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Most Sensitive Detector Yet Fails To Find Any Signs of Dark Matter 293

Posted by timothy
from the turn-on-the-light-and-the-dark-escapes dept.
ananyo writes "A U.S. team that claims to have built the world's most sensitive dark matter detector has completed its first data run without seeing any sign of the stuff. In a webcast presentation today at the Sanford Underground Laboratory in Lead, South Dakota, physicists working on the Large Underground Xenon (LUX) experiment said they had seen nothing statistically compelling in 110 days of data-taking. 'We find absolutely no events consistent with any kind of dark matter,' says LUX co-spokesman Rick Gaitskell, a physicist at Brown University in Providence, Rhode Island. Physicists know from astronomical observations that 85% of the Universe's matter is dark, making itself known only through its gravitational pull on conventional matter. Some think it may also engage in weak but detectable collisions with ordinary matter, and several direct detection experiments have reported tantalizing hints of these candidate dark matter particles, known as WIMPs (Weakly Interacting Massive Particles). Gaitskell says that it is now overwhelmingly likely that earlier sightings were statistical fluctuations. Despite the no-shows at XENON-100 and LUX, Laura Baudis, a physicist on XENON-100 at the University of Zurich in Switzerland, says physicists are not ready to give up on the idea of detecting WIMPs. They may simply have a lower mass, or may be more weakly interacting than originally hoped. 'We have some way to go,' she says."
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Most Sensitive Detector Yet Fails To Find Any Signs of Dark Matter

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  • by GameboyRMH (1153867) <gameboyrmh@gm[ ].com ['ail' in gap]> on Wednesday October 30, 2013 @03:29PM (#45284175) Journal

    Pulling in other posts below it :D

  • by Anonymous Coward

    Just sayin'...

  • Maybe (Score:5, Insightful)

    by Anonymous Coward on Wednesday October 30, 2013 @03:38PM (#45284307)

    Maybe it's just not there.
    Dark matter always reminds of the 18th century hypothesis of the aether.

    http://en.m.wikipedia.org/wiki/Luminiferous_aether

    Same principle. Same made up matter that no one can see or detect but somehow fills the entire universe.

    • Re:Maybe (Score:5, Insightful)

      by TheCarp (96830) <sjcNO@SPAMcarpanet.net> on Wednesday October 30, 2013 @03:57PM (#45284553) Homepage

      Yes but I could pick another example, the nutrino and say it sounds like that too:
      "In 1930 Wolfgang Pauli proposed a solution to the missing energy in nuclear beta decays, namely that it was carried by a neutral particle " ( http://www.ps.uci.edu/physics/news/nuexpt.html [uci.edu] )

      It makes perfect sense. You have theories that test to a high confidence in every way you can test them, then you find an anomaly in specific instances. Whats the response? Take those theories and attempt to narrow down the properties of what would cause the anomaly.

      It obviously doesn't always produce a hypothesis that pans out as correct, but, can you really say that Aether theory was so bad? It was wrong, yes, but, it lead to the creation of experiments that answered new questions and ultimately, shaped the theories that came after it.

      and...at the time... that is, after light was shown to be wave-like AND before we knew that there was no motion relative to its "medium", postulating Aether made a lot of sense.

      • Re:Maybe (Score:5, Insightful)

        by icebike (68054) on Wednesday October 30, 2013 @04:28PM (#45284947)

        True, even failed theories advance science in some way or other.
        However at some point you have to let them go.

        The summary where it clearly states:

        Physicists know from astronomical observations that 85% of the Universe's matter is dark,

        I suggest they KNOW no such thing, and merely postulate dark matter to get their equations to balance. But how many such equation balancing inventions are laying in the dustbin of Physicists' revised theories over the years?

        Unless or until the Physicists can find fault with the detectors, all of which have failed to find a trace of something allegedly composing 85% of the universe , it would seem that the whole "dark matter is known to exist" statement needs to taken down a notch. Detectors designed to their own specs fail to produce a single trace. It doesn't matter that there are very precise measurements of exactly how much the equations are out of balance.

        • by timeOday (582209)
          This seems to be largely a game of semantics. It is known that 85% of gravitation is unaccounted for by current theories about gravity and observed matter, and "dark matter" really has little more definition than "gravity generator" does it? You find some effect, you name the cause of it "X", and so long as everything discovered subsequently doesn't contradict anything your asserted about "X" too much, you are credited as the discoverer of X.
        • by kwbauer (1677400)

          So you know that this something doesn't exist because we have failed to detect it when it was named as it is because we have yet been able to detect it?

