Questions about Sound in Space

POSTED BY: BlueBomber
UPDATED: Tuesday, November 30, 2021 06:47
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PERFESSERGEE

Friday, June 10, 2005 12:16 AM

Well folks, we appear to have forgotten the other half of the sound/EM "wave" dichotomy: sound waves require a medium because they are actually pressure waves that involve compression and decompression of molecules in space (not "outer space", just space). The medium can be pretty much anything - air, water, the Earth, etc. "Outer space" isn't really a true vacuum, it just doesn't have a high enough density of molecules for compression waves to propagate. As to whether EM radiation is a wave, a particle, or both at the same time remains to be seen.

2 cents worth from an academic.

perfessergee

BIKISDAD

Friday, June 10, 2005 1:23 AM

As I remember it (from a long time ago), "outer space" was thought to contain about one hydrogen atom per cubic meter - or really close to a complete vacuum - which is why sound doesn't propogate. The probability that each hydrogen atom in a cubic meter will bump into the one in the next cubic meter (and thereby propogate sound waves) is so statistically insignificant as to be infinite(ly small).

If someone has an update on the one hydrogen per cubic meter figure, that would be great. There's probably been a lot more study on the subject since I learned that.

Apathy on the Rise. No One Cares.

FINN MAC CUMHAL

Friday, June 10, 2005 4:33 AM

Quote:
Originally posted by bikisdad:
If someone has an update on the one hydrogen per cubic meter figure, that would be great. There's probably been a lot more study on the subject since I learned that.

It sounds a little low to me. I think the density of interstellar hydrogen is more on the order of a million Hydrogen per cubic meter.

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Qui desiderat pacem praeparet bellum.

BIKISDAD

Friday, June 10, 2005 5:24 AM

I suppose it would really depend on where you took the measurement. If it's taken within a solar system, such as ours, there would probably be at least as much hydrogen as you mentioned (probably more), and probably a lot of other trace elements, as well.

If you took it within the galaxy, but far between solar systems, it would be significantly lower, probably no trace elements, but still a lot of hydrogen.

Lowest of all would be a measurement taken in inter-galactic space - millions of light years away from any galaxy. That really represents the majority of the volume of the universe and that's where I think the density of hydrogen would be very, very low. I don't think it could be as high as a million per cubic meter, or you would have star formation occuring all over the universe, rather than just within concentrated areas like galaxies.

However, when you say inter-stellar space, as in between stars within a galaxy, that makes a lot of sense because there is star formation going on within galaxies all the time. So a density of a million per cubic meter makes a lot of sense.

I was really looking for the density in inter-galactic space, rather than inter-stellar space within a galaxy.

Apathy on the Rise. No One Cares.

PERFESSERGEE

Friday, June 10, 2005 8:49 AM

Mea culpa! It occurs to me that while we've discussed sound vs. EM transmission on this thread, we've perhaps missed the point of the original question. The reason that there is no sound in space is that human ears (and the "ears" of every other species on this particular beautiful planet) respond to compression waves. Where compression waves can't propagate we can't hear them. We terrestrial organisms respond to "sound" in a variety of ways (think of your reaction to your favorite form of music as opposed to a firetruck siren). We also respond to EM radiation in a variety of interesting ways, but that's a different matter.

perfessergee

GROUNDED

Friday, June 10, 2005 10:33 AM

Quote:
Originally posted by Finn mac Cumhal:
Yep.

Care to elaborate?

FINN MAC CUMHAL

Friday, June 10, 2005 1:06 PM

Quote:
Originally posted by Grounded:
Care to elaborate?

Not really. I’m not sure it is useful to get into speculation on Relativity and Quantum foam theories. The luminiferous ether was dismissed because the scientific community preferred Relativity. In the end, however, both are still theories.

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Qui desiderat pacem praeparet bellum.

FINN MAC CUMHAL

Friday, June 10, 2005 1:19 PM

Quote:
Originally posted by bikisdad:
I was really looking for the density in inter-galactic space, rather than inter-stellar space within a galaxy.

Okay, if you’re talking about empty space between galaxies then 1 hydrogen per cubic meter is probably a good estimate.

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Qui desiderat pacem praeparet bellum.

BIKISDAD

Friday, June 10, 2005 1:23 PM

The persistent use of the term "Theory" to describe the laws of physics is unfortunate. Some theories are, indeed, proven facts, whereas others are disproven hypotheses. It would be mucho helpful if the scientific community would come up with a nomenclature for differentiating between the two so that people wouldn't constantly lump them into the same bin.

Apathy on the Rise. No One Cares.

GROUNDED

Friday, June 10, 2005 3:20 PM

Quote:
Originally posted by Finn mac Cumhal:
Quote:
Originally posted by Grounded:
Care to elaborate?
Not really. I’m not sure it is useful to get into speculation on Relativity and Quantum foam theories. The luminiferous ether was dismissed because the scientific community preferred Relativity. In the end, however, both are still theories.

There are good reasons to believe the ether doesn't exist:

http://en.wikipedia.org/wiki/Michelson-Morley_experiment

Don't tease people with lines like: "And we shouldn’t be too quick to dismiss the “ether” theory either." if you don't want to discuss them. This is a message board - it's primary purpose is for discussion!

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