Sound waves impinge on the eardrums and pinnae (the fleshy parts of your ear), setting off a chain of mechanical and neurochemical events, the end product of which is an internal mental image we call pitch. If a tree falls in a forest and no one is there to hear it, does it make a sound? (The question was first posed by the Irish philosopher George Berkeley.) Simply, no—sound is a mental image created by the brain in response to vibrating molecules.
