Dark matter is a mysterious substance that makes up about 85% of the matter in the Universe. It doesn’t interact with regular matter, at least not very often, and so physicists are having a devil of a time figuring out what it is.

Lately there’s been a lot of talk about dark matter. Some say they’ve seen it, other say no. One particularly controversial experiment is known as DAMA/LIBRA. It’s located beneath the Italian mountain of Gran Sasso, and it’s claiming to see an annual fluctuation of dark matter as the earth flies through a galactic halo of the stuff.

But an American experiment says that whatever it is DAMA has seen can’t be dark matter, at least not any kind of dark matter predicted by current theories. The experiment, which was placed underground in a City of Chicago pumping station, should have seen a signal if DAMA was right, but it came up empty-handed (their results have just been accepted to the journal Physical Review Letters).

The DAMA group is tenacious, and I personally doubt this will be the last word on the matter