Never let it be said that I don’t tackle the big questions.
Today’s big question is that familiar old philosophical chestnut (yes, I know, at least three of these adjectives are redundant) : “If a tree falls in a forest and nobody is there to hear it, does it make a sound?”
Why now you ask? For some reason it came up over a pre-Christmas dinner with some mates, and a fairly loud and prolonged argument ensued between two of us in particular. Fortunately the general volume in the restaurant was approximately that of a 747 at take-off, so no harm done. What is remarkable is that the bulk of the argument was had prior to any significant alcohol being consumed. Go figure.
So, what’s the answer? I’m firmly in the negative, while my friend (who, by the way, is a physics teacher), argued for the affirmative.
My argument is as follows:
1. The problem actually has a clue in it: it refers to someone ‘hearing’ the tree fall.
2. The process of hearing is done in the brain, after the sensory input is converted into electrical signals. That is what we call ‘sound’.
3. What is the sensory input? Simply sound pressure waves (as per Physics 101), which you can picture as ripples on a pond. It is these sound pressure waves which stimulate the various bits of our ears, causing the brain to register a ‘sound’.
4. Therefore, if there is no organ or device to convert the pressure waves into a perceived ‘sound’, then the falling tree cannot be heard.
Using a recording device doesn’t help either. In that case, the pressure waves are converted by transducers into patterns on tape or disc or memory of some kind, which we still can’t ‘hear’. In order to hear what is recorded, the device must convert those recorded patterns back into pressure waves, and for this we use some nice electronics, and critically, speakers. How do speakers work? They feature a membrane which bounces back and forth to disturb the air in precise ways, replicating the original sound pressure waves.
There are also thought experiments we can do to confirm this view.
For example, let’s remove the medium – the air. Does the tree make a noise now? No, even though we may be standing right next to it, we will ‘hear’ nothing. Why isn’t the tree making a noise now?
Let’s imagine a race of aliens who visit us, who have never evolved the ability to sense sound pressure waves, just as we have never evolved the ability to see in the infra-red part of the spectrum. Will they ‘hear’ the falling tree? Maybe they have developed some other sort of sense organ which is sensitive to changes in the visual field, resulting in a flight response. They may even ‘see’ the sound pressure waves as a colour, but it’s not necessarily perceived as sound.
So, all you budding philosophers, you may now proceed to shoot me down in flames.