During the day I usually leave a Stack Overflow page open on one of my screens. While I'm working on another screen I can see whenever the question or an answer is voted on immediately, and I get message alerts whenever someone answers or replies to one of my posts immediately as well.
I was just wondering how this is accomplished without having to refresh the page. Is the browser constantly communicating with some server in the background? I really like this feature and want to know more about how it works.