Further Thoughts About The Semantics of the Double Slit Experiment
Swinton Roof
Sept. 7, 2001
The have been many attempts to interpret the unusual results of Quantum Theory. Most interpretations accept a paradox and experimental givens as their starting point and then try to come up with an interpretive mechanism to explain the paradox in terms of additional features of nature or theory. Other interpretations simply say there is no interpretation possible. I want to suggest a third possibility - re-evaluate the original givens in the experiment and pay especial attention to the semantics of description. This is what I shall do with the double slit experiment. The reader may discover in the process, that what he thought he knew may not be what he should be thinking in this experiment.
In my previous paper "A Semiotic Analysis of the Double Slit Experiment", I explore the experiment in terms of signing and demonstrate that the semantics are consistent and really don't reveal a paradox. The paradox turns out to be a semantic issue. The paper, however, did not explore the source of this semantic error. That is what will be done here.
At the very heart of the double slit paradox is the apparent contradiction of having a particle go through two slits at the same time and conversely, the paradox of having mere knowledge influence the outcome i.e. If you do determine a particular path, the interference disappears. The entire paradox hinges on viewing the photon as a discrete particle, but the experiment is classical and there is no paradox so long as the light has not been reduced down to emitting photons one at a time . Thus we need to focus on how 'particle' enters the experiment. How do we know the light is emitting particles anyway?
The usual method of getting the light source down to emitting a particle at a time is to reduce the intensity with a filter until a photomultiplier tube detector flashes one blip at a time. At least I believe that is the case. At any rate, the question still remains - How do we know the light is emitting particles? The answer goes back to the very origins of Quantum Theory. The photoelectric effect established the quantum nature of light. J.J. Thompson and Milikan had previously established the mass and charge of the electron and the means thus to measure it's energy by observing it's path across an applied voltage and magnetic field. Einstein used this previous work to analyze and explain the photoelectric effect.
The basic photoelectric effect is that electrons are emitted from a special surface when light of the proper frequency shines on it. It was found that the energy of the released electrons was exactly proportional to the frequency of the light, not it's intensity. The number of electrons emitted was exactly proportional to the intensity, but the momentum or energy of the electrons was defined only by the frequency of the light. No other frequency would produced an ejection. The energy was quantized. No other energies were permitted. The total intensity of light was measured in discrete multiples of a fixed minimum energy. Einstein showed that the relation was E = h * f where E = energy of electron, h = Planck's constant, and f = frequency of light. I believe this was indeed the experimental method for determining Planck's constant, at least during that time period.
Einstein postulated that light was emitted in discrete packets with an energy determined by the above relation. I assume that thorough checks were made of the experimental apparatus to determine that no other energy was leaking out or appearing as heat, stray light etc. Physicists were forced to accept the quantum nature of light and gave the name 'photon' to these particles. The experiment is so convincing that once the label 'photon' was applied, everyone more or less accepted the indubitable results, strange as they were. An exact formula for the phenomenon indeed made it ironclad.
Unfortunately this is when semantics entered the picture. Now I wish the reader to invoke his basic idea of what a particle is. I imagine that most readers will say, something that has a certain mass and a certain size - usually very small, and probably not easily divided. Some may include energy in the description, but I believe the first two features are most definitive of the word particle. Now if you just step back and think, you will realize that nowhere in the above experiment are mass and size a factor. They are for the electron, but the photon has no mass or size! What happened? Well, all previous experiments with light had revealed a wave nature and waves aren't quantized. They are continuous and spread out. If it wasn't a wave well, then it had to be a particle! A special kind of particle, but a particle.
Once the label 'photon' was put on light, it stuck. This in essence is a semantic abduction! Once 'photon' became accepted, then the word 'particle' became inextricably associated with 'photon'. The only aspect of light quantized in the experiment was the energy. In fact the two most defining aspects of the word 'particle' are mass and size - neither of which is a property of light! This unfortunate semantic mistake locked physics into viewing the quantum theory of light as expressing a wave/particle duality - a paradox. The experiment, though, says absolutely nothing about particles! Think about this for a while until the truth begins to sink in. This semantic error has run so deep through Quantum Physics that it is almost gospel. It has even spawned all sorts of absurdities such as alternative universes, and all sorts of implicit mechanism to explain the many other paradoxes that emerged as a result of faulty thinking!
Now one may argue that the electrons are particulate and are kicked off the surface at very specific physical locations. But what does that tell one about the nature of the light itself. How do you know that that particular electron wasn't somehow critically disposed to absorb at that postion due to thermal jostling. Which electron absorbs the so called photon is random on the macroscale, but yet again, does this mean the photon is a particle? does it even mean that that exact point is where the photon struck? Of course not! Just how big is the photon anyway? In the end, all we know is it's energy. It is very important to understand that no one ever even observes a photon directly. No physicist sees little waves or particles running around and striking electrons. This fact cannot be overstressed. all of our knowledge is based on information which consists of physical measurements which are physically observable! Any added interpretations are extra semantic baggage thrown in to make more sense. More sense can be an error however when you throw in things that really dont belong - things like mass and size for instance.
