Throwing Light on the Matter


Fifty years of sweat in cosmology and particle physics has culminated in this: two blips, just nanoseconds long, on scraps of semiconductors half a mile underground. Scientists couldn’t be more ecstatic.

The blips occurred in an abandoned iron mine in northern Minnesota, where scientists have built a lab to search for exotic matter. Astronomers in the 1970s discovered that there’s not enough normal matter (such as atoms) to keep galaxies intact with gravity, and they began calling the missing stuff “dark matter.” Further work indicated that dark matter actually makes up a quarter of the universe. (Most of the rest, 70 percent, is another mystery substance that is unrelated, “dark energy.”)

Meanwhile, particle physicists realized that the big bang at the beginning of time produced loads of particles that scarcely interact with normal matter and therefore remain invisible to us as they zip through the cosmos. They named them “weakly interacting massive particles,” WIMPs. Lo and behold, these particles had, at least on paper, the same properties as dark matter. The hunt was on.

Scientists set up shop in the old Soudan iron mine to filter out cosmic rays from space that can overwhelm the sensitive WIMP detectors. Their enter- prise was so well shielded that it became like hanging around for Godot—lots of tedious nothing. But Godot kept his appointment this time: scientists announced in December that, twice in two years, a particle of dark matter streaming through the earth tickled a detector.

It was exciting, but there’s a one-in-four chance both blips are an anomaly, so the Soudan lab will keep searching, and a new, more sensitive detector beneath the Italian Alps joins the hunt this fall. Best of all, the Large Hadron Collider smashing atoms at a complex in Switzerland (CERN) could someday produce dark matter directly.

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Sam Kean is the author of six science books, including The Disappearing Spoon and The Icepick Surgeon.


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