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Most Sensitive Detector Yet Fails To Find Any Signs of Dark Matter
ananyo writes "A U.S. team that claims to have built the world's most sensitive dark matter detector has completed its first data run without seeing any sign of the stuff. In a webcast presentation today at the Sanford Underground Laboratory in Lead, South Dakota, physicists working on the Large Underground Xenon (LUX) experiment said they had seen nothing statistically compelling in 110 days of data-taking. 'We find absolutely no events consistent with any kind of dark matter,' says LUX co-spokesman Rick Gaitskell, a physicist at Brown University in Providence, Rhode Island. Physicists know from astronomical observations that 85% of the Universe's matter is dark, making itself known only through its gravitational pull on conventional matter. Some think it may also engage in weak but detectable collisions with ordinary matter, and several direct detection experiments have reported tantalizing hints of these candidate dark matter particles, known as WIMPs (Weakly Interacting Massive Particles). Gaitskell says that it is now overwhelmingly likely that earlier sightings were statistical fluctuations. Despite the no-shows at XENON-100 and LUX, Laura Baudis, a physicist on XENON-100 at the University of Zurich in Switzerland, says physicists are not ready to give up on the idea of detecting WIMPs. They may simply have a lower mass, or may be more weakly interacting than originally hoped. 'We have some way to go,' she says."
Pulling in other posts below it :D
"When information is power, privacy is freedom" - Jah-Wren Ryel
Just sayin'...
Maybe it's just not there.
Dark matter always reminds of the 18th century hypothesis of the aether.
http://en.m.wikipedia.org/wiki/Luminiferous_aether
Same principle. Same made up matter that no one can see or detect but somehow fills the entire universe.
...that maybe they're not seeing it because it's just not there?
Just a suggestion.
So undetected dark matter pulling stuff together more than expected and undetected dark energy pulling stuff apart more than expected.
Hmmm. Isn't it possible that the theory is just wrong about how gravity and spacetime works at really large scales?
Where are we going and why are we in a handbasket?
from astronomical observations that 85% of the Universe's matter is dark"
They don't *know*, they're deducing this from reconciling observed data with general relativity but it's far from certain.
However relativity is not infallible, maybe it's true only in a special case -- like how Newtonian mechanics works great but only in a special case (bigger size than quantum scale, less velocity than ~1/10 c, etc)
Maybe at very large size and mass such as galaxies, general relativity doesn't hold and there's a better theory for explaining motion and gravity. If so we wouldn't have to invent nonexistent dark matter to account for the faster-than-expected galactic rotation and other things.
Several different experiments have tried to measure dark matter directly in the lab, and the experimental situation is pretty confusing. This plot shows the confidence intervals and exclusion limits for various experiments (but it does not include LUX yet). The shaded regions are confidence intervals, that basically say "we've seen dark matter, and its properties lie somewhere in this region. But the dotted lines say "we haven't seen it, and if it exists, it can't lie above these lines".
What is strange, then, is that all of the detections are in regions that have been excluded by other experiements. LUX just makes the situation even more strained by pulling those upper bounds even lower. Still, those bounds and intervals depend on assumptions about the properties of dark matter, and it may be possible to reconcile the results.
It will be interesting to see what happens to those tentative detections when they get more data. My bet is that in the end some systematic effect will be found to be responsible for the apparent signal. Or (much less likely) that they were just flukes. But who knows?
Of course they hadn't considered it earlier! What fools they've been shown to be!
(Hint: If you're a random commenter on Slashdot, then, yeah, the experts in the field have probably considered your idea before you suggested it.)
HAND.
that was an awful lot of words to say "i should shut up"
it's spiders.
teeny-weeny black spiders.
hundreds of Quattuordecillions of teeny-weeny black spiders per cubic centimeter, crawling between the very fabric of creation.
crawling in your ear, in your eye.
