The Hardware That Searches For Dark Matter (hackaday.com) 104
szczys writes: Deep in a gold mine in South Dakota, the Large Underground Xenon experiment waits in the darkness for a tiny flash of light that signals that dark matter actually exists. So far we theorize that it does exist, and have gone to great lengths to build hardware to detect dark matter. Very cold, very pure liquid xenon sits waiting for a dark matter particle to strike the nucleus of a xenon molecule, producing a distinct pattern of photons through scintillation. An array of photomultiplier tubes detect the photons, whose pattern is processed by FPGAs on custom boards connected using HDMI. The experiment has generated a list of properties not possessed by dark matter; running for several years no evidence of the particles interacting with the xenon have been found. But when the data collection concludes this year, a much larger version of the impressive hardware will be built.
Why not just walk around barefooted in the dark... (Score:2, Funny)
Why not just walk around barefooted in the dark until you stub your toe on it? That's how I usually find things I otherwise cannot detect any other way.
Temba ... his arms wide ... (Score:4, Interesting)
Hmmm .... so I'm going to have to stretch my little monkey brain and hopefully someone more knowledgeable can chime in ...
I see reference to WIMPs in the article, so in some ways do we consider Dark Matter to be kind of like a neutrino? All around us but not generally interacting with us?
So instead of there being vast tracts of stuff we simply can't figure out where it is, it's spread throughout?
The overall underground detection mechanism sounds like the Sudbury Neutrino Observatory, or that Ice Cube deal in the Antarctic (Russia?)
I've always thought it wasn't assumed to be floating around us but not interacting, but I ain't no particle physicist.
Is Dark Matter more like neutrinos than not? Or entirely different, but with enough commonality to confuse a layman?
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Neutrinos are light and very fast. Dark matter if it exists as predicted, would be heavy and very slow. Their common property would be rarely interacting with 'normal to us' matter.
Re:Temba ... his arms wide ... (Score:4, Insightful)
Why do they need fast FPGA detectors, if they never detect anything? Really slow detectors would be just as good at generating no results.
If there are in fact no results, then they need to be sure of it. Hence fast detectors and FPGA processors are used.
A failed experiment can still be an important one. The Michelson-Morley experiment [wikipedia.org] was a failure, yet it started a scientific revolution that led to Einstein's theory of relativity.
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I don't know the details, but the signals they are looking for are particular distributions of light. There are a lot of background processes that produce light, but in patterns or distributions that can be subtracted out. The experiment is carefully designed to have small backgrounds with respect to the signals they hope for, but I'm sure there is still a lot of data being generated.
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Yes, good point. I should have included that the frame-rate needs to be fast enough to discriminate events of short duration. Hence the need for fast detectors.
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I am sure they have 100s to 1000s of channels and FPGAs are probably the cheapest solution not because of speed but because of high integration and ease of use. The alternative would be either an ASIC or board level integration.
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Why would we expect to see it if we merely multiply the size of the experiment?
Because the event rate scales with the mass of the detector: if you have to wait one hundred years for one event with a 1kg detector, you only have to wait 1 year with a 100kg detector, and a month with a 1000kg detector.
Maybe have an engineer included in the hunt!
Wow! I bet they never thought of having engineers help build the detector! Those silly scientists.
Re:Temba ... his arms wide ... (Score:5, Informative)
I see reference to WIMPs in the article, so in some ways do we consider Dark Matter to be kind of like a neutrino? All around us but not generally interacting with us?
So instead of there being vast tracts of stuff we simply can't figure out where it is, it's spread throughout?
WIMPs, Weakly Interacting Massive Particles is what they suspect dark matter to be. It interacts very weakly, possibly only via gravity which is almost undetectable in the scale of individual particles. Thus it tends to pass right through everything. They are assumed to have some cross section so can possibly interact with themselves and other particles if they hit directly head on which is what this experiment seems to be trying to detect. It's thought when they interact with themselves, they annihilate, so they do not slow each other down and do not form disk shapes such as solar systems or galaxies. Otherwise, they float around, only affected by gravity, so the form a spherical cloud called a halo around other gravitational objects such as solar systems and galaxies in which they fall into orbit.
