Arstechnica has a quite good breakdown of scientists utterly failing to detect dark energy or axion-based dark matter by bouncing neutrons off of neutron mirrors.
Their experiment takes the form of a very cold beam of neutrons. These neutrons float into a chamber containing two neutron mirrors. As the neutrons travel through the chamber, they bounce back and forth between the mirrors, finally exiting at the other end, where they hit a neutron detector.
If you know the angle at which the neutrons hit the first mirror, the distance between the mirrors, and the size of the mirrors, you will know exactly which direction the neutrons will be headed when they exit the chamber. By placing the detector at the right location, you will see lots of neutrons. However, if gravity is not exactly the strength that you expect, or the neutrons are slowed because they stopped to play with a passing dark matter particle, then the detector will see fewer neutrons.
I don't know about you lot but this type of thing excites me. It's proper science at its best; perform an experiment and get jazzed about a conclusive result. No worries about who believes what, just Scientific Method all up in your face.
(Score: 2) by c0lo on Monday April 21 2014, @07:26AM
At the time of the experiment, God made the dark energy not interested in cold neutrons, even if He put all the necessary amount of it in the whole Universe.
...
(after which he went ahead playing another round of craps, just to spite Einstein)
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 1) by cubancigar11 on Monday April 21 2014, @07:34AM
Here is the relevant quote from article:
"In amongst the many theories for dark matter, a particle family called the axion is one contender."
The experiment found no evidence of such particle(s) under predefined window of precision. Then the scientists improved the experiment and increased the precision by several magnitudes, but were still unable to detect axions.
This proves that axions might not exist, disproving one of the many theories that explain dark matter.
What it does not do is 'fail to find Dark Matter or Energy'.
What the f*ck, really? We can do better.
(Score: 2) by The Mighty Buzzard on Monday April 21 2014, @12:07PM
You try in the space you're allowed for a headline. If you can beat it, put in for editor.
My rights don't end where your fear begins.
(Score: 2) by cosurgi on Monday April 21 2014, @02:20PM
yep. You can volunteer as editor :)
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#\ @ ? [adom.de] Colonize Mars [kozicki.pl]
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(Score: 1) by cubancigar11 on Monday April 21 2014, @02:34PM
I wish :( I am down on DS-Algo for amazon interview preparation. Also, I am no where near American time zones.
(Score: 2) by mrcoolbp on Monday April 21 2014, @03:53PM
Actually, the editing team could use more non-US time zone coverage, most of us are in the US.
(Score:1^½, Radical)
(Score: 2) by cosurgi on Monday April 21 2014, @07:47PM
yeah non-US timezones are good for us, if you are interested, just let us know.
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#\ @ ? [adom.de] Colonize Mars [kozicki.pl]
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(Score: 1) by cubancigar11 on Tuesday April 22 2014, @12:36PM
Thanks you guys. I will definitely contact you after I clear my interview.
(Score: 3, Informative) by kebes on Monday April 21 2014, @02:58PM
So, really, the question is now about identifying the nature of this matter and energy. So it would be more correct to say that these experiments help refine our understanding of dark matter and energy (in particular by excluding some regions of parameter space, and thereby falsifying some candidate explanations for the fundamental origin of these matter/energies). This is really nice work, and extremely exciting. Anytime we can learn something new about the fundamental nature of reality is a good day for science. Moreover, the fact that they were able to do such fundamental measurements on such a simple setup bodes well for us making more fundamental discoveries. (Neutron beams and neutron mirrors are not what one usually thinks of as 'simple', but they are inexpensive compared to giant particle accelerators and space-telescopes, at least.)
(Score: 2) by HiThere on Monday April 21 2014, @06:29PM
Sorry, must disagree. We haven't found dark matter, what we've found is evidence for mass-like effects that we can't see. "Finding dark matter" would mean being a lot more specific about what that "mass-like effect" was caused by. It being caused by mass is, perhaps, the most reasonable conjecture, but it's not the only one. Axions are one proposed "thing that could be found" They weren't.
I put similar qualifications around the term "dark energy". Remember, giving something a name doesn't really tell you anything new. Saying "dark energy" doesn't tell you anything more than "the universe appears to be expanding slightly faster than current theories predict, we don't know why", it's just shorter. Maybe it is energy. Maybe the cosmological constant isn't as simple as we've assumed. Maybe lots of things. And we don't know.
FWIW, I didn't read the original article, but this doesn't sound like something that would be expected to detect any evidence for "dark energy". Ruling out axions with certain properties, however, sounds like good work (though of course it needs to be replicated, preferably with a different experimental design).
