The Ongoing Challenge of Understanding Quantum Mechanics
Written on
In my earlier piece, I examined the peculiarities surrounding Quantum Mechanics. I concluded with a thought from Feynman: “Quantum Mechanics is so confusing that I don’t even know if there’s a problem.” Now, I aim to delve into why this confusion is so significant, complicating our interpretations of Quantum Mechanics and fueling ongoing debate.
There exists a multitude of competing interpretations, showcasing a diverse spectrum of preferences among researchers, even at the highest academic levels. Thus, the question of interpretation remains unresolved, and discussions are perhaps more vibrant now than ever before.
I will concentrate on the _Many Worlds Interpretation_ and the _Copenhagen Interpretation_, as they provide the starkest contrast in their descriptions of reality, leading to astonishing implications about our universe. Although Bohmian Mechanics is intriguing, I find it somewhat more complex; for those interested, I recommend seeking further information.
Additionally, I will explore the allure of linking consciousness with quantum mechanics. The history of quantum interpretations is peculiar, illustrating that even a community regarded as one of the most logical and analytical—namely, theoretical physics—can be vulnerable to human tendencies such as personality cults, political agendas, and dogmatism.
Sean Carroll has remarked on the embarrassment faced by twentieth-century physics for clinging to an outdated interpretation of quantum mechanics for too long, particularly since early discussions on the subject were often discouraged. A notable example is how Everett, the creator of the Many Worlds Interpretation, was essentially marginalized within the physics community. However, I will not recount that narrative here; interested readers can begin with David Albert's insights on Sean Carroll’s Mindscape Podcast.
In this article, I will strive to succinctly explain why the strangeness of quantum mechanics complicates its interpretation.
The Copenhagen Interpretation
The prevailing view among modern physicists continues to be the Copenhagen Interpretation, formulated by Heisenberg and Bohr in Copenhagen between 1925 and 1927. This interpretation was the focus of my introductory quantum mechanics course.
In my previous article, I discussed the nature of quantum measurement and highlighted the peculiarities that arise during such processes. I introduced the concept of a wave function and the fundamentally probabilistic nature of quantum measurements.
> The wave function encapsulates all known information about spin, embedding the statistical characteristics of the measurement within the fabric of reality. A spin wave function can be expressed as follows:
> spin = up z (50%) + down z (50%)
At the heart of the Copenhagen view lies the notion of _wave function collapse_. This concept posits that a quantum system—essentially every object in existence—remains somewhat undefined until an observer measures it, at which point it collapses into a defined state known as an eigenstate of an observable.
In this framework, the observer is considered to induce the collapse of the wave function upon reading the measurement device, as post-measurement, we observe a specific outcome rather than a distribution of probabilities.
Collapsing the Wave Function
Starting with the wave function:
spin = up z (50%) + down z (50%)
When we measure it, we encounter two potential outcomes:
- spin collapses into up z (50%)
- spin collapses into down z (50%)
However, this presents a modeling challenge within the theory. The observer is not treated as a quantum system due to its unique, inexplicable role in causing the wave function collapse. There is no inherent rationale for why a passive "observer" should possess such a distinctive trait.
A potential resolution is to consider the observer as a quantum system. Since every entity in the universe is a quantum system, it is logical that the measuring device should also be one. This is actually the approach taken in the standard quantum measurement known as _von Neumann measurement_.
We represent this interaction with a vector product between quantum states (denoted with a bold x), resulting in an entangled state:
total system = (observer measures up spin z) x (spin up z)
The observer is described by a wave function, meaning the observer measuring one outcome remains part of the larger total state of the system. The wave function of the system can be expressed as:
total system = (observer sees up z) x up z + (observer sees down z) x down z
This expression does not reflect what the individual observer perceives; rather, the observer witnesses only one branch of the wave function!
Observers = (observer sees up z) x up z or (observer sees down z) x down z
The critical distinction between these two lines lies in the “+” versus the “or.” If we utilize _+_, both branches persist. Conversely, using _or_ indicates that the wave function collapses to one possible measurement outcome, rendering only one result real, as stipulated by the Copenhagen Interpretation.
