A friend wrote to ask: Will we ever be able to “to record (and playback) sounds and voices that were uttered hundreds (or thousands) of years ago?”
After all, we find life forms in amber, captured as in a sort of video still…
Experimental physicist Rob Sheldon says that, if we look carefully at the nature of sound, we will be able to see why we probably can’t somehow capture sound waves still reechoing in the world:
1) You asked if the energy of the sound could reflect or reverberate for a while. One can imagine a steel box that admits a loud sound and then hermetically seals the door. How long would the sound reverberate in the box? About as long as the diffusion rate in a gas. Yes, it would last longer than a travelling wave, but even a standing wave (think of a jump rope held on the ends), will eventually decay away as the organized motion of the gas turns into disorganized thermal energy. After a second or two, the gas in the steel box would be quiet and slightly warmer than it was before as the energy in the sound became thermal energy. But there would be no sound.
2) There is no sound in space, because there isn’t (hardly) any air. TIE fighters cannot be heard. An atomic bomb creates an expanding shell of plasma that, in the case of the largest atomic explosion in history, the Czar Bomba 50-100MTon explosion, the expanding blast wave was 30 km in diameter. If it had been in a vacuum, presumably the shell would be still expanding out past Pluto. When stars go supernova, we can see the shell of expanding gas for centuries–the Crab Nebula has been expanding since 1054AD.
3) Sound stops travelling long before the dilution of the gas reaches an absolute vacuum. The Moon’s atmosphere is about 1 million atoms per cubic centimeter, but still it isn’t enough to create a sound. Think of traffic as a moving fluid. When its 2am, a car that stops on the road doesn’t cause a traffic jam. But at 5pm, even driving 20 mph below the speed limit causes a traffic jam behind the vehicle. Likewise a sound wave is like the traffic jam on the highway that propagates backwards down the interstate. When there aren’t enough cars, there is no traffic jam, and no sound wave travelling backwards down the highway.
So it feels like: No
Rob Sheldon is the author of Genesis: The Long Ascent and The Long Ascent, Volume II .