Copenhagen Interpretation

This is an excerpt from the book series Philosophy for Heroes: Continuum.

What is the ontological view of the Copenhagen interpretation?

The unexplained mystery of thermal radiation (among others, like the photoelectric effect) led to the theory that light comes in packages: the quantum theory. The first interpretation to explain the quantum theory epistemologically was the Copenhagen interpretation. It was first formulated in 1927 by Niels Bohr, John von Neumann, and Werner Heisenberg, and became the most popular explanation of what is actually going on at the quantum level.

It stated that particles do not exist (meaning that they do not have definite properties) as long as you do not measure (observe) them. The “observation” part does not depend on whether a human scientist is actually looking at the particles; a measuring device interacting with a particle is enough. Before the measurement is taken, a particle exists only as a probability, e.g., 50% outcome A / 50% outcome B. But after the measurement, is it reduced to a single value. For example, take the process of flipping a coin: while it is in the air, you cannot tell on which side it will land. Only once you “take the measurement,” i.e., catch the coin, it is reduced to heads or tails. In the Copenhagen interpretation, this process is called the “collapse of the wave function.”

With that in mind, let us look again at a common experiment, the already mentioned “double-slit experiment.” You have a screen on the right side, and a screen in the middle with either one or two slits (see Figure 3.12). In classical mechanics, if you shoot small particles of matter on a screen with one slit, a simple probability distribution shows up on the screen on the right side: most of the particles will hit the middle. With two slits, you end up with two peak locations on the right screen. On the other hand, if you were to send a water wave through the slits, two separate waves would come through, each interacting with the other, resulting in an interference pattern, where parts of the wave reinforce each other, and parts cancel each other.

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In quantum mechanics, this kind of interference pattern also shows up with particles. Even if you send individual particles one after the other (as opposed to a continuous stream of particles), an interference pattern will emerge. With only classical mechanics in mind, it looks as if the particle passes through both slits and then interferes with itself: it acts like a wave. This wave behaves differently from classical waves as you will ultimately see only one outcome (and not a “wave” hitting everything in its path).

In this context, we have to remember the previous section about Heisenberg’s uncertainty principle. We cannot observe something without somehow interfering with a particle. For our eyes (or a camera) to work, we need to cast light waves on an entity. This means that adding any type of detector (“observer”) near the slits to check through which slit the particle passed will not help: this will collapse the wave function and the wave will return to acting like a particle.

But what exactly is an “observer”?

The Observer

In classical science, we look at the world from the outside. Entities and events of every kind are dissected into their parts and then separately surveyed and categorized. This includes the observing scientist and the test equipment: in order to create an observer-independent model of reality, the result of the test must not be influenced by the test itself. This also makes it possible for the experiment to be repeated by other scientists.

Example When measuring the heat generated by a chemical reaction, the temperature first has to be controlled by putting the experiment into a sealed container of constant temperature and leaving the scientist outside in order for the body temperature to not influence the result. This is at least the basic philosophy of classical physics. This approach has brought us as far as the moon—at least the moon landing could have been successful with classical mechanics only.

For, as this interpretation now stands, it is always necessary to assume an observer (or his proxy in the form of an instrument) which is not contained in the theory itself. If this theory is intended to apply cosmologically, it is evidently necessary that we should not, from the very outset, assume essential elements that are not capable of being included in the theory. —David Bohm, The Undivided Universe [Bohm and Hiley, 1995, p. 4-5]

The challenge is that if you focus only on the “how” (epistemology) and not on the “what is” (ontology), you end up being a disembodied observer. But in fact, there is no such thing as a disembodied observer, as you are always part of any experiment you are doing. At the small scale, you cannot observe a particle “from the outside” without influencing its state, no matter what precautions you take. As we have concluded in the first book, epistemology and ontology are strongly intertwined! You cannot start with epistemology and then create an ontology out of it and vice versa.

To repeat a quote we have read in Philosophy for Heroes: Knowledge:

[Ontology] and epistemology are simultaneous—what exists and how we know it are the foundation that starts together. And that’s why the very first axiom is “Existence exists, and the act of grasping this implies there is something, and we have the faculty for being aware of it.” And thereafter we shift back and forth, “We have consciousness,” “A is A,” “Existence is independent of consciousness,” “We acquire knowledge by reason,” and so on. [Ontology and epistemology] are completely intertwined. —Leonard Peikoff, Understanding Objectivism [Peikoff, 2012, p. 170]

Many technologies of the last century—whenever accuracy was needed—be it the atomic clocks used for the Global Positioning System (GPS), lasers, semiconductors for computers, or Magnetic Resonance Imaging (MRI), rely on quantum mechanics (and the theory of relativity). There, you are dealing with very low energy levels requiring high accuracy. When experimenting with individual particles, the influence of the observer becomes significant. As discussed in the section about Heisenberg’s uncertainty principle, any measurement of these particles would influence their impulse or location.

