The universe doesn't move right. Which is to say, galaxies spin and move away from each other at a velocity suggesting they're much more massive than what scientists can see—all the stars and other stuff that's visible is a scant 5 percent of the total calculated mass. So what's the rest? "Dark matter." Mysterious, invisible something to make the numbers work. And what's that made of? Well...funny story.
Over the last few decades researchers have come up with a lot of possibilities—most recently a group of Japanese researchers re-pitched pions, a subatomic particle that helps hold atomic nuclei together. One of the central missions of the proton-smashing Large Hadron Collider is to figure out dark matter, exactly. But so far none of the hypothesized suspects have panned out. Like what? Here's an incomplete list of the possibilities so far:
Weakly Interacting Massive Particles (WIMPS)
Massive Compact Halo Objects (MaCHOs)
Robust Associations of Massive Baryonic Objects (RAMBOs)
Macroscopic objects (macros)
Brown dwarf stars
White dwarf stars
Neutron stars
Black holes
Axions
Neutrinos
Neutralinos
Sterile neutrinos
Gravitinos
Photinos
Extradimensional mass
Defects in the quantum-field topology of the universe
Non-Newtonian, non-Einsteinian gravity
A "hidden valley" parallel dark-matter universe
Cat photos*
*No one thinks it's cat photos.
