The Phantom Cat
Why Schrödinger‘s Cat Paradox is So Important?
“God does not play dice with the universe.” – Albert Einstein
Or does he?
Thought experiments are the intellectual crucibles to transform abstract thoughts into profound insights. And no thought experiment captures the attention quite like Schrödinger's cat. Conceived by the Austrian physicist Erwin Schrödinger in 1935, this paradox seeks to illustrate the peculiarities of quantum mechanics, challenging our understanding of reality and observation. This enigmatic feline does not belong to any family rather it creates her own, with her peculiarity, absurdity and with a sense of nonsense. To describe our reality in microscopic world is extremely difficult. The electrons spin, the protons and neutrons exhibit exotic properties, the strong force remains potent even at the tiniest scales and the Uncertainty Principle asserts its influence, ensuring that interactions among particles are spread like a complex web, it is almost impossible to measure anything without disturbing the system. But scientists are stubborn, and they get together to interpret and put forward a standard set of rules for the measurement of such kind of system. There are two different interpretations for the measurements of microscopic world each one with its own perks and demerits. The Copenhagen Interpretation and The Many Worlds Interpretation. But for the sake of simplicity, we will confine ourselves with the prior one.
The Problem
During the 1920s Heisenberg was an assistant to Niels Bohr in Copenhagen. The Copenhagen interpretation, popularized by Niels Bohr and Werner Heisenberg, suggests that physical systems generally do not have definite properties prior to being measured. Instead, measurement forces the system into one of the possible states. It’s like saying we don’t know how much of some flour is inside a 5kg bag, until we put the bag on a weight machine. Schrödinger's thought experiment was designed to critique this Copenhagen interpretation of quantum mechanics, which posits that particles exist in all possible states until measured.
The Paradox
In a simple yet profoundly unsettling setup, Schrödinger proposed a cat placed in a sealed box with a radioactive atom, a Geiger counter, a vial of poison, and a hammer. If the Geiger counter detects radiation, the hammer breaks the vial, releasing the poison and killing the cat. According to quantum mechanics, until the box is opened and observed, the cat exists in a superposition of states—simultaneously alive and dead. Provided you have put a constraint on the meowing of the cat. This paradox starkly contrasts the classical view where the cat must be either alive or dead, not both.
According to quantum mechanics, until the box is opened and observed, the cat exists in a superposition of states—simultaneously alive and dead. This paradox starkly contrasts the classical view where the cat must be either alive or dead, not both. Provided you have put a constraint on the meowing of the cat.
So, we have a problem and a deep one. It raised several questions about our objective reality and its nature. What constitutes a measurement? Why does observation seem to affect reality? And does consciousness play a role in the collapse of the wave function?
The Role of Observer
In his book “The Black Swan” Nassim Nicholas Taleb (It’s a wonderful read!) discussed about the problem of induction. No matter how many times you feed a turkey before the Thanksgiving that tells nothing about the state of the turkey after the Thanksgiving (dead). So, the state of the turkey is unknow till the Thanksgiving appears. In our case the state of the turkey (dead or alive) is the microscopic system, the Thanksgiving Day is the measurement. And the person usually feeds the turkey is the observer.
In classical physics, observers are passive, merely recording pre-existing properties of objects. In quantum mechanics, the act of observation seems to play an active role in determining the outcome of a measurement. This notion is encapsulated in the famous quote by physicist John Wheeler, "No elementary phenomenon is a phenomenon until it is a registered phenomenon." In other words, reality at the quantum level does not crystallize into a single outcome until it is observed. But the counter argument is, if an observer can affect a reality, then the very purpose of an observer is defeated, and she no longer remains a passive entity to the system rather become an active one. Scientists who believe quantum physics is perfectly consistent generally defends this by arguing that the very act of observation is what defines an observer. Thus, the act of observation also changes the state of the observer too. Instead of asking what causes the collapsing of the state to a particular observation, one could ask why am I prone to observe this particular observation? And the answer according to the Copenhagen interpretation would be, ‘It is the observation of this particular state is what makes the observer.’ It also leads to the Many Worlds Interpretation of the Quantum Mechanics which says, “there is no wave function collapse, and every time a "random" event occurs, the universe splits into multiple branches representing different outcomes.” But we will save it for some other issue.
Causality
In his paper ‘Quantum causality’ the author Časlav Brukner argued that
“Traditionally, quantum theory assumes the existence of a fixed background causal structure. But if the laws of quantum mechanics are applied to the causal relations, then one could imagine situations in which the causal order of events is not always fixed, but is subject to quantum uncertainty.”
The debate between realism, instrumentalism and causality is central to interpreting quantum mechanics. Realism asserts that the physical world exists independently of our observations, while instrumentalism views theories as merely tools for predicting observations, without making any claims about the underlying reality. While the concept of acausality claims that the coincidence between events inside our mind and the outside world may be causally unrelated yet it may have another unknown connection. This is where Quantum Physics steps out of the mathematical formulation and starts invading to the philosophical regime. The Copenhagen interpretation leans towards instrumentalism, suggesting that quantum mechanics does not describe an objective reality but rather provides a framework for predicting measurement outcomes.
Quantum Mechanics and Consciousness
But hold on, there is more. If it already did not confuse you enough here is another scientist to help. Eugene Wigner in 1961 published another thought experiment called Wigner’s Friend. In his famous thought experiment Wigner asked what if, an observer W observes another observer F who performs a quantum measurement on a system. If these two observers formulate a statement about the system according to the laws of quantum physics, they will contradict each other. This interpretation of Wigner alongside Von Neuman lead to a new interpretation of Quantum Physics called, “The von Neumann–Wigner interpretation” it says:
The consciousness of an observer is the demarcation line that precipitates collapse of the wave function, independent of any realist interpretation. The mind is postulated to be non-physical and the only true measurement apparatus.
This paradox is one of the most powerful metaphors of quantum theory and so is the most misunderstood one. The argument Schrödinger put forth was to contradict the traditional view of quantum physics in accordance to the Copenhagen Interpretation but it is projected as if the paradox is to embellish the notion of superposition of states and to extend it even to the macroscopic world. Which could not be further from the truth. The scientists have been arguing for decades to give a satisfactory explanation for the paradox but they have been failing to do so for a very long time. It remains one of the Unsolved Problems in Physics till date. If I had to summarise this whole paradox in a single question it would translate into:
“Can our mere curiosity kill the cat?”
The answer is of course you guessed it, “Yes” and “No”.
Thanks for reading SCIENTIA, if you have made this far please consider being a subscriber. If you like our work you can pledge your support to bring you well researched article.
An excellent post. I wonder if Dirac had a unique interpretation based on his mathematical beauty obsession, and qualifying himself a failure at age 78.