|MadSci Network: Physics|
Dear Melody! Although light and sound waves may be described by similar mathematical equations, their physical origin is quite different. The fact that sound waves cannot travel trough vacuum but light waves can has nothing to do with light being `waves and particles' at the same time (a notion that is confusing anyway and should, in my opinion, not be taught). Sound waves are density fluctuations in a gas, a liquid or a solid. When a sound wave travels through air, a `snapshot' of the density of air molecules at a certain time shows a modulation which is, in the simlplest case, periodic. Without the presence of a gas or a solid, there are no density fluctuations and thus no sound waves. In other words, sound needs a `carrier' material to propagate. No carrier, no sound. Light consists of electromagnetic waves, i.e. electric and magnetic fields arranged in such a fashion as to propagate over large distances. These fields do not need a `carrier' like sound waves, they `live' in pure vacuum. One could say that an electromagnetic field is a certain state of the vacuum (physicists call it an `excited state', and that's where the notion of light being particles begins, but that is another story). In the time before Einstein's special theory of relativity, physicists believed that light needed a carrier which they called `ether'. Einstein showed that the ether was not necessary, or even obstructive, in the description of light. As to the second part of your question, I think that you want to know what happens if e.g. an explosion happens in vaccum. In air, a fraction of the energy goes into sound waves which we perceive as `booooom' or something like that. In a vacuum, this energy is available for the kinetic energy of the bomb fragments, because the explosion does not have to accelerate air molecules to produce sound. So, the bomb fragments would just travel a little faster in a vacuum than they would in air. I hope that my comments have provided satisfactory answers to your questions. Feel free to submit subsequent questions to the MSN! You can also send e-mail directly to my address if you prefer. Bye, Georg.
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