Oh, and a vacuum may not really be void of matter.
Light from the sun speeds toward Earth Kieff on Wikimedia Commons
Can you trust nothing in life? A new physics paper suggests that the speed of light in a vacuum may not be constant, and that a vacuum isn't actually entirely empty of stuff.
The paper, by a team of French physicists, finds that the speed of a photon in a vacuum fluctuates by 50 quintillionths of a second per square meter, the Christian Science Monitor reported. In addition, it posits that vacuums may actually have extremely short-lived particles in them that keep appearing and disappearing.
For the rest of the story: http://www.popsci.com/science/article/2013-03/speed-light-vacuum-varies-slightly-study-finds?src=SOC