Applying this reasoning to Schrödinger’s Cat, upon opening the box, there exists only one reality in which the cat is either alive or dead. If we adopt the plus sign, the cat exists as both alive and dead simultaneously.
But where is it alive and where is it dead?
Is There More Than One World?
Assuming we employ the plus sign, this “branching” arises naturally when treating the observer as a quantum mechanical entity. The _total wave function of the universe_ splits into various outcomes, creating distinct worlds after each measurement.
In one world, the observer measuring the spin sees spin up, while it appears that a parallel world exists where the observer witnesses spin down.
These two worlds then proceed to develop independently! If we consider the entire measurement process from a quantum perspective—something we have no solid reason to avoid—the _Many Worlds Interpretation_ emerges more organically from quantum mechanics than the Copenhagen Interpretation, as it does not necessitate arbitrary assumptions regarding wave function collapse.
You may think that a minor detail, like the spin of an atom, wouldn’t significantly affect the universe's evolution. Yet, even the smallest difference can lead to profound changes.
Let me illustrate with a brief thought experiment:
Imagine establishing a _quantum casino_ where you gamble on spin measurement outcomes. You wager $100 on each measurement. The casino operates as a non-profit, so if you win, you receive $200; if you lose, you get nothing.
After a night of gambling, let’s say you place bets on 100 spin measurements. On average, your results might not be extraordinary; you could win and lose a few hundred dollars.
However, if you subscribe to the _Many Worlds Interpretation_, you can rest assured that there exists one version of you who had an incredible night, winning $10,000 and purchasing a new car, while another version sits in bed lamenting the loss of their daughter’s college fund.
This scenario is not merely theoretical; it is a consequence of one of the most prominent interpretations of quantum mechanics.
Pretty strange, right?
I'll give you a moment to absorb this with an image of stones on a beach.
I hope this provides clarity. Now, let’s return to the question of wave function collapse.
What Could Cause the Collapse of the Wave Function?
The collapse of the wave function occurs at the moment we observers become aware of the measurement outcome. According to von Neumann’s perspective, this is facilitated by “an abstract ego” that represents the measurement result's information content.
Figures like von Neumann and Wigner emphasize the importance of considering the observer’s subjective experiences for a comprehensive understanding of quantum mechanics. This consideration naturally leads to the idea that _consciousness_ plays a role.
The ambiguous relationship between consciousness and quantum mechanics has fueled a myriad of pseudoscientific theories, often propagated by figures like Deepak Chopra or the quantum healing community.
I am not aiming to delve into that debate here. The relationship between quantum mechanics and consciousness remains unresolved, though more scientifically grounded efforts are emerging to connect the two concepts.
Nevertheless, without a robust theory of consciousness, it is premature to assert that consciousness possesses the unique ability to collapse wave functions.
I believe a different perspective shift may yield more fruitful insights.
Quantum Mechanics as a Theory of Information
As highlighted in my previous article, epistemology (what we know about the world) and ontology (what exists) intersect within quantum mechanics. If we define reality based on our measurements, then reality is inherently influenced by our measurement processes.
Disentangling our role as observers from the so-called “objective” reality proves challenging.
For me, the most promising yet not fully developed approach to reconciling quantum mechanics' issues is to view it as a theory of information. Wheeler famously coined the terms “It from Bit” and “It from Qbit,” while Carl Friedrich von Weizsäcker explored the concept of “Urtheorie,” alongside numerous other theorists tackling this challenge.
Information could serve as the fundamental unit of reality, linking objective, material aspects of the world to subjective experiences—an endeavor long pursued by proponents of Neutral Monism.
Thus, discussing an objective world independent of observers becomes somewhat futile, akin to Kant's argument that a viewpoint "from nowhere" is fundamentally inconsistent.
Perhaps this perspective may clarify our role in interacting with quantum phenomena.
However, as you can likely discern, clarity remains elusive, evoking both excitement and frustration.
Ultimately, that’s the essence of quantum mechanics, and we might need to come to terms with it eventually!