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2k.
2004-May-24, 11:02 PM
Hi there,

as you can see i'm new to these forums...

i have a (probably stupid) question....

it is the belief that there is no sound in space, which i accept but don't fully understand why not? i can almost get my head around that in the absence of air space is a vacuum. however where i have trouble is sound is transmitted as a wave, allbeit at a lower frequency than radio, now if radio signals can be sent and recieved why not sound? I am not in any way proficent with physics and i have only recently discovered my interest in astronomy so please be gentle :)

i have searched the forum but not had much success.

Sam5
2004-May-24, 11:17 PM
Hi there,

as you can see i'm new to these forums...

i have a (probably stupid) question....

it is the belief that there is no sound in space, which i accept but don't fully understand why not? i can almost get my head around that in the absence of air space is a vacuum. however where i have trouble is sound is transmitted as a wave, allbeit at a lower frequency than radio, now if radio signals can be sent and recieved why not sound? I am not in any way proficent with physics and i have only recently discovered my interest in astronomy so please be gentle :)

i have searched the forum but not had much success.



Sound and light are two different kinds of “waves”. Sound definitely needs a pre-existing “medium”, such as air, for it to be transmitted. A “wave” of sound is sort of like if you had a million ping pong balls lined up on a long table. If you hit one end of the balls, you would see the first ball hit the second one, then the second one would hit the third one, etc., etc. And you would see this motion as a very fast “wave” moving through the line of ping pong balls, even though each ball moves less than a single millimeter.

Sound is a traveling disturbance of the air that starts at a sound emitter. But, if we have a simple whistle in deep space, where there is no air, then, well, there can be no air blowing through the whistle and no disturbance in the air, since there is no air.

Light, on the other hand, is... well, we are still trying to figure that out. It has often been described as tiny little wiggling electric and magnetic fields that oscillate back and forth as they zip through space. Because of this, they are often thought of as being “self propagating”, thus not needing a pre-existing “medium” like air to travel through.

While both light and sound are called “waves”, they are not the same kind of waves. They have some similarities, but they have a lot of differences too.

siriusastronomer
2004-May-24, 11:19 PM
IIRC sound waves are longitudinal waves. They move through the air (or anything else) by pushing particles into one another (kinda like a domino effect thing) in space, there's nothing for them to push. light waves (radio waves) are traverse waves and therefore can travel through a vaccum because they don't need that tangible medium to pass through. sound waves and radio waves are differnt types of waves which is why one can travel through a vaccum and the other can't.

make sense? sometime's i'm really horrible at explaining things like this...

Quantum_Raider
2004-May-24, 11:24 PM
Hi 2k,

You should check some of the BA's movie reviews e.g. Review: Star Wars: Attack of the Clones (http://www.badastronomy.com/bad/movies/starwars_aotc_review.html)

He explains why sound doesn't travel in space plus alot of other "taken for granted" movie madness in easy to understand explanations.

Normandy6644
2004-May-24, 11:25 PM
IIRC sound waves are longitudinal waves. They move through the air (or anything else) by pushing particles into one another (kinda like a domino effect thing) in space, there's nothing for them to push. light waves (radio waves) are traverse waves and therefore can travel through a vaccum because they don't need that tangible medium to pass through. sound waves and radio waves are differnt types of waves which is why one can travel through a vaccum and the other can't.

make sense? sometime's i'm really horrible at explaining things like this...

I think it would be better to call light waves electromagnetic waves, as opposed to radio waves. As Sam5 mentioned, the standard picture of light is the oscillating electromagnetic fields. The reason there is no sound in space (or any vacuum) is that sound is just the vibration of the molecules in the air at a certain frequency, producing a "pitch." The molecules slam into one another until they slam into your eardrum, which vibrates at the same frequency.

If you take a physics class you will most likely see the demonstration of a bell ringing and then the air is sucked out by a vacuum, at which point you no longer hear the sound. You can probably find it online somewhere too...

George
2004-May-24, 11:31 PM
Certainly not a stupid question as the "aether" was established (for a while) to explain how light, being a wave, could travel.

To answer your question...when you throw a rock in the water, you see a "wave" move away from it. This is pressure in the water. Similarly, sound is made up of air "waves" that happen when air molecules are somehow pressuriezed such as when you clap your hands. These prssurized air molecules push on adjacent molecules which is how the wave travels and finally makes it to your ear. The more times a "wave" hits you in a second, the higher the pitch.