Re:Temba ... his arms wide ... (Score:4, Informative)
I see reference to WIMPs in the article, so in some ways do we consider Dark Matter to be kind of like a neutrino? All around us but not generally interacting with us?
Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos. The difference is that Dark Matter must be a much heavier particle than neutrinos in order to explain the astrophysics, because neutrinos don't clump enough under gravity.
There's a reason why this model is taken seriously: it's possible to calculate how such particles are created very early in the Big Bang. It turns out that if the particle responsible for Dark Matter was created in thermal equilibrium in the very early universe, its abundance today depends only on its interaction strength (not, for example, its mass). If you calculate that interaction strength corresponding the Dark Matter abundance implied by astrophysical measurements, you get exactly the same interaction strength as neutrinos. A pretty amazing coincidence!
Re:Temba ... his arms wide ... (Score:4, Insightful)
Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos.
Everything else you wrote is spot on, but WIMPs have been ruled out as truly Weakly interacting (where Weak with a capital W means "by the exchange of W or Z bosons) for almost a decade now. The original Weak Miracle posited WIMPs to be truly Weakly interacting, but now they are held to be sub-Weak, interacting most likely through Higgs exchange, but we kept the name. Really we should rename them wIMPs at this point.
Also I hate whoever decided to use Weak and Strong as formal names for those respective interactions.
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Everything else you wrote is spot on, but WIMPs have been ruled out as truly Weakly interacting (where Weak with a capital W means "by the exchange of W or Z bosons) for almost a decade now.
Quite correct. I should have said closely related to the force by which neutrinos interact.
WIMPS million times less detectable (Score:5, Interesting)
http://www.physics.purdue.edu/... [purdue.edu]
neutron hitting uranium nucleus: 1 barn
helium nucleus hitting gold nucleus: 100 barns (Rutherford experiment 1911)
anti-neutrino captured by proton making a neutron: 10E-17 barns (first detected 1956)
WIMP hitting a xenon nucleus: 10E-21 barns? (year???) need to 10,000 times better than neutrino detector
Numbers are actually ranges including factors like particle energy and angle.
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No, because it is interacting with us and producing gravitational effects etc - we just can't see it.
Xenon molecule, huh? (Score:2, Interesting)
How does that work?
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Re:Xenon molecule, huh? (Score:4, Informative)
Oh dear, Software know-it-alls...
Xenon _can_ bond with itself. It's in a field known as "Plasma Physics". It's not that easy, but I've done it.
First, you need an ECR-IS. Slip in a bit of 4He, ionize it, and set up your initial Cyclotron Resonance spirals of Electrons. Now inject just a sniff of Xenon. (We used 136Xe.) Set up your particle detector downstream of the Analyzer and look for Mass 140- Xenon Helide. Note that this can _only_ exist in the +1 charge state.
Once you've tuned this out, Analyze for Mass 272- +1(136Xe(2)). The best production that I've seen was ~10e2 per second.
Note that various species exist roughly in cylindrical shells within the ECR Plasma, depending on mass and charge state, so very fine adjustments of the ECR Magnetic Fields, RF, and Vacuum can be used to selectively optimize for any given shell. (You'll see a lot of atomic Xenons, all the way up to +54, if you have a good enough ECR.)
We started out with something easier initially- Helium Hydride, on the suggestion of Mike Pryor. One doesn't even need an ECR-IS for this. It's easy to get ~10e14 Helium Hydrides per second with a regular Plasma Source.
Note that all this actually has practical applications, involving Ion Implantation. On the theoretical side, Astrophysicists are delighted; it's rare that they can actually experiment on something, instead of just observe and calculate.
Code Monkeys should stay away from commenting on any Physics more complicated that rolling a ball down an inclined plank, and timing it with a stopwatch.
Re:Xenon molecule, huh? (Score:5, Informative)
See also here. [wikipedia.org] Note the comment about a Xe-Xe bond in Xe(2)Sb(2)F(11).
It has been known since 1962 that Xenon can form compounds with other elements. Most of them involve Fluorine, because it is a seriously badass element when it comes to stealing electrons. It can even oxidize Oxygen.
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I wondered something similar - How do they know it WILL work? Not being a physicist myself - my uninformed-self wonders if they built a hypothetical system to detect a hypothetical material?
