According to researchers from the Harvard Medical School and the University of California, San Diego, happiness spreads through their social networks like an emotional contagion. The study shows that the chances of friends living within a mile of participants who were happy were 25% higher, and that the chances of their friends and even the friends of those friends also have an increase in their chances of happiness even if they did not know the participant at all.
They found that sadness exhibit the same quality, but that it does not spread as efficiently as happiness. Apparently the famous saying that says: "Laugh and the world laughs with you, weep and you weep alone" is true! If you would like to read the full article you can find it here.