You Make Tree Sounds

If a tree falls in the woods and no one is there to hear it, does it make a sound?

No.

            In fact, technically even of someone is there it still doesn't make a sound. Sound, you see does not exist on its own. What does exist is motion, in the form of waves traveling through the air. Your eardrums, which are a thin membrane stretched like a the skin on a drum, are a biological device specifically calibrated to detect these motion waves, as long as they fall within a certain range. Your brain then takes the pattern of that wave the eardrum is now vibrating in and it translates it in a biofeedback loop with your conscious mind where you experience it as sound.

Until those waves reached an ear conspiring with a brain to interpret that motion as sound, that tree made no noise at all. 

Here is what that tree actually did. It converted the potential energy of it standing up into the kinetic energy of it falling down. The impact of the tree hitting an impenetrable ground meant that the energy of its fall had to be transferred somewhere. Most of that was absorbed by the much bigger Earth. Imagine a baby punching a blue whale. The impact, however also created a shockwave that jostled the air around it. That shockwave traveled outward from air molecule to air molecule, in the pattern of a wave similar to the ripples you would see traveling outward after dropping a pebble into a serene body of water. 

            If those waves of energy fall within the range that your eardrums are calibrated to detect, your brain then interprets it as sound. If it falls below that range, your brain creates no perception of sound and if it falls above, the membrane of your eardrum tears and your brain translates it as the chaos of a really loud noise, after which you hear absolutely nothing, as your measuring device is now broken.

It may seem like we're splitting hairs here. 

One might say that because those motion waves exist and because those waves within that range are what we define as sound, then the tree does make a sound, even if no one is there to perceive it.
            What if you ear membrane were thinner and more sensitive? Then yes, you might interpret the minute fluctuations of a mosquito breathing as sound, but your eardrum might be torn apart from the rumble of a fart. What if the membrane were thicker? Then perhaps the shockwave of an explosion would sound like beautiful humming, as its energy passes through the rest of your body, perhaps tearing apart your internal organs.

            Things sending wave fluctuations in the air right now that you do not interpret as sound: your finger wiggling. Your hair growing. Trees falling a mile away. Heat. The molecules that our noses detect and our brains translate as odors. Light that our eyes detect and our brains interpret as sight. 

            All of these are wave motions that fall within a range our ears are not optimized to detect. Or, if our ears are capable of detecting them, the algorithm our brains use to interpret informational input from the ears filter them out. This filtering and interpreting is an interesting process. What if the brain got confused or had a tweak in its algorithm where it translated the inputs differently. This actually happens all the time. 

There are people who see color patterns when they listen to music. 

There are people who taste metallic objects when holding them. Full disclosure: I actually can taste certain rocks with my hands. It started one day when I was holding a piece of malachite, which is an ore of copper. This rock gives off no coppery smell and my hands were nowhere near my face, yet my brain was telling me it tasted like I was sucking on a penny. Since then, this has happened with many other rocks. It also happens with some metals. I recently inherited my grandmother's old silverware. I cannot use it, because just by touching it, like when I'm setting the table, it tastes like I'm sucking on a nickel. Let me tell you, nickel is not a spice you would ever want use to enhance the flavor of a food. Unless, of course your brain accidentally translated such a flavor as salty, which would be no more strange than me tasting a piece of quartz with my thumb or someone else seeing colors when they listen to Mozart.

            So back to that tree falling in the woods. It is making a wave, not a sound. Someone there interprets that wave as sound. Someone else might see colors and some one else might taste it. If the impact is strong enough, the exact same wave that your ears interpret as sound might fall within the calibration of your skin's sensitivity where you nerves interpret it as touch. 

That said, let’s go back to the question.

If a tree falls in the woods and no one is there to hear it, does it create a wave pattern in the air that a being with a thinly stretched membrane in their ear would interpret as sound, as long as it fell within a certain optimized range that a brain, attached to that membrane, didn't filter out?

            Yes.