My software side wonders: Did they build a unit-test and confirm the system will work as designed?
Dark Matter has this history of just slipping by unnoticed. If they don't know the system works are they attempting to prove a negative?
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My software side wonders: Did they build a unit-test and confirm the system will work as designed?
Of fucking course. They calibrate the detector with neutron sources. Do you think they're complete idiots?
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Well, really they don't know that it will work. They're building a hyper-sensitive detector for particle interactions along the same lines as neutrino detectors. They can be sure it will detect very infrequent interactions, and they know what neutrinos look like, so they're hoping for anything else.
Of course, if dark matter doesn't interact with familiar matter* at all, or only does so at higher energy levels than matter drifting through the Solar system, it won't find anything.
*I almost said "normal matt
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I wondered something similar - How do they know it WILL work? Not being a physicist myself - my uninformed-self wonders if they built a hypothetical system to detect a hypothetical material?
From reading the wikipedia page, I suspect they'll see individual incident(s) (cosmic rays such as neutrons should cause multiple incidents), probably also from not directly above as cosmic rays will be most common from above rather than through the Earth but fairly independent of Earth's sheilding for a WIMP. Then of course make sure that the instruments themselves aren't causing the readings, or other unforeseen causes. From likely incidents, they can figure out an energy to estimate mass and velocity of
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How does that work?
Scintillation in liquid Xenon happens when Xe atoms are ionized and temporarily form molecules [arxiv.org] before returning to a neutral state and emitting photons.
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A more directly relevant reference is here [arxiv.org].
It's also entirely likely that the person who wrote the summary wrote "molecule" when they meant "atom"...
Xenon molecules are not waiting to be struck (Score:2)
Scintillation in liquid Xenon happens when Xe atoms are ionized and temporarily form molecules before returning to a neutral state and emitting photons.
Then TF summary is wrong when it says "liquid Xenon sits waiting for a dark matter particle to strike the nucleus of a Xenon molecule".
It's also entirely likely that the person who wrote the summary wrote "molecule" when they meant "atom"...
This. TFA doesn't contain the word "molecule," only TF summary does. Would make no sense for this detector to contain macroscopic quantities of exotic polyatomic Xenon molecules.
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yeah don't anthropomorphize monoatomic xenon, it just hates that. Xenon hexafluoroplatinate however is cool with it.
HDMI cables? (Score:1)
Why are they using HDMI cables to transmit the information?
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They are using the Low Voltage Differential Pairs to transmit some information and single ended bidirectional connections for other data. Let's you use one HDMI port for multiple data sources.
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Perhaps because they are cheap off the shelf commodity items that carry lots of bandwidth and they didn't have the money to reinvent a wheel? Naw, couldn't be...
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You don't understand the System. The HDMI extortion mob could care less about HDMI cabling on dark matter detectors, provided the scientists are not slapping HDMI-Compliant trademarks on them and selling them for home Dark Matter Detection use. And even then only if they're actually making money on them. If they're making enough money, they'll soon be fighting patents filed for 'Detecting Anomalous Tenebrous Particles via Interconnecting COTS Technology' and other absurdly general ideas scammed through the
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Could well be true, but then our theory of gravity is wrong because stars in galaxy rotate at wrong speed at given distance from center.
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more likely anonymous cowards on slashdot are ignorant and uneducated in physics
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Which physicists think dark matter is real? They all do.
It's settled science !!
See scientists are smart and we are all grovelling fools in their presence. We can't possibly make our own opinions
Go check out this website about the brilliant thing
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Bacon, you know, who is sometimes referred to as the father of science (but in truth abandoned by modern scientists).
Converging validity is the false hope people leaned on in The Emporer's Clothes. Broad is the path that leads to destruction and many follow it!
Better to be happy and counted among fools I say.
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Unclear is if you intended to be persuasive.
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It's been a while since I've read Bacon, but apparently it's the same for you (or you've abandoned him too). The idols of the tribe are basically groupthink, and it's certainly something to avoid. What AC is talking about is multiple independent lines of evidence, which is completely different. If everybody claims something and says it's common sense, it's often very worthwhile to quantify it or formalize it or try to find where it breaks, and that's countering the idols of the tribe. If a line of inve
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Most science today is researchers getting paid to prop up certain political opinions. This is a case where ideology isn't really related to the outcome, but reference to the prevalance of the view is taken as evidence of its truth.
