Now that I'm sober I don't sleep. While laying awake last night I was thinking about the popular thought exercise "If a tree falls in the forest, and nobody is there to hear it, does it make a sound?" (There was a storm, and I live in a hundred acre wood.) One might be tempted to say that one knows from experience that it of course makes a sound. Well first of all we must clarify what we mean by "nobody" or "somebody". Can "somebody" be an animal of some sort, or does it have to be a human? The answer to this determines the answer to the original question. If there are no animals or humans, there are no eardrums. If there are no eardrums, there are no sounds. The tree, or whatever it smashes into does not make a sound. Eardrums and brains working together is what makes sound. The tree falling makes variations in air pressure, which travel though the air. If an eardrum gets in the way, it vibrates. The brain turns the vibrations into sound sensations.
Somebody please argue with me. I'm not really sure about this. Also, do plants hear? I know they respond to sound (or actually, pressure waves in the air), but I don't think that they hear sounds in the traditional sense.