Introduction
There has always existed a fine line between Philosophy and Physics, In this piece I will discuss Plato's allegory of the cave who's physical counterpoint lies in Schodinger's "cat in the box" analogy, this will give us some scope for a discussion about what I would deem to be the most important experiment ever carried out in Physics, the Young's double slit experiment, an experiment which truly tests the limits of human perception. With these things in mind we will answer the question "If a tree falls in the woods and no one is around to hear it, does it make a sound?"
The allegory of the cave
The allegory of the cave, as described by Plato in the republic is a scene comprised of a cave containing a small fire and a group of people who have been confined from birth to only view one wall of the cave. Unawares to the cave dwellers, another group of people stand behind them placing various objects into the light cast by the fire, resulting in images being formed on the cave wall. As far as the cave dwellers are concerned, the projections on the wall of the cave constitute their reality and in this context a philosopher is defined as one who can distinguish this quasi reality from the true nature of reality. That is, they are aware that something is creating the projections on the wall of the cave. But the cave dwellers can only speculate as to what creates these projections.
One way of viewing this dilemma was presented by Aldous Huxley in the book The doors of perception where he suggests that rather than being completely oblivious to the true nature of reality, our brains are acting as perception filters, providing us with only the information it deems necessary for survival. This notion has intimations in eastern philosophy in the notion of a Dharma-body where all knowledge is stored in a higher state of consciousness and needs only the correct cipher to unlock it. Contradictory notions came from the philosopher John Locke, who said the mind is a blank slate which can only be inscribed by experience and therefore no notion could be innate in the mind of man. Regardless of these view points, both men are still staring at the wall of a cave, speculating about what lies behind it.
Schrodinger
There are many misinterpretations of Schrodinger's cat and what it means, I would like to think however, that I am extending the analogy and hopefully not tarnishing it. Schrodinger's cat is meant as a thought experiment to explain a range of quantum phenomena, including superposition and entanglement. The basic set up is a cat in a box alongside a radioactive source, a radiation detector and a bottle of poison. We choose a radioactive source that has a 50/50 chance of undergoing a decay (I have chosen the word 'chance' very carefully here), this decay causes the radiation detector to enter alarm and activates a mechanism which smashes the bottle of poison, thus killing the cat. So assuming the cat has some form of cognition, it's aware that it's fucked. But what about the external observer? What about us? The only way for us to know if the cat is dead or alive is to open the box, but until that point the cat is in a superposition of being dead and alive simultaneously. The experiment is also supposed to demonstrate how micro-scale phenomena like radioactive decay can influence macro-scale events like life and death by means of some mechanism. This has parallels to the allegory of the cave in the sense that we are the cat in the box and to rationalize our existence we have created another box upon which we place order and measure, just as the cave dwellers have done with the projections on the cave wall. This I feel at least qualifies the notion of uncertainty; that there is a fundamental flaw in our reasoning that is governed by a mechanism we cannot comprehend; the ones making the shadows on the cave wall if you will.
The Young's double slit experiment
Many attempts have been made to characterize this uncertainty and even to quantify it. In physics the uncertainly principle is manifested in the measurement of conjugate variables. I have previously discussed the notion that there exist physical quantities that cannot be measured simultaneously, such as position and momentum. When one quantity is the measured the other becomes indeterminate. The Young's double slit experiment consists of two equally proportioned slits in a piece of card, onto which a laser is shone. As the light passes through the slits it is split 50/50 between slit A and slit B and everything is fine. But what happens if a single photon (that is a single packet of light) is shone on both slits? Where does the photon go? To slit A or B? The answer is we don't know, and if we did know, we would already know if the cat was dead or alive. We would also know what casts the shadow on the wall of the cave and indeed we would understand the mechanism that constitutes our reality.
To my mind, uncertainty is a inevitable fact of life, nothing becomes certain or known until it has been perceived and measured by an observer. This leaves only one possible answer to the question, "If a tree falls in the woods and there is no one around to hear it, does it make a sound?" and that answer is: we don't know. We could of course place a recording device in the vicinity of the tree and presuming it falls, it would make a sound; but only as a result of measurement. This act of observation has altered the outcome of events, avoiding the question of whether or not the tree makes a sound when left unobserved. The same applies for the Young's double slit experiment. When we observe whether the photon goes through one slit or the other, the light being absorbed by our eye, or by the optical detector causes the photon to be bent in a different direction, again dodging the question of what happens to the photon if left unobserved. Many attempts have been made to adjust the double slit experiment to avoid tampering with the photon while observing it, this field of study is called weak observation and is founded on Busch's theorem that there is "no such thing as a free lunch", that is, no information can be gained from a system without disrupting it and although it is a field of much merit, the researchers are still just staring at the wall of a cave.
