If a tree falls in the woods and no one's there to hear it, does it make a sound? Sound is a label or abstraction for a phenomenom. An abstraction can never perfectly replicate the phenomenom it is referring to. The concept of sound is not an objective truth. It was invented by animals and only exists in their minds. Does a painting exist when you aren't looking at it? It takes observation to label something a painting, whether it is a physical object or any other idea. I would say object permanence is an illusion. Babies are right not to innately believe in it.