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Physicists Build Donut-Shaped Magnet To Find 'Ghost-Like' Dark Matter Particle (cnet.com)

Posted by BeauHD on from the build-it-and-they-will-come dept.

An anonymous reader quotes a report from CNET: One of the central puzzles in particle physics is discovering what particle (or particles!) makes up dark matter — the form of matter that is responsible for 85 percent of the mass in the known universe. Some physicists believe searching for a hypothetical particle known as an "axion" could lead to a better understanding of dark matter and to hunt for it, a team of U.S. physicists have recently designed and tested a basketball-sized, donut-shaped apparatus that can seek it out.

It has been believed that axions may be detectable by looking at an unusual type of neutron star known as a "magnetar". These small, erupting stars create some of the most powerful magnetic fields in the universe. Because of their giant magnetic power, axions would be converted to radio waves in the presence of the magnetar -- and thus, detectable by telescopes on Earth. That strange cosmic phenomenon inspired theoretical physicists to create the impressively-named ABRACADABRA experiment (the full name is "A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus" so the theorists deserve a round of applause for that backcronym). The experiment consists of a donut (or "toroid") shaped device, dangled in a freezer just above absolute zero and fine-tuned to create its own magnetic field. If axions exist, the magnetic field in the middle of the donut could reveal them. The study has been published in the journal Physical Review Letters.

25 of 154 comments (clear)

  1. "Dark" "Matter" by Anonymous Coward · · Score: 2, Insightful

    It's responsible for 85% of the mass of the known Universe, but we can't seem to find any. Yes, you in the back? No, there's no way we're mistaken, next question?

    1. Re: "Dark" "Matter" by Anonymous Coward · · Score: 2, Insightful

      A Nobel Prize is up for grabs to anyone who can come up with a testable idea that does a quantitatively better job of reconciling theory and measurement. That's why some of the smartest people in the world are working on it. Why don't you step in and best them all?

    2. Re: "Dark" "Matter" by Anonymous Coward · · Score: 2, Interesting

      I don't need to know the answer to recognize hand waving and wishful thinking when I see it. I can produce an incorrect proof that P = NP, does that mean you can't criticize it if you don't have a valid proof to the contrary?

    3. Re: "Dark" "Matter" by jellomizer · · Score: 2

      If your proof that P = NP is incorrect but not yet independently identified, or had found a fault. But your proof is more of a Postulate or a Theorem.

      One can still criticize a proof even if they cannot produce a counter proof. Because your proof isn't the final outcome but the steps to get to that point.
      I don't have you discredit your Poof of P = NP by proving that P != NP but by going threw the steps in your poof, finding the error in your logic, often making an assumption or muddying the proof with other methods such as "Proof by intimation" by often stating something like "It is now obvious to anyone with a half a brain that from point A we now lead to point C."

       

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    4. Re: "Dark" "Matter" by ThePyro · · Score: 5, Informative

      Don't be so quick to dismiss dark matter! We have good reasons to speculate about the existence of a particle which doesn't normally interact with electromagnetic fields. In the example above, huge clusters of galaxies collided with each other and the ordinary matter slowed down as a result of the collision, but gravitational lensing suggests that the center of mass (i.e. dark matter) got separated during the collision. It's not a slam dunk, but it's an interesting result that suggests there's more going on than just an incomplete model of gravity.

    5. Re:"Dark" "Matter" by Sarten-X · · Score: 4, Insightful

      Since this is Slashdot, I'll throw in a car analogy, in the time-honored tradition.

      You can see my car, a good distance away on level ground. It seems to be moving away from you. With more observations, you can tell it's not just moving, but actually picking up speed.

      Since the ground certainly seems level, and you don't see anything else around, it's a safe assumption that my car does indeed have an engine, and someone's driving it away from you.

      Now, the problem is that engine doesn't actually create any power. It just transfers the energy from its fuel, so it's also a safe assumption that my car has a fuel tank (or batteries, if electric), and that's providing the energy for the acceleration.

