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Scientists' Biggest Search For Dark Matter To Date Just Turned Up Nothing (sciencealert.com) 161

Peter Dockrill, reporting for ScienceAlert: For something that's hypothesised to make up more than 80 percent of the mass of the entire universe, it's no easy thing to detect the existence of dark matter. That's the conclusion the world is coming to today, after scientists announced that a massive $10 million experiment to find traces of elusive dark matter particles had failed after an exhaustive 20-month search. "We've probed previously unexplored regions of parameter space with the aim of making the first definitive discovery of dark matter," said physicist Cham Ghag from University College London in the UK, one of the scientists who took part in the Large Underground Xenon (LUX) project based in South Dakota. "Though a positive signal would have been welcome, nature was not so kind! Nonetheless, a null result is significant as it changes the landscape of the field by constraining models for what dark matter could be beyond anything that existed previously."Ars Technica has more details.
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Scientists' Biggest Search For Dark Matter To Date Just Turned Up Nothing

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  • by Anonymous Coward

    I keep looking for my imaginary friend, but he's never there.

    • I keep looking for my imaginary friend, but he's never there.

      At least this research shined some phlogiston on the subject of dark matter.

      • LoL. That may be an apt comparison, but we definitely know something is going on, and dark matter seems the most likely explanation. All this failure to detect really means is that several of the suspected types of dark matter are definitely not there, so now that have to look for the others. Either they'll find those, or fail to find them and someone will have to figure what less likely thing is causing those effects we've definitely seen that we thought was caused by dark matter.

        It's kind of like the ball
        • Analogy - you are in a dark room with lit objects on the other side of the room and something heavy is on your foot but you can't see what it is.
          Gravitational effects tell us that things are there but it's too dark to see them.
  • by Anonymous Coward

    Well, the dark matter explanation feels a bit hacky anyway. Hopefully some better explanation will gain traction.

    • by Ultra64 ( 318705 ) on Friday July 22, 2016 @07:14PM (#52563609)

      >the dark matter explanation feels a bit hacky anyway.

      Dark matter isn't the explanation, it's the question.

      We observe things like: https://en.wikipedia.org/wiki/... [wikipedia.org]
      but we don't know what is causing them. "Dark matter" is just a short way of saying "whatever it is that is responsible for these things we are observing".

      • by gtall ( 79522 )

        No, it is more than that. Astrophysicists give the attribute of "gravity" to dark matter. In fact, that was the reason they promulgated the idea, i.e., galaxies would fly apart otherwise so there must be something we cannot see which supplies the extra gravity.

        They do not entertain the idea that maybe their laws are wrong, or that some other phenomenon might be affecting gravity.

        • by Anonymous Coward on Friday July 22, 2016 @07:54PM (#52563849)

          If you can come up with some way to modify gravity in such a way match more than one or two of the dozen plus lines of evidence supporting dark matter, you've got a guaranteed PRL publication. Of course every attempt so far has failed pretty miserably.

        • by yndrd1984 ( 730475 ) on Friday July 22, 2016 @08:38PM (#52563985)

          They do not entertain the idea that maybe their laws are wrong, or that some other phenomenon might be affecting gravity.

          Sure, MOND [wikipedia.org] never happened.

          • MOND doesn't eliminate the "need" for Dark Matter, does it.
            • From the wiki:

              MOND is an example of a class of theories known as modified gravity, and is an alternative to the hypothesis that the dynamics of galaxies are determined by massive, invisible dark matter halos.

              It started out as a replacement for DM. 30 years later, with more evidence supporting DM, it's more like a ready-made replacement if DM fails, or an add-on if some of the observed phenomena aren't explained by a more refined DM theory.

              • Still, it fails in situations that otherwise have a "dark matter" explanation, just slightly fewer of them. It's not a solution to the problem.
                • MOND doesn't eliminate the "need" for Dark Matter, does it.

                  Still, it fails in situations that otherwise have a "dark matter" explanation, just slightly fewer of them. It's not a solution to the problem.

                  Dark matter itself is only a partial solution, so...

                  You seem to have some strong feeling on the subject - could you explain?

          • MOND is dumb anyways. What we call gravity arises from spacetime. When matter is condensed from energy, what is left is spacetime. There is more spacetime near matter which causes a pressure towards matter. This is what we call gravity.

            Why is this important? Because there are areas of the universe where the universe has already ended. The concept of time moves faster the further away it is from the matter that it is part of (e=mc^2 simplified).

            In summary, galactic rotation curves are flat because time is fa

            • What we call gravity arises from spacetime. ... The concept of time moves faster the further away it is from the matter that it is part of (e=mc^2 simplified).

