RALEIGH, N.C. — Physicists racing to detect the mysterious substance known as dark matter are thinking outside the box by looking inside the cell. A new proposal for tracking dark matter particles relies on strands of DNA.
All the ordinary stuff in the universe, from the atoms in people to the hot plasma in stars, makes up only about 5 percent of the universe’s mass and energy. Nearly one-quarter of the universe is composed of dark matter. (The rest is an even more puzzling entity known as dark energy.) Though several experiments claim to have detected dark matter, the results don’t agree and aren’t definitive.
Katherine Freese, a theoretical physicist at the University of Michigan in Ann Arbor, proposed October 28 at the New Horizons in Science meeting that a new kind of DNA-based detector could not only spot a leading candidate for dark matter, called WIMPs, but could also determine incoming particles’ direction of flight. The proposal also appeared online earlier this year at arXiv.org.
“It’s a very smart way to apply technology developed from biology to a fundamental particle physics problem,” says Jocelyn Monroe, a dark matter physicist at MIT and the University of London.
A halo of WIMPs, short for weakly interacting massive particles, is thought to encircle the galaxy. As the sun orbits the galaxy’s center, it should encounter a “wind” of WIMPs from the direction of the constellation Cygnus. At any point on Earth, such a wind should strengthen and weaken daily as the planet rotates.
Freese and her colleagues’ proposed detector, which would be sensitive to these fluctuations, consists of a stack of thin gold sheets with single-stranded pieces of DNA hanging from them. When a WIMP smacked into the nucleus of a gold atom, the nucleus would whiz off, cutting through the DNA at specific locations in the strands.
Scientists would then collect and sequence the DNA to reconstruct the path traveled by the nucleus, and by extrapolation, that of the WIMP. If the detector spotted the daily fluctuation and the particles’ paths proved consistent with the WIMP wind’s direction, it would be compelling evidence that the signals came from dark matter.
“The advantage of these detectors is that the difference between DNA bases is a nanometer, so it’s much better resolution,” says Freese — about a thousand times better than current detectors.
The device could be a fraction of existing detectors’ size, as well as cheaper.
Still, the technique has yet to be demonstrated, says Joel Schnur, a biomolecular scientist at George Mason University in Fairfax, Va. “What is the real sensitivity to cleavage of DNA? How many particles will come down over time? And, can it detect them?” he asks.
If the project goes forward, Freese and colleagues could begin to answer some of these questions.