Check out the new, thought-provoking questions dealt with in the just-released PBS series of Closer to Truth: http://www.pbs.org/closertotruth
"In recent years, new technologies have brought waves of astonishing new discoveries inundating cosmologists: A Universe whose expansion is speeding up not slowing down? Gravitational lenses revealing distant galaxies formed near the beginning of time? Galactic jets shooting out thousands of light years? Black holes with the mass of a billion Suns lurking at the center of galaxies, swallowing entire stars in a single bite? Dark energy, emerging from nothingness, thwarting gravity and controlling the destiny of the Universe?..."
"DARK MATTER
Roger Blandford: Dark matter is a form of matter whose identity we don't yet know. We see evidence for it in our galaxy, in other galaxies, and in the clusters of galaxies, and indeed in the universe at large. We call it dark because it doesn't have lights associated with it. It doesn't have stars that create starlight associated with it. It doesn't appear to be like the matter that you and I are made out of. It appears to be some other sort of matter. We suspect that it in fact it is a fundamental particle of a sort that has not yet been described.
DARK ENERGY
Roger Blandford: When we try to describe the way in which the universe is accelerating, we cannot do that with matter, either light or dark alone. We need some extra force in the Newtonian sense, an extra substance present that has properties that are different from regular matter, either dark or light. And we call that the dark energy."