              *facepalm*

              In summary, galactic rotation curves are flat because time is faster and space is smaller where there is less matter.

              Then why doesn't the same thing happen in the solar system? If it did, we wouldn't have had a mystery in the first place.

              • What we call gravity arises from spacetime. ... The concept of time moves faster the further away it is from the matter that it is part of (e=mc^2 simplified).

                *facepalm*

                In summary, galactic rotation curves are flat because time is faster and space is smaller where there is less matter.

                Then why doesn't the same thing happen in the solar system? If it did, we wouldn't have had a mystery in the first place.

                It does happen in the solar system.
                http://www.astronomy.ohio-stat... [ohio-state.edu]
                Read paragraph 7 in particular. That is all.

                • In summary, galactic rotation curves are flat because ...

                  Then why doesn't the same thing happen in the solar system?

                  *Article that doesn't mention rotation curves*

                  Does that summarize our discussion well enough?

                  Relativistic effects happen almost everywhere, but they can't explain galactic rotation curves.

        • by mrsquid0 ( 1335303 ) on Friday July 22, 2016 @09:15PM (#52564155) Homepage

          Many people have spent a lot of time looking for ways to explain single like galaxy rotation curves, stellar velocities in globular clusters and elliptical galaxies, the structure of galaxy clustering and what-not without success. The simplest explanation has always turned out to be that there is some sort of extra matter that we cannot see. Dark matter requires the smallest number of assumptions out of all explanations that people have proposed so far. By Ocham's Razor it is probably the right solution. And by Grabthar's Hammer you shall be avenged.

        • by lgw ( 121541 ) on Friday July 22, 2016 @09:25PM (#52564211) Journal

          No, it is more than that. Astrophysicists give the attribute of "gravity" to dark matter. In fact, that was the reason they promulgated the idea, i.e., galaxies would fly apart otherwise so there must be something we cannot see which supplies the extra gravity.

          They do not entertain the idea that maybe their laws are wrong, or that some other phenomenon might be affecting gravity.

          That was true quite a few years ago, when there were many theories for galactic rotation rates, including MOND (precisely "the idea that maybe their laws are wrong"), hot dark matter, and cold dark matter which might be WIMPs or MACHOs.

          Then we got more data.

          WIMPs won out because they also explain gravitational lensing and the early universe. The cosmic microwave background radiation observations were decisive. The predictions made WIMPs were right on the money - turns out the early universe had just the predicted amount of (a) matter, that (b) wasn't moving near the speed of light, and (c) before block holes, brown dwarfs, etc could have formed.

          That's how science works. Scientists do not lack creativity - there was a whole forest of ideas to explain galactic rotation rates. But as more observations of unrelated phenomena come it, only "some sort of particle" was left standing. Falsifiable theories were falsified.

          This experiment was a bit silly IMO - it was just a detector much like the detectors we built for neutrinos, which had never shown any signs of dark matter before. It was very much a case of "well, we know how to build this sort of detector already, so let just build a big one and hope for the best".

        • by Anonymous Coward

          Yup, at no point has anybody in the astrophysics or cosmology community considered any other theory.

          https://en.wikipedia.org/wiki/Alternatives_to_general_relativity

          No, wait, they have and you're talking out your ass.

  • Still Valid (Score:5, Insightful)

    by Anonymous Coward on Friday July 22, 2016 @06:05PM (#52563315)

    A null result is actually more valuable than an inconclusive result would have been.

    • Re: Still Valid (Score:4, Insightful)

      by Bite The Pillow ( 3087109 ) on Saturday July 23, 2016 @01:57AM (#52565009)

      Null result is valuable if you know what you're looking for, can prove that your detector works, and still detects nothing. In this case, we have a detector that may work for some guesses as to what dark matter is.

      So the only value here is knowing that dark matter is not any of the things this detector would find. And lest you claim that is valuable, we don't know why it didn't work, so we can't rule out a lot of stuff.

      Considering it was $10 million and being upgraded with 5x spending, it seems deliberately half hearted, a first stab to test for false positives, or get lucky. Build the environment and staff, then commit.

    • The problem with a null result is it is often not specific and not causal. Consider the example of testing to see if electricity is making it to a lightbulb. We go into the room and observe the light is on. That was the test. It's on. Electricity is there. Now for the null results. The light is not on. Does that mean the electricity isn't there? Maybe, maybe not. Maybe the bulb is just blown.

