This is a fascinating talk from Alex Filippenko (Richard & Rhoda Goldman Distinguished Professor in the Physical Sciences at UC Berkeley), a record 9-time winner of the "Best Professor" award at Berkeley.
The above graphic is useful, but we can disregard the whole "big bang" thing - it's more likely our universe is one of many and that the universe may recycle itself - see Roger Penrose (Conformal cyclic cosmology). The dark energy paradox works is Penrose's model.
Published on Jan 13, 2014
We expected the attractive force of gravity to slow down the rate at which the Universe is expanding. But observations of very distant exploding stars (supernovae) show that the expansion rate is actually speeding up, a remarkable discovery that was honored with the 2011 Nobel Prize in Physics to the teams' leaders. Over the largest distances, the Universe seems to be dominated by a repulsive "dark energy" -- an idea Albert Einstein had suggested in 1917 but renounced in 1929 as his "biggest blunder." It stretches space itself faster and faster with time. But the physical origin and nature of dark energy, which makes up about 70% of the contents of the Universe, is probably the most important unsolved problem in all of physics; it may provide clues to a unified quantum theory of gravity.
About the Speaker: Alex Filippenko is the Richard & Rhoda Goldman Distinguished Professor in the Physical Sciences. His accomplishments, documented in about 700 research papers, have been recognized by several major prizes, and he is one of the world's most highly cited astronomers. In 2009 he was elected to the National Academy of Sciences, and he shared part of the Gruber Cosmology Prize in 2007. He has won the top teaching awards at UC Berkeley and has been voted the "Best Professor" on campus a record 9 times. In 2006 he was selected as the Carnegie/CASE National Professor of the Year among doctoral institutions, and in 2010 he won the ASP's Emmons Award for undergraduate teaching. He has produced five astronomy video courses with "The Great Courses," coauthored an award-winning textbook, and appears in numerous TV documentaries including about 40 episodes of "The Universe" series. An avid tennis player, hiker, and skier, he enjoys world travel and is addicted to observing total solar eclipses (11 so far).