Scientists believe they have found evidence of dark matter, the invisible substance believed to comprise three-quarters of the matter in the universe, in a defunct iron mine in northern Minnesota. The tentative detection of two dark-matter particles, known as weakly interacting massive particles (WIMPs) for their tendency to pass unimpeded through ordinary matter, was made by the Cryogenic Dark Matter Search (CDMS) project and announced by several laboratories, partners in a consortium that manages the project.
Despite the announcement, project scientists acknowledge that there is still about a 25 percent chance that the detections were caused by some other unrelated effect, and that they will need at least five detections before they can definitively state they have found this mysterious form of matter.
The detections were made by cryogenically cooled sensors at the bottom of the Soudan Iron Mine, a location that shields the detectors from more ordinary stray particles. To reach the underground laboratory, a particle would have to pass through half a mile of iron-rich rock. And to be detected, the WIMP would still have to collide with the nucleus of an atom in the sensor's Zip detectors (see photo). These employ state-of-the-art thin film superconducting technology using 250g germanium and 100g silicon crystals, which are capable of recording the extremely low energy generated by such a collision. Such collisions are extraordinarily rare, if indeed the detections are valid.
Dark matter was first proposed in the 1930s by astronomer Fritz Zwicky to account for the fact that clusters of galaxies remain cohesive despite not having enough visible matter to keep them from flying apart. Therefore, there must be additional matter, unseen and undetectable by normal means, to keep them gravitationally bound.
Cosmological evidence of dark matter has been gathered through the measuring of gravitational lensing by galaxy clusters. (In an effect predicted by Einstein's General Theory of Relativity, the gravity of massive objects such as a cluster of galaxies will bend the light coming from more distant objects.)
The elusive dark matter has been a holy grail for both astronomy and particle physics, and its definitive detection would be a major advance in our efforts to understand the universe.
More...
December 18, 2009 6:47 PM
First of all, thank you for a superb description of what dark matter is at the end of the article there. It's worth noting that our observations of bodies in the galaxy and calculations of how the "bright" masses in the solar system should behave also don't entirely match up with what Kepler says, which led to the notion that something else may be going on - some unaccounted-for mass that was exerting some kind of "extra" force on the bright masses.
Beyond that though, this is the same type of analysis that led to (different lab scenario, admittedly, but it just reminds me) the discovery of neutrinos, and the definitive proof that they existed. 25% is still pretty high variance though, I bet there are some very interesting experiments being cooked up right now to bring those numbers down.
December 19, 2009 11:42 PM
This is terrific news, despite the high uncertainty.
Alan_h, referring to your: "It's worth noting that our observations of bodies in the galaxy and calculations of how the "bright" masses in the solar system should behave also don't entirely match up with what Kepler says,..."
For our galaxy, I agree (that was what Fritz Zwicky's said), but AFAIK the non-Keplerian form of planetary orbits cannot be attributed to dark matter. It is rather the effect of multibody perturbations and also relativistic corrections for the inner planets.
December 23, 2009 2:19 AM
I had a sandwich the other day but absent-mindedly left it on the credenza. A few days later I returned and the sandwich was getting moldy. I hypothesized that this black mold could be dark matter. Being extremely hungry, I foolishly ate the aged, moldy sandwich.
Just hours later, the dark matter proved itself, because it went right through me. But enough of that. My current project is building a toilet-paper-mache particle accelerator at the South Pole.
It is extremely unfortunate that I left my Doobie Brothers tape on a super cooled magnet, the tape hasn't sounded the same since.
I may not have a college degree for each brain cell in my head like some of you folks, and I don't know diddly about quantum fizzicks and astrotomical consolations, but I'm just saying thank goodness Kepler discovered electricity by flying his kite in a thunderstorm or we would all be thinking the stars are really far away and not just pin holes in the fabric of space and even more importantly, whether Van Gogh was acting prematurely when he cut off part of his ear with a Ronco Showtime knife. Did Van Gogh's relatives psychically foresee a day, a time in the future when they might face great financial gain when they place Vincent's withered, severed ear on the shopping block on a thing called E-bay? Who nose.
January 10, 2010 12:53 PM
If there's another clue, it might be having to do with dark matter being obtained from a vessel out of the at;mosphere and near the quarry in another galaxy.
January 19, 2010 8:16 AM
JWA III, you win the internets for today.
March 31, 2010 1:09 AM
HMMM! This is my first time to this site.
I couldn't help but smile as I read the article.
Are you trying to tell me that some scientists have found 2 wimps down in a defunct mine shaft and think they are "dark matter" but we need to send 3 more wimps into the mine, and hope they bump into some atoms to be sure? I suppose the theory is that if nobody missed the wimps then it would be conclusive proof that they really were transparent matter and could rightfully be classified as "dark matter" :)