      The test was to determine something specific based on some specific assumptions and using specific measurements. The

  • . . . just follow my friend 'Harvey' - he'll take you straight to it, despite the funky geodesics.
  • Perhaps, if they built a giant flashlight....
  • by Locke2005 ( 849178 ) on Friday July 22, 2016 @06:13PM (#52563357)
    "I don't think you appreciate the gravity of the situation."
  • by x_t0ken_407 ( 2716535 ) on Friday July 22, 2016 @06:34PM (#52563435) Homepage

    From Ars:

    The LUX detector (Large Underground Xenon) is designed to pick up signs of weakly interacting massive particles, or WIMPs, when they engage in one of their rare interactions with normal matter.

    There are indeed other candidates for dark matter, WIMPs being only one of those. This experiment searched specifically for WIMPs, which only rules them out, while of course the other remaining candidates remain to be explored.

    • by TechyImmigrant ( 175943 ) on Friday July 22, 2016 @06:38PM (#52563449) Homepage Journal

      From Ars:

      The LUX detector (Large Underground Xenon) is designed to pick up signs of weakly interacting massive particles, or WIMPs, when they engage in one of their rare interactions with normal matter.

      There are indeed other candidates for dark matter, WIMPs being only one of those. This experiment searched specifically for WIMPs, which only rules them out, while of course the other remaining candidates remain to be explored.

      It sets an upper bound for how strongly they interact with matter we know about, if they exist. And it's a very low upper bound indeed.

    • by crgrace ( 220738 ) on Friday July 22, 2016 @06:40PM (#52563453)

      It doesn't actually rule out WIMPs, it just (for the most part) rules out WIMPs with specific characteristic. Much larger, more sensitive detectors (both Xenon and Argon) are on the drawing boards for future searches.

      Just like supersymmetry, it is very hard to actually rule something out.

      • Thanks yeah I was coming back to say that haha! I had only skimmed the article and specifically the first part, which mentioned that only WIMPs had been searched for with the detector and relieved my fear that my pet physics fascination had been thoroughly disproved, lmao!

      • by lgw ( 121541 )

        Personally, I think those detectors are very likely to be a waste of time. We're just building what are basically better neutrino detectors, not because there's any reason to think dark matter will interact with them, but because it's a detector we know how to build!

        I guess partly it's a case of whether dark matter is "massive particles that interact via the weak force" or "massive particles that interact weakly" (via some other force) - if it's the latter, these detectors aren't likely to work.

        There are l

    • by rubycodez ( 864176 ) on Friday July 22, 2016 @06:44PM (#52563477)

      results didn't rule out WIMPS, only certain kinds of WIMPS. A new detector the LUX-ZEPLIN will be 100 times as sensitive and continue the search

      • Thanks for the correction! I hadn't read that far yet before jumping to post about the misleading title hahaha. Dark matter fascinates me...I was an astrophysicist researching dark matter in another life :/

      • results didn't rule out WIMPS, only certain kinds of WIMPS. A new detector the LUX-ZEPLIN will be 100 times as sensitive and continue the search

        True, but this is getting quite interesting. The constraints are squeezing the WIMP theory into a corner now. People who had been betting that dark matter would have been detected by now and beginning to suspect that the new detectors will also fail to find it.

        • I would rather they found nothing and a new force or component of gravity we can't deal with would be the cause. Also no supersymmetric particles, just the recent way-too-light Higgs boson being the last thing discovered. physicists would go apeshit

  • Dark matter is proposed because galaxies hold together despite having greater rotational speed than 'normal' matter would keep together, yes? There's is presumed to be a black hole at the center of all galaxies, yes? How is the (equivalent?) mass of a black hole estimated? For instance, if matter is dynamically spiraling into this black-hole (not in a stable orbit), might orbital assessments of the black hole's mass be wrong?
    • by Anonymous Coward on Friday July 22, 2016 @07:01PM (#52563545)

      The orbital period of a star in a galaxy depends, to first order, on the amount of mass that is closer to the centre of the galaxy than the star. (That's a consequence of gravity being an inverse-square force.)

      The distribution of stellar orbital velocities in a galaxy indicates that there is additional mass, not at the centre, but distributed amongst the stars in a galaxy. An inventory of the visible mass shows there is nowhere near enough to account for the velocity distributions. Therefore, it is inferred that there is invisible, or dark matter, that accounts for the discrepancy. It has nothing to do with mismeasuring the mass at the centre of the galaxy, whether it's a black hole or not.

      • Thank you. If it's got to be distributed throughout the galaxy then that answers that nicely.
      • The orbital period of a star in a galaxy depends, to first order, on the amount of mass that is closer to the centre of the galaxy than the star. (That's a consequence of gravity being an inverse-square force.)

