This age old thought exercise arose in work today.
I have come down heavy on the side that the tree makes no sound.
My argument to get it kicked off is that it is scientifically impossible to prove that an observer independent reality exists. According to the scientific method if a hypothesis is not testable then it is not "scientific". Not to say it is not true, absence of proof is not proof of absence after all.
So I challenge anyone to find a way to test the hypothesis that reality exists independent of a conscious observer.