Dark Energy

The idea of dark energy being responsible for the accelerating expansion of the Universe has been discussed passionately by cosmologists in the past few years. The idea was first introduced by Albert Einstein in the early 20th century as a "cosmological constant" that would allow "his" Universe to remain static. As is well known among physicists, after Hubble's discovery of the expanding Universe, Einstein called the cosmological constant "the greatest blunder of [his] life." Here is a nice little article about our current views of dark energy and the expansion of the Universe:

Ripples in Spacetime Could Explain Dark Energy