What would Bacon say about researchers trying to find a way to "hide the decline" and failing to find ways to reject others peer reviewed studies because it doesn't align with their bu
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I'm guessing that the "issue" is that our theories about what dark matter actually IS are wrong enough that we don't understand how to detect it.... Or, there is some observation lens that makes "dark matter" appear to be necessary to account for things, but it's really just appears that way do to local conditions or doesn't exist here, deep in a gravity well next to a star. Ah, some physicist's PHD thesis awaits...
But what do I know.. I'm just a computer programmer who's late to get lunch and has had too
Lets see ... (Score:2)
Dark matter! Yeah, that's the ticket.
Probably looking for illegal grease [slashdot.org].
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actually there's someone out there already working on a way to hack into their network so that they can run bitcoin mining on them. i bet however that they'll probably find that the scientists secretly installed bitcoin mining on them already... ostensibly to help justify the insane cost of the equipment. so now you know the _real_ reason why they haven't found any so-called dark matter....
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i bet however that they'll probably find that the scientists secretly installed bitcoin mining on them already...
Makes sense. Liquid xenon would be a great coolant, so you can overclock the crap out of the rigs. They'll be able to convert bitcoin into the toys they really wanted to buy, when they could only get funding for this "dark matter" grailquest. Face it, if you couldn't find a nail with your hammer, a bigger hammer is not likely to be the most effective way to proceed.
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actually there's someone out there already working on a way to hack into their network so that they can run bitcoin mining on them. i bet however that they'll probably find that the scientists secretly installed bitcoin mining on them already... ostensibly to help justify the insane cost of the equipment. so now you know the _real_ reason why they haven't found any so-called dark matter....
Yea, until somebody went through and put SETI clients on all of the systems.... No intelligent life found here... Beam us up!
Not HDMI (Score:3)
processed by FPGAs on custom boards connected using HDMI.
Just because you use hdmi cables doesn't make it hdmi.
Tanya roy (Score:1)
Re:keep waiting (Score:5, Insightful)
It's a lot more likely that dark matter and dark energy are just math errors that don't take into account proper universe/space expansion and doesn't understand how gravity really works.
Care to show your math on that? We can then compare it to all the scientists who already did the math a few million times showing the same results you say are wrong.
There is even a Nobel prize or three in it for you.
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molecular xenon exists, used in some lasers
How ignorant is ignorant enough? (Score:5, Informative)
Dark matter and dark energy have multiple [medium.com] independent lines of supporting empirical evidence. I presume you are willfully ignorant of this. Perhaps you can manage to keep it to yourself next time.
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Well, it might be time to think about what evidence we have and come up with some alternative theories about what "dark matter" might actually be. Somehow, it seems that we might have a situation where the "settled" part of the science might explain the evidence quite well, but the reality is we are wrong because the next logical step doesn't line up with the theories.
I'm not saying we are wrong about this, only that the longer we fail to construct experiments that give us the expected results, the more l
Re:How ignorant is ignorant enough? (Score:4, Informative)
There are many alternative theories about what dark matter is. All the evidence, from multiple independent sources, limits this to "some kind of matter, not moving fast like neutrinos do".
The failure of the few attempts at detectors doesn't contradict that at all. It simply rules out categories of hypotheses about what sort of particles might make up dark matter. There's really isn't some "settled" idea about that - there are many, competing ideas.
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As lgw said, no one has a settled idea of what dark matter is or where it comes from. We have detected that it exists and have a few constraints on what its properties must be, but there is no "theory of dark matter" per se.
Look at how long it took to go from Ben Franklin's experiments with lightning to the theory and detection of the electron. Or from Newton's work on optics to the photon. The twentieth century advanced our knowledge of physics phenomenally, so that now we are left with studying phenomenae
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We are saying the same thing... I'm saying that this "dark matter" theory may be obvious, but we are short on details given that our attempts to experimentally verify the details are failing... It's time to go back to other promising ideas and see if we can either prove or eliminate them too, we may have conflated unrelated observations here.... Keep thinking and looking...
