When

Originally a poem by Sharon Olds. Reads as:

"I wonder now only when it will happen, when the young mother will hear the noise like somebody's pressure cooker down the block, going off. She'll go out on the yard, holding her small daughter in her arms, and there, above the end of the street, in the air above the line of the tress, she will see it rising, lifting up over the horizon, the upper rim of the gold ball, large as a giant planet starting to lift up over ours. She will stand there in the yard holding her daughter, looking at it rise and grow and blossom and rise, and the child will open her arms to it, it will look so beautiful."

I imagine that's what is being read at the end of the song.

This is about the beauty of a nuclear bomb exploding, which is about to kill a watching family (and by extension) all life on earth.

Coow, yes, and it's interesting that he doesn't sing the first line of Old's poem. The most pessimistic word in the poem is the "only" in the first line, which implies that the bomb WILL go off for sure. By leaving that part out, the "WHEN" of the title also becomes a question about whether the bomb will go off, rather than the straightforward assertion of the poem that it WILL go off.

Slightly more ambiguous and open to possibility than the absolute miserableism of the Olds poem.