In this blog post, we explore the strange world of quantum mechanics in an easy and interesting way through Schrödinger’s cat thought experiment.
‘Steven Hawking’ said, “If I hear someone talking about Schrödinger’s cat, I pull out my gun.” The reason he drew his gun was because he was so sick of hearing about Schrödinger’s cat. Anyone who majored in physics has likely been exposed to Schrödinger’s cat so much they never want to hear about it again. This thought experiment has been endlessly repeated and discussed, from textbooks to academic papers to public lectures. So, to physicists, it might feel like an old joke. But Schrödinger’s cat story is undoubtedly an intriguing thought experiment that allows even non-physics majors to glimpse the strangeness of the quantum world. Aren’t you curious what Schrödinger’s cat story is, and why even ‘Steven Hawking’ mentioned it?
Schrödinger’s cat is a thought experiment proposed to criticize the Copenhagen interpretation, which introduced uncertainty into physics. Imagine a box containing a cat, connected by a valve to a chamber filled with poison gas. Beside the box sits a machine that detects radiation. If radiation is detected, the valve opens, killing the cat. If no radiation is detected, the cat survives. Now, suppose a radioactive substance with a 50% probability of decaying within one hour is placed inside. After one hour, is the cat dead or alive? Or should we say it exists in a strange state, neither dead nor alive?
The interpretation of the Copenhagen school, which Erwin Schrödinger so despised, is as follows: Before opening the box, the cat was in a superposition of both alive and dead states. However, the moment it is observed, it collapses into one definite state. If the physics term ‘superposition’ feels a bit difficult, let me give a simple example to explain it more easily. Imagine a box containing a single ball that must be either red or blue. However, in the quantum world, a superposition state where the ball can simultaneously be both red and blue is possible. Only by taking it out of the box and observing it can we confirm it is one color. In other words, a superposition state refers to a situation where a single object (the ball) probabilistically possesses two states (red and blue) simultaneously. Thus, the Copenhagen interpretation broke with the traditional physical viewpoint that an object must possess only one state, proposing a new quantum mechanical perspective where two states can coexist probabilistically.
This interpretation sparked significant backlash among physicists at the time, including Erwin Schrödinger. The reason was that scientific facts were not deterministic, independent of observation, but instead emerged probabilistically through observation. In the classical physics world established by Isaac Newton, all objects were always precisely predictable by physical laws and therefore could not possess two states simultaneously. However, according to the quantum mechanical interpretation developed by the Copenhagen School, the coexistence of two states in a superposition state had to be acknowledged. This was tantamount to completely collapsing the existing physical worldview. Quantum mechanics revealed a reality that was utterly ‘bizarre,’ completely different from the physical world we experience daily. The debate surrounding it extended beyond the scientific community, influencing diverse fields like philosophy and the humanities.
Ironically, however, this thought experiment, devised by Erwin Schrödinger to challenge the Copenhagen interpretation, ultimately served to advance the theory further. Through this, the Copenhagen interpretation redefined observation as a crucial interaction that had previously been overlooked. While we might easily think of observation as simply seeing with our eyes, in science, observation is more accurately described as an interaction with the experimental system. The ability to see what’s inside a box occurs because photons reflected off the object inside interact with the photons entering our eyes. In other words, quantum mechanics revealed that the act of observation is no longer independent of the system being observed; it is an act of mutual interaction.
Schrödinger’s cat was devised to critique quantum mechanics. However, it ultimately serves as a thought experiment that greatly aids in understanding both the paradoxical aspects of quantum mechanics and the new physical worldview it introduces. It is also an experiment that helps us grasp the new meaning the act of observation takes on compared to classical physics. In classical physics, everything was deterministic, and observation was merely an act of confirming results. In quantum mechanics, however, observation itself becomes the act of creating the result, completely transforming our fundamental understanding of the physical world. It is my hope that this article provides readers with an opportunity to visualize Schrödinger’s cat experiment in their minds and experience the mystery and strangeness of the quantum world.
