A new paper says that one dark matter candidate hasn’t killed anyone

Physics

We may not know what dark matter is, but one thing we do know: it doesn’t appear to have killed anyone by slamming into them – an event that would, at the very least, result in serious injury.

So you can scratch that one off your list of things to worry about in this worrisome world. Which is great and all, but was not the purpose of the pre-print paper that describes these findings.

According to physicists Jagjit Singh Sidhu and Glenn Starkman of Case Western Reserve University, and Robert Scherrer of Vanderbilt University, the fact that no one has died of a dark matter impact allows us to apply constraints to the mysterious stuff itself.

“Our results,” they report, “open a new window on dark matter: the human body as a dark matter detector.”

On the surface, this sounds like some pretty out-there science; for now, we can all read their paper – titled “Death By Dark Matter” – on the pre-print website arXiv, until the scientific community and peer review gives it a closer look, too.

Dark matter continues to be a thorn in the side of cosmology. We know there is something out there generating more gravity than can be accounted for by detectable matter. In fact, the way stars and galaxies move indicates that up to 85 percent of the matter in the Universe is this mysterious undetectable mass. So, we call it dark matter.

Researchers have some pretty whizz-bang detectors out there on the hunt for dark matter, and they have shown us some pretty amazing things. But to date, there have been no conclusive detections of the stuff itself.

Another way to go looking for something is to figure out what it isn’t. That’s where asking if dark matter has slammed into people like mysterious ghost space bullets could be a valuable question.

Macroscopic, or macro dark matter in particular refers to dark matter candidates that would elastically scatter off normal matter across a wide geometric cross-section.

According to the team’s calculations, it’s particles of this dark matter – which they refer to as “macros” – that you wouldn’t want to be smacked with.

“The closest analogy to a macro collision with a human being is a gunshot wound,” the physicists write.

“Note that we are working with a very different range of projectile sizes and velocities from typical bullets. Macros typically have hypersonic velocities but very small geometric cross-sections in our parameter range of interest (as small as 1 micron).

“Hence, their destructive effect is likely to be qualitatively different from that of a bullet; a macro impact typically heats the cylinder of tissue carved out along its path to a temperature of 10 million Kelvin, resulting in an expanding cylinder of plasma inside the body.”

Wait. What.

It’s okay though. Even using a much more conservative benchmark for the effects – the muzzle energy of a .22 rifle – no macro-related deaths were observed over a 10-year period across Europe, the United States, and Canada.

These results constrain macros that may be detectable here on Earth to below a physical size of a few microns, and a mass of about 50 kilograms. The effect on the human body of macros smaller than that is yet to be investigated, but it’s possible that this, too, could be constrained in the future.

As for other dark matter candidates, some of those are yet to be explored; although two separate papers have found that weakly interacting massive particles, or WIMPs, are very unlikely to be causing cancer in humans.

We’ll all be sleeping sounder for that piece of information.

The team’s paper can be found on the pre-print website arXiv.

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