Dark matter is certainly nothing if not elusive. If dark matter does not exist in some form or other, there are serious problems with much of what astrophysicists think they know about the evolution of the universe. There are numerous types of astrophysical observations which can be explained by the existence of dark matter. But these explanations are contingent upon both the existence of dark matter in the form of some sort of as yet unknown particles (“WIMPs“) and also the correctness of accepted fundamental laws of physics – such as Newtonian gravity. If dark matter doesn’t exist, then the fundamental laws are also called into question.
To identify dark matter, experiments like DAMA, CRESST and CoGeNT look for weak-force-mediated collisions between atoms on Earth and WIMPs in the dark-matter halo of the Earth’s home galaxy, the Milky Way. Such collisions should cause individual atomic nuclei to recoil, and with the right apparatus such recoils can be observed. To screen out the confounding effects of cosmic rays, though, such experiments are best located underground.
Fortunately, three independent experiments that have been searching for traces of dark matter particles now have positive results. Although the probabilities of all these results being flukes are very small, they are not yet small enough to establish the existence of WIMPs beyond a reasonable doubt. The three ongoing experiments, as well as a number of others, continue to accumulate data. In particular, WIMPs could also be detected by the Alpha Magnetic Spectrometer now operating on board the International Space Station. WIMPs might even be created at the Large Hadron Collider.