A scientific system buried deep below the Earth, constructed of ultrapure materials held hovering over absolute zero, has finally stirred. This isn't an attack by misbegotten monsters but an encouraging clue to the main mystery of the universe: dark matter.
The kind of matter with which we are familiar -- atoms and molecules, and indeed every particle we have ever created in a laboratory known as baryonic-- only makes up about 5% of the universe. Another 25% is dark matter, a kind of particle that is massive and weakly interacting. The remaining 70% is dark energy, which is not even a particle -- it's a smoothly-distributed energy field that remains persistent in density even as the universe expands. The ongoing effort to understand dark matter and dark energy is the most important task of twenty-first century cosmology.
The Berkeley Cryogenic Dark Matter Search II (CDMS II) does exactly what it says - it's cryogenically cooled, it's searching for dark matter, and this is the second time they've done it. High purity low temperature crystals of germanium and silicon vibrate are disturbed by anything impacting on them, and they're buried under seven hundred meters of iron mine to make sure most of "anything" can't make it. One thing that could conceivably come down and stir things up is a WIMP, a Weakly Interacting Massive Particle - one of the options for dark matter.
The system is so shielded that over an entire year users only expect 0.8 events, and in 2008 they saw two. This is a tantalising taste of data: analysis indicates that the event energy matches the model for dark matter WIMPs, but even after screening out as much noise as possible it simply isn't enough signal to be sure. Scientists, you see, double-check and confirm things before shouting about them (unlike others who - for example - might hack unprocessed e-mails, strip random sentences out of context, then start screaming about all kinds of nonsense.)
This excitement is motivating instead of mob-making: the research team are upgrading the equipment with Super-CDMS stacks of crystal which will triple its efficiency. Space satellites, subterranean sensors, and that little LHC thing: we want this dark matter stuff.
The bulk of the dark matter that makes up 75% of the universe is believed to be nonbaryonic, which means that it contains no atoms and that it does not interact with ordinary matter via electromagnetic forces and includes neutrinos, and possibly hypothetical entities such as axions, or supersymmetric particles. Unlike baryonic dark matter, nonbaryonic dark matter did not contribute to the formation of the elements in the early universe, so its presence is detected only by its gravitational attraction.
TrackBack URL for this entry:
Listed below are links to weblogs that reference Has Missing Dark Matter of the Universe Finally Been Detected?: