Back in 1989, before any cosmological constant had been discovered, Dr. Weinberg used the anthropic principle to set limits on the value of the constant. Suppose instead of being fixed by theory, it was random from universe to universe. In that case the value of the cosmological constant in our universe may just be an "environmental effect," he explained, and we shouldn't expect to be able to predict it exactly any more than you can calculate how much rain will fall in Seattle this Christmas.
In his paper, Dr. Weinberg argued that lambda in our universe could not be too big or the repulsive force would have prevented the formation of galaxies, stars and us. Since we are here, the constant should be small.
The recently discovered "dark energy" causing the cosmic acceleration fits comfortably inside Dr. Weinberg's limits, vindicating in a way the anthropic approach.
Dr. Weinberg compared the situation to a person who is dealt a royal flush in a poker tournament. It may be chance, he said, but there is another explanation: "Namely, is the organizer of the tournament our friend?"
http://www.nytimes.com/2003/10/28/scien ... ed=2&8hpib