Quote Originally Posted by hoglahoo View Post
But if it cannot be heard, you say it ceases to be sound. And if nobody is around to hear it, it cannot be heard!
The sound waves are capable of being detected irrespective of if someone is there to detect it or not. They do not have to have someone or something there to detect them to be detectable. Even at that, they may be in a frequency that a human can detect but a dog can. That doesn't mean that the sound doesn't exist. There are trillions of nuetrinos going all through our bodies (traveling in and out) that we can not see or detect in any way, but the fact that we don't observe/recognize that it is happening doesn't mean that it isn't happening.

Fwiw, I've seen documentaries where cameras were left in forest and they picked up the sounds from fallen trees. No one was there, and predictably sounds were made. It's not as nuanced a question as we might think.