      Now back to dark matter...

      Galaxies don't have engines or fuel tanks, but we've recently confirmed that they are actually accelerating... and far more than makes sense for the amount of mass and energy we've seen. To use another car analogy, it's like having a horse-drawn cart keeping up with a race car... It's enough to suggest something really fishy is going on.

      When something fishy happens in astrophysics, it means either our formulas or our models are wrong. Since our formulas seem to be correct everywhere else, we've started looking for this "dark matter" stuff, under the suspicion that it might hold the energy we're looking for... like finding rockets hidden under the bottom of the horse-drawn cart.

      It is still possible that our formulas are wrong... but to match other experiments' results, they'd have to be off by an extremely small amount in some cases, and extremely large amounts in other cases. That means not just a tweak to a scalar value somewhere, but restructuring equations entirely...and we'd still need some kind of reason for the discrepancy. Draft horses don't run at race car speeds, and if they did, they wouldn't look like draft horses.

      Looking for dark matter and the dark energy it caries is actually the simpler solution. The theory fits well with our existing observations, and doesn't require completely overhauling our understanding of how the universe works. If we keep running experiments like the one in TFA and finding nothing, we'll start the huge undertaking to figure out what else might be happening, but for now this is the sensible approach.

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    6. Re: "Dark" "Matter" by Anonymous Coward · · Score: 2, Insightful

      We've discovered a bunch of particles in the past 50 years, why is it wishful thinking to assume that there might be more?

    7. Re: "Dark" "Matter" by jellomizer · · Score: 3, Insightful

      Dark Matter hasn't been proven yet. However its hypothesized nature does fit into the mathematical models of the trended data of the observed universe.
      Right now with our understanding of gravity and the universe expansion it would seem that we need more mass then what is observable. Could it be something different, yes. But the point of this article, is try to find ways to detect this "Dark Matter" where we then can either show that it does exist and now it is observable (no longer being dark matter) we can study it further and see if its properties does indeed help fill out all the number to match our models.

      If we see that n^2 = 9 n will be equal to 3 or -3, both fit the model. However chances are it will be 3 not -3 as positive values are more common then negative ones.
      This isn't good enough to pass a math test, however if we are going to make a model of the universe, we should pick the more common and simplest answer then trying to explain the more complex model.

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    8. Re:"Dark" "Matter" by greythax · · Score: 2

      There are billions of WHOLE PLANETS we can not directly "see" yet, and you have a problem with the idea that there might be some widely diffuse clouds of exotic matter that we can't identify? Wow, you have a lot of faith in telescopes without much in the people who made those telescopes.....

    9. Re: "Dark" "Matter" by Anonymous Coward · · Score: 2

      Dark Matter hasn't been proven yet. However its hypothesized nature does fit into the mathematical models of the trended data of the observed universe.

      But this is no surprise because the nature of Dark Matter are made to fit into the mathematical models. Dark Matter is "invented" to fill the gaps.

    10. Re:"Dark" "Matter" by Anonymous Coward · · Score: 3, Interesting

      You might counter that, OK, we could call it DOGFOOD instead of dark matter, but the current consensus is that DOGFOOD is some kind of particle. Alright, great. Then where is the evidence that it's a particle? Normal particles are great because you can smear a bunch of them in a petri dish and look at them under a microscope. Quantum physics aside, particles are definite things that definitely exist in definite places. Is dark matter comprised of particles in the same sense? If so, show me the petri dish. If not, why call whatever DOGFOOD is made of particles?

      OK, if you feel it's a bad name then fine. I have no particular dog in that race.
      In fact you have at least one if not two generations of people behind you on that one, not wanting to use the word "dark" to reference something unknown.

