If a tree falls in a forest and no one is around to hear it... (Definition of sound)

… does it make a sound?

This question was on the “Hypotheticals” episode of QI. I thought the answer was obvious; yes, it makes a sound, which exists independently of our perception. However, there was an argument about the definition of sound, that is whether or not the oscillation of air pressure itself is sound, or if it is just the cause of it. I’ve never seen sound defined as being something that depends on our perception of it. Is the answer as obvious as I think, or is there more to the definition of sound?

Wiktionary offers both definitions:
[li]A sensation perceived by the ear caused by the vibration of air or some other medium.[/li][li]A vibration capable of causing this.[/li][/ol]I was surprised to find them in this sequence. I would have thought #2 to be the primary - or even the only - definition.

Like many words, “sound” has a variety of meanings.

The first definition from Merriam Webster (additional meanings are included):

Historically, the definition of sound as a sensation came first. The definition of sound as sound waves came later, once scientists understood the mechanism by which sound was transmitted.

Whether or not a tree makes a sound if it falls unheard depends entirely on which definition you choose.

What does your favorite dictionary say? What do 5 more dictionaries say. What do 10 of your close friends say? Word definitions are not philosophical questions. With a few highly technical exceptions, word definitions are also not bright lines; “sound” can and does mean both vibrations and (human?) perceptions of vibrations.

I regret you are all being species-ist.

If there is no human around in the forest, the area will be full of other live creatures - birds, a heck of a lot of insects, mammals, even more insects, lizards and so on. Most of them have pretty good hearing and they will certainly hear the tree falling.

So, the Zen thought is interesting as a mind focus, but scientifically the answer is clear.

If a tree falls in a forest and no one is around to hear it, there will be a big crashing noise.

I regret that you speciously accuse me of being a specieist. :wink:

So what happens if a tree falls in a forest and only Helen Keller is there?

Even if you’re using the sound as sensation definition, you might think there’s a built in hypothetical - there’s a sound wherever you would hear something if you were there to hear it.

Now go read your Berkeley and get back to us. :stuck_out_tongue:

You could hear the squeals of a bunch of frightened squirrels.

Clearly they can hear in the way a microphone can hear. But do they have an accompanying sensation of sound?

<runs out of room>

OP’s presumption that the tree makes a sound independent of our perception is perhaps to you an “obvious,” but not to everyone, particularly since the fundamental work of the philosopher theologian Berkely (pron. “Barkly”), A Treatise Concerning the Principles of Human Knowledge (1710). The following limerick is often quoted for a succinct summary of two alternate stances:*

There was a young man who said "God
must find it exceedingly odd
To think that the tree s**hould continue to be*
When there’s no one about in the quad."

*"Dear Sir: Your astonishment’s odd;
*I am always about in the quad.
*And that’s why the tree
*Will continue to be
Since observed by, Yours faithfully, God"

BTW,UC Berkely (with an Americanized pronunciation) was named after the philosopher.

ETA: Just saw that **Gorznak **got there first. But I spent more time on the damn formatting!:wink:

I have always thought of this as the equivalent of a Zen Koan: the point is NOT the answer; the point is to *respect the question *- and the assumptions and perspectives that can be brought to it - and how they make us consider our world differently as a result…

If she is there when it falls, the tree is likely to fall on her. As she is dead, she is unlikely to care about this.

While this occurs, the noise will have stirred up a lot of reaction from animals and birds. As a result, they will be making a lot of noise about the event. A large number of wood eating insects will be advancing on the tree, mandibles at the ready.

And far from the scene, the Zen master will be meditating on the issue, clapping one hand idly.

I just read this in my Psychology book yesterday. It says the answer is NO.

It explains the answer by saying that sound requires a brain to register the energy of the sound waves. The waves themselves are not sound. So, if there is no brain there to register the waves, there is no sound.

Now, go find a forest and clear out anything that has a brain so we can have some silently falling trees.

When the likelihood of the tree’s falling is unknown, and you are not there to check, Helen Keller is in a schmeared quantum state.

But if you knew in advance the tree would fall, does it have free will?

Why should my knowledge of its state have anything to do with how the state was achived?

Because if you know its state, then the tree can effectively only achieve that state. If you know it will fall, the tree has no choice but to fall. It only has an illusion of free will. Or does it?

It has the illusion of Tree will. That is why the tree will fall.

You cannot know if it will fall–it is in a forest w/ nobody there to hear it. This defines metaphorically a closed container about which no-one has any chance to measure the predictability. The only way you know that the tree has fallen is to check it by going into the forest. If you know that it will fall–say, you sawed it* across except by an inch and it was windy–and then out of the forest, it is extremely likely, but not guaranteed, that it will fall. But a) it no free will, tree will (as said above) nor an illusion of either; and most importantly you have changed the rules of the game.

At this point I will go hug a tree and slip out. I feel a chain being jerked in my crotch…:wink:
*I sawed I sawed a putty tat.