If a tree falls in a forest and no one is there to hear it, does it make a sound?

"Simply, no - sound is a mental image created by the brain in response to vibrating molecules. Similarly, there can be no pitch without a human or an animal present. A suitable measuring device can measure the frequency made by the tree falling, but truly it is not pitch unless and until it is heard."

Daniel Levitin - This Is Your Brain On Music