evidence that extra-galactic dark matter is not just a mistake
  • The map streches back to half the life-span of this universe. That means that if a single unit of a radioactive atom exists in the universe with just the right value...
    Uh-oh! It just reached half-life! Nasa better hurry up and find this long lasting nuclear element before its lost forever. We wasted the first half of this universe's existance, lets not waste the second.
    Oh wait...this statement would only be true if the universe was ending at exactly this moment and the hubble did this scan half-a-u
  • RTFA (Score:2, Insightful)

    by Swimport (1034164)
    "We understand statistically what those galaxies are supposed to look like,"
     
    So this map is based on what they assume the universe should look like. Then they use how its different to find where the dark matter might be. Doesnt sound 100% certain by any means, but its a nice picture.
    • Re: (Score:2, Insightful)

      Actually astronomers do :). Most galaxies are "disk galaxies", i.e. lenticulars and spirals. Face-on (viewed from above), they look like a disk. So they should look like ellipsoids when viewed on the sky, due to their inclination. But this basic shape gets distorted when viewed through a lens (in this case, the lens is a massive object in front). The distortions are very small, so what astronomers do is that they measure the shape of as many galaxies as possible in a given region, and look for a statistical
    • by TMB (70166)
      It's not so much that they assume what the universe should look like, as that they assume a particular property of the universe - that it's isotropic on large scales. Therefore, on average we view galaxies from a random angle and so the orientation of their images on the sky is random. You then look for statistical deviations in the orientations of the images due to lensing of the light by matter along the line of sight.

      Isotropy is an assumption, but we have never detected a significant deviation from isotr
  • Are all the "solid" areas of the 3d shape a roughly similar density of dark matter?

    Seems to me there would be a wide range of density distributions. If so there must have been a human decision to decide
    which level of density constitutes matter vs. empty space in this 3d depiction. I wonder how the 3d shape would change
    if we arbitrarily moved this balance point of requisite density up or down the scale.
  • I don't know how much weight this "dark matter" theory holds (pun intended). But I was immediately interested when I saw their translucent blue 3d render of the stuff.

    I wonder how many other people that works for...

  • You should call it "Light Challenged" matter in this age of political correctness. Be more sensitive to other matter people!
  • Here. [hubblesite.org]

    I've tried to find something about whether this tells us something new about the properties of dark matter, but so far no luck. Anyone have a link to something more informative?
  • Here are the press release links: Nature [nature.com], Hubble Space Telescope [hubblesite.org], European Space Agency [esa.int] and Subaru Telescope [naoj.org]. The COSMOS project web page can be found there [caltech.edu].
  • and why is it a related link? Is there something special about dido@@@imperium...ph [mailto]?
  • Dark matter is becoming as household a term as "black hole". But what makes it dark? It's matter that doesn't interact with electromagnetism, so we can't see it - though its gravitation makes it detectable by other means. But what kind of matter doesn't interact with electromagnetics? Have we ever physically obtained any? Synthesized any? And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not?
    • But what kind of matter doesn't interact with electromagnetics?

      Any elementary particle that is electrically neutral.

      Have we ever physically obtained any? Synthesized any?

      If by "any" you mean "electromagnetically non-interacting", then there are neutrinos. If you mean "the kind of dark matter that is needed to account for astronomical observations", then no, we haven't.

      And supposedly something like 70% of the dark "matter" is energy. How does non-dark energy interact with electromagnetism, where the dark "stuff" does not?

      What is "non-dark energy"? Photons? I don't understand the question.

      • by Doc Ruby (173196)
        AFAIK, the Standard Model doesn't call for 70% of the mass of the universe to reside in neutrinos, or even 10%. Does the standard model describe the majority of mass as non-electromagnetic?

        Photons aren't energy, they're matter with an energy equivalence proportional to their frequency. Maybe the descriptions of "dark energy" are inaccurate - they're describing dark matter at high energy. Perhaps neutrinos, or some other non-interacting particle in motion. But dark energy [wikipedia.org] is described as different from famil
  • I thought that we weren't 100% certain that dark matter even exists
  • by binarybum (468664) on Monday January 08, 2007 @03:13AM (#17505218) Homepage
    now I can hang my map of dark matter up right next to my picture of albino polar bears walking the tundra in a blizzard.

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