Over the past decade, astronomers have become convinced that normal matter-stuff like atoms, electrons, and everything else we have ever observed-makes up only 4 percent of the universe. And the other 96 percent, you ask? Well, they’re not so sure. Part of it is called dark matter,
a name that nicely reflects our ignorance, but as scientists start to expand our options of what this dark matter could be made of, they must concoct names for the various candidates. So, in the June 20 issue of Science, Princeton University astrophysicists Jeremiah Ostriker and Paul Steinhardt go through the active list, including:

* Cold collisionless dark matter (CCDM)

* Strongly self-interacting dark matter (SIDM)

* Warm dark matter (WDM)

* Repulsive dark matter (RDM)

* Self-annihilating dark matter (SADM)

* Fuzzy dark matter (FDM)

Lest you become confused, we should point out that the latter, FDM, is not the same as cuddly dark matter (CDM), the stuff that hovers about lonely astronomers when they’re working at night in cold observatories. Nor should any of the above be mistaken for theory-saving dark matter (TSDM), a variant of expedient dark matter (EDM) that most often appears when conventional thinking is unable to explain observed phenomena. TSDM and EDM also belong to the larger class of grant-guaranteeing dark matter (GGDM), which only the most accomplished scientists have the power to manipulate.