4 ms·

Does a sound ever stop?

by TekMol 8y ago

zaarn 8y ago
Yes, once it's kinetic energy drops below that of the average air molecule, it'll become imperceptible to instruments; lost in the noise, or rather, becoming part of the noise.
- jacquesm 8y ago
  Interesting. Besides 'Brownian' noise you are probably correct that whatever noise remains is to some extent the result of a lot of stuff that happened in the past that is too small now in influence to be identified. I never looked at it that way, thank you.
  - Pyxl101 8y ago
    Specifically, the energy that is sound will gradually dissipate into energy that is heat. Brownian motion happens on the microscopic level; we perceive it on the macroscopic level as temperature. Temperature is essentially the combined, average kinetic energy of Brownian motion. Most types of energy gradually turn into heat, including light, macroscopic kinetic energy, released gravitational potential energy, etc. If you catch a baseball, the kinetic energy of the baseball turns into heat within your muscles (and skin, in the form of friction between the ball and your hands). If you walk down stairs, the gravitational potential energy that you're releasing turns into heat as well, as friction in your joints. Light shining on your skin turns into heat and warms it, as on a bright and sunny day. The electrical energy of a computer converts largely into heat, hence the need for cooling. There are also theories that all matter may eventually decay, including all atoms and eventually even protons after 10^34 years (though proton decay has not yet been experimentally observed). https://en.wikipedia.org/wiki/Proton_decay https://en.wikipedia.org/wiki/Proton_decay As someone on Quora wrote, "Heat is energy's final grave". The concept of "heat death of the universe" derives from the idea that, eventually, most forms of energy will decay into heat.
    - garmaine 8y ago
      Heat (motion of molecules) is noise (motion of molecules) in this context.
      - deleted 8y ago
        [deleted]
- TekMol 8y ago
  Just because an instrument cannot hear it, does that really mean it does not exist anymore?
  - zaarn 8y ago
    There is no evidence remaining that the sound exists. It would be like trying to detect an energy below the noise floor of vacuum energy; there is no proof that you can construct that it exists. Once it's part of the background noise floor, it effectively seizes to exist.
    - TekMol 8y ago
      Well, you just repeated the argument that when we cannot measure it anymore it does not exist anymore. But my question is: Is that true? Why? We also cannot measure stuff outside of the observable universe. Yet we do not say nothing exists beyond the observable universe.
      - zaarn 8y ago
        Because there is no reasonable way to possibly prove the sound still exists. To find out if something beyond the observable universe exists, you simply wait for the light to reach you. Every minute your observable universe grows larger and you see more stuff, the obvious conclusion is that there is more stuff. But the random movements of air molecules allow for no analysis that there is a quantum of a sound traveling through it. It cannot be reasonably proven that the sound still exists. You can't wait to see if you notice more random sounds or anything, it's gone, part of the background noise. The information in the sound has been destroyed for any way to measure it via the movements of air molecules.
        TekMol 8y ago
        You cannot wait for light from beyond the observable universe. That is the definition of the observable universe. The universe is expanding. The further away something is from us, the faster it is moving away from us. The part outside of the observable universe is so far away, that it is moving away from us at a speed faster then light. So we will never know anything about it.
matthewowen 8y ago
Yes. As the waves propagate their amplitude generally decreases. Imagine dropping a rock in a pond, and picture how the wave worked around it drops as it expands. There's both diffusion of the force over a wider area and there's some inertia in the materials that the wave has to overcome.
- TekMol 8y ago
  Constant decrease does not imply ever hitting 0.
- hanoz 8y ago
  However, truly the pond will never be the same again. Nor, chaos theory tells us, will the world. In time, across the globe, countless lives will be lived and lost which never would have been lived and lost had the rock not been dropped in that pond.
prmph 8y ago
Is information ever lost? Not a rhetorical question, I genuinely want to know. Once the vibration due to a sound become smaller than a certain level, do quantum effects make it disappear entirely
- kurthr 8y ago
  Not just quantum effects (although they can dominate especially at low temperatures or superfluid/conducting states), but thermodynamic effects. Once the energy falls below ~kT/2 in a dissipative system (quadratic hamiltonian terms) you've lost the information.
- TekMol 8y ago
  I find that hard to imagine. Let's take the information 'The universe exists'. How can that information get lost? Wouldn't the universe have to disappear for that to happen? I have never heard about a model of reality where that is a possibility.
  - gbear605 8y ago
    I think by information they mean more concrete things. For instance, imagine a bird landing on a branch. If someone is around to see it, they know that if happened. If no one is around though, once the bird flies away and the branch stops shaking, the information that a bird had landed on the branch is gone.
- archgoon 8y ago
  > Is information ever lost? From a practical perspective, yes; but I get the feeling you're not asking that ;). Let's say that we know everything possible about the universe at a time t (in some reference frame). Can I reconstruct what happened at any time in the past? If I can, then it seems reasonable to say that 'no information has been lost' (going the other way suggests that no information gets created either). A lot of Physicists seem to think the answer is yes, we can construct the past if we actually knew everything. The evolution of the wavefunction is unitary, so you should be able to run the universe backwards to find out what happened (unless wavefunction collapse is real, in which case, we're losing information all the time). Note that in order to do this, you need to know the entire wave function; which isn't measurable. However, under our current understanding of black holes, the answer seems to be "Looks like it?" https://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox Since we don't know how to resolve General Relativity with Quantum Mechanics, we can't really say with confidence whether the universe can 'be played backwards' or not.