        The distribution of stellar orbital velocities in a galaxy indicates that there is additional mass, not at the centre, but distributed amongst the stars in a galaxy. An inventory of the visible mass shows there is nowhere near enough to account for the velocity distributions. Therefore, it is inferred that there is invisible, or dark matter, that accounts for the discrepancy. It has nothing to do with mismeasuring the mass at the centre of the galaxy, whether it's a black hole or not.

        This also holds true for the affect of gravitational lensing produced by distant galaxies.

    • Dark matter is not about single galaxies holding together, but about the galaxies holding to each other for no aparent reason.
      The center mass if a galaxy, if there is one, is calculated by the rotation speed of said galaxy.
      Just like Mercury is orbiting the sun faster than Venus, Earth etc.
      And regarding to the distance, a planets orbit speed is a function of the mass in the center.

    • The mass distribution in the galaxy can be determined by measuring the orbital velocity of stars at different distances and positions, which includes not only stars in the galactic disk but a spherical halo that surrounds the entire disk. It turns out that most of the mass of the galaxy is in that apparently nearly empty halo. We can rule out invisible gas, black holes, and any form of solid matter or known particles as the source of this mass, because we could detect them with other means at our disposal.

  • dark matter is today's epicycles

    • by Kjella ( 173770 )

      I get the feeling that dark matter is today's epicycles

      Well you're not the first one, there have been multiple attempts to modify gravity so that it gives the right answers without introducing additional matter. Unfortunately that tends to break other results that our current theory of gravity gets right and trying to "fix" that usually ends up in just as convoluted theories as dark matter/dark energy. Personally I think it's easy to feel like solid matter is a wall but we know radio transmissions pass through it like it was nothing. And neutrinos pass through

    • No, that's the Standard Model. To be fair there are a good 18 orders of magnitude to traverse between it and the fundamental nature of reality, so it's better than nothing.
  • The Michelson-Morley experiment was experiment that turned up nothing, and lead to the development of general relativity. Perhaps this experiment will also turn nothing into something.

  • by michaelcole ( 704646 ) on Friday July 22, 2016 @07:09PM (#52563581)
    A null result is only a "fail" if you're not actually interested in science.
    • by gtall ( 79522 )

      Oh, you must mean science funding agencies. For them, a null result results in quick financial death for the funded science program.

  • But I fucking told you so!!

    I have nothing to go on other than my own impertinence and pigheadedness, but I am convinced that simply adding mass to the equation is not what is needed to solve it. Yes, our models look right when we add that mass, but I think it's something else going on. Something fundamental, misunderstood, and/or some emergent interaction of other forces.

    • by Anonymous Coward

      But I fucking told you so!!

      I have nothing to go on other than my own impertinence and pigheadedness, but I am convinced that simply adding mass to the equation is not what is needed to solve it. Yes, our models look right when we add that mass, but I think it's something else going on. Something fundamental, misunderstood, and/or some emergent interaction of other forces.

      Fucking beautiful explanation--you just have to figure out how to change those models without breaking the rest of the models. Nobody who has some clue as to what the fuck they are doing thinks that our models are 100% complete or 100% accurate--so standing around telling people they're wrong if fucking useless and contributes nothing to the search for the solution.

      You want to be useful? Try getting your level of skill up to the same level as the people who are actually doing the work; because otherwise y

  • That's because there's no such thing as dark matter or dark energy. In 50 years, we'll look back at this theory (and "junk DNA") as a quaint historical silliness, the way we look at "the ether/aether" today.
    • by Livius ( 318358 )

      Unless.... the aether was dark matter all along!

      • by Anonymous Coward

        Unless.... the aether was dark matter all along!

        Sorry, it doesn't work that way. Perhaps you should actually study the theories rather than reading the pop-sci executive summaries of them you would understand.

        But sincerely I hope you're joking, but I'm too drunk, (6 shots 99 proof + 2 shots 60 proof), to tell the difference, and too many people are too fucking stupid to understand the difference.

  • This is great timing. I like how the LUX researchers' conceptual description of WIMPs sounds exactly like neutrinos: https://medium.com/starts-with... [medium.com]
  • What is the 'parameter space' that they were searching? Is it an accepted term in physics? I'd expect to find nothing in my parameter space except for variables (and a number of logical and conceptual errors).
  • so, the search was successful, then.
  • > Well, the thing about a black hole - its main distinguishing feature - is it's black. And the thing about space, the colour of space, your basic space colour, is black. So how are you supposed to see them?

    Given that there may several exaquintrillion tonnes of asteroids, planetesimals [nasa.gov], rocky planets gas giants [spaceref.com], black, brown and red dwarves and even reasonably large stars [scitechdaily.com], roaming around that we are only just beginning to be able to see, a large amount of dark matter may well turn out to be regular matte

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