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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.
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?
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.