Have a great day today, listeners, because for many of you it will be your last — according to Harold Camping, a Californian radio preacher. He says the world will end tomorrow, May 21st. And his followers across the country are attempting to persuade unbelievers before it is too late. Harold Camping has predicted the end of the world before, and so have many others. Fortunately they haven't come true, so we have to ask, why do prophecy beliefs remain popular?

All this week, we've been talking with our friends from Scientific American about endings — how cultures fade, and natural resources dwindle. Today, we’re focusing on something even bigger: the end of human life as we know it — in other words, the apocalypse. The question of course, is how will it happen? Nuclear war? a killer virus, or perhaps an environmental disaster?