[jimbob]

Not being a physicist or anything, but I think we're talking about the universal expansion constant. I think Einstein first proposed it, but was so disgusted with the idea that the constants of the universe would change over time, that he discarded it. However observational evidence has brought the idea back into vogue. It's either the fabric of space-time is slowly changing it's rate of expansion, or there is a type of "anti-gravity" energy that is capable of driving matter apart. Roll it in with dark matter, and you've got one whacky universe!