      • Re:Maybe (Score:4, Informative)

        by Sique (173459) on Wednesday October 30, 2013 @04:29PM (#45284953) Homepage
        That's what they are doing with the experiment. They know that there is a difference between the observed gravitation inside the galaxy and the expected gravitation from the visible matter. They know a lot of properties the missing matter has not: it doesn't interact with anything else than gravitation. Thus it does not interact for instance with the electromagnetic force, it is thus electrically neutral. It has no magnetic spin. It does not absorb photons. It does not interact with visible matter except by gravitational force.

        This experiment tries to find some other interactions, but none so far were detected.

        • Neither electric fields, magnetic fields nor gravity fields consist of particles. So perhaps we ought to call it dark energy. It might form a "gravity-dark energy" pair analogous to electro-magnetism.

          Much as magnetic fields interact with electric fields, perhaps dark energy interacts with gravity, giving us indications of it, but not being measurable using particle detectors (as the one described in the article).

          Thoughts, anyone?

          • by Sique (173459)
            I have some doubts about the field character of Dark Matter. My main concern is that we can't measure it on Earth. We can measure the gravity, despite being very weak, and thus determine the Gravity constant, on Earth. If Dark Matter was some kind of gravity-like or at least gravity-interacting field, why can't we measure it directly on Earth despite its relative strength being about four times that of visible (baryonic) matter? Why does it spare Earth and the whole Solar system? Here, General Relativity de
    • Re:Maybe (Score:4, Informative)

      by lgw (121541) on Wednesday October 30, 2013 @03:57PM (#45284557) Journal

      We can certainly detect dark matter. The CMBR studies have show it fairly directly (we've "observed" dark matter as much as we "observe" things with an electron microscope or radio telescope). The ratio of "normal" matter to "dark" matter in the early universe has been measured to 2 significant digits (perhaps more since last I looked into it).

      The unknown part is what dark matter is made of. We know it's there, we just don't know what it is.

      • Re: (Score:2, Insightful)

        by Anonymous Coward

        All we know is that there is something creating a gravity-like effect on large scales. We don't even really know how gravity works, so I don't think we can know dark matter 'exists' per se, as a type of matter, until we fully understand how gravity works at macro and quantum scales, the number of dimensions of the universe, the shape of the universe, etc... For all we know, the effect which we attribute to dark matter could just be a consequence of some other fundamental property of the universe that we kno

        • by c++0xFF (1758032)

          Plausible. But before we go down that path, I say we try the more conventional means of explaining dark matter ... Occam's Razor, and all that.

      • Re:Maybe (Score:5, Insightful)

        by icebike (68054) on Wednesday October 30, 2013 @04:33PM (#45285013)

        We can certainly detect dark matter.

        No, we can't.
        We only know to what extent our speculation and our math fails to completely work to our satisfaction.
        Se we invent a black-box term to get the math to work out. We are quite precise in our invention.
        We design instruments to detect this stuff that the math predicts is there. Instruments fail, time after
        time.

        You always need to consider the fact that it might be something else in the math that is wrong.
        Otherwise, you might just as well attribute it to unicorns.

        • by lgw (121541)

          The thing is: instruments did detect the presence of something that was
          * Matter
          * Not interacting with electrons or photons
          * At the ratio to normal matter (quite accurately) predicted by a dark matter theory for galaxy rotation

          Many theories were invented "to make the math work out" for galaxy rotation, and one of them made a quite accurate prediction of what we eventually measured about the early universe. Now we're trying to make additional measurements, because while we've measured dark matter at a large

          • Re:Maybe (Score:5, Informative)

            by boristhespider (1678416) on Wednesday October 30, 2013 @06:06PM (#45286057)

            I'm a professional cosmologist, and I have to take issue with your first statement. The instruments did not, and categorically have not, detected the presence of something that is matter. If they had, that would be a direct detection of dark matter, and a Nobel prize would already be sitting on their desk. What they have detected are indirect signals of dark matter. It is very hard to reproduce the observations - particularly the cosmological observations - without adding at least one component of dark matter. So the observations are typically interpreted in terms of dark matter.

            But this is very much not, strictly speaking, necessary. What we have is something that has an effect which, when viewed through a Robertson-Walker model, looks for all the world like a species of massive, weakly-interacting particle (or two or three such species - no-one ever said there has to be only one). On smaller scales, we have what for all the world appears to be a large amount of mass that can't be seen.

