Based on thorough observations of the sky, astrophysicists noticed years ago that the shape and motion of galaxies and other objects cannot be explained with visible matter, the matter we know from stars and planets. The data suggested gravitional forces that can only be explained by what physicists called dark matter.
Many speculations exist about the origin and composition of dark matter.
One attempt to solve the dark matter problem hypothesizes the existance of an undiscovered particle already existed in the very early universe. One can calculate the abundance of these particles in the universe today. Gravitational forces should keep WIMPs within our galaxy. We can imagine a cloud of WIMPs clumped around our galaxy, with the solar system sweeping through this cloud as we orbit the center of the Milky Way. Building a detector here on earth, physicists try to identify the WIMPs.