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The competing hypotheses (MOND, MACHOs) were disproven. There's nothing else that would remotely fit in with other observations of the universe (chiefly Relativity). If you're secretly harboring a misguided grudge against Einstein you have more options, but if you're willing to discard one of the most well-verified theories in the history of science, why even bother pretending to be empirical? Just say "God did it" and be done.
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LOL, Einstein was right, but we have yet to come up with a unified field theory that ties everything up in a nice neat bow. I cannot help this nagging feeling that once we happen on the solution that allows a unified field theory that a lot of this confusing stuff like "dark matter" might just disappear along with a lot of Hawking's musings such as his most recent "Soft hair" idea for black holes to solve the information paradox problem. Like Newtonian physics gave way to Relativity as the math and theory
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I have had similar thoughts and sincerely hope that this is the case.
“The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka!” (I found it!) but “That’s funny ”
Pretty much sums up the whole dark matter subject for me at this point.
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Just so you are aware, I definitely want this experimentation to continue. What I want more is an answer to all of the phenomena described in the article you linked, and eventually I want a couch made from dark matter, if it exists. Which has yet to be determined.
That being said, lets talk about this. Lets use your article so there is no confusion or even problem with your point. Your linked article (which I read a while back, among many others) is titled "Five Reasons We Think Dark Matter Exists." Its n
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In short, "supporting empirical evidence" and "empirical evidence" are explicitly not the same thing
No one will ever directly perceive dark matter, or any other subatomic phenomenon. You have a made-up standard of evidence. I agree that StartsWithABang is a poor excuse for a pop sci outlet, but it works well enough for a quick rebuttal. Dark matter is at least as real as black holes, which have never been directly detected either. If we must say either "dark matter exists" or "dark matter does not exist" the first one is more correct. I am not particularly interested in semantic arguments or arguments abo
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If we don't find anything, how long do we keep looking?
There's a point at which the detectors will get sensitive enough that they start seeing neutrinos, and then the neutrino signal will swamp any Dark Matter signal. This is a couple of generations away in terms of technology development.
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If we don't find anything, how long do we keep looking? Given that it is inherently difficult to prove the existence of something that is by definition elusive, what are the chances it isn't there in the first place? Furthermore, how much looking with no results will get us a reasonable certainty of that?
Yes, dark matter is elusive. But so are neutrinos, and we managed to find ways to observe them. Dark matter is postulated to interact via the weak force, just like neutrinos, so their detection strategies are similar.
The longer we look without seeing anything, the lower the estimate will be for the density of dark matter. At some point that density may fall well below what is expected from other experiments and theories. At that point one starts to doubt the theories, and to look for ways to revise them. Bu
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The longer we look without seeing anything, the lower the estimate will be for the density of dark matter. At some point that density may fall well below what is expected from other experiments and theories. At that point one starts to doubt the theories, and to look for ways to revise them. But you need to look long enough to be sure the theories are wrong. Also, it could be that dark matter exists, but has a much lower density than theory predicts. To confirm that, you need to keep looking. Obviously not forever, but as long as you can.
You don't identify what type of "density" you are referring to - mass density or particle density. For mass density we have a very good idea of what it is from direct measurement of its gravitation - that is not really a matter of theory. Now particle density depends on what the mass of what the particles are. There we have room for lots of uncertainty, and of course there is the even bigger uncertainty about how the interact with known types of matter - regardless of particle density.
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You don't identify what type of "density" you are referring to - mass density or particle density. For mass density we have a very good idea of what it is from direct measurement of its gravitation - that is not really a matter of theory. Now particle density depends on what the mass of what the particles are. There we have room for lots of uncertainty, and of course there is the even bigger uncertainty about how the interact with known types of matter - regardless of particle density.
Excellent points. Thanks for the improvement.
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Lack of results doesn't always mean lack of progress, the lack of results can sometimes be interesting and still help us learn new things. if we already knew how to detect, and all the properties of WIMPS then why bother building the experiment to begin with? we would have nothing new to learn.
Finding out what properties WIMPS dont have helps refine our current theories. Some of those theories may have predicted we would see some of those properties, but because experimentation rules it out we now know t
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