"The answer to this question depends on the definition of sound. Since sound does not exist without our hearing of it, sound does not exist if we do not hear it. However, when a tree falls, the motion disturbs the air and sends off air waves. This physical phenomena which can be measured by instruments other than our ears exists regardless of human perception (seeing or hearing ) of it. Putting together, although the tree falling on the island sends off air waves, it does not produce sound if no human is within the distance where the air waves are strong enough for a human to perceive them."