Sure, you have all probably heard this question, but have you actually thought about it? Thomas Andrews has!! Here are his thoughts....
In this case we are asked if the tree makes a sound as it falls (not if we can hear it) and can be easily answered as yes with the aforementioned definition of sound because the tree moved through air and created a disturbance of particles-sound.
The best way to describe the situation is with people of the deaf community. These people never hear anything and those born deaf have no concept of hearing at all, but does that deny the existance of sound? So, when a sound is made and not heard, the fact that the sound is made cannot necessarily be denied.
Another angle: Does that same tree still exist when you are not looking at it, just as it would make a sound when falling if you were not there to hear it? I would think so; unless you believe in some weird metaphysical philosophy where little goblins construct the world we live in as we come upon it (and I'm not making that up, it's a real concept!).
Therefore, the tree does make a sound as it falls, even if no one hears it.
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