Children find fascination, or alternately horror, in imagining what goes on in their rooms when they leave home, or what goes on under their beds when the lights go out. In the imagination, toys become animate and monsters form out of the syrupy ether of darkness, as soon as one turns one's back on an environment. Adults too share in this obsession. People set up cameras to see if anything happens in their rooms when they leave. They ask themselves questions a to whether unobserved trees falling in an unobserved forest produce a sound.
Normally, upon investigating these questions it turned out that there where no monsters beneath the bed, that one's toys very likely remained in place and inanimate for the duration of one's absence from an undisturbed room. That, in the absence of intruders, the only action caught on the video camera left to record one's empty flat while one visited the grocery store was the changing light, the accumulation of dust, perhaps the movement from floor to couch and back of a dog or cat, or, given the presence of a time-lapse system and a longer duration, the normally imperceptible growth of one's houseplants, rendered visible. Still, the unobserved tree falling in the forest does in fact make a sound. The splintering crash of the this tree, though unheard, resonates down to the root of our perceptual and cognitive processes and this essay will be about why and how, and beyond this, will open a discussion of what sound is, what it is made of, and later what time is itself, and what it is made of.
Let's begin with the tree. Only the most dedicated solipsist would suggest that an unperceived event does not exist. Some take the situation still further to the point at which any event not perceived or experienced directly by themselves as observers cannot be said to exist. Such persons would do well to consider their own birth, or better, their conception. Luckily, none of us where around to witness that! Still, the affect of the action of our own conception in the womb is visible in terms of our existence. So unless the universe is far stranger than can even begin to be discussed here, extrapolating from what we know about other people and their bedroom behaviors, we can assume that something similar happened between our parents, and that this brought us into existence. Most of us would agree that this was not an action we witnessed (no doubt fortunately) and yet, here we are.
Thus, events do not need to be perceived directly to be said to exist. In fact, even their effects need not be perceived as we constantly assume or become convinced of the reality of objects and situations by the mere plausibility of them. Consider, for example, a news broadcast. We hear about an environmental crisis in Madagascar. YWould a reasonable person question the existence of weather in Madagascar, or the island itself? Of course not. If a friend brings you a report of a new restaurant in the neighborhood, you likewise accept the existence of such a restaurant. Why? Firstly, because the event is simply possible, and more than that, it is likely, it is ordinary. Secondly, analyzing the motivations of the speaker, we find that there is no reason we should doubt our friend's enthusiastic report, and we may even alter our plans for the afternoon and choose to visit this restaurant with our friend, similar to the way we may alter our commute based on the traffic report on the morning radio. In such a way we accept the existence of things we cannot see, and even modify our behaviors based on the mere plausibility of the existence of some situation, and the absence of a reasonable reason to doubt it.
A tree has fallen in the forest. Did it make a sound? Have you ever witnessed a tree fall in the forest that did not make one?
On such grounds an idea can be said to have an existence, at very least in terms of it's effect, similar to that of a physical object immediately perceived. There is something else, however, hiding in the question itself: a tree falls, unobserved, in the forest. Does it make a sound? Well, based on what we have discussed, yes. It makes an unobserved, unheard sound. Yet there is something strange in this, something that reaches both the physical and perceptual roots of what a sound is in itself, and this has to do with questions of utility, that is, with the tone the question is asked in. Thus, two further philosophical questions present themselves.
The first question is "what is a tree to itself?".
Beginning from a basic stance, it is clear that if a tree had any kind of consciousness or awareness at all that it would likely be very different from our own. We have completely different physiologies, for one thing. Thus, the second question: "Does a tree call itself a tree?" Unlikely, especially given that even among humans we don't agree on what a tree is or what it should be called (for example in Czech language a tree is "strom" and in Hindi it is " "). So then, with some sadness, the discussion must be narrowed. If an Englishman observes a tree falling in the forest and then is asked for a report, they will likely reply something to the effect of "a tree has fallen". Still, this event, as experienced by the tree itself, by an insect on the tree, or a squirrel on the ground, would no doubt be characterized quite differently than by our Englishman. So then, returning to our original question with the modifications we have based on the two questions above we rephrase it to read: "If a tree falls in forest, in the absence of an observant Englishman, has a tree fallen?" The action, of course, happens either way. The experience of it, is infinite.
This approach negated a highly important element of the original question. Looking back to the original, it is clear that the question was not, in fact, about the existence of the tree itself, but the sound which a tree might make upon falling. This is even more mysterious when one considers that sound is simply radiative energy. Our Englishman calls it "sound" simply because it is perceived the way most of what we have been taught to call sounds are perceived, that is, by the ears. Of course, if one takes a physicist like Harry F. Olson's definition, as expressed in the second edition of his seminal acoustics text from 1967:
"Sound is an alternation in pressure, particle displacement, or particle velocity which is propogated in an elastic medium, or superposition of such propagated alterations. Sound is also the auditory sensation produced through the ear by the alterations described above."
than one can see that here sound can exist apart from it's sensation. In addition, it is common (citation and example here) to simplify the above definition to "sound is a wavelike disturbance in an elastic medium", and here, as in the first part of the previous definition it is clear that an opening exists, as not only need sound not be heard, but sound need not even be hearable.
Though at first this seems surprising after a moment, it is clear that this is not a new idea. Dog whistles produce a sound. We cannot hear it. Still, we refer to it as a sound. Still it is interesting to consider the fact that sounds need not even be audible. Rather, like the sounds that make up earthquakes, they may simply be the energy, and medium around them, that is, that which resonates, determines how they are characterized.
I can hear the critical chorus rising even now: "But we are not," they sing forth in my imagination, "questioning the existence of radiation. We are asking a question about a tree in a forest." Therefore, let us return to common practice definitions of sound as heard energy, and continue to try and get to the bottom of this. "Tree" "falling" "inside forest" "unobserved". Does it "make" a "sound"?
Ignoring the ambiguities inherent in the quoted words above and forging forth with the common practice definitions of these things we nevertheless find ourselves stuck. How can that portion of the energy that would normally be heard, as produced by a tree falling unobserved in a forest be heard energy if no one, not even a squirrel, snake, bird, or insect, is there to hear it? One must again simply rely on the plausibility argument, extending to what one knows about the system called "forest". We know of no soundless forests, as all known forests are dependent on the pressurized atmosphere of our planet. Therefore, just as it is eminently plausible for a tree to fall unobserved, it is likewise expected that such a tree would produce a sound, though an unobserved, that is to say an unheard, one.
In the next section we will consider this common practice definition of sound, as "audible energy", and in particular what such a definition means in terms of our utility of sound in general.