P.S.: This isn't the first time that axions with certain properties have failed to be detected. Each such experiment puts constraints about what the possible "dark matter" could be. But currently "dark matter" feels sort of like the "luminiferous ether". Yeah, there's something there, but we may be very wrong about what.
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(Score: 2) by kebes on Monday April 21 2014, @07:29PM
In the case of dark matter, we will obviously never observe it by its electromagnetic influence, but we've measured its gravitational influence in multiple different ways. We've measured its average density based on cosmic expansion, its signature in the CMB [wikipedia.org], etc. And we've measured its spatial distribution by inference from the distribution of luminous matter, and more directly by things like gravitational lensing [wikipedia.org]. There is much we don't know about it, but we're way beyond its original status (where it was indeed just a placeholder name for a curious unexplained observation). The evidence is quite strong that dark matter is indeed matter (not MOND [scienceblogs.com], etc.). Using a few reasonable precepts, we can even say something about the temperature of dark matter [scienceblogs.com].
As I said, whether a particular level of confidence warrants a word like "found" is to some extent a matter of preference. Obviously there is a whole lot we don't know about dark matter and dark energy. But it's quite different from the "luminiferous ether". The ether was assumed to exist, but then no measurement was able to find it. Dark matter instead was discovered through measurements. It is an observation arising from experimental data. There is much we don't know about it... but then again that's true of every measured entity in our physical theories. E.g. we don't actually understand what spacetime is at a fundamental level (quantized field? emergent phenomenon?
(Score: 2) by HiThere on Wednesday April 23 2014, @12:19AM
At the time that the luminiferous ether was believed in, many people thought that they had experimental evidence for it. It's just that the evidence didn't show what they thought it showed. I'll agree that we have measurements that show that *something* is there. And that that "something" produces the kind of effects that something with mass that was otherwise indetectible would produce. I just think people tend to believe that the "something" is a particular kind of thing without good evidence. Maybe it is. My suspicion is that it's a lot more complex than what we are presuming. Perhaps something rather like axions are a part of dark matter, but not most of it? Perhaps there are lots of different kinds of dark matter? All we know is that it appears to be matter that is gravitationally bound, and much of it doesn't act like "hot" dark matter. Please note that with a complex substance the experiments to detect any particular part of it need to be a lot more sensitive...which may explain why it hasn't been detected.
OTOH, I'm not a real fan of super-symmetry as a solution to this problem. In many ways it would produce just the (lack of) effects detected, but again it's expecting the universe to fit our preconceived notions, when it doesn't have a history of doing so in the past.
All that said, this is *WAY* out of my field of competence. My understanding is that most particle physicists think that something in super-symmetry will explain things. But so far the evidence is lacking. What they've got is an attractive theory. Maybe they're right. Perhaps the LHC will reveal this with the next (current?) round of upgrades.
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(Score: 2) by FatPhil on Monday April 21 2014, @09:50PM
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 3, Informative) by snick on Monday April 21 2014, @04:28PM
Actually, that's _exactly_ what this experiment did. It failed to find any evidence of dark matter or energy.
No one claimed that this experiment was the be-all end-all of dark matter detection. It is explicitly called out as testing one theory among many. And of course a single experiment may have been designed incorrectly, or maybe there was a flaw in the execution or analysis. But that is _always_ the case with all experiments.
We need to get over our insecurities when it comes to science. Positive results are positive and negative results are negative, and let the chips fall where they may. No single experiment is going to change the prevailing theory, but to insist that we shape our reporting of experimental results to be sure that they kowtow to the prevailing theory is bullshit.
This experiment failed to find evidence of dark matter or energy. If that scares you, then go wank over some other experiment that has found evidence of dark matter or energy.
(Score: 1) by cubancigar11 on Tuesday April 22 2014, @12:22PM
Okay, you have no idea of what the experiment. Also, not everyone is a wanker so grow up.
No, it failed to find axions. I thought that was very clear in the article and my comment as well. Axion != dark matter. There is another comment above [soylentnews.org] which better explains it.
(Score: 0) by Anonymous Coward on Monday April 21 2014, @12:24PM
No, you CANNOT know "exactly which direction", and you never will. A neutron is a quantum mechanical system, so forget about "exactly"s. Maybe most of the neutron beam can be targeted with some accuracy, but that's it.
This knowledge was not meant for you. Deal with it.
(Score: 2) by MrGuy on Monday April 21 2014, @02:09PM
You're right you can't know exactly where they're heading. What you CAN know with a quantum mechanical system is the expected probability distribution of the directions with very strong accuracy.
So you can know, given the strength of the beam, pretty precisely how many neutrons you expect to see at a given spot.
