## Thursday, 4 December 2008

### No Matter - No Sound

Light travels through a vacuum. Sound does not travel through a vacuum. A vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. Sound is the vibration of molecules, and since there is nothing in a vacuum , there are no molecules to vibrate. Therefore sound is the vibration of matter - without matter there could be no such thing as a sound wave. A sound wave can be described as a disturbance that travels through a medium, transporting energy from one location to another location. Sound is an inherent property of matter, and perhaps we could also say, that matter is a property of sound. If the entire Universe is electromagnetic energy vibrating at different frequencies - what place does the mechanical energy of soundwaves have in this vast scheme?

An electromagnetic wave is thought of as a transverse wave. The waves of the sea can be thought of as a transverse wave. If you look at the waves on the sea, they seem to move towards you, however the particles that make up the wave only move up and down. On the other hand, a soundwave is a longitudinal wave, where the particles move along with the wave, backwards and forwards along the direction in which the wave is travelling. It makes me think of a long line of commuters trying to get on a tube, where it's the middle of the morning rush and everyone is late for work. The wave begins with those pushing at the very back, it moves forward down the line for a bit, but then it hits a wall of people further down the line, and they start pushing back with their shoulders. The line squeezes (compression) before the energy is pushed forwards down the line again, and then there is something of a stretch (rarefaction) between the commuters until it hits another apparent wall. The wavelength can be measured as the distance between the centre of two compressions. Eventually though, the big shove at the back reaches those passengers trying to board the train. It's as if the energy from the back of the line shuffles along to the front. These sites make a much better job of illustrating this....
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l1b.html

So, we have the energy of the Universe - light moving at vastly different wavelengths and frequencies - which takes the form of matter and electromagnetic radiation. Then we have soundwaves which are produced when the various wavelengths of matter vibrate against one another. Matter is an incredibly intense electromagnetic wave, and one has to wonder what forces are at work, when these waves interact with one another to release this incredible energy we know as soundwaves.