Most Sensitive Detector Yet Fails To Find Any Signs of Dark Matter 293
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."
Maybe (Score:5, Insightful)
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.
Have they considiered... (Score:2, Insightful)
...that maybe they're not seeing it because it's just not there?
Just a suggestion.
Re:Have they considiered... (Score:4, Insightful)
Hur hur, yeah, stupid scientists with their "degrees" and their "experiments."
What a bunch of losers.
Re:Maybe (Score:5, Insightful)
Yes but I could pick another example, the nutrino and say it sounds like that too:
"In 1930 Wolfgang Pauli proposed a solution to the missing energy in nuclear beta decays, namely that it was carried by a neutral particle " ( http://www.ps.uci.edu/physics/news/nuexpt.html [uci.edu] )
It makes perfect sense. You have theories that test to a high confidence in every way you can test them, then you find an anomaly in specific instances. Whats the response? Take those theories and attempt to narrow down the properties of what would cause the anomaly.
It obviously doesn't always produce a hypothesis that pans out as correct, but, can you really say that Aether theory was so bad? It was wrong, yes, but, it lead to the creation of experiments that answered new questions and ultimately, shaped the theories that came after it.
and...at the time... that is, after light was shown to be wave-like AND before we knew that there was no motion relative to its "medium", postulating Aether made a lot of sense.
Re:Maybe (Score:2, Insightful)
All we know is that there is something creating a gravity-like effect on large scales. We don't even really know how gravity works, so I don't think we can know dark matter 'exists' per se, as a type of matter, until we fully understand how gravity works at macro and quantum scales, the number of dimensions of the universe, the shape of the universe, etc... For all we know, the effect which we attribute to dark matter could just be a consequence of some other fundamental property of the universe that we know nothing about.
Re:Maybe (Score:5, Insightful)
True, even failed theories advance science in some way or other.
However at some point you have to let them go.
The summary where it clearly states:
Physicists know from astronomical observations that 85% of the Universe's matter is dark,
I suggest they KNOW no such thing, and merely postulate dark matter to get their equations to balance. But how many such equation balancing inventions are laying in the dustbin of Physicists' revised theories over the years?
Unless or until the Physicists can find fault with the detectors, all of which have failed to find a trace of something allegedly composing 85% of the universe , it would seem that the whole "dark matter is known to exist" statement needs to taken down a notch. Detectors designed to their own specs fail to produce a single trace. It doesn't matter that there are very precise measurements of exactly how much the equations are out of balance.
Re:Maybe (Score:5, Insightful)
We can certainly detect dark matter.
No, we can't.
We only know to what extent our speculation and our math fails to completely work to our satisfaction.
Se we invent a black-box term to get the math to work out. We are quite precise in our invention.
We design instruments to detect this stuff that the math predicts is there. Instruments fail, time after
time.
You always need to consider the fact that it might be something else in the math that is wrong.
Otherwise, you might just as well attribute it to unicorns.
It is very hard to avoid dark matter (Score:5, Insightful)
The main lines of evidence for dark matter:
* Galactic rotation curves [wikipedia.org]
* Velocity distribution in clusters of galaxies [wikipedia.org]
* Gravitational lensing [wikipedia.org] in general
* The Bullet Cluster [wikipedia.org] in particular
* The pattern of positions of galaxies in the universe [wikipedia.org]
* The pattern of Baryon-acoustic oscillations [wikipedia.org] in the cosmic microwave background [wikipedia.org] and in the galaxy distribution
* The primordial distribution of light elements in the universe [wikipedia.org]
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 [ggpht.com]. 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 [wikipedia.org] 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 [wikipedia.org], 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 [wikipedia.org], 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
Re:Maybe (Score:4, Insightful)
Re:Maybe (Score:1, Insightful)
"Instruments fail, time after time."
Instruments failed time after time to detect the neutrino, until it was detected.
Instruments failed time after time to detect the aether, until it was demonstrated not to exist and a better explanation found.
There is no expiration date on speculative explanations, there is only corroboration or falsification.
Re:Maybe (Score:4, Insightful)
Yes, in a sense. I have a strong suspicion that if we were able to do a proper statistical mechanical analysis of the situation we'd see some odd emergent behaviour -- a galaxy is, after all, a rarified gas of about 10^9 interacting, confined bodies. We'd get different behaviour in a cluster, and different on cosmological scales.
Of course, I may be wrong and what we'd get out would be effectively pressureless dust, which is what we currently put in. Thep roblem is that at the minute we can't do a proper statistical mechanical analysis. We don't even have a full theory to work with, though there's progress here, too.