A long time ago — that is, in high school — I thought I would study either neuroscience or astrophysics. They had the same attraction: a promise to apply the precision of science, its rigor of method and mind, to questions that high schoolers take very seriously, like: Who am I? What is my place in the world? What does it all mean?
I figured that neuroscience would take on these questions by looking inward, by thinking about thinking — just the kind of thing that could get a teenaged introvert seriously lost in an internal house of mirrors. Set against the claustrophobia of this perpetual reflection, astrophysics was a relief: an outward-looking science, one in which you could find yourself by losing yourself, figure yourself out without thinking about you at all.
So that’s what I picked. And the farther out from Earth you get — out past the apocalyptic asteroids, past the rovers’ tread marks, past the point where the sun stops being The Sun and starts being just another star — the more exotic and less human-centric the questions become.
At least, that’s how it usually works. But now, a group of astrophysicists has proposed a new way to study one of the deepest mysteries of outer space right here on Earth, using a drill and a microscope instead of a satellite and a telescope.
The mystery is dark matter, that invisible stuff that seems to bind galaxies and galaxy clusters together with the force of its gravity. For decades, astrophysicists have been amassing evidence that dark matter really exists. Not only does it exist, but it accounts for about 85 percent of the mass of the universe, making the “ordinary” matter that makes up people, planets and stars barely a footnote in the larger cosmic story.
Yet despite years of searching, researchers haven’t been able to confirm the detection of a single dark matter particle. While physicists have spun endless hypotheses about the true nature of dark matter, the leading idea is that dark matter is made up of “weakly interacting massive particles,” or WIMPS for short. That means that the particles are relatively massive compared to subatomic particles like protons, and they interact primarily through gravity and something called the weak force, which comes into play when particles get really, really close to each other.
Because they can breeze right through ordinary matter, WIMPs are hard to detect firsthand, but physicists are trying. The basic strategy is to build a detector — cryogenically cooled crystals, or a vat full of something like liquid argon or xenon — with plenty of atomic nuclei for WIMPs to run in to. Bury the detector underground to insulate it from things like cosmic rays. Then, look for the telltale ricochet of a WIMP in the detector.
Dark matter hunters have been following this search plan for years without much to show for it — though as they rule out certain classes of WIMPs, they can begin to home in on what the particles’ true properties might be. But all those nondetections got one team of researchers wondering: What if, instead of searching for WIMPs that happen to be whizzing though the Earth today, they could find evidence of “fossilized” ones that passed by hundreds of millions of years ago? In an article posted online, they propose searching for traces of WIMPs in ancient minerals buried almost 10 miles underground, excavated from the same ultra-deep boreholes used for things like oil exploration.
These ancient WIMPs could etch microscopic tracks in the rocks that might be visible using today’s scanning technology, they argue. They calculate that this “paleo-detection” method could be significantly more sensitive than today’s best limits, depending on what the real WIMP mass turns out to be.
Will the method pan out? We’ll have to wait and see.
A long time ago, I thought the best way to understand the universe and our place in it was to look up, out and far away. But maybe the answers to those big questions are actually right under our feet, just waiting for all the stargazers to turn around and start digging.