            Any of this could be down to a modification of gravity. We know the nature of gravity roughly up to the position of the Voyager craft -- call it 300AU to be generous. We are extrapolating that a thousand times to get to galactic scales, a million times to get to cluster scales, and a thousand million times to get to cosmological scales, all without evidence. Of course, without a better theory to replace relativity, it's the best we can do, so we do it - but don't try and claim that instruments have detected that it is matter (they haven't), nor that we are wedded to particulate dark matter (with caveats, we aren't; the caveats are firstly that neutrinos have a mass and are therefore a rather warm dark matter, and secondly that it seems rather unlikely that there isn't at least one species of weakly interacting matter which would act as CDM, but maybe not in sufficient abundance to answer our woes).

            • by lgw (121541)

              But all we ever detect is indirect signals about something, no? And anything detected by any instrument could always be some new, previously unknown effect that just happens to look like what we expect from theory - but that's not very helpful to say. I'd say we detected dark matter in the same way we detected the Higgs boson - a theory made some specific predictions about what we'd see under the circumstance, and we saw something nicely matching the prediction.

              The fact that the same theory quantitatively

              • Re:Maybe (Score:5, Interesting)

                by boristhespider (1678416) on Wednesday October 30, 2013 @07:29PM (#45286821)

                The difference here is that whereas normally the "indirect" signals we receive are photons directly from a particle, or indeed a measurable and reproducible influence on known quantities in a laboratory setting (which includes the tracks of known particles through accelerators), dark matter is not easily amenable to such tests. We only see it (interpreting "it" loosely -- the way I use the words, 'dark matter' should be interpreted as 'the fact that galaxies, clusters and the universe as a whole act as though there is more matter than we observe', which is probably infuriatingly vague :( ) through its gravitational effects, and by the sheer weakness of gravity and the impractical idea of creating, well, galaxies in a laboratory setting it is never going to be directly detectable that way.

                The Higgs boson, on the other hand, was seen in reproducible experiments. I do agree that we can quibble on whether it was a direct detection, or whether it was indirect, given that its existence was ultimately deduced from the pattern of particles around it - but there are big differences. For one thing, a (relatively) quick analysis of the shrapnel from a collision that produced a Higgs will point to a particle of a particular mass and nature. That can then be reproduced (albeit at a low likelihood, given the nature of the experiment), and has been. We only even saw announcements from CERN when two independent experiments both reported an excess at the same mass. (In particle physics these certainly used to be called "resonances" -- when you find that collisions with a particular energy change nature dramatically, you can be pretty certain there's a particle there. For all I know, they're still called resonances, but my particle physics is second-hand through textbooks and therefore about 25 or 30 years out of date.)

                It basically comes down to a detection on local scales, under conditions we can control, through a force other than gravity. We can't examine anything through gravity - it's uselessly weak, and impossible to control. That's a "direct detection", and can be through interactions with photons, or the influence of the new particle on the particles we observe coming out of its interactions and annihilations, or anything along those lines that can be seen, influenced, reproduced, observed. We can't do that with the evidence for dark matter. All we have is that galaxies rotate faster than they should (and they do, unequivocably), and that clusters should not really be bound (but they are, equally unequivocably), and that we cannot account for this with our current theories of gravity. The easiest solution is at least one particulate dark matter, certainly -- but if that exists it *is* amenable to production in a lab, even if to actually observe it we would have to wade through ten times more data than the LHC pours out, or a billion times more. But that isn't the only solution, because the only evidence we have is through gravity, and there is absolutely no reason at all (and it would be a mild form of intellectual blindeness) to prematurely declare that "dark matter" is definitely particulate and not, say, a sign that gravity does not behave on kpc scales the way it does on AU scales, let alone on Mpc and Gpc.

    • Or the 20th century hypothesis of the neutrino.
    • The theory may be incorrect, but at the same time, we're able to try and discover the boundaries of where our direct knowledge ends and our theories begin. As we define those bounds better and better, we make it easier to recognize other discoveries that might fill that hole and provide an actual explanation for what we're seeing.

      Long story short, wrong or not, the theory is a useful one, even if it's only serving as a stand-in for the actual phenomena that explains those observations.

    • Possible, although unlikely. The -CDM model does an astonishingly good job of modeling the observed universe. But, that doesn't mean it is right.

      In the case of aether, people didn't stop investigating it until a) experiments that should have observed no matter what saw no evidence of it and b) another theory that agreed with this new data came along.