In the first book, Philosophy for Heroes: Knowledge, we stressed the important difference between the approach in Objectivism and in (classical) science. In Objectivism, you start out with your own existence to make a statement about the world. Its basic axiom is “I exist, I have an identity, and I can be conscious about this fact.” So, the essence of philosophy is to understand yourself as being part of reality, rather than isolating yourself from reality as a passive observer. Hence, at least on the epistemological level, our philosophy is in line with modern physics.

But having confirmed the quantum theory with our philosophy is not enough. The theory only provides an epistemological explanation.

What is really going on?

Quantum theory is primarily directed towards epistemology which is the study that focuses on the question of how we obtain our knowledge […] It follows from this that quantum mechanics can say little or nothing about reality itself. In philosophical terminology, it does not give what can be called an ontology for a quantum system. —David Bohm, The Undivided Universe [Bohm and Hiley, 1995, p. 2]

Example The idea of the Copenhagen interpretation that nature stops and sits on her hands when a measurement is made is strange, ontologically speaking. Imagine a lake. There is someone throwing stones into the water, causing lots of ripples. Now, close your eyes. You can no longer see the ripples in the water, but you assume that they are there. Then, you hold your hand in the water to feel the ripples splashing against your skin. Suddenly, aside from the water splashing against your arm, the whole lake becomes quiet. You have “collapsed the wave function” of the lake into “real water particles hitting your hand” by taking a measurement. You remove your hand from the water, and open your eyes: the lake is again full of ripples.

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Taken to its conclusion, the Copenhagen interpretation posits that nature is undefined until it is observed. That poses a problem: what about the observer? An undefined observer cannot observe until another observer observes the observer. An undefined entity has no properties! Ultimately, this adds an infinite recursion (see Figure 3.13) to the answer—with no explanation who the “first observer” would have been. It is then argued that this would be proof that the universe has some sort of supernatural observer (e.g., God) that observes everything in order for it to come into existence.

[…] from some popular presentations the general public could get the impression that the very existence of the cosmos depends on our being here to observe the observables. I do not know that this is wrong. I am inclined to hope that we are indeed that important. But I see no evidence that it is so in the success of contemporary quantum theory. […] The only ‘observer’ which is essential in orthodox practical quantum theory is the inanimate apparatus which amplifies microscopic events to macroscopic consequences. —John Stewart Bell, Speakable and Unspeakable in Quantum Mechanics [Bell, 1988, p. 170]

Similarly, physicist Erwin Schrödinger saw a problem with the Copenhagen interpretation. To illustrate the problem, he came up with the thought experiment “Schrödinger’s cat.” In this experiment, there is a decaying nuclear isotope connected with a detector which releases a deadly gas into a box that contains a cat (see Figure 3.14). With the ontological interpretation of the Copenhagen interpretation, the cat would be both dead and alive: just like the particle, it would have no definite properties; the cat would be the macroscopic representation of the (supposedly) undefined state of the microscopic particle.

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[…] the Copenhagen interpretation as such totally evades the real question, which is how the quantum-mechanical description at a microscopic level becomes converted into a classical one at the macroscopic level […] —David Bohm, Quantum Implications: Essays in Honour of David Bohm [Bohm, 1991, p. 93]

The crux is the detector that connects the microscopic with the macroscopic world. It is as if you held a pin that is so pointed that there is but a single atom at its end, touching another particle. In that regard, your hand holding the pin is “classical,” the particle is “quantum mechanical,” and the pin is something in between. This “something in between” is the very point of the example, showing that the concept of splitting both “worlds” does not make sense.

How exactly is the world to be divided into speakable apparatus […] that we can talk about […] and unspeakable quantum system that we cannot talk about? How many electrons, or atoms, or molecules, make an “apparatus?” —John Stewart Bell, Speakable and Unspeakable in Quantum Mechanics [Bell, 1988, p. 171]

QUANTUM WEIRDNESS ·  The concept of quantum weirdness refers to the unintuitive results we see when looking at effects in the quantum world. Intuitively, we expect everything to act the way it does in our immediate, slow-moving and high-energy “macro-world.” But for particles, this intuitive approach does not work, hence we call the quantum world “weird” in that regard.

Because there is no clear line between the microscopic and macroscopic world, the Copenhagen interpretation of ontology needs to be cast into question. While this approach of seeing the observer and observed as two separate worlds is very problematic, this of course has no influence on the quantum theory, i.e., the mathematical calculations of how particles behave at a quantum level. But it has everything to do with the ontological interpretation of these results. And as we will see in the following pages, there are other interpretations based on the same mathematical calculations that do not introduce such “weirdness.”