What is Schrodinger's Cat? The Thought Experiment Behind Quantum Mechanics.

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Has a math problem or a peculiar word ever confused you? Have you ever felt your efforts to end your confusion to be frivolous? Has the difficult math problem or word word been on a test? Despite your effort towards finding an answer, have you come up short? Did you say to yourself, “there must be no answer to this question. This question is a paradox.” Indeed, if your math question relates to Schrodinger’s Cat thought experiment, you are probably right in calling it a “paradox.” Brace yourselves, my friends, as I seek to understand and explain the Schrodinger’s Cat thought experiment and its interpretations.

The Wave Function and the Copenhagen Interpretation

The creator of the thought experiment, Erwin Schrodinger, an Austrian-Irish physicist, was also responsible for developing Schrodinger’s Wave Function. The wave function can predict future actions of subatomic particles, explaining – with natural inaccuracy – the potential actions of everything from subatomic particles to the entire universe. The wave function and surrounding quantum mechanical phenomena are responsible for quantum mechanics’ various interpretations.

The Copenhagen Interpretation posits that all particles in quantum mechanics are in superposition (all states at once) until observed, at which point they are “forced to choose a state.” Schrodinger devised this mind-numbing thought experiment in an attempt to explain and support the Copenhagen Interpretation and its superposition component.

The Thought Experiment

Let us imagine Schrodinger’s Cat; first, you will need to imagine a few items occupying a box:

  • A cat (obviously)

  • A radioactive substance (uranium, plutonium, radium, radon, etc.) 

  • An internal monitor to detect radioactive decay (known as a Geiger Counter).

  • A flask of poison (Schrodinger, in his original formulation of the experiment, used cyanide)

  • A hammer

  • A lever attached to the hammer and the detector

The thought experiment is quite understandable, but the implications and interpretations thereof are not. In the experiment, the Geiger Counter detects radioactive decay occurring in a small amount of uranium (or any other radioactive element, of course). If the counter detects radioactive decay, the lever will fall, releasing the hammer on the flask of cyanide (we will use cyanide as the poison), breaking the vial, releasing the cyanide, and killing the cat. However, if the Geiger Counter does not detect radioactive decay, the lever will not fall, the cat will not be exposed to the cyanide, and the cat will, therefore, not die. 

Implications of the Thought Experiment

All quantum particles, before they are “observed,” are bound to the realms of Schrodinger’s Wave Function. According to the Copenhagen Interpretation, when these quantum particles are unobserved, they are in superposition – the particles could be in multiple states at once (e.g. an electron could be both a wave and a particle). The phenomenon was first made evident by a famous experiment known as the double-slit experiment: in 1801, English physicist Thomas Young designed the double-slit experiment to prove that light was only a wave, but found out that light acted as both a wave and a particle. Quantum physicists use this experiment to explain how a subatomic particle (like an electron) can act like a wave and still create an interference pattern. 

Precise measurement of quantum particles under current knowledge of quantum mechanics is, unfortunately, impossible. As one attempts to measure the particle, the waveform in the particle previously in superposition collapses. Waveform collapse is the transformation of a “spread-out wave function to a localized particle.” In other words, the wave function, the description of a particle’s states, collapses into a single state; it is “where the other states go” that is up to interpretation.

Schrodinger’s Cat simplifies phenomena at the quantum level. Based on the Copenhagen Interpretation, the unobserved cat is both dead and alive because it is in superposition. Only when the box is opened and its inside seen, does the wave function collapse, presenting to the observer either a dead cat or a living cat. One or the other – one is evident, one appears to vanish.

We do not know, however, exactly what happens to the other possible outcome. Let us say that there is a 50% chance that the cat will either be alive or dead. If, for example, the observer opened the box and saw a dead cat, where would the alive cat outcome go? The Copenhagen Interpretation explains that only one outcome would be determined based on fundamental probability – and the other would, essentially, vanish – but there are other interpretations that seek a more cohesive explanation of waveform collapse. The thought experiment is considered a paradox because of the contradiction presented in it – and thus in the Copenhagen Interpretation.

Interpretations of Quantum Mechanics and Schrodinger’s Cat

Copenhagen Interpretation

The Copenhagen interpretation maintains the scientific consensus and is the principal interpretation of quantum mechanics. The interpretation argues that, once observed, a quantum system abandons its superposition and the waveform collapses (when it is observed), becoming only one of the states it had previously been in (in this situation, the cat is revealed to be either dead or alive). 

A central issue with the Copenhagen Interpretation arose from Neils Bohr, one of its fathers, who did not consider the wave function an actual physical phenomenon, but instead a statistical tool. Nevertheless, he warned that the waveform of the system in quantum mechanics would collapse long before a conscious observer opened the box (in this situation, the Geiger Counter is a measurement tool and would thus collapse the waveform in the particle). Any measurement, whether performed by conscious beings or unconscious detectors, will always collapse the waveform of a quantum system. His concerns raise the question over what defines an “observer,” a question which is still considered and unanswered.

Many-Worlds Interpretation

The many-worlds interpretation is easily the most popular (culture) interpretation of the Schrodinger’s Cat thought experiment paradox. First proposed by physicist Hugh Everett, this interpretation does not single out the observation of quantum systems and subsequent waveform collapse as a “special event” where all other states are lost. Rather, when the waveform collapses, both the alive and dead forms of the cat will persist, but the two events will be decoherent from each other. In other words, when the box is opened and the event is observed, in one alternate reality (universe) would see a dead cat, while in another alternate reality the observer would see a living cat.

Unfortunately, the interpretation is widely considered to be unfalsifiable. An unfalsifiable claim is pseudoscience, as much as popular culture hates to say it. However, some proponents of the theory (e.g. Sean Carroll) claim that MWI is proven by mathematical formulas and can be physically falsifiable.

A thought experiment explaining many-worlds is known as the quantum suicide machine. Imagine a gun pointed at a conscious observer, with a 50/50 chance of the gun discharging a bullet every minute. Assuming superposition and the many worlds interpretation apply in the experiment, every minute the waveform would collapse, splitting up into two different realities: one in which the observer is shot and killed instantly, and another in which the observer survives. This waveform collapse would continue on forever, and in one reality the victim of the machine would be effectively immortal. As long as a probability remains, there will always be a living conscious observer continuing to undergo this waveform collapse. On the other hand, if the Copenhagen Interpretation is correct, then the waveform would collapse into only one reality based on the 50% probability of the observer either dying or not dying. Simple laws of probability would apply in determining the fate of the observer.

Wrapping it up

It is without question that quantum mechanics is one of the universe’s most complicated phenomena – at least that we know of. Nevertheless, the wondrous complication brought to us by quantum mechanics further demonstrates the beauty of our universe. I hope that the wacky concept confused you enough that you became curious enough to continue researching. I can assure you that you will feel very rewarded once you have begun to understand the very basic, non-mathematical aspects of quantum physics. Take care and stay curious, everyone.

If you have any questions, comments, or corrections, please comment on this post or email learningbywilliam@gmail.com with your concerns. Thank you.


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