“The idea of the existence of WIMPS fits with many cosmic measurements, including the inferred gravitational fields of galaxies and clusters of galaxies, the observation of gravitational lensing, and the patterns of the cosmic microwave background radiation. The snag is that no WIMP has ever been detected directly, and a number of Earth- bound experiments are actively searching for them. It's possible that instead of there being dark matter, there is something incomplete in our understanding of the nature of gravity itself.”