SPIDERS.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
The main lines of evidence for dark matter:
* Galactic rotation curves
* Velocity distribution in clusters of galaxies
* Gravitational lensing in general
* The Bullet Cluster in particular
* The pattern of positions of galaxies in the universe
* The pattern of Baryon-acoustic oscillations in the cosmic microwave background and in the galaxy distribution
* The primordial distribution of light elements in the universe
We know of some kinds of dark matter already: There is a huge amount of neutrinos left over from the big bang, and since these interact very weakly with other stuff, they definitely qualify as dark. Other known kinds of dark matter are black holes, and compact, cold objects made out of baryons (normal matter). So dark matter exists.
The problem is that there isn't enough of the normal kinds of dark matter. To match the pattern in the cosmic microwave background and the amount of hydrogen, helium and lithium in the universe, one needs by far most of the dark matter to be non-baryonic (i.e. not normal matter, but something like neutrinos, but heavier). This kind of dark matter is something we have to postulate exists in order to match observations. But when we do assume it exists, the theory matches observations extremely well. As an example, look at the CMB power spectrum as mesured by Planck. The error bars are so small that you mostly can't see them, and the points lie smack on top of the theory curve. But only if dark matter is included.
And it just so happens that the amount of dark matter that makes theory match the points in that graph also makes the element abundances, galaxy distribution, lensing observations and galaxy cluster velocities work too. Such a coincidence is pretty telling, I think.
But yes, people have tried to avoid dark matter by modifying gravity instead (though nowadays, the most common motivation for modifying graivty is to avoid dark energy). MOND is an example of that. MOND is like normal Newtonian gravity as long as the gravitational acceleration is large (like in the solar system), but instead of falling to arbitrarily low values as distances increase, the gravitational acceleration has an effective minimal value that it approaches as you move away. And such a constant value is just what you need to get the flat rotation curves we observe in galaxies. Which is the problem MOND was invented to solve.
MOND is an elegant solution for galaxies, but it loses all its elegance and predictive power when you try to apply it to the other areas where dark matter shows up. And in some cases it is plainly ruled out as an explanation. MOND, like Newtonian gravity, is a central force, which means that the force points towards the mass that generated it. But in the Bullet cluster, the gravitational force points towards areas with little visible matter, away from areas with much visible matter. This is impossible to fit into MOND. So the Bullet cluster basically killed MOND.
Some of MOND lives on in TeVES, which is an attempt at a relativistic version of MOND. Sadly TeVES has none of the simplicity and elegance of MOND, and while it can explai
I think he just misunderstood when she didn't want to go down on him.
Everything is better with chainsaws.
There is no dark matter. Changing our view of the nature of space can however explain what we observe. Einstein tried to show the way when he described gravity as the deformation of space.
We incorrectly deduce that there must be unseen mass because the outer edges of galaxies move at a rate that implies missing mass. We use the doppler shift of light to measure the speed of the stars in the galaxy. We assume that the speed of light and the speed of gravity are the same as they pass through the usual three dimensions of space. In a theoretical vacuum this may be true, but we live in a universe filled with matter and charged particles.
By changing our assumption and considering space as two three dimensional fields, electrostatic and gravitational that are superimposed upon each other we can easily reconcile what we see. The galactic center has a stronger gravitational field than the outer edge of the galaxy and gravitational space is compressed relative to electrostatic space. When we use light as a yardstick we fail take into consideration that the galactic gravitational field is compressed where the galactic electrostatic field is not.
This the Electro-Gravitic theory of space and provides a clear explanation for dark matter, dark energy, refraction and the unification of the strong force and gravity without resorting to anything we have not already proven experimentally or incredibly complex math that defies human understanding.
Greed is the root of all evil.
Neither electric fields, magnetic fields nor gravity fields consist of particles. So perhaps we ought to call it dark energy. It might form a "gravity-dark energy" pair analogous to electro-magnetism.
Much as magnetic fields interact with electric fields, perhaps dark energy interacts with gravity, giving us indications of it, but not being measurable using particle detectors (as the one described in the article).
Thoughts, anyone?