Google's algorithm has always relied on crawling the web and storing cached versions of pages in its index as it goes along. Unfortunately, this technique doesn't work so well when it comes to searching tweets and facebook posts, where there's the constant need for up-to-the-second relevance. In fact, Google even admitted that twitter was better at real time search than they were. Now they're trying to step up their game because they can't let someone else beat them at search!
When you are searching something in Google then your are getting something from Google at that time right? Google doesn't hold you on the queue, so that's the real time search. I think like this way, because I don't care about it anymore as this project of Google was shut down in 2011.