'Astronomers have compiled evidence that what we've always thought of as the actual universe...represents a mere 4 percent of what's actually out there. The rest they call, for want of a better word, dark: 23 percent is something they call dark matter, and 73 percent is something even more mysterious, which they call dark energy.

'"We have a complete inventory of the universe," Sean Carroll, a California Institute of Technology cosmologist has said, "and it makes no sense." Scientists...have hardly a clue about dark energy.'

"Probing the Biggest Mystery in the Universe"
by Richard Panek
Smithsonian
April 2010


'The dark energy can take several forms, one provided by Einstein's resurgent cosmological constant and another related idea called quintessence...Quintessence, if true, would also be an energy field that permeates the universe. It can be disturbed and interact with itself. It is this aspect that distinguishes it from the cosmological constant which is...well...constant...If this all sounds rather fuzzy, this is because it is. This is research in progress. In research, confusion is good. It means that something doesn't hang together and you're about to learn something new. This is an exciting time in cosmology.'

Understanding the Universe: From quarks to the cosmos
Don Lincoln