A few years ago, this blog looked at some work examining the likely effect of dark matter on the human body. The thinking was that if dark matter fills the universe and the Earth is sweeping through vast oceans of the stuff, then our bodies would be constantly bombarded with dark matter particles, causing problems such as genetic mutations and cancer.
But after careful consideration, researchers decided that the risk was minimal. They calculated that although dark matter particles called WIMPs (weakly interacting massive particles) might be constantly hitting us, they were considerably less of a problem than cosmic rays, which also bombard us and are known to cause mutations of all kinds.
Today, Olga Chashchina from the Ecole Polytechnique in France and Zurab Silagadze from the Budker Institute of Nuclear Physics in Russia take another look at this problem. These guys make a different set of assumptions about the type of stuff that dark matter is made of.
And this time, their conclusion is much more dramatic. They say that the consequences of this kind of dark matter are much more serious and could lead to diseases associated with mutations, such as cancer.
The key difference between the earlier analysis and this one is the type of dark matter involved. Nobody knows what dark matter is made of or even whether it exists at all. Astronomers hypothesize its existence because it conveniently explains an otherwise puzzling observation.
Distant galaxies spin so rapidly that they require powerful gravitational forces to hold them together. But when astrophysicists add up all the matter they can see in galaxies, it cannot possibly generate the required pull.
That’s why they think these galaxies must be filled with other stuff they can’t see—dark matter—and that this generates the gravity that holds them together. Indeed, for the sums to add up, about 80 percent of galactic mass must be dark matter.
But what could this dark matter possibly be? Astronomers think it must interact only very weakly with ordinary mater, otherwise we would have already seen its effects. So a leading candidate is the WIMP, the subject of the first study.
But another idea is that the universe could have an invisible partner made of exact mirrors of all the particles known to exist today. In this view, there would be mirror protons, neutrons and electrons which interact to create form mirror atoms, rocks, meteorites, planets, stars and so on.
This parallel stuff is called mirror dark matter and it has all the same properties of ordinary matter but interacts with it only weakly and via gravity. “The resulting mirror world very much resembles our ordinary one, as far as the existence of various familiar astrophysical objects is concerned,” say Chashchina and Silagadze.
The question that Chashchina and Silagadze investigate is what would happen when certain configurations of mirror dark matter hit other configurations of ordinary matter. And their results are anything but benign.
The key interaction between mirror and ordinary matter is between ordinary photons and mirror photons. This interaction causes mirror dark matter to gain an ordinary charge.
That’s an important difference from other types of dark matter because the charge interacts with ordinary matter just like any other charge. “The point is that the mirror matter provides a completely new type of radiation hazard not found in WIMP-type dark matter models,” say the researchers.
So a collision between a mirror asteroid and Earth would be catastrophic. This is highly unlikely, but Chashchina and Silagadze say a much more probable event is a collision with mirror micrometeorites in the form of mirror dust particles that are likely to fill the mirror universe.
They go on to calculate how these mirror micrometeorites would transfer energy to ordinary matter in a collision. In particular, they examine what might happen if mirror dark matter meteorites hit an 80 kilogram lump of meat. “When moving through a human body they deposit a lot of energy greatly exceeding energy deposition from cosmic-ray muons,” they say.
This will tend to dissipate as vibrations that rearrange biological molecules. “We can thus speculate that the mirror micrometeorite, when interacting with the DNA molecules, can lead to multiple simultaneous mutations and cause disease,” conclude Chashchina and Silagadze.
Indeed, they go further: “It can turn out that mirror micrometeorites are much more dangerous carcinogens than other natural radiation sources.”
That’s interesting because malignant cancer cells contain far more random mutations than can possibly be caused by ordinary mutation processes. Biologists have long puzzled over what could do this, so the idea that mirror dark matter could be to blame is tantalizing.
But there’s no need to cover yourself with tinfoil just yet. The truth is that nobody knows what sort of dark matter fills the universe. Indeed there are various other ways to explain galaxy rotation speeds that don’t involve dark matter at all. So it may not even exist. In which case, all this calculating and worrying will have been in vain.
Ref:arxiv.org/abs/1509.05139: Dark Matter as a Cancer Hazard