MadSci Network: Astronomy
Query:

Re: Why doesn't sound travel in outerspace?

Date: Sun Mar 6 19:58:15 2005
Posted By: Phillip Henry, Staff, Physics, Lockheed Martin & Florida Tech
Area of science: Astronomy
ID: 1109834906.As
Message:

Thank you for your question. While it is true that there are molecules in 
space, the distance between them is enormous. Sound is a pressure wave 
through a medium. We are most acquanted with audible sounds, transmitted 
through the air. Here on earth, there are billions times billions of 
molecules per cubic foot. But in space, its more like a few molecules per 
cubic foot. But one can still have a pressure wave form and propogate 
through that medium - but the intensity of that pressure wave is 
exceedingly small and the wavelengths exceedingly long, usually 
undetectable. But we have made observations of at least one "sound" in 
space. http://www.space.com/scienceastronomy/blackhole_note_030909.html
The notes from this humming black hole are far below any audible tone, 
but it does represent a pressure wave in space. Now also please note, 
this black hole is in a region of space with higher than normal gas 
density than much of space.

So to return to your question, you are correct in that sound can travel 
in space, but in general the density of the molecules in space are so 
very thin - one would need an exceedingly sensitive instrument to detect 
it. To borrow a line from a famous movie trailer, in space no one can 
hear you scream.


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