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Physicists Build Donut-Shaped Magnet To Find 'Ghost-Like' Dark Matter Particle (cnet.com)
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.
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.
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.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
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:
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.
don't know what a torus is
Torus is made by Ford.
Have gnu, will travel.
Is one of those physicists named Homer, by any chance?
#DeleteFacebook
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.
You do not have a moral or legal right to do absolutely anything you want.
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.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.
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.