A temporal signature

It’s stuff like this that makes me feel like we’re living in the future.

You can’t usually hear it with your own ears, but the electrical grid hums at a frequency around 50Hz, with minute fluctuations here and there. Any audio recording made within earshot of a wall outlet or a lightbulb can pick it up, however minutely – ask any audio engineer to hear a lament about this.

It turns out that for the past seven years, at a forensic lab in south London, the Metropolitan Police have been continuously recording of this hum and its fluctuations. Why? So they can determine with absolute certainty whether an audio recording has been edited.

If an audio recording made in London during the past seven years is intact (and if it wasn’t taken in the wilderness, away from electrical mains), the police will be able to match up the fluctuations in its electrical hum with the ones they recorded on a particular date and time, precisely indicating when the recording was made. And if the hum doesn’t sync up exactly with the police’s version, it’s a sure bet that someone has tampered with it.

If life were like it is on Star Trek: The Next Generation, I think they’d be calling this a “temporal signature.”