      People who trot out the tired old "dark matter is just like aether!" line typically do so while patting themselves on the back for their cleverness, while

  • from the article :
    "... physicists are not ready to give up on the idea of detecting WIMPs. They may simply have a lower mass, or may be more weakly interacting than originally hoped....We have some way to go"

    So former wimps are having a hard time finding WIMPs themselves? That's an interesting turn of events !!
  • ...that maybe they're not seeing it because it's just not there?

    Just a suggestion.

    • So undetected dark matter pulling stuff together more than expected and undetected dark energy pulling stuff apart more than expected.

      Hmmm. Isn't it possible that the theory is just wrong about how gravity and spacetime works at really large scales?

      • by MrL0G1C (867445)

        Nice to hear some skepticism here on Slashdot. It certainly seems like scientists desperately want dark matter and dark energy to exist because their numbers are never adding up. It looks like bad science when they keep fiddling with the numbers to patch up their deficient theories.

        • by Zalbik (308903) on Wednesday October 30, 2013 @04:33PM (#45284997)

          It looks like bad science when they keep fiddling with the numbers to patch up their deficient theories.

          Or to put it another way:
          1. Scientists come up with theories to explain a phenomenon
          2. Test to confirm
          3. New observation breaks the theory
          4. Theory refined to account for new measurements
          5. Goto 2

          That doesn't look like bad science at all.

          The dark matter thing is stuck at step 2 as it may be either (a) the theory is wrong or (b) dark matter is really really hard to test for.

          Science is a process, not a big book of answers. If you want a big book of answers there are any number of religions willing to accommodate you. Just be aware that the answers you get may be (1) vague, (2) contradictory and (3) of limited predictive use.

          • Yes, and the big problem is that a better, more testable #1 hasn't come along. We're stuck with dark matter at #2 until the variances seen can have another plausible explanation.

      • by lgw (121541)

        No for dark matter, because the strong evidence is from the early universe. Yes for "dark energy", because the term (like "cosmological constant") is just a placeholder for "there's something we don't know yet about how gravity and spacetime works at really large scales". Also, there's something we barely understand about it at very small scales - postulating "faster than light expansion of the early universe" explains a lot of data, but not much progress on a mechanism for it, or whether it's the same as

      • by SEE (7681)

        Possible, yes, it just seems less likely than the existence of WIMPs.

        The trouble is the Bullet Cluster lensing pretty much requires non-visible matter, even with the theories that assume relativity is wrong at large scales. It seems you can reconcile TeVeS with the Bullet Cluster using lots of neutrinos instead of WIMPs, but then when you plug that sort of neutrino abundance in TeVeS, you apparently get other inconsistencies elsewhere.

        (Now, apparently STVG manages to handle the Bullet Cluster and galactic

      • by jmv (93421)

        At this point, the two are mostly equivalent. For example, Einstein's original "cosmological constant" in the general theory of relativity *is* a form of dark energy.

    • by wonkey_monkey (2592601) on Wednesday October 30, 2013 @03:51PM (#45284485) Homepage

      Hur hur, yeah, stupid scientists with their "degrees" and their "experiments."

      What a bunch of losers.

    • by invid (163714) on Wednesday October 30, 2013 @03:52PM (#45284505) Homepage
      It's there. We've detected it from its gravity. They were just hoping that it wasn't completely dark. It's starting to look like it is. The trouble with it being completely dark is that would make it difficult to prove any theories about it. What they're doing is searching for their keys under the streetlight when they've probably fallen down the sewer.
      • by icebike (68054)

        We THINK we detected some anomaly in gravity. Even that isn't certain.

        When you look into that, the Galaxy Rotation Curve [wikipedia.org], (the source of much of the dark matter speculation), is itself pretty much of a huge kludge of assumptions and guesses.

    • That is a possibility however it would conflict with known data so far. Seeing how it took almost 50 years to confirm Higgs boson after it was theorized, 110 days is not a long stretch of time.
    • by tylersoze (789256) on Wednesday October 30, 2013 @03:54PM (#45284525)

      Guess they should have given up on the Higgs boson search 10 years ago, too? A negative results is not a "failure", it just constrains things a little more.

      The most compelling evidence for dark matter is http://en.wikipedia.org/wiki/Bullet_Cluster [wikipedia.org]

      Obviously we should always be open to alternate hypotheses, but at the moment dark matter is still the most straightforward explanation.

