Schrodinger's conceptual model of probable described a closed box containing a cat and a vial filled with a radioactive, poisonous substance. Only if one atom decayed and emitted an electron, the vial would break. The chances that this would happen and the cat would die or that it would not and the cat would continue to live are 50-50. What does this mean? In the everyday world of common reality there is no such thing as a half-dead or half-alive cat, irrespective of the presence of an observer. In quantum physics, however, either both probabilities (of a dead cