One of the most puzzling components of the Universe has to be dark matter. Although we have extraordinary astrophysical evidence that the normal matter in the Universe — the stuff made out of known particles in the Standard Model — cannot account for the majority of the gravitational effects we observe, all of that evidence is indirect. We still have yet to obtain a shred of repeatable, verifiable direct evidence for whatever particle might be responsible for dark matter. The total evidence places very tight constraints on any non-gravitational interactions