Now that real-time Web has become an invaluable source for breaking news (think Miracle on the Hudson, or the Fort Hood Massacre), it is tempting to defer to the wisdom of Twittering crowds to find out what is happening now.
The problem is that social media is also the perfect venue to blow almost anything out of proportion.
Rumors flew that:
The Twittersphere was convinced something was wrong, but no major news organizations had reported anything on the incident and the MTA wasn't reporting any service delays around Grand Central.
With no news to source, bickering began over whether this was failure on the part of the news organizations, or yet another Twitter hoax. The only glimmer of evidence was a Tweet from 511 reporting police activity in Grand Central Station.
It wasn't until an hour after the initial Tweets that Tweeters saw any resolution -- Gothamist was able to confirm that Grand Central Station had been briefly evacuated after a "suspicious package incident" at 1:36 p.m. that was cleared by 2:11 p.m.
So something happened, but nothing that would rise to the level of being noted by even a local paper.
This happens regularly on Twitter -- a fake Twitter account announced the death of Cincinnati Bengals wide receiver Chris Henry hours before he passed and celebrity death hoaxes were all too common over the summer.
These Twitter "facts" get recycled the same as gossip: A critical mass of Twitter users happily retweet the unsourced rumor in the hopes that someone, somewhere, will follow up on it.
The problem comes when truth gets in the way of the narrative. While the initial information -- that the 4/5/6 had been rerouted -- was correct, the tweets that revealed everything was fine became buried beneath a flurry of panicked retweets. A twitpic revealing a peaceful Grand Central was knocked out of the real-time Web by misinformation.
Which makes social media a lot like other types of mass media: Once a story is set in a certain direction, it takes on a life of its own.