Did You Hear Me?

Besides politics, one of the great points of contention in human existence is this question:

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

It's interesting because the question has philosophical implications as well as scientific ones. For centuries philosophers have questioned the very existence of an event that has not been observed. To me this is puzzling. The argument that an event exists only if it has been observed seems to deny almost fourteen billion years of the known universe before human beings. It seems reasonable to me that if all the stuff that took place in the universe before we came along didn't actually happen, or even happened in a slightly different way, we ourselves wouldn't exist. Yet to this day there is still no definitive, empirical proof that there is existence in the absence of an observer. It's a little like me saying that since I have not observed the perspective of a human being other than myself, I cannot prove their existence. In other words, maybe I just dreamed you and everybody else up.

Just sayin'.

The scientific answer to the tree question is a little more straight-forward. I would say it all depends upon your definition of the word "sound." 

My definition of sound is the physiological perception of disturbances of air pressure. For me, perception is the key, it is the difference between the mere propagation of acoustic waves and a Beethoven sonata. There is no question that a tree falling (or a player piano playing Beethoven) in the forest, creates the air pressure disturbances necessary to create sound waves that organisms, human and otherwise perceive as "sound".  However, without any of those organisms around to perceive it, there is no perception. Therefore sound waves, a purely physical phenomenon, certainly are formed, but sound, a physiological phenomenon, is not.

That's my humble opinion.

On the other hand, if you define sound as nothing more than the physical production of sound waves, our poor, solitary tree does indeed go crash, boom, bang, and whatever other sound a falling tree makes. 

All this is enough to give me a headache but I'm about to make it worse. Where does vision play in all this? How would you even pose the question? In other words: if a tree falls in the forest without anyone around to see it, then what?

If you conclude that question with: "would it be seen?" the answer should be self-evident.

Perhaps a more salient ending to the question might be: "would there be an image of it?"

The perception of vision, like the perception of hearing, depends upon specific physical requirements in the outside world. To put it simply, in the case of hearing, we need an atmosphere, and something to disturb it like a falling tree. Conversely, like the slogan for the old sci-fi movie: "In space, no one can hear you scream." 

In the case of vision, we need light, and something to reflect it. We do not "see" objects by coming in direct contact with them, but rather with the light that reflects off them. We're able to differentiate one object from another visually because every object reflects light differently. Some objects reflect more light and conversely, absorb less light than others. Others absorb more light and reflect less. Therefore brighter objects reflect more light than dark objects. In addition, most objects reflect certain wavelengths of light more than others. Since wavelength defines the color of light, a red object for example reflects mostly red light and absorbs mostly green and blue light. *

To complicate matters, we see details in objects because each tiny piece of an object reflects light differently. To further complicate it, some object parts may receive direct light, while others are in shadow, illuminated by a secondary light source, quite often, more reflected light.

Every object part reflects rays of light in all directions in front of it. That's a lot of light rays. Now multiply all those rays by every minute detail of everything we see in front of us, which by themselves could number in the millions, and we realize that the number of light rays buzzing by us in every conceivable direction at any given moment of illumination is truly staggering.  One might call that chaos. 

So out of all that, how do we manage to cut through all the chaos and see anything?

Well for starters, we only see light if we look directly at the source of the light, which often isn't a good idea, or when it reflects off something. Fortunately, we don't see light as it zips through space. If we did, all we'd ever see would be a constant cloud of white light, even at nighttime where we'd see rays of sunlight as they pass by us into space. The light from the stars would do the same but their effect would be negligible, drowned out by the light of our own star, light years closer to us, just as they are during daytime.

In order for anything to be "seen", an image first has to be created. Nature has given us a splendid image creating device, our eyes. The chaos of all those billions of light rays bouncing about before our eyes is minimized by the fact that only a small handful of rays from each detail we're looking at, actually lands upon our eyes. It is the job of the cornea and the lens of our eye, to converge the rays of light from each tiny detail into one spot. If all is working properly, the rays reflected off of each object that pass through the iris of the eye, meet the retina at the place where they converge into one spot, and each of those spots are arranged upon the retina depending upon the unique angle in which they entered the eye. Put all these spots together and you have a faithful image projected upon your retina of the world in front of you, only upside down and backwards.

 

That image is then transmitted via the optic nerves to our personal image processor in our brain which performs its magic nearly instantaneously.

 

So there's our answer, without eyes to create them, again, human and otherwise, there would be no images, case closed.

 

But not so fast...

Nature has provided other much simpler image creating devices, tiny holes. We've all seen images created by these "pinholes" as photographers call them, but probably few of us have realized it. If you're outside on a cloudless day in summer, when foliage is at its fullest, you'll see shadows of tree branches and leaves strongly defined on the ground. Sometimes however, the leaves overlap in such a way that they only allow a tiny amount of sunlight to pass through. When that happens, we see disks of light dancing around on the ground which is often called "dappled light". We may assume these are ordinary shadows until we realize that the openings provided by the leaves are of many different shapes but are hardly ever perfect ellipses. What we are looking at in fact are not shadows, but images of the surface of the sun projected onto the ground courtesy of these "pinhole" apertures in the small gaps between the leaves.

Then there is the camera which most people don't realize was a discovery rather than an invention. The first discovery of the camera obscura (literally dark room) probably occurred in prehistoric times when our cave dwelling ancestors noticed in their otherwise dark caves, that a tiny opening to the outside on a sunny day created an image of the outside world on the wall opposite the opening. Who knows, perhaps these images were the inspiration of the first works of art, cave paintings.

Obviously, these camera obscura and tree pinhole images existed long before people and non-human animals existed, so yes, an image of our tree falling in the empty woods may have been created. But probably not as these images require a very specific set of circumstances. If, however, the light conditions were just right and an image was made by a well-placed pinhole, then comes the inevitable question: what if no one was around to observe the image?

I give up.

 

*This brings up an interesting point. The leaves of most plants are green, meaning they reflect green light while absorbing other types of light. We know that the function of leaves is to convert the energy transmitted by light into food for the parent plant. Therefore, the plant is deriving its sustenance from the light it is absorbing, such as red and blue light, while the light it is reflecting, green light, is more or less useless to the plant. Funny isn't it, that the color most associated with life, is green. Nature is a funny thing.