But, yeah. The article is pretty informal with its science terminology ("Hiding neutrons in the beer fridge" is the section heading for the statement you correctly take issue with, for example).
But reserve the bile for the article author, not the experimenters, who designed a simple, elegant, and highly accurate experiments that's produced some really interesting results. The SCIENCE is "it works, bitches!" [xkcd.com] level elegant. The article is hardly journal quality.
(Score: 3, Interesting) by MrGuy on Monday April 21 2014, @02:12PM
...how similar in concept, construction and results this is to the Michelson-Morley experiment, [wikipedia.org] which disproved the prevailing "lumineferous aether" theory of electromagnetic waves.
This experiment tells us nothing about how the universe DOES work, but it pretty elegantly establishes some surprising ways that it DOESN'T. Which is sometimes what we need from science.
There are more things in heaven and earth, etc. etc.
(Score: 2) by HiThere on Monday April 21 2014, @06:37PM
I wouldn't say surprising. This isn't the first time axions with certain proposed properties have failed to be found. But it's a much nicer experiment than those I've heard about before (which only tried to detect axions as an afterthought when processing the data.)
I don't really know, but it may well be that this experiment removes most of the more plausible axion possibilities. Or most of the ones that could account for any large fraction of the "dark matter". (My personal expectation is that "dark matter" will not prove to be one thing, but a complex of lots of different things, some of which barely interact with each other, and others of which do. I don't have any theoretical backing for this, and I'm definitely not a cosmologist, but every time we've discovered something new it's inevitably turned out to be more complicated than we at first thought it would be.)
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(Score: 3, Informative) by kebes on Monday April 21 2014, @03:05PM
1. Realization of a gravity-resonance-spectroscopy technique [nature.com], Nature Physics, DOI: 10.1038/nphys1970 [doi.org], 7, 468-472, (2011).
2. Gravity Resonance Spectroscopy Constrains Dark Energy and Dark Matter Scenarios [aps.org], Physical Review Letters, 112, 151105 (2014) DOI: 10.1103/PhysRevLett.112.151105 [doi.org] Preprint available here [arxiv.org]
This is very cool work because the setup is relatively simple (although extremely sensitive). As they note in the first paper's abstract: "The experiments have the potential to test the equivalence principle and Newton's gravity law at the micrometre scale." In other words, they have devised a very clever and sensitive way to measure gravity using quantum effects; this can have a whole bunch of applications.
In the second paper they apply it specifically to making a local measurement of dark matter and dark energy. They also note some other cool results: they confirm the expected scaling-law of gravity at distance scales of microns and energy-scales of 10-14 eV. I believe this has implications for candidate alternative theories of gravity. They note: "our experiment paves the way for the use of GRS to probe new particle physics and to search for non-Newtonian gravity with high precision. Moreover, GRS may turn out to be an ideal tool for testing hypotheses on large extra dimensions at the submillimeter scale of space-time."
Although their result is in some sense a null-result (simply confirming existing theories, and not identifying any hints of new particles), this is extremely valuable because it constrains any theory that would attempt to modify our theories of gravity, to hypothesize new particles or forces, to explain dark matter or energy, etc.
(Score: 0) by Anonymous Coward on Monday April 21 2014, @04:26PM
or ... the method of creating a neutron also absorbed some tachyons that flip
the overall field for dark matter so that they cannot interact with the neutrons
from the past?
(Score: 2) by Gaaark on Monday April 21 2014, @05:12PM
I follow Julian Barbour and his more Machian view-point (but i am not a physicist):
His view seems to be that dark matter and energy do not exist at all, which is why they cannot find it.
Don't have time (at work) to look up his points, but he has some interesting articles and his 'video' which seems weird, but actually makes some points about space and time being separate (instead of Einsteins view that they are inseparable) because time does not really 'exist'... that time is emergent from objects moving in/through space.
I find it interesting, at least.
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by HiThere on Monday April 21 2014, @06:46PM
The versions of that theory of time that I've looked into (not his) have added an extra space dimension or so (except for one, that reduced everything to 2-D) and then defined time as a monotonic ordering of events in that space. To me this sounds both plausible, and just about identical to standard theory. The 2-D theory has to do with the energy/information containable within a sphere having a limit that's proportional to the area of the surface of the sphere. Perhaps somebody who understands it better can explain it. (OTOH, there's also a deterministic version of quantum theory that considers ordinary space-time as the projection of deterministic events in a higher dimensional space. Again, I can't [well, haven't] followed it.)
OTOH, please note that when two models are canonically isomorphic, then which description you use for them is just an interpretation. Different interpretations are more useful for different purposes, but they are equivalent in validity. And I have a strong suspicion that that's what's going on here.
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