Schrödingerâs cat
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What is Schrödingerâs cat?
Erwin Schrödinger introduced the Schrödinger's cat thought experiment in 1935 to challenge the application of quantum mechanics at the macroscopic level.
In this thought experiment, a cat is sealed in a box with a device that has a 50% chance of releasing poison based on the decay of a radioactive atom. According to the Copenhagen interpretation of quantum mechanics, until the box is opened, the cat exists in a superposition of both alive and dead states. Schrödinger found this idea "quite ridiculous" and designed the experiment to highlight concerns about the existing interpretation of quantum mechanics.
The thought experiment has since become central to discussions of quantum mechanics and the measurement problem, which questions how and when the wave function of a quantum system collapses into a definite state upon observation.
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Why did Erwin Schrödinger create the cat experiment?
Erwin Schrödinger introduced the Schrödinger's cat thought experiment in 1935 to challenge the Copenhagen interpretation of quantum mechanics, which he found unsatisfactory. Unlike Newton's equations, which gave concrete answers, the Copenhagen interpretation depended on probability.
Schrödinger devised a scenario with a cat in a box with a device that had an equal chance of either releasing poisonous gas and killing the cat or not. According to the Copenhagen interpretation, until the box is opened, the cat exists in a superposition of both alive and dead states, which Schrödinger found ridiculous. He intended the experiment to highlight concerns about the application of quantum mechanics to macroscopic objects and provoke discussion among scientists.
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How does the experiment describe a cat being both alive and dead at once?
The Schrödinger's cat experiment is a thought experiment that illustrates the paradoxes of quantum mechanics when applied to everyday objects.
In this experiment, a cat is sealed in a steel chamber with a device containing a radioactive substance, a Geiger counter, and a flask of hydrocyanic acid. There is a 50% chance that one atom of the substance will decay in an hour. If this happens, the Geiger counter triggers a hammer to break the flask, releasing the poison and killing the cat.
According to the Copenhagen interpretation of quantum mechanics, until the box is opened and the system is observed, the cat exists in a superposition of states, simultaneously both alive and dead. This superposition is described by the psi-function, which includes both possibilities in equal parts.
Schrödinger designed this experiment to highlight how "ridiculous" it is to apply quantum mechanics to the macroscopic world.
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What is superposition in quantum physics?
In quantum physics, superposition is the ability of a quantum system to be in multiple states simultaneously. Schrödingerâs cat is a thought experiment illustrating this concept, where a cat in a closed box exists in a superposition of being both alive and dead until observed.
Before measurement, the system is in a combination of all possible states. Measuring an observable disturbs the system, causing it to "choose" one state. This principle is central to quantum mechanics, but it leads to conceptual challenges, such as the measurement problem, and remains a topic of philosophical and scientific debate.
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How does observation affect the outcome in the Schrödingerâs cat experiment?
The Schrödinger's cat thought experiment illustrates the complexities of quantum mechanics when applied to everyday objects.
In this experiment, a cat is placed in a box with a device that has a 50% chance of releasing poison based on the decay of a radioactive atom. According to the Copenhagen interpretation, until the box is opened (i.e., the system is observed), the cat exists in a superposition of both alive and dead states.
The act of observation forces the system to "choose" one state, collapsing the wave function and resulting in the cat being either definitively alive or dead. This raises questions about the role of the observer in determining the outcome of quantum events.
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Why is Schrödingerâs cat important for understanding quantum mechanics?
Erwin Schrödinger introduced the Schrödinger's cat thought experiment in 1935 to challenge the Copenhagen interpretation of quantum mechanics. The experiment involves a cat in a box with a vial of poison that breaks if an atom decays. The atom exists in both decayed and non-decayed states until observed, leading to the cat being paradoxically in both alive and dead states simultaneously.
Schrödinger's equation describes the probability waves governing the motion of small particles. The Copenhagen interpretation suggests that until observed, the cat exists in a superposition of both alive and dead states, which Schrödinger considered "quite ridiculous". This thought experiment highlights the conflict between quantum mechanics and classical physics, questioning the application of quantum mechanics to everyday objects.
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Schrödingerâs cat, thought experiment designed by theoretical physicist Erwin Schrödinger in 1935 as an objection to the reigning Copenhagen interpretation of quantum mechanics.
Often considered as central to quantum physics as Isaac Newtonâs laws of motion are to classical physics, the Schrödinger equation, which he had devised in 1926, is essentially a wave equation that describes the form of probability waves (or wave functions) that govern the motion of small particles and how these waves change over time. Solutions to the equation take the form of wave functions that can only be related to the probable occurrence of physical events. Schrödinger used the equation to predict the qualities of a hydrogen atom, and the equation remains a fundamental building block of quantum mechanics.
However, Schrödinger himself was displeased with how the equation came to be interpreted, namely, the Copenhagen interpretation (so called because its main proponent, Niels Bohr, lived in that city). Unlike Newtonâs equations of motion, which provided concrete answers to questions of the universe, the Copenhagen interpretation of Schrödingerâs equation depended on the more abstract notion of probability. Instead of precise locations and quantities, quantum mechanics could only produce results no more concrete than the probability of an electron existing in a certain spot after a certain amount of time.
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Schrödinger felt that while quantum mechanics was valid in describing the blurriness of the subatomic world, applying quantum mechanics indiscriminately led to strange consequences, writing in his paper âThe Present Situation in Quantum Mechanicsâ (1935):
One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
Schrödingerâs cat argues that, in the Copenhagen interpretation, until an observer opens the box and reveals the catâs fate, the cat is both alive and deadâa state described as a âsuperposition.â Schrödinger thought that the cat being both alive and dead was âquite ridiculousâ and intended his thought experiment to challenge other scientistsâ suppositions about quantum mechanics. However, scientists have since been able to place particles such as ions and photons in superposed states. French physicist Serge Haroche and American physicist David Wineland won the 2012 Nobel Prize for Physics for their work in devising experiments to create such âSchrödinger cat states,â in which particles can be observed as simultaneously being in two different states.