      As for it being matter, this comes out of the Friedmann equations.
      "Matter" is something with an energy density that scales to the inverse cube (^ -3) of the universes scale factor.
      "Radiation" is the other option, which has an energy density that scales to the inverse forth power(^ -4) of the scale factor.

      The observations wouldn't exist if dark matter was only to the inverse power of -4, and we do observe it obeying scaling to the inverse cube.
      It also can't have the same density everywhere in space, since then it wouldn't interact with itself, and all observations show that it does. We also see this in the CMB, and we see it from gravitational lensing effects around galaxies.

      Short version, radiation wouldn't cause the observations, matter would. There aren't any other options to pick from.
      It also started out uniform and later clumped together, a property shared by 100% of all matter we see, from planets to stars to galaxies to filaments.

      As for if it is a *particle*, that only stems from the fact all of the matter we know is in the form of a particle, and we don't know if any matter that isn't a particle.
      Short version again, if it isn't a particle, what would it be? There are no other options we know of to pick from.

      I mean, we aren't even very sure about what gravity actually is at this point.
      Most think it should be a particle (graviton) but some think it is an attribute of the universe being manifested and not within it at all.
      If it turns out gravity isn't a particle, not to put words in anyones mouth, but I'd guess you would see nearly everyone more than willing to 'jump ship' and change the default assumption of what dark matter could be to that.

      But so far the universe has consistently behaved quantized when dealing with matter, and so would anything causing the dark matter effects we see. Like I said it's a default assumption and is for a very good number of reasons.

      It is far more logical to start going down the list of things we know are possible and rule them out before we start day dreaming about what has so far shown consistently to not be possible.

      Why start trying to rule out non-existent items on a non-existent list? When we have a perfectly good list of things that do exist to rule out from.

    11. Re:"Dark" "Matter" by swillden · · Score: 2

      and doesn't require completely overhauling our understanding of how the universe works.

      If I were to bet on precisely where we are getting this question wrong, this would be where I threw my money.

      The problem with this view is that it's completely unproductive. Okay, so you start by throwing out everything from Newton onwards? What do you replace it with? Something different, sure, but where do you even start to figure out what the shape of that replacement is? And in the meantime how do you calculate rocket trajectories, etc.? Well, obviously you have to continue using what you threw out, so you didn't actually throw it out, did you?

      No, the best bet is to continue using what we have that appears to work in all of the other cases and trying to fill in the holes. Maybe the effort to find dark matter and dark energy to explain the discrepancies won't work, but even if it doesn't, maybe the search will show us something else that begins to give us a clue about how to fix the models.

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    12. Re: "Dark" "Matter" by Darinbob · · Score: 2

      125 years ago we couldn't detect electrons and they were only a theory. 51 years ago we hadn't detected any quarks and only theorized about their existence. So why today does it make sense for a lay person to put down their foot and say "it's nonsense!" when they hear about some other form of matter that we can't detect?

      Slightly apropos, the word "quark" in German is slang for "rubbish" or nonsense.

    13. Re:"Dark" "Matter" by thereddaikon · · Score: 2

      Dark Matter is merely the name given to the observation. It's not a theory stating that the universe is full of black stuff that's hard to see. There are many competing ideas on what exactly dark matter is. The possibility that we just have got gravity wrong again is one of them. Once we can account for the observations then it will no longer be called dark matter. It will be called something more appropriate.

      This is something that layman reporting on physics often does a poor job of explaining. It's often presented as Dark Matter is a specific thing and scientists have been spending years trying to find data to prove it. That's bad science and not at all how it works. The reality is, dark matter and dark energy are just placeholder terms for observed behavior of the universe and there are many possible causes for those observations. They've been spending the last 30 years going down the list and crossing the possibilities off with clever new experiments and ever better observations.

