Something else must surround and suffuse every galaxy, some kind of gravitational glue.
Cosmologists dubbed it dark matter, as it sheds no light. And, they say, it far outweighs all the ordinary matter — stars and planets — that they can account for.
The leading candidate for this mystery substance: subatomic particles called WIMPs, or “weakly interacting massive particles.” They can’t be seen, but they should be nearly everywhere (at least in our galactic neighborhood). If true, every once in a great while, a zooming WIMP will by chance smack the nucleus of an atom like a well-struck cue against an eight ball.
For two decades, physicists have built detectors crammed with dense crystals and other heavy materials to try to catch WIMPs in this act. The results have been largely equivocal. There’s no smoking WIMP signal yet — although hints have appeared.
Proposals for the next generation of dark matter detectors run into the tens or hundreds of millions of dollars. One such project would require an empty mine filled with a cubic kilometer of gas.
Now, though, a group of big-name theoretical physicists and biologists has proposed a radical new type of detector that dangles DNA as dark-matter bait. At coffee-table size, it would be much less expensive than other proposed detectors, they say.
Call it the ultimate mashup of biology and cosmology.
“For the very first time, an important problem in physics can be solved by techniques from another science,” said Andrzej Drukier, the physicist-turned-biologist who struck on the idea.
Drukier proposed a DNA detector in a 2010 talk at UCLA. Soon after, Katherine Freese, a University of Michigan theoretical physicist, joined him. The pair are well placed to leapfrog the hunt for dark matter: In 1986, they laid out the theoretical rationale that led to the current generation of detectors.
This spring, Drukier and Freese drove to the San Diego home of Charles Cantor, a pioneer of the Human Genome Project who built a successful DNA technology company, Sequenom.
They eased past Cantor’s Maserati, Freese recalled, and sat around his pool overlooking the Pacific, batting around ideas. A challenge immediately appeared.
“When you’re trying to think across such a vast range of disciplines, finding a common language is difficult,” Cantor said. “So we scribbled lots of pictures on pieces of paper — pictures instead of equations.”
From those scratchings, a rudimentary design emerged, a cube about three feet on a side.
In it, thousands of strands of DNA hang from sheets of gold, like row upon row of beaded curtains. A WIMP zooms in — or so they hope — and hits a gold nucleus, which shakes free and tears through the DNA curtains, slicing them. (Gold, with its relatively heavy nucleus, makes a good choice for a material to rip through the DNA.) The severed DNA drops to the bottom of the detector, where it’s collected. Standard DNA-reading machines — off-the-shelf technology — then reconstruct the path of the WIMP through the curtains.