How are quantum observers different and why they invoke a sense of understanding this underlying reality of ours, while it has actually no equivalent in our daily lives. “Prima facie quantum theory does differ from classical physics regarding the relationship between physical entities and consciousness.” (Shimony, 759)
The realm of quantum mechanics, with its wave functions, superpositions and entanglements, seems surreal and distant from our everyday experiences. Yet, these quantum phenomena make up the very fabric of our reality. The transition from this quantum strangeness to our familiar, classical world remains a central puzzle in physics, and much of this intrigue revolves around the concept of the "observer." It has inspired countless tales of how our conscious choices or the focus of our awareness towards reality will somehow magically influence it – the Dunning-Kruger effect has struck yet again. Or with words of the famous philosopher of science for constructive realism – Fritz Wallner, “there’s no real-world constructivism, it’s a purely scientific phenomenon at work in the realms below our perceptible or even perceivable universe.” (Wallner, 53). But let’s go one step back.
At the heart of quantum mechanics lies the wave function, a mathematical construct that encodes the probabilities of different outcomes for quantum systems. It contains a real part (blue) and an imaginary part (red). They are both equally important and together provide a complete description of the quantum state. The "imaginary" in this context doesn't mean that it's fictitious or not real in a practical sense. Instead, it refers to the mathematical concept of imaginary numbers. An imaginary number is defined as the square root of a negative number depicted with the symbol "i", where i² = -1. (cf. Pierce) On the right side there’s a probability distribution of finding a specific particle within the wave function. (Pic 1)
Imagine this wave to oscillate constantly instead of being stationary and you will understand that the moment a particle is
found the whole wave function “collapses” to a single outcome. "Collapse" in this sense doesn't mean the wave function physically crumbles or falls apart, but rather, it's a metaphor for the
rapid and seemingly discontinuous change from a spread-out wave of probabilities to a single, localized reality upon measurement. (cf. Ross)
This measurement is the act of observation. But who or what constitutes this observer? Does observing require consciousness, or can inanimate objects get it done?
Contrary to popularized views, the observer in quantum mechanics doesn’t necessarily refer to a conscious entity. It can be as mundane as a particle detector or even interactions with surrounding particles. This is when the concept of decoherence enters the scene. Decoherence describes the process by which a quantum system, through interactions with its environment, loses its distinctively quantum behavior and begins to behave more classically. (cf. Bacciagaluppi) This isn't because the system abandons its quantum nature but because its quantum information becomes intertwined or "entangled" with the environment, rendering quantum superpositions challenging to observe.
All matter, including what we term the "environment," is composed of quantum systems. The paradox appears when quantum entities interact with this environment. Despite the environment itself being quantum in nature, the sheer complexity and number of these interactions result in rapid decoherence. The quantum information, instead of being localized within a system, becomes dispersed. This dispersion masks the intrinsically quantum behavior of systems, making them appear classical.
It was actually Erwin Schrödinger (among others) who used a seemingly real-world phenomenon - a cat - to introduce quantum mechanics and its intricacies to the general public by asking a simple question: Is the cat sitting in a closed box attached to poisonous apparatus activated by a decaying radio-isotope alive or dead and how do we know?
Several interpretations have tried to answer this question such as
1. Copenhagen Interpretation: This is one of the most widely taught interpretations. It posits that it's meaningless to assign a reality to the cat (or any quantum system) until an observation is made. The act of measurement causes the wave function to collapse to a definite state.
2. Many-Worlds Interpretation: This suggests that at the point of measurement, the universe splits into multiple branches. In one branch, the cat is alive, and in another, it's dead. Both realities exist in parallel universes.
3. Objective Collapse Theories: These theories suggest that wave functions collapse spontaneously over time, without the need for an observer. This would mean that the cat would naturally evolve into a definite state of being alive or dead after a certain time.
4. Pilot Wave Theory (or de Broglie-Bohm Theory): This interpretation posits that particles always have definite positions and are guided by a "pilot wave." In this view, the cat would always be either alive or dead, but our knowledge is limited due to the probabilistic nature of the guiding wave. (cf. Lewis)
So as you can see, there’s still no constructive or magical aspect to any of these ideas. None state that by looking at something you will create a new reality for the thing you’re personally looking at. Amidst these varied interpretations, one thing is clear: our classical intuitions almost always mislead us when navigating the quantum domain. While the macroscopic world seems definite and deterministic, the underlying quantum world operates by different rules, where probability reigns supreme.
Simply assume the classical reality we perceive might be an emergent phenomenon from countless underlying quantum events. Imagine endless quantum "collapses" or interactions happening so frequently and swiftly that the macroscopic world simply emerges as stable and predictable. Our everyday reality, in this view, is like a "slowed-down" cinematic projection of rapid quantum frames.
But why don’t we see cats that are simultaneously alive and dead or objects hovering in mid-air? The continuous interactions and "measurements" by the environment on quantum systems might be the key. These continuous interactions ensure that macroscopic objects appear to possess definite properties, like a specific position or velocity.
Lastly, while we strive to comprehend the quantum realm, it's crucial to recognize the limitations of our perceptions and intuitions at the fabrics of reality. The observer, whether conscious or not, plays a pivotal role in this dance between the quantum and the classical realm. And while we might feel estranged from the quantum world, it's worth remembering that it's not the quantum world that's strange, but perhaps our classical perceptions that leads us astray. So while the search for definitive answers still continues and may never be finished let’s at least try use the right tools to discuss the impossible nature of our reality.
by mario
Bibliography:
Bacciagaluppi, Guido: The Role of Decoherence in Quantum Mechanics (2020) https://plato.stanford.edu/entries/qm-decoherence/ (reviewed 01.11.2023)
Lewis, Peter J: Interpretations of Quantum Mechanics: https://iep.utm.edu/int-qm/ (reviewed 01.11.2023)
Pierce, Rob: Imaginary Numbers (2023): https://www.mathsisfun.com/numbers/imaginary-numbers.html (reviewed 01.11.2023)
Ross, Douglas: I don’t understand Quantum Physics – Wavefunction Collaps: https://www.southampton.ac.uk/~doug/quantum_physics/quantum_physics.pdf (reviewed 01.11.2023)
Shimony, Abner: Role of the Observer in Quantum Theory: Am. J. Phys. 31, 755–773 (1963) https://doi.org/10.1119/1.1969073
Wallner, Fritz: Culture and Science: A new constructivistic approach to philosophy of science; lectures on constructive realism (1996–1999). (= Philosophica 20). Braumüller, Wien 2002,
Images:
Pic 1: https://en.wikipedia.org/wiki/File:StationaryStatesAnimation.gif