Space doesn't have molecules or anything similar to allow simple sound waves to travel. Sound abhors a vaccuum. :-?

Light, much to the surprise of scientists about 100 years ago, does not need anything but space itslef to travel. Light does not pressurize anything. It is a wave of electromagnetic properties and does not need to push or shove anything in front of it to advance itself.

BTW ... Welcome to the Board. :) =D>


[Edit: Gee. I started typing with 0 posts. Man I'm slow] :-?

2k.
2004-May-24, 11:41 PM
Thanks for the replys :)

it's all starting to make more sence now, if only i could have taken physics when i was at school (at the time the school i went to didn't have a seperate physics course) it would make my understanding of this easier. perhaps an evening class would help?

thanks also for the welcomes, i'm sure over the coming months i'll be asking more daft questions :roll:

Quantum_Raider
2004-May-24, 11:58 PM
thanks also for the welcomes, i'm sure over the coming months i'll be asking more daft questions :roll:

There is no such thing as a "daft question" only daft answers :D

Weird Dave
2004-May-25, 09:42 AM
IIRC sound waves are longitudinal waves. They move through the air (or anything else) by pushing particles into one another (kinda like a domino effect thing) in space, there's nothing for them to push. light waves (radio waves) are traverse waves and therefore can travel through a vaccum because they don't need that tangible medium to pass through. sound waves and radio waves are differnt types of waves which is why one can travel through a vaccum and the other can't.

make sense? sometime's i'm really horrible at explaining things like this...

Small clarification: light can travel through a vacuum because it is formed of electromagnetic fields, not because it is transverse. You can have transverse sound waves in solids (these happen in earthquakes, I believe), as well as the transverse waves and ripples on the surface of water. Neither of these could occur in space.

Just to confuse you, there can be sound in space (http://science.nasa.gov/headlines/y2003/09sep_blackholesounds.htm), caused here by a black hole. This is because space (especially in certain areas) is not quite a perfect vacuum. The few atoms it does contain are enough to carry pressure waves, but probably only at ultra-low frequencies and ultra-large amplitudes (volumes) (does anyone know this for sure?). Certainly, there is no way space can carry sound from a spaceship to a microphone, or anything like that.

iFire
2004-May-25, 12:30 PM
The way I understand it is that sound is a compression of air caused by disturbances that just anything creates. Radio waves are part of the EM spectrum which our visible light also belongs. (I often consider everyting in the EM spectrum a form of light, (a) because it sounds cool, and (b) I, uh, just do :P)

thefish7
2004-May-25, 03:13 PM
I've always had a question related to sound in space. I understand that sound needs a medium and that space is a near vacuum... The sticking point for me is that its a near vacuum... If you disturb the one very rare molecule hanging around in space and it happens to fly somewhere, quite unimpeded by other molecules until wham it happens to find another one, and transmits its kinetic energy to that new molecule and then the process repeats... Have you created sound, or anyway, a pressure wave?

George
2004-May-25, 03:48 PM
I've always had a question related to sound in space. I understand that sound needs a medium and that space is a near vacuum... The sticking point for me is that its a near vacuum... If you disturb the one very rare molecule hanging around in space and it happens to fly somewhere, quite unimpeded by other molecules until wham it happens to find another one, and transmits its kinetic energy to that new molecule and then the process repeats... Have you created sound, or anyway, a pressure wave?

I think "sound" must be heard which is a function of our ears. If the molecules can push the ones next to your ear drum hard enough and rapid enough, then it would sound like something. Your ear has limits of about 20 pulses per sec to about 20,000 puleses per sec. (or something close to that). A single pulse blast would probably cause a reverberation in the fluid of the inner ear that would also create a "sound".

George
2004-May-25, 03:59 PM
Oops. Sound does not have to be heard. It can be above or below our range of hearing and still be sound. Similar to light as it is not restricted to our visual range.

There are sounds we can not hear and light we can not see and things you are not suppose to touch (least, that's what Mom says). :)

Jason Thompson
2004-May-25, 04:06 PM
If you disturb the one very rare molecule hanging around in space and it happens to fly somewhere, quite unimpeded by other molecules until wham it happens to find another one, and transmits its kinetic energy to that new molecule and then the process repeats... Have you created sound, or anyway, a pressure wave?

http://news.bbc.co.uk/1/hi/sci/tech/3096776.stm

A black hole hums in B flat, apparently.

