With the observation of two subatomic particles among an array of billions, in what is likely the coldest environment on earth, scientists believe they may have taken a step into the virtually unknown realm of dark matter.
Researcher Lauren Hsu of the Cryogenic Dark Matter Search experiment presented the new and tantalizing results in a talk at Fermi National Accelerator Laboratory, about 30 miles west of Chicago, on Friday, December 18, 2009. The experiment had two separate sightings that could be Weakly Interacting Massive Particles. It could be the first laboratory observation of dark matter, which makes up about 25 percent of the mass in the universe.
Or maybe not. Particle physicists live and die with statistical analysis, and scientists in the CDMS experiment calculate that their result has a 20 percent chance of being nothing but background radiation. One particle was spotted in each of two different detectors, within the ranges of mass and scattering patterns that have been predicted for WIMPs.
The Hunt for Dark Matter
Scientists predict that WIMPs would have masses equivalent to some atomic nuclei. However, they would only rarely make contact and scatter off particles of the everyday bright matter that we see all around us. Bright matter defines our everyday experience, from stars to atoms, but it makes up only five percent of the mass of the universe.
The hunt for dark matter has been going on for more than 75 years, since its existence was predicted in 1933. The history of that search is traced in an eminently readable style by Dan Hooper, a particle astrophysicist at Fermilab, in Dark Cosmos: In Search Our Universe’s Missing Mass and Energy (HarperCollins, NY 2006; ISBN-13: 978-0-06-113032-8).
If fear of physics is an obstacle to your curiosity about the dark side of the universe – the 25 percent that is dark matter, the 70 percent that is dark energy – Hooper has the antidote. He uses plain and lively language to explore all the complicated-sounding concepts that prepare the reader to confront what might be the most fascinating “big picture” questions facing science in the 21st Century: What role does the dark side – dark matter and dark energy – play in making our universe function the way it has for nearly 14 billion years?
Black Holes, White Dwarfs, MACHOs and WIMPs
With a minimum of math – beyond Einstein’s famous E=mc(2) – Hooper leads a tour through black holes and white dwarfs; through the analogy of Doppler Effect in sound waves, to red shift in astronomical observations of distant cosmic objects; on to gravitational lensing and relativity. He’ll discuss the prime theoretical suspects for dark matter – MACHOs (Massive Halo Objects) on the cosmic scale, and WIMPs on the subatomic scale – and show why WIMPS have won out as the likeliest candidate.
Along the way, you’ll wonder why physics wasn’t this fascinating in high school or college. And you’ll be well-prepared to appreciate the impact of possible discoveries like the results announced by CDMS.
The CDMS detectors are located a half mile below the surface in the former Soudan iron mine, located in the northeast corner of Minnesota. The detectors are made of silicon and germanium, and chilled to a fraction of a degree above absolute zero (-273 C or -459 F). Particles must pass through a half mile of the earth’s crust, and then penetrate layers of shielding before reaching the ultra-sensitive detectors.
Where Dark Matter Might Lead Humans
Dark matter has been inferred from many astronomical observations and from measurements of the cosmic microwave background, the glow left over from the first light in the universe about 300,000 years after the Big Bang. But the CDMS results would be the first laboratory observation of dark matter, if they stand up.
As Hooper notes, discovery is what makes science so exciting.
And he asks: “Could the discovery of dark matter’s identification start a domino effect of scientific progress? Could it lead to the discovery of a grand unified theory, or the understanding of dark energy or a Theory of Everything?”
If any of those discoveries is on the horizon, Hooper’s book will serve as your guide.
Mike Perricone - For nearly a decade, I served as Senior Editor and science writer in the Office of Public Affairs at Fermi National Accelerator Laboratory ...
Join the Conversation