has anyone ever been killed by dark matter?

According to the best data we have available, nearly a quarter of the universe is made up of an invisible but massive entity known only as dark matter. So, ask a trio of scientists, if matter as we know it is outnumbered five to one, there are two questions we should try to answer if we want to find out more about what dark matter really is. First, could it be larger than atoms and molecules, forming clumps big enough to have an impact on the human body? And second, if a gob of dark matter traveling through space is such a major part of the universe, couldn’t it hit a human at relativistic speeds, injuring, if not outright killing them?

It seems absurd at first glance. Just imagine patients stumbling into a hospital with what looks like a gunshot wound claiming they didn’t hear any gunshots or even a distant popping sound, but suddenly discovered they were shot through by some mysterious force. It would be a very difficult claim to prove since investigations have to rule out any potential enemies, gun fights in the radius of a few miles, contract killers with silencers, and witnesses lying to the police that they heard and saw nothing to protect themselves from possible or imaginary retaliation by real criminals they know or imaginary ones they think may be after them.

can death by dark matter be a choice for coroners?

Even then, Occam’s Razor would dictate that we still rule their injuries to be gunshot wounds since we don’t know if dark matter could interact with the molecules and atoms of our bodies. And the same logic would apply to bodies of lost or missing people found in the wild without a satisfactory cause of death, especially since their cadavers would decompose or get picked at by scavengers, degrading possible evidence of an exotic cause of death and making coroners and medical examiners lean towards listing exposure or blunt force trauma from falls as the culprits behind their demise, even if the exposure and trauma came after they were shot by a relativistic round from outer space.

Yes, it’s impossible to categorically rule out even a rare, one in a billion chance of something like this happening over the nearly 200,000 years of modern human existence and more than 108 billion people who have ever lived for any length of time, anywhere on our planet. But this is why science doesn’t try to prove a negative. It’s a logically and logistically impossible task. Instead, it looks for evidence that something happened, and without proof that dark matter is made of particles, those particles can interact with ours, can combine into large enough bits to actually do real damage to living tissues, and without seeing people and animals falling down with mysterious wounds on a regular basis, we really shouldn’t worry about it.

how weird questions can keep science in check

But if that’s the case, why even bring this up? Just like we saw with the idea that Planet Nine may be a primordial black hole, the point is to put very practical constraints on theories we often see floating in the clouds of mathematical abstraction. As mentioned, we don’t actually know if dark matter is even a particle. It’s true that some astronomers claimed to spot galaxies free of dark matter, presenting this as proof that dark matter must be made of particles, but after a second, more thorough look, we know this not the case and every experiment to create or detect some sort of suitable dark matter particle has failed. For all we know, it could be a trick of gravity on a macro scale and only matter when we’re talking in cosmological terms.

Asking a question as simple as whether we could get brained by a chunk of it may seem absurd, but it’s a great way to get researchers thinking about what it is they’re trying to understand in very concrete, real world, human scale terms. Knowing if you can see, touch, or hear something tells you what you may be dealing with, how to detect it, and where to look for it. The math explaining how our universe works is well tested and tells us that there’s a lot we still don’t know about why our observations don’t fit together neatly. But the more time we spend with our equations, the more abstract our ideas about the cosmos can become, which is why it’s always a good idea to take a step back and re-ground oneself in real world physics.

See: Sidhu, J., Scherrer, R., Starkman, G., (2019) Death and serious injury from dark matter, arXiv: 1907.06674