George
2004-May-25, 04:16 PM
If you disturb the one very rare molecule hanging around in space and it happens to fly somewhere, quite unimpeded by other molecules until wham it happens to find another one, and transmits its kinetic energy to that new molecule and then the process repeats... Have you created sound, or anyway, a pressure wave?

http://news.bbc.co.uk/1/hi/sci/tech/3096776.stm

A black hole hums in B flat, apparently.

Weird Dave, above, linked this also. However, I do not understand it. Is the black hole oscillating it's event horizon or something and creating pressure on incoming molecules which carry the energy out? Is the fabric of space getting jolts releasing energy along the way somehow?

There is a thread on this discovery around here somewhere but, as I recall, no one gave much of an answer.

Glom
2004-May-25, 05:46 PM
But light is really a particle.

milli360
2004-May-25, 05:51 PM
Small clarification: light can travel through a vacuum because it is formed of electromagnetic fields, not because it is transverse. You can have transverse sound waves in solids (these happen in earthquakes, I believe), as well as the transverse waves and ripples on the surface of water. Neither of these could occur in space.
I was thinking of the same examples, but I don't think that the transverse waves count as sound waves. Love waves (http://earthquake.usgs.gov/image_glossary/surface_wave.html) are tranverse (not, as some people think, perverse). Another example would be ripples in a rope as you wave one end.

George
2004-May-25, 06:56 PM
I was thinking of the same examples, but I don't think that the transverse waves count as sound waves.

I would think they would be sound waves as long as you turn your ear sideways. :)


Sound: An oscillation in pressure, stress, particle displacement, particle velocity, etc., in a medium with internal forces (e.g., elastic, viscous), or the superposition of such propagated oscillations.
2. A sensation evoked by the oscillation described above in the human ear.

I suppose any oscillating particle motion can be considered sound.

Laser Jock
2004-May-25, 07:39 PM
But light is really a particle.

No, light is light. It has properties we associate with particles and properties that we associate with waves. But light is what it is. That said, there's very few problems that can't be solved by just assuming light is a wave. Usually there is no need to quantize the E&M field at all.

But I don't think we want to turn this into a properties of photons thread. See my sig.

milli360
2004-May-26, 10:45 AM
I suppose any oscillating particle motion can be considered sound.
Sure, why not. :)

George
2004-May-26, 11:58 AM
I suppose any oscillating particle motion can be considered sound.
Sure, why not. :)

Yep. It sounded good to me. :P

milli360
2004-May-26, 01:31 PM
Sometimes it's hard to hear the forest for the trees.

Tensor
2004-May-26, 02:34 PM
Sometimes it's hard to hear the forest for the trees.

Only if the tree falls and there is no one around to see it.

sarongsong
2004-May-30, 11:35 PM
...A black hole hums in B flat, apparently---Jason Thompson The precise note Whoopi Goldberg sought in 'Jumpin' Jack Flash'.
"...silence is in the ear of the beholder, and ears come in a variety of configurations...As Delory said, "The most exciting sounds are likely to be ones that we don't even know about yet."
http://space.com/scienceastronomy/mystery_monday_030922.html

Lorentz
2004-Jul-18, 01:32 AM
[quote="2k."]Hi there,

as you can see i'm new to these forums...

i have a (probably stupid) question....

it is the belief that there is no sound in space, which i accept but don't fully understand why not?
[]


There is a cutoff to sound waves or compressional waves. A compressional wave can't be shorter than the mean free path of the atoms in the gas that propagates. By mean free path I mean the distance that one atom can move before it crashes into another atom. In between solar systems, the mean free path can be light years long. Inside the solar system, miles is more particular. Any compressional wave with a lshorter wavelength is highly attenuate and dissappears, and is not well defined anyway.

Try to draw a sound wave in a medium which has atoms further apart than the wavelength of the sound wave. You may run into difficulties.

Actually, there are compressional waves with wavelengths hundreds and thousands of light years long. The "arms" of a spiral galaxy are antinodes of compressional waves. So if you call any compressional wave a sound wave, there they are. But the microphone may be expensive.

Brady Yoon
2004-Jul-18, 06:54 PM
Does this mean we can't hear a supernova explosion or a spacecraft getting hit with an object, even if we are right next to them?