It appears that a 75-year-old hunt may finally end in the capture of an elusive prey. Tantalizing results from an old underground iron mine in Minnesota suggest that a direct detection of dark matter is just around the corner. Such a discovery would validate a key component of current big bang models as well as provide additional tools for understanding how well-designed this creation is to support humanity.
The first hints that a non-luminous substance existed in the cosmos came from observations made by Fritz Zwicky back in the 1930s. By studying the Coma cluster of galaxies, Zwicky calculated that the gravitational mass of the cluster significantly exceeded the amount predicted based on the light detected from the cluster. Almost 40 years later, galaxy rotation curves measured by Vera Rubin demonstrated that the bulk of the mass in these galaxies extends beyond the region containing visible stars. In 1992, the Cosmic Background Explorer satellite (COBE) established that we lived in a universe with a flat geometry, which strengthened the case for dark matter’s existence. Yet, 75 years after Zwicky’s first observations, the elusive dark matter had never been detected except for its gravitational influence.
Results from an experiment conducted 2,000 feet underground, in the Soudan Underground Laboratory in Minnesota, may have detected collisions between dark matter collisions and normal matter. The researchers, participants in the CDMSII collaboration, assembled a detector using germanium capable of measuring the recoil of a dark matter particle colliding with a nucleus in the detector. In order to distinguish any dark matter events from background processes, the detector is cooled near absolute zero (to minimize thermal background) and located deep underground (to minimize cosmic-ray background events).
Left: Entrance to the Soudan Underground Laboratory. Right: View of the partially assembled CDMS II detector.
After nearly two years of operation (2007–2008), the CDMS collaboration announced the detection of two candidate dark matter events.1 Given the duration of operation and characteristics of the detector, the expected background was 0.9 +/- 0.2 events. As such, the detector needed to see at least five events in order to claim a definite dark matter detection. The detector saw two events, which means there’s a 25% chance this tentative detection is simply a background fluctuation. However, with even more sensitive detectors under construction, these initial results hint that a direct detection of dark matter is eminent.
RTB anticipates a definitive detection within the next five years. Such a find would validate a key component of big bang cosmology, namely that dark matter comprises a significant fraction of the universe’s energy budget. Furthermore, it will give scientists a tool to better understand the nature of dark matter, which will also reveal more evidence for the idea that the universe is designed to support life.
1. The CDMS II Collaboration, “Dark Matter Search Results for the CDMS II Experiment,” Sciencexpress, published online February 11, 2010.