How often does dark matter collide with the human body?

Dark matter, say physicists, is everywhere. They say this because the gravitational forces that we observe in the known Universe are greater than the mass of visible matter would lead us to believe is possible. Dark matter, scientists speculate, is the source of the missing mass; in fact, by some estimates, dark matter accounts for at least 80% of the mass in our galaxy.

So where the Hell is it?

The short answer is: we don't know, but logic dictates that we'd basically have to be swimming in anything so abundant; there are likely billions upon billions of dark matter particles passing through your body at this very second. But how many of these particles could actually affect you?

To find out, researchers Katherine Freese and Christopher Savage calculated how often one of these billions of particles actually collides with one of the atomic nuclei in your body. Their result? Depending on which dark matter model you subscribe to, the average person (average being a mass of ~70kg) will experience between 30 and 100,000 dark matter/nucleus collisions per year. As for the potential health effects of these collisions? Freese and Savage decline to weigh in, but we're willing to bet they'd be pretty negligible — not that you could do much to avoid them, anyway. [arXiv via Technology Review]
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