Harold Camping thinks the end of the world is on Saturday, May 21, 2011. He even pinned down the hour (6 p.m. local time).

Camping is as precise as he is confident - he said the Bible guarantees his prediction.

However, people have predicted the end times (and failed in their prediction) in the past. What happened when their predictions were invalidated by the world's continued existence?

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In 1992, Camping published a book that theorized the world would end in September 1994. However, back then, he only said there was a high possibility. When the world didn't end in September 1994, Camping simply said he made a calculation mistake.

In 2011, however, he doesn't have that luxury because he has painted himself into a corner with the certainty with which he declares the end date.

The Jehovah's Witnesses is another organization that predicted the end times. According to multiple sources, it predicted the end of the world in 1914, 1925, and 1975. The failures of their predictions, however, didn't seem to have hurt the organization in the long-term; today, it boasts at least 12 million members worldwide.

The Millerites believed the world would end on October 22, 1844. In anticipation, many of them sold their material possessions. When the world didn't end on October 22, 1844, many Millerites left the sect - some in dire financial straits.

Others predicted different end dates or claimed that the world fundamentally changed in an invisible way. Many people outside the Millerite community viciously mocked them for their failed prediction.

If Camping's prediction fails come May 22, 2011, some of his followers will be ruined financially - some of these people have already emptied their bank accounts to either indulge in luxury or buy advertising space for Camping's May 21 message.

Upon failure, Camping himself and some of his followers will likely claim an error in calculation. Others will bitterly leave his movement.

Meanwhile, the public and the media will look on with pity, amusement, and scorn.