The Mystery of Dark Matter

dark matterReported by Catherine Yochum ’15

Dark matter: we know you’re out there. But how do we find something we can’t see? Blas Cabrera, a leader of the Cryogenic Dark Matter Search (CDMS) collaboration, presented a Kibbe Lecture at Bowdoin to explain current efforts to pin down this elusive quarry. The Kibbe Science Lecture Fund was established by Frank W. Kibbe ’37 and his wife, Lucy H. Kibbe.

All of the matter we can see in the universe amounts to only 5 percent of what’s truly there, according to astrophysicists. The unknown 95 percent is dark energy and dark matter, so called because essentially we’re in the dark about its identity. Dark matter doesn’t emit or reflect light, or any other electromagnetic radiation, which is why it has never been detected.

So what makes scientists think dark matter is there at all? Back in 1934, astronomer Fritz Zwicky wrote a paper about the “coma cluster,” a group of about one thousand galaxies clustered together. Zwicky demonstrated that it was impossible for these galaxies to be bound together just by the pull of the stars and gas we could see – indicating that the possible existence of matter that was escaping our detection.

This idea, which did not receive much attention at the time, has since been bolstered by more and more astrophysical observations. But it’s one thing to have indirect evidence and another to identify the particles themselves. Scientists have determined that none of the particles known to science make good candidates. The leading hypothesis is that dark matter is made up of something that hasn’t been discovered yet: “Weakly Interacting Massive Particles,” or WIMPs.

The CDMS collaboration and other groups are using an array of strategies to search for direct evidence of such particles. At facilities such as a lab buried deep in a mine in Soudan, Minnesota, scientists have been trying to detect cosmic dark matter directly as the particles pass through the laboratory. Other experiments – for instance, at the IceCube Neutrino Observatory in Antarctica – look for gamma rays scattered by WIMP activities. The Large Hadron Collider in Switzerland attempts to produce dark matter through high-energy collisions.

Bowdoin is playing its own part in the quest, as physics professor Madeleine Msall works on models of the materials that make up dark matter detectors, and Msall’s honors student Dan Palken ’14 uses modeling to determine how much energy should be deposited in detectors by dark matter particles (read about Palken’s recent visit to CDMS’s underground lab in the Minnesota mine).

So far, we’re still in the dark. But Cabrera anticipates that WIMPs will be either confirmed or ruled out as the source of dark matter within the next 5-10 years. Here’s to shedding light on one of the universe’s biggest mysteries.

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