Quote Originally Posted by Dane McArdy View Post
I take issue with the word useful.

The energy wave exists. Whether or not some thing recieves it doesn't matter as to it's nature. Light exists, and all creatures see it differently. Bees see into a specturm we don't.

Dogs hear pitches we can't. So if I blow a dog whistle in the presence of a human and a dog, it's a sound, but if I remove the dog, it's no longer a sound?

Again, it's being egocentric to say that something is useful, or defined because we say it is. Some one hearing the energy wave doesn't change it's natuer. I might reshape it as it bounces of the object and moves in a different direction, and it might cause a chain reaction, such as nerves sending signals, eardrums vibrating and so forth. But those are reactions to the energy wave.
I just thought I would put in my 2 copper.

Sound is nothing more then vibration of mass at specific frequencies. As such, it is only considered sound if there is a receiver that can translate the frequency as sound. While the vibration caused by the crash of a falling tree would exist it is only considered 'sound' when something is around to hear it.

So, no receiver means no sound, but that does not mean there is an absence of energy transfer.