Does sound travel faster or slower in space?

It is often said that sound doesn’t travel in space. And it is true… in empty space. Sound is pressure waves, that is, propagating changes in pressure. In the absence of pressure, there can be no pressure waves, so there is no sound.

But space is not completely empty and not completely devoid of pressure. Hence, it carries sound. But not in a manner that would match our everyday experience.

For instance, if you were to put a speaker in interstellar space, its membrane may be moving back and forth, but it would be exceedingly rare for it to hit even a single atom or molecule. Hence, it would fail to transfer any noticeable sound energy to the thin interstellar medium. Even the somewhat denser interplanetary medium is too rarefied for sound to transfer efficiently from human scale objects; this is why astronauts cannot yell to each other during spacewalks. And just as it is impossible to transfer normal sound energy to this medium, it will also not transmit it efficiently, since its atoms and molecules are too far apart, and they just don’t bounce into each other that often. Any “normal” sound is attenuated to nothingness.

However, if you were to make your speaker a million times bigger, and let its membrane move a million times more slowly, it would be able to transfer sound energy more efficiently even to that thin medium. And that energy would propagate in the form of (tiny) changes in the (already very tiny) pressure of the interstellar medium, i.e., it would be sound.

So yes, sound can travel in the intergalactic, interstellar, interplanetary medium, and very, very low frequency sound (many octaves below anything you could possibly hear) plays an important role in the formation of structures (galaxies, solar systems). In fact, this is the mechanism through which a contracting cloud of gas can shed its excess kinetic energy and turn into something compact, such as a star.

How fast such sounds travel, you ask? Why, there is no set speed. The general rule is that for a so-called perfect fluid (a medium that is characterized by its density and pressure, but has no viscosity or stresses) the square of the speed of sound is the ratio of the medium’s pressure to its energy density. The speed of sound, therefore, can be anything between 0 (for a pressureless medium, which does not carry sound) to the speed of light divided by the square root of three (for a very hot, so-called ultrarelativistic gas).

This information was taken from Quora. Click here to view the original post.

Do you know more about the speed of sound now?

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What are your thoughts on this subject?
Linda Salter
I do not know anymore than I knew before I read the article. It did not make the concept any clearer than it was before I read the article.
Dec 5, 2018 5:58PM
Ilias Tsiabardas
It's good to know few things about sound travel in space and much more ,thanks for sharing
Jan 16, 2020 7:45PM
Don Racette
Leonard Dixon What they said all SOUNDS reasonable to me.
Jun 1, 2019 5:49PM
David Holmes
seamus512, Radio signals travel perfectly well in space just as light travels in space.
Apr 6, 2019 4:41PM
So if sound doesn't travel through space what are all those radar dishes listening to pointed towards space?
Mar 10, 2019 5:03PM
WOW! I did not know that. Thank you for educating us.
Feb 14, 2019 12:14AM
Humberto Carrasco
Dec 6, 2018 5:14PM
Michael Johnston
So do I build a big speaker or what?
Dec 6, 2018 2:38AM

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