    14. Re:"Dark" "Matter" by Pfhorrest · · Score: 2

      It sounds like you are talking about dark energy rather than dark matter. Dark energy is whatever it is that is accelerating the expansion of the galaxies away from each other. Dark matter is whatever is keeping galaxies gravitationally bound into themselves given the rates that we observe them spinning (at which rates the mass accounted for by visible matter would not be enough to keep all the stars in them from flying apart into intergalactic space).

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  2. Donut shaped? by 140Mandak262Jamuna · · Score: 5, Insightful
    We were freshman in IIT, having passed JEE, head high in the clouds, top 1000 All India Rank, all the orientation speakers calling us creme-de-la-creme of India. First Chemistry 101 class. Reading ahead for the class, our study group found there are some electron orbital stuff, n orbital, p orbital etc. One of them was described to be doughnut shaped. All of us were stumped. We did not know what a doughnut was or what it would look like.

    Then one from our study group found an American chemistry text book with pictures. It spelled doughnut as donut, but had a picture. We exclaimed, "It is a damned torus! Why wouldn't they call it a torus? Why use this weird thing donut/doughnut". In the class Prof PJ Narayanan said, "... it says doughnut in the text book. Doughnut is like a vada but it is sweet not savoury, they make in the West..."

    If slashdot is going to call itself "news for the nerds" the least it can do is to call that shape by its proper name, a torus.

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    1. Re:Donut shaped? by Anonymous Coward · · Score: 5, Funny

      Well this discussion just went pear shaped

    2. Re:Donut shaped? by 140Mandak262Jamuna · · Score: 3, Informative

      It is street food. Very popular. Lentil batter deep fried in oil. You will find it in almost all Indian restaurants. Garnishing would differ. Traditional South Indians serve vada with a couple of sauces (sambhar and chutney) on the side. North Indians serve it as the patty in a sandwich, called vada-pav.

      --
      sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
    3. Re:Donut shaped? by Anonymous Coward · · Score: 3, Funny

      you torus a new one

  3. Not Theorists! by Roger+W+Moore · · Score: 2

    Theorists develop the underlying theory of physics by suggesting extensions to existing laws to solve problems or by calculating what existing laws predict for given situations. These physicists have built, and are running, an experiment. They are collecting and analysing the data to test a theoretical prediction of a new model of physics which makes them experimentalists, not theorists.

  4. Re:LOL ... wow ... by RoccamOccam · · Score: 2

    The really odd thing is that it wasn't a backcronym. The researchers just happened to get lucky with the name.

  5. Arxiv version of paper by As_I_Please · · Score: 3, Informative

    Here's the pre-print on arxiv: https://arxiv.org/abs/1901.106...

    The primary result in this paper is the validation of the experimental design using a scaled-down version. From the paper:

    ABRACADABRA-10 cm represents the first step in an experimental search program, which aims to ultimately be sensitive to ADM in the coupling range preferred by QCD axions. Future phases of ABRACADABRA will require larger magnets with higher fields, improved shielding, and strong mitigation of mechanical vibration. Augmenting the techniques described here with a resonant amplification readout and scan strategy will also greatly improve the sensitivity of a future full scale ABRACADABRA detector. We have already begun engineering studies towards designing and building such a detector and ABRACADABRA-10 cm creates a strong foundation for this ongoing work.

  6. Oblig. Bad Car Analogy by PPH · · Score: 4, Funny

    don't know what a torus is

    Torus is made by Ford.

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  7. Physicists build donut-shaped magnet by DontBeAMoran · · Score: 4, Funny

    Is one of those physicists named Homer, by any chance?

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  8. Re:Hang on... by iggymanz · · Score: 2

    The axion was a particle postulated to answer the question of why strong interactions, those between quarks, conserve charge-parity. If it exists it would have detectable properties. The range of its mass, and the fact it could be changed into a photon by a strong enough magnetic field.

    Even without considering it a candidate for dark matter, it would be a huge experimental breakthrough for QCD (quantum chromodynamics, our most useful model of quarks and their interactions) theory to find the particle or to confirm it doesn't exist.