Physics and Intuition
Physicists experienced an intellectual problem early in the twentieth century when they first encountered Einstein’s Special Theory of Relativity. I would define this problem as the failure of intuition. Most of classical physics could be learned by extending intuitive ideas that people learn informally in their normal life experience. Anyone who has been pushed knows what a force is, and anyone who has fallen notices that the earth exerts a pull on us. Newton and others quantified these effects with mathematical rules that are still of enormous value to all scientific endeavors.
When Michelson and Morley showed and Einstein postulated that light travels at the same speed for all observers, human intuition was suddenly challenged in a major fashion. After all everyone knows that a ball thrown on a moving train is traveling faster than a ball throw in the station. In addition Einstein’s mathematics implied that time itself was “relative” and that no two distinct events were unequivocally “simultaneous”. To further the confusion, before people were even comfortable with the peculiarities of relativity, quantum theory came along and challenged the very concept of “thingness” i.e. were “things” particles or waves.
This latter problem remains an incompletely solved mystery even today. In this short paper I will outline what I think is the solution to this issue. By “solution” I mean a way of thinking about the world that once adopted makes quantum theory intuitive. My approach is arguably just a variation on Bohr’s Copenhagen interpretation with an admixture of philosophical empiricism. It elaborates on (restates?) Bohr in a way that I think can be fairly easily accepted if we shed some of the prejudices we all acquire early in our childhood. The problem is that we acquire them so early we never think of them as being assumptions.
To illustrate I begin my story in Munich in 1993. In February of that year our first grandchild (a boy) was born in Munich. We were naturally excited and flew over to view the chosen one when he was only a few weeks old. One evening as my wife and daughter were preparing dinner, I was left alone with little Alex to protect him from whatever evil spirits prowled Drachensee Strasse in the early evening. I watched him closely and noticed how his eyes darted about looking here and there, (I have since noticed that all babies do this even the unchosen) I thought he must be wondering who this strange middle aged guy with a mustache was. Then I had my epiphany. Alex didn’t see a moustache or a man. He saw only a swirl of changing colors in his visual field. His mind was receiving and trying to process an avalanche of data that had been burying him ever since he entered the world a few weeks before. In some way that we incompletely understand, he was gradually organizing the patterns of visual and auditory data he was receiving into “things” his mind could remember and identify when they appeared again. We all proceed along this path usually labeling the first real thing we put together as “mama”.
The main point here is that “things” are composed of “data” that the human mind receives. The data is external to ourselves. The things we create are in our mind. I think this was what Dr. Johnson meant when he famously kicked the stone to disprove “Bishop Berkeley’s ingenious sophistry” (see "Life of Johnson", James Boswell, Aetat. 54, Aug. 6, 1763). The data that the impact of shoe and stone sent to his mind was from external reality. However I would contend the "stone" was just a mental construct he (and the rest of us) put on some visual data. That particular mental construct is of enormous practical value in the avoidance of toe stubbing. In the end it is the “practical value” of all the mental constructs we call “science” that is important.
In what follows I will use the term “data” to refer to the information we receive from what we call the outside world (outside meaning external to our thoughts). I will use “mental constructs” to refer to the names we give to certain data patterns and to the theories we posit to describe how those patterns interact.
Per Descartes all we know is that we are thinking, essentially an internal activity. It is the data we receive from our senses that gives us something to think about. Confusion arises because as very small children we get some mental constructs so fixed in our mind that we endow them with an external reality that they may not deserve, but by so doing we derive a very useful model of the world.
Quantum theory and the various experiments confirming its curious nature challenge this model. The issue I believe is that the macro world in which we live our daily lives constantly sends us (like Alex) avalanches of data. Hence the necessity and value of the aforementioned model. The micro situations studied in quantum theory are at the other end of the data spectrum. They have a great paucity of data. On the one hand, the quantum particle drifts towards the double slit without interacting with anything. On the other, a baseball hurled towards a batter experiences a google of interactions by the time it crosses the plate. This swarm of interactions (often referred to as “decoherence”) gives us a deeply seated notion that proper objects exist continuously in time. Thus we invent the concept of a subatomic particle even though we have never really seen one in the conventional way that Ted Williams saw an approaching pitch.
I would maintain "particle" is a bad word to use in the quantum domain because it plays to our prejudice towards the continuous existence of objects when quantum experiments are telling us just the opposite. We have been in denial for almost a century. Only data points (measurements) exist externally to ourselves!!!
Of course we have been taught that a particle is also a wave so perhaps waves continuously exist. This is at least what people who are concerned about wave collapse seem to believe. However what is it that is waving. It is sometimes said there is a probability wave. Is probability some kind of ethereal medium permeating space? No, probability waves are mental constructs existing internally in our minds!!!
I will give an analogy which though it deals with classical macro phenomena illustrates that the wave equation is a mental construct and therefore quite collapsible. Let us recall one of those World War II movies that show a naval intelligence unit trying to track an enemy battleship. The scene shows a large room with an extensive map of the Pacific ocean laid out on the floor. A scout plane near the limit of its range suddenly sees the battleship and radios its position to headquarters, and then must turn back towards its base. A little model of the ship is placed on the map at the point of sighting. Now the problem becomes where is it going. A clever young lad (probably a physics graduate student in civilian life) starts to work out a function that gives the probability density of the ship being at coordinates x and y at time t. He would base his formula on the direction the ship was headed, its speed, and other guesses as to ports it might call at, what missions it might be on, etc. After some hours this position probability density function would have non-zero values spread out over a rather large space of ocean. Now suddenly a radio report is received from another scout plane giving a precise sighting of the battleship. The young man’s (wave?) function has collapsed! Interestingly though there is no great intellectual crisis in the war room over this mathematical discontinuity. No one had ever endowed this equation with a quality of external reality. It was clear to all that it was merely a useful mathematical construct. Upon receiving the new sighting our hero would proceed to derive a new equation based on the latest available data.
I realize that this differs from a double slit experiment in that the battleship does have (in a macro sense) a continuous reality while it was not being observed by the US Navy. An interview with one of its sailors would easily establish this fact. The course of the battleship is the ultimate in decoherence. On the other hand our quantum particle does seem to truly disappear when we are not looking. What does "looking" mean? It means interacting. "Interacting" means making a detectable change in the environment. No interaction, no particle. A wave perhaps, but a wave is just a mental construct.
My contention is that when a double slit type experiment is performed the only data is the emission event and the constraints of experimental apparatus. The wave equation (the mental construct) is derived based on this knowledge. When we know a particle is emitted we have a piece of data (initial condition). The wave equation then evolves (a bad word as it may imply external existence to the casual reader). The wave equation is our brilliantly derived predictor of what is going to happen. Unlike classical physics it yields outcome probabilities rather than unequivocal results. Nonetheless it is very useful. Once something does happen (a detector is triggered), we can discard our equation and construct a new one based on the additional data we have just received much like our Naval officer when he received the second sighting.
Of course, if we change the experimental set up a new predicting equation is required even if we make the change while the particle is in motion (it has not yet interacted with anything). This is essentially Bohr’s complementarity idea and decoherence.
In summary I think if one can summon the will to discard the idea of the continuous existence of “things” one will find quantum theory much more intuitive. To do this one has to carefully examine why we are so attached to the continuous concept. The evidence for it is completely set in the macro world. The evidence against it is set in the micro (quantum) world. I would contend continuous existence is an “effective theory” that breaks down at small scales. We even feel that our thoughts are continuous, but we would be hard pressed to separate them into even millisecond intervals.
For the philosophically inclined I know much of the above was posited long ago as empiricism, skepticism, etc. My ideas here were derived to" fit the data". To the extent they coincide with those of well known philosophers the data may constitute a sort of "proof" of their ideas. I am not going to speculate on this as my knowledge of the pertinent philosophical schools is at best very sketchy.
