How will the world end in the immediate future?
Slate has a both serious and fun look at this question, allowing users to suggest up to five of one hundred forty-four possible problems that could bring about the end of America and/or the world. These include alien invasion, a swine flu epidemic, and Vermont achieving independence, among many other options.
The application focuses primarily on the United States and its demise, but many problems you could throw into your chosen apocalypse would impact the entire world (e.g. asteroid collision).
What nightmare scenario do you choose?
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But overall, the experiment fails with the inclusion of 12/21/2012.