Most physicists are saavy enough not to think of photons as having a mass and size, but nonetheless after using the 'particle' word so many times and noting countless experiments that beg one to use this word, they fall prey to actually experiencing semantic discord at some of the experimental results. It's a semantic issue! In fact, the very use of the word 'photon' as a noun means one is semantically disposed by connotation to think of a photon as a thing, when actually the physical experiment itself never revealed any thing at all except electrons! In fact, one can quite happily re-formulate quantum theory (actually it's an interpretive matter, not a matter of changing any equations) to simply restate all photon-electron interactions as electron-electron couplings ( or other: electron-positron etc.). This is because for every 'apparent photon' absorbed by an electron, that 'apparent photon' was emitted somewhere else by another electron. This is indeed how the speed of light and it's energy is determined! By making measurements on electrons! The emission event (barring certain quantum situations and relativity) always occurs prior to and some distance from the absorption event. Energy does seem to be traveling across space and time and it is indeed quantized. It's a semantic thing. We naturally tend to think of action at a distance as involving some sort of bullet or mechanism to accomplish the change, when actually the only real knowledge we have is of a CORRELATION between two events in space time.
It is interesting to note that the force of gravity always had a singular one-sided result on both sides of the equation (always attractive) and there was no experiment that could detect any sequence or order to the effect i.e. it was instantaneous.Therefore simple action at a distance was simply accepted for gravity without question. When one thinks about it, gravitational energy is really spread across both attracting bodies i.e. it resides in the system relationships as a whole. No intermediary transmission of particles was invisioned (although there are attempts at quantum gravity descriptions now being made). Quite simply put, it was the time lags involved with electron-electron correlation experiments, that invited physicists to imput moving particles as carriers of energy into the interpretive picture. Why weren't physicists able to reason out electron-electron energy changes as a system property, just as it is with gravity? Probably because of our experience with macrosize human scale objects. Once the photon/particle terminology was accepted into wide use, it influenced the development of quantum theory for the next 70 (?) years.
Once one realizes that the original starting theory has invalid semantic conclusions, one must then also realize that most current interpretations or conjectures of quantum theory inherently contain these very same semantic flaws which need to be weeded out or at least looked at to see if they produce invalid conclusions. Semantic abduction is not peculiar to physics. It occurs every where novel ideas are explored. It just takes time for the true relations to emerge and the the fluff to be discarded.
The reader may be wondering what kind of interpretation I would prefer for a photon. Ok, let's do it this way - If one insists on using the word 'photon' in a virtual particle sense only, like we use the zero digit as a null place marker in arithmetic, then I will acknowledge this as a valid use, but only as long as one understands the symbolics of the abstraction and the semantics of that convention! When one takes this stance, the photon can have only one meaning - it is purely a symbolic shorthand for Schroedinger's quantum wave equation. Feynman was perhaps one of the few physicists who understood this and developed ways to solve the equation by using techniques such as summing over all possible paths that an imaginary particle might have taken. It is when one uses the word 'photon' in a colloquial sense that the problems erupt and paradoxes appear. Feynman himself slipped into this trap and actually thought there was a true paradox of nature in the double slit experiment, but at least he had the sense not to identify the imaginary with the real. Subsequent physicists have not always been so enlightened.
To repeat, I said beore that at the very heart of the double slit paradox is the apparent contradiction of having a particle go through two slits at the same time and conversely, the paradox of having mere knowledge influence the outcome i.e. If you do determine a particular path, the interference disappears. The semantic issue here, is that we are using the word 'particle' in a colloquial sense with all the qualities that light was never demonstrated to have! To add insult to injury, we have grossly identified the experimenter's knowledge as being the deciding factor, even when we know that the experiment works exactly the same, even when the observer isn't present at all. The knowledge of which slit is involved is really an example of physical information as a process of system selection - it is an example not of knowledge but of causal linkage. Knowledge doesn't emerge as descriptive of relations until the experiment runs long enough for the conclusive pattern to emerge one detector hit at a time on the final output screen. Knowledge didn't influence the outcome because knowledge doesn't appear until after selections are made. This is an example of dirty little secrets that semiotic investigation exposes.
Once one undergoes the shock and depression of having his semantic illusions torn asunder, a new level of understanding can be achieved. The world is still quite mysterious and difficult to explain, but an appropriate mode of investigation can then proceed. One new insight is that the nature of reality can only be partially known and that our knowledge is a blend of the object of knowledge plus the particular selective process used to acquire that knowledge. Our understanding is quite literally colored by or dependent on our perception to begin with, and it is an implicitly active process involving intentionality. As we design and carry out experiments, the instumentality we construct will quantify (not just qualify!) what we observe. And I do mean quantify in a very literal sense of the word. That is why quantum physics is so darn quantified. Symbolics is quantification, by the way.
One last note: The 'is' word IS especially deadly as it IS quite literally a semantic short circuit which identifies the sign as being the referent! Why use it? Because it's useful of course! Just remember to mind your 'p's and 'q's, children.
"It depends on what 'is' means." ... Bill Clinton
"No one knew how correct old Bill really was!" ... Rasputin11
P.S. For further reading you can get more depth on the double slit experiment by reading my paper "Quantum Diaries" on my web site essays page at: