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In astronomy and cosmology, dark matter is hypothetical matter that is undetectable by its emitted radiation, but whose presence can be inferred from gravitational effects on visible matter. According to present observations of structures larger than galaxies, as well as Big Bang cosmology, dark matter and dark energy account for the vast majority of the mass in the observable universe. Dark matter is postulated to partially account for evidence of "missing mass" in the universe, including the rotational speeds of galaxies, orbital velocities of galaxies in clusters, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.
Join UCSD Physicist Kim Griest as he takes you on an exploration of two of the major unsolved questions in the physical sciences: What might be the fate of the universe and what is the nature of the dark matter which ultimately decides this fate? Series: "UCSD Millennium Lectures"