If a tree falls in the forest and no one is around, does it make a sound?
If you said 'no', you're probably one of those annoying pseudo-intellectuals trying to sound smart (and failing). Please stop.
When I say 'yes'--the correct answer--people assume I'm being all naive and not understanding the point they're trying to make. The truth is their point is stupid. Lemme asplain:
Sound is not in your head. I know, you think you're super-clever for pointlessly redefining this common English word (and scientific term) in terms of qualia1 instead of the physical phenomenon it really is, but you're really not. Crack open a dictionary, or an encyclopaedia, or a physics textbook. It will tell you that sound is vibrations. Physical. Not mental. Stop redefining this word. You're not Locke2.
Some of you more clever people may object, 'Oh, no! you misunderstand: I'm an idealist3'. Tell me, then, Mr. Idealist, if no one is around, how is there a tree to fall? You could, of course, explain that God is always in the Quad, but now you seem to be arguing that God is deaf. I don't buy that.
1 Being an annoying pseudo-intellectual, you probably don't know what 'qualia' means. Well, it's what you're redefining 'sound' to refer to. The 'what it's like' in your head.
2 Locke annoys me so I take cheap shots at him whenever possible. (Anyway, I'm sure he did something immoral at some point in his life so it's okay to treat him like a rabbit wolf and off him2b.)
3 The less clever of you probably think I mean I-think-things-should-be-perfect idealist. I don't. I mean Barkley. Imagine The Matrix without the computers. The entire world is nothing but ideas or perceptions in our minds. Yeah, you think it's a stupid idea (or maybe you've decided to believe it because it'll make you sound clever). Please go read something by Barkley before doing either of those. It's a lot more sophisticated than you or Sam Johnson take it to be.