Posted by on Dec 9, 2009 in Interesting Facts | 3 comments

0119-tree-falls-sound

How could I call myself an amateur factologist, and I do… just not out loud… but how could I if I didn’t take a timeless questions of the ages and put an expiry date on it. The question is: If a tree falls in the forest, and nobody is around, does it make a sound?

This question was originally posed, though not in these words, in 1710. It was part of a book proposing that a thing would cease to exist if it was not being perceived at any given moment. It talked of a tree in a garden. Would the tree be there if there was nobody looking at it, or feeling it, or smelling it, or hearing it? (oh ya… or licking it?) In the original context, it was unanswerable.

I answer matter-of-factly, NO. So much for the intended philosophical debate. But really, if this is a question of scienceĀ  there is a definite answer. (aka: definitely not)

In the physical world, a falling tree knocks into the atoms floating around the air. Those atoms are pushed aside, bumping into the atoms next to them. Like dominoes, so it goes with the atoms in the air bumping into the next atoms and a compression wave is produced, radiating outwards. (exactly the same as dropping a pebble in a pool. Just replace the air atoms with water atoms.)

So the atoms are jiggling, and they are jiggling in a pattern that we have called a sound wave. But it’s not “sound”. There was no magical transformation where the jiggling atoms became something called sound. It’s still just jiggling atoms. So the falling tree makes no sound. It merely creates a compression wave in the atoms around it.

The fact that we can hear these waves and perceive them as sound is, on the scale of the universe, really nothing more than a cute parlour trick of evolution.

That’s my answer. (which, turns out, was first published in 1883)