Suppose human civilization collapses one day. That's not such a zany notion—lots of past civilizations have collapsed. Maybe there's nuclear war, or giraffe flu, or maybe the Yellowstone supervolcano finally heaves and spews. It's a fat disaster for awhile, but eventually things settle down. New civilizations form, people figure out electricity, and so forth. (Actually, as Kurt Cobb argues, it might not be possible to start an industrial society from scratch a second time 'round, since we've already used up most of the easiest-to-access ores and fuels. But ignore that.)

Anyway, the question: Would historians of the future be able to examine our hard drives and servers and study what twenty-first-century folks got up to? (Surely all the best info on what caused the apocalypse will be in digital form.) How much of our data would still be intact? Apparently, no one really knows for sure:

Hard drives were never intended for long-term storage, so they have not been subjected to the kind of tests used to estimate the lifetimes of formats like CDs. No one can be sure how long they will last. Kevin Murrell, a trustee of the UK's national museum of computing, recently switched on a 456 megabyte hard drive that had been powered down since the early 1980s. "We had no problems getting the data off at all," he says.

Modern drives might not fare so well, though. The storage density on hard drives is now over 200 gigabits per square inch and still climbing fast. While today's drives have sophisticated systems for compensating for the failure of small sectors, in general the more bits of data you cram into a material, the more you lose if part of it becomes degraded or damaged. What's more, a decay process that would leave a large-scale bit of data readable could destroy some smaller-scale bits. "The jury is still out on modern discs. We won't know for another 20 years," says Murrell.

Most important data is backed up on formats such as magnetic tape or optical discs. Unfortunately, many of those formats cannot be trusted to last even five years, says Joe Iraci, who studies the reliability of digital media at the Canadian Conservation Institute in Ottawa, Ontario.

Actually, though, we don't even need to consider the apocalypse. The fragile state of digital storage is already causing trouble. NASA has a few people racing to recover old images from its Lunar Orbiter missions in the 1960s, which are currently stored on magnetic tapes and may not be long for this world. And the National Archives is struggling to preserve its digital records, which tend to rot faster than paper records.

A related tale of disintegrating media comes from Larry Lessig's Free Culture—though this one has a twist. There are a lot of films that were made after 1923 that have no commercial value anymore. They never made it to video or DVD; the reels are just collecting dust in vaults somewhere. In theory, it shouldn’t be too hard to digitize these films and put them in an archive. But alas, thanks to the Sonny Bono Copyright Term Extension Act that was passed by Congress in 1998, any film made after 1923 won't enter the public domain until at least 2019.

That means these films are still under copyright, and anyone who wanted to restore them would have to track down the copyright-holders (not always easy to do) and probably hire a lawyer. And who's going to go through that much trouble just to restore some obscure movie that only a few people might ever watch? Yet a lot of these older movies were produced on nitrate-based stock, and they'll have dissolved by the time 2019 rolls around, leaving nothing behind but canisters of dust. It's sort of tragic.

On the cheery side, post-apocalyptic historians will presumably have less trouble snagging copies of Avatar and Titanic—that's the sort of digital media most likely to survive, if only because there are so many copies lying around. So James Cameron will be our Aeschylus, huh?