Do sound waves ever really disappear or does the amplitude approach 0 for infinity? If so, could sound be amplified to listen to the past?
Banned
Do sound waves ever really disappear or does the amplitude approach 0 for infinity? If so, could sound be amplified to listen to the past?
Order of Kilopi
Nope, it couldn't Essentially, within a short time after they are emitted, sound waves become far too jumbled and muted to get any information from them.
Order of Kilopi
If the sounds didn't disappear completely, the air would forever get
noisier and noisier, louder and louder. The sound energy mostly turns
into heat, which then then mostly turns into infrared radiation and
escapes into space. What can be heard with a good set of ears is
pretty much what is there. So, if you can't hear it, the sound is
gone.
-- Jeff, in Minneapolis
http://www.FreeMars.org/jeff/
"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"
"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves
Established Member
Well, if I can move into full on sci-fi mode for a moment, what about this one scenario I saw on an X-Files episode:
They took a 2000 year old clay pot and "read" it with a laser in a similar manner that a record player needle "reads" the surface of a vinyl record. The idea proposed in that episode was that, just like the grooves in the record are made by a needle vibrating with the sound of the original music, then the clay pot should have similarly "recorded" the sound of the room it was in as it was made, including the words that were said by anyone present.
Is this theoretically sound and just technologically not feasible, or is it altogether theoretically impossible?
Order of Kilopi
The latter. As Jeff Root explained, at some point any signal degrades into what is known as "noise", and there is no more information carried by it. Reading a clay pot would produce nothing but noise, for talking to a pot will do nothing but make the pot a tiny bit warmer. No technology, no matter how advanced, can "undo" thermodynamics.
Established Member
Well, don't vinyl records and their predecessors work by having a sound vibrate a needle that etches corresponding crooves into a material, and these grooves can later be read by a similar needle?
I suppose the lack of a focusing instrument like a needle is what would make the clay pot consist only of noise.
Order of Kilopi
They actually did the same thing on CSI once. The part that was left out of the description here was that the pot was being spun on a wheel with a brush being applied to texture th outside. The sound vibrations were transferred to the furrows in the outside of the pot, and "read" later. I'm also pretty sure that I first saw this idea on a Discovery Channel show, but I can't recall which one, and it may well have had woo-ish leanings.
I'm Not Evil.
An evil person would do the things that pop into my head.
Established Member
CSI might have gotten it from The X-Files, but in The X-Files, it was presented as something abnormal that only applied to that bowl because of what was going on in the room at the time being magical or paranormal.
It was called the Lazarus Bowl, because its legend said that it had picked up the energy in the room when Jesus was bringing Lazarus back to life. It would bestow magical properties of some kind onto someone who ate or drank from it. When someone discovered texture on it like vinyl record grooves or something like that and scanned it to try to play back sound, and managed to filter out junk noise, what they got was the sound of a man telling someone to rise and walk in Aramaic... followed by "I am the walrus, I am the walrus, Paul is dead, koo-koo-kachoo... except that there is no Aramaic word for 'walrus' so what it really says is 'I am the bearded cow-like sea beast'..."
In other words, even in The X-Files, it was not only a legend of a miracle instead of a normal effect of pottery, but also turned out to be a hoax.
(Why would someone be potting at a time like that, anyway?)
Order of Kilopi
In the spirit of the OP, the sound is gone (or there is no sound in a record). The needle doesn't pick up sound, it creates a vibration based on movement from the groove which is then translated into new sound.Originally Posted by BISMARCK
[quote=_Tog]..I'm also pretty sure that I first saw this idea on a Discovery Channel show, but I can't recall which one, and it may well have had woo-ish leanings.[/url]
I've seen many references... but the Mythbusters did actually give it a try.
Established Member
This is an intriguing notion, and I have experienced it.
Back in 1987 while working at an auto-parts store, part of my job was to turn rotors and drums (resurface them).
We had to put a "chatter" belt on them to keep sound waves from being "recorded" on to the surface.
You would be amazed at some of the sounds you could hear while turning a rotor or drum without the chatter belt.
I had one that you could actually hear traffic on, where a bit of sand had lodged itself between the brake and the rotor and recorded short bursts of car horns and road sounds.
But that's a mechanical issue, and is just repeating an analogue recording.
Sound doesn't record to a wall when you talk unless it is mechanically put there.
Order of Kilopi
They actually tried the bowl experiment on Mythbusters in episode 62. It was ruled busted.
Established Member
Sounds don't last forever.
Not becuase they decay into 'noise' (what is noise but sound?).
But because they decay into heat, by doing work on gas and solids, and by contributing to the Brownian motion - the heat - of gases.
Increasing the entropy of the Universe.
As do all organised, low entropy functions.
John
Established Member
Sounds quickly become "unrecoverable" by any known means, but the universe never forgets. The impact of a sound made or a word uttered is never entirely lost
Established Member
If a man speaks in a forest and there is no woman to hear him...
is he still wrong?
Established Member
If a man speaks in a forest and there is no woman to hear him...
is he still wrong?
He was wrong before he spoke. (Just ask a woman.)
Banned
Even if he hadn't spoken, he'd still have been wrong. Aren't we always wrong?
Order of Kilopi
What you mean by heat is just noise with zero correlation length.
Order of Kilopi
This story was based on a theory developed by a guy in England who said that the wood or metal stylus that etched a grove around old clay pots acted as a recording needle and vibrated enough to cause the grooves in old pots to contain wiggles due to sounds in the room where the pots were made. However, his opponents said that just the scraping of the pot by the stylus would generate sound and all that could have been recorded was the scraping sound of the stylus on the pot.
It would have been possible for the ancients to record sound onto a pot, but they would have needed to use a physical amplification method with the stylus, such as having it attached to a large metal disk which could have acted like a mechanical microphone.
Order of Kilopi
The idea about the groove in the clay pots was first reported on Arthur C. Clarke's Mysterious World TV show back in the 1980s. He briefly discussed people who had theorized how some of the ancients could have accidentally recorded sound.
Some ghost chasers in England proposed that walls could have recorded sounds of the past, but they never proposed any physical mechanism that could have actually produced such a recording.
Certainly, walls would vibrate a little when people talk inside a room, but there is no known way where they could record the sound.
The first known sound recordings were produced in the 1850s by etching vibration waves onto smoked glass, as the glass was moved slowly passed a stylus. The stylus was something like a boar’s bristle attached to the center of a metal disk which acted like a microphone. These recordings could not be played back. They were used only so the scientists could visualize sound waves. Edison studied these early recordings and later invented a method to make them more permanent and in a way where they could be played back. His late 1870s mechanical microphone was essentially of the same kind that had been invented in the 1850s.
Order of Kilopi
It’s more than just a needle. The needle vibrations need to be greatly amplified. Just a needle alone won’t vibrate very much. But a needle with one end attacked to a metal disk, about the size of a tin can lid, with a certain type of mechanical link, such as the disk, a thin metal arm attacked to the center of the disk with the other end of the arm attached to one end of a needle, then that will cause the point of the needle to vibrate much more when it cuts the groove. This is how the first recordings were made, with this type of mechanical microphone.
So a stylus alone doesn’t vibrate enough to be able to record sound onto a clay pot. The free end of the stylus must be attached to some large hard metal membrane so that the point of the stylus will be vibrating when it touches the pot.
Established Member
Ah ok. I see. Well, I suppose that people 2000 years ago had sufficient materials to record sound into a pot, but that's it.
Order of Kilopi
Right. The question is, did some ancient Egyptian scientist actually figure out a way to do it and are there any old 5,000 year old clay recordings that haven't yet been discovered.
Order of Kilopi
And to make matters worse, the free end of the stylus would have been dampened by the person's hand.
Order of Kilopi
Right, he would have been holding the important vibrating and etching end of the "needle".
Order of Kilopi
Here is a method of recording some sound onto photographic film as shown in Tyndall's book from 1867:
http://www.uh.edu/engines/tuningfk.gif
Posting Permissions
Reply With Quote