Because there is no reasonable way to possibly prove the sound still exists. To find out if something beyond the observable universe exists, you simply wait fo

Because there is no reasonable way to possibly prove the sound still exists. To find out if something beyond the observable universe exists, you simply wait for the light to reach you. Every minute your observable universe grows larger and you see more stuff, the obvious conclusion is that there is more stuff. But the random movements of air molecules allow for no analysis that there is a quantum of a sound traveling through it. It cannot be reasonably proven that the sound still exists. You can't wait to see if you notice more random sounds or anything, it's gone, part of the background noise. The information in the sound has been destroyed for any way to measure it via the movements of air molecules.