I just read what the song is about and now the lyrics and video make a lot more sense. Killer song.
"The idea for the song came from a particularly chilling detail found at Hiroshima and Nagasaki; when the atomic bombs went off the shadows of people whose bodies were vaporized still remain burned onto the walls and the ground where they once stood. To me, this is goddamn horrifying. I thought- "What if the souls of those dead remain trapped in the shadows?"
The idea was to have the song written from a future where civilization has failed, the Earth is in ruins and the few remaining survivors live a horrible existence. The untold millions of shadows from this future, burnt into stone, look back at us in the present time and judge us for bringing about the apocalypse that, though we saw it coming, we did nothing to avoid."