      • by MrL0G1C (867445)

        So, this dark matter, what is it? Because it seems to me that it hasn't been defined properly, it's just a massive kludge that scientists did when their observations didn't make scientific sense according to our current best theories of physics.

        Dark matter is a theory without basis, it says oops, our measurements don't make sense. What is it, axions? - a type of particle that hasn't even been proved to exist. Dark matter is a theory shakily based on other unproven theories, proposed because the initial theo

        • by tylersoze (789256)

          Actually the money is on SUSY (supersymmetric) particles, which from a mathematical point of view really "should" exist. Meaning it would be odd that the universe exhibits all these other symmetries, but not that supersymmetry. Basically it's one of those things that if you understand the math it totally makes sense there should be this whole other class of particles, otherwise it looks like a kludge if you don't. Obviously just because those two things fit neatly with each other, hey there should be these

    • Of course they hadn't considered it earlier! What fools they've been shown to be!

      (Hint: If you're a random commenter on Slashdot, then, yeah, the experts in the field have probably considered your idea before you suggested it.)

  • clearly it's too dark to see so they should just use a flashlight.

  • Physicists know (Score:5, Interesting)

    by Spy Handler (822350) on Wednesday October 30, 2013 @03:49PM (#45284457) Homepage Journal

    from astronomical observations that 85% of the Universe's matter is dark"

    They don't *know*, they're deducing this from reconciling observed data with general relativity but it's far from certain.

    However relativity is not infallible, maybe it's true only in a special case -- like how Newtonian mechanics works great but only in a special case (bigger size than quantum scale, less velocity than ~1/10 c, etc)

    Maybe at very large size and mass such as galaxies, general relativity doesn't hold and there's a better theory for explaining motion and gravity. If so we wouldn't have to invent nonexistent dark matter to account for the faster-than-expected galactic rotation and other things.

    • However relativity is not infallible

      EVERY SINGLE TIME someone says they have broken relativity, even with "proof", it is later shown to be wrong.
      • They probably said the same about Newtonian physics. There's a difference between jumping on every bandwagon driven by a guy who's "unlocked the true secrets of the universe" and refusing the call a scientific theory infallible.

    • by SEE (7681)

      Maybe at very large size and mass such as galaxies, general relativity doesn't hold and there's a better theory for explaining motion and gravity. If so we wouldn't have to invent nonexistent dark matter to account for the faster-than-expected galactic rotation and other things.

      Maybe. Physics does have people working that line (TeVeS with massive neutrinos to explain the Bullet Cluster, Moffat's STVG). But WIMPs still are considered the most likely candidate.

    • by jabuzz (182671)

      That would be nice but actually physicists have only been using Newtonian mechanics to model galactic rotation. Mostly because doing it with General Relativity is too hard, and simulating it on a supercomputer is probably only been possible for the last couple of years, and even then it would take millions of CPU hours.

      The biggest death nail for dark matter is if it makes up 85% of the matter of the Universe how come the solar system is utterly devoid of it? Remember General Relativity can explain the motio

  • by amaurea (2900163) on Wednesday October 30, 2013 @03:54PM (#45284517) Homepage

    Several different experiments have tried to measure dark matter directly in the lab, and the experimental situation is pretty confusing. This plot [ggpht.com] shows the confidence intervals and exclusion limits for various experiments (but it does not include LUX yet). The shaded regions are confidence intervals, that basically say "we've seen dark matter, and its properties lie somewhere in this region. But the dotted lines say "we haven't seen it, and if it exists, it can't lie above these lines".

    What is strange, then, is that all of the detections are in regions that have been excluded by other experiements. LUX just makes the situation even more strained by pulling those upper bounds even lower. Still, those bounds and intervals depend on assumptions about the properties of dark matter, and it may be possible to reconcile [blogspot.co.uk] the results.

    It will be interesting to see what happens to those tentative detections when they get more data. My bet is that in the end some systematic effect will be found to be responsible for the apparent signal. Or (much less likely) that they were just flukes. But who knows?

  • Matter of fact, it's all dark.
  • The dark matter theory has always felt a bit contrived to me. But I don't have the background to make an cogent argument against it, nor have standing for my words to carry weight.
  • by TheSync (5291)

    I still think it is lots of baryonic matter in black holes or whatever, aka MACHOs [wikipedia.org](Massive Compact Halo Object).

  • Anytime I lose something in the dark I just get a bigger flashlight. All we need to do is launch a giant version of those 30 LED flashlights you can get at Harbor Freight for like $2. It has to be in pink though just to make it pretty.

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