Does a sound ever stop?

by TekMol 8y ago

Does a sound ever stop?

Yes, once it's kinetic energy drops below that of the average air molecule, it'll become imperceptible to instruments; lost in the noise, or rather, becoming part of the noise.

jacquesm 8y ago
Interesting. Besides 'Brownian' noise you are probably correct that whatever noise remains is to some extent the result of a lot of stuff that happened in the past that is too small now in influence to be identified. I never looked at it that way, thank you.
- Pyxl101 8y ago
  Specifically, the energy that is sound will gradually dissipate into energy that is heat. Brownian motion happens on the microscopic level; we perceive it on the macroscopic level as temperature. Temperature is essentially the combined, average kinetic energy of Brownian motion. Most types of energy gradually turn into heat, including light, macroscopic kinetic energy, released gravitational potential energy, etc. If you catch a baseball, the kinetic energy of the baseball turns into heat within your muscles (and skin, in the form of friction between the ball and your hands). If you walk down stairs, the gravitational potential energy that you're releasing turns into heat as well, as friction in your joints. Light shining on your skin turns into heat and warms it, as on a bright and sunny day. The electrical energy of a computer converts largely into heat, hence the need for cooling. There are also theories that all matter may eventually decay, including all atoms and eventually even protons after 10^34 years (though proton decay has not yet been experimentally observed). https://en.wikipedia.org/wiki/Proton_decay https://en.wikipedia.org/wiki/Proton_decay As someone on Quora wrote, "Heat is energy's final grave". The concept of "heat death of the universe" derives from the idea that, eventually, most forms of energy will decay into heat.
  - garmaine 8y ago
    Heat (motion of molecules) is noise (motion of molecules) in this context.
    - deleted 8y ago
      [deleted]
TekMol 8y ago
Just because an instrument cannot hear it, does that really mean it does not exist anymore?
- zaarn 8y ago
  There is no evidence remaining that the sound exists. It would be like trying to detect an energy below the noise floor of vacuum energy; there is no proof that you can construct that it exists. Once it's part of the background noise floor, it effectively seizes to exist.
  - TekMol 8y ago
    Well, you just repeated the argument that when we cannot measure it anymore it does not exist anymore. But my question is: Is that true? Why? We also cannot measure stuff outside of the observable universe. Yet we do not say nothing exists beyond the observable universe.
    - zaarn 8y ago
      Because there is no reasonable way to possibly prove the sound still exists. To find out if something beyond the observable universe exists, you simply wait for the light to reach you. Every minute your observable universe grows larger and you see more stuff, the obvious conclusion is that there is more stuff. But the random movements of air molecules allow for no analysis that there is a quantum of a sound traveling through it. It cannot be reasonably proven that the sound still exists. You can't wait to see if you notice more random sounds or anything, it's gone, part of the background noise. The information in the sound has been destroyed for any way to measure it via the movements of air molecules.
      - TekMol 8y ago
        You cannot wait for light from beyond the observable universe. That is the definition of the observable universe. The universe is expanding. The further away something is from us, the faster it is moving away from us. The part outside of the observable universe is so far away, that it is moving away from us at a speed faster then light. So we will never know anything about it.

matthewowen 8y ago

Yes. As the waves propagate their amplitude generally decreases. Imagine dropping a rock in a pond, and picture how the wave worked around it drops as it expands. There's both diffusion of the force over a wider area and there's some inertia in the materials that the wave has to overcome.

TekMol 8y ago
Constant decrease does not imply ever hitting 0.
hanoz 8y ago
However, truly the pond will never be the same again. Nor, chaos theory tells us, will the world. In time, across the globe, countless lives will be lived and lost which never would have been lived and lost had the rock not been dropped in that pond.

prmph 8y ago

Is information ever lost? Not a rhetorical question, I genuinely want to know. Once the vibration due to a sound become smaller than a certain level, do quantum effects make it disappear entirely

kurthr 8y ago
Not just quantum effects (although they can dominate especially at low temperatures or superfluid/conducting states), but thermodynamic effects. Once the energy falls below ~kT/2 in a dissipative system (quadratic hamiltonian terms) you've lost the information.
TekMol 8y ago
I find that hard to imagine. Let's take the information 'The universe exists'. How can that information get lost? Wouldn't the universe have to disappear for that to happen? I have never heard about a model of reality where that is a possibility.
- gbear605 8y ago
  I think by information they mean more concrete things. For instance, imagine a bird landing on a branch. If someone is around to see it, they know that if happened. If no one is around though, once the bird flies away and the branch stops shaking, the information that a bird had landed on the branch is gone.
archgoon 8y ago
> Is information ever lost? From a practical perspective, yes; but I get the feeling you're not asking that ;). Let's say that we know everything possible about the universe at a time t (in some reference frame). Can I reconstruct what happened at any time in the past? If I can, then it seems reasonable to say that 'no information has been lost' (going the other way suggests that no information gets created either). A lot of Physicists seem to think the answer is yes, we can construct the past if we actually knew everything. The evolution of the wavefunction is unitary, so you should be able to run the universe backwards to find out what happened (unless wavefunction collapse is real, in which case, we're losing information all the time). Note that in order to do this, you need to know the entire wave function; which isn't measurable. However, under our current understanding of black holes, the answer seems to be "Looks like it?" https://en.wikipedia.org/wiki/Black_hole_information_paradox https://en.wikipedia.org/wiki/Black_hole_information_paradox Since we don't know how to resolve General Relativity with Quantum Mechanics, we can't really say with confidence whether the universe can 'be played backwards' or not.