Schrodinger's cat
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Schrödinger's cat is a famous illustration of the principle in quantum theory of superposition, proposed by Erwin Schrödinger in 1935. Schrödinger's cat serves to demonstrate the apparent conflict between what quantum theory tells us is true about the nature and behavior of matter on the microscopic level and what we observe to be true about the nature and behavior of matter on the macroscopic level -- everything visible to the unaided human eye.
Here's Schrödinger's (theoretical) experiment: We place a living cat into a steel chamber, along with a device containing a vial of hydrocyanic acid. There is, in the chamber, a very small amount of hydrocyanic acid, a radioactive substance. If even a single atom of the substance decays during the test period, a relay mechanism will trip a hammer, which will, in turn, break the vial and kill the cat.
The observer cannot know whether or not an atom of the substance has decayed, and consequently, cannot know whether the vial has been broken, the hydrocyanic acid released, and the cat killed. Since we cannot know, according to quantum law, the cat is both dead and alive, in what is called a superposition of states. It is only when we break open the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive). This situation is sometimes called quantum indeterminacy or the observer's paradox: the observation or measurement itself affects an outcome, so that the outcome as such does not exist unless the measurement is made. (That is, there is no single outcome unless it is observed.)
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If the idea of experimenting on a cat bothers you, substitute a rat for the cat -- or even better yet substitute a slug for rat. The thought experiment remains the same no matter who or what is the target of it.
[Source]
Schrödinger's cat is a thought experiment, sometimes described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects, resulting in a contradiction with common sense. The scenario presents a cat that may be both alive and dead, depending on an earlier random event. Although the original "experiment" was imaginary, similar principles have been researched and used in practical applications. The thought experiment is also often featured in theoretical discussions of the interpretations of quantum mechanics. In the course of developing this experiment, Schrödinger coined the term Verschränkung (entanglement).
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Schrodinger's Cat
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Often it is explained that: by observing events (ie. measuring them) we change the quantum state of those events, and so the "original course" of those events.
In other words, the observer IS part of the Experiment. According to strict interpretations of Quantum Physics. Unavoidably so.
Shorter still: By measuring the things, we change the things.
[Source] -- larger image
So what say you? Were Schrödinger's conclusions right or wrong? Hopelessly entangled or haplessly indeterminate? The radioactive clock is clicking ...