The fact that no one has died from being struck by dark matter is enough proof to rule out certain ideas about the mysterious stuff, according to one new theory paper.
There’s a conundrum facing physicists: Most of the universe’s mass appears to be missing, based on observations of the universe’s structure, how galaxies move, and how they seem to warp distant light. Thousands of physicists are now hunting for what might be producing these effects. But the mere fact that we’re alive here on Earth can offer some insight as to what dark matter isn’t, and the researchers behind the new paper say the human body itself can serve as a dark matter detector.
There are plenty of dark matter candidates, most of which have something in common: They feel the force of gravity, but do not interact via the other physical forces, like electromagnetism. That means that, rather than “dark,” it’s better to think of it as “invisible” or “transparent.” Scientists have spent a lot of time and effort building detectors in order to find this dark matter. Most of their experiments operate under the same strategy, which is to build an incredibly sensitive sensor, shield it from any potential sources that could cause false positives, and wait. Scientists for the last decade have been most interested in the idea of WIMPs, or Weakly Interactive Massive Particles, that would be perhaps around the size of the heaviest existing subatomic particles.
Most recently, scientists Jagjit Singh Sidhu and Glenn Starkman, both from Case Western Reserve University, and Robert J. Scherrer from Vanderbilt University considered another class of particles that would be macroscopic, and around or less massive than a human being. But here’s the thing: If such a particle existed, and given how much dark matter we expect there to be in the universe, such a particle should at some point have caused an unexplained gunshot-like wound in a human being, according to the paper published on the arXiv physics preprint server.
Basically, this paper provides just with a thought experiment something other research has provided with a lot of expensive equipment: a constraint, meaning a range of characteristics that scientists should not bother hunting for.
“It’s good to be sure we are fully cognizant of our most basic physical constraints, which include not breaking every day life,” Chanda Prescod-Weinstein, assistant professor of physics and astronomy at the University of New Hampshire, told Gizmodo in an email. “This exemplifies one of the challenges that theoretical physicists face when imagining how to solve problems like finding an explanation for dark matter.”
One physicist not involved in the study, James Beacham, a particle physicist with the ATLAS Experiment at CERN’s Large Hadron Collider, liked the study but didn’t think it went far enough—he wants to see data that shows they’re aren’t actually some number of unexplained, gunshot-like wounds happening around the world. “[A]t the end of the day, though, I think this paper is fascinating because it’s an example of how a null result—or something that seems to be looking like a null result, like the lack of WIMP dark matter in our current experiments—can inspire people to think in new ways,” he told Gizmodo in an email.
This isn’t the first time that scientists have considered the effect that dark matter could have on the human body. A 2012 paper by Katherine Freese from the University of Michigan and Christopher Savage from the Nordic Institute for Theoretical Physics considered what harm WIMPs would have on human beings, and found that they wouldn’t be dangerous, or at least not any more worrisome than other daily radiation exposure sources. Freese told Gizmodo she had no complaints about the new work.
To be honest, there are perhaps more pressing questions at hand, like why we haven’t found any sign of dark matter yet and whether that’s because we’re wrong about some element of the laws of physics. Ultimately, dark matter might look nothing like the standard WIMPs that scientists are currently searching for.
I suppose there are worse ways to go than to be struck by a rogue clump of dark matter, especially if your death were to solve one of biggest mysteries in physics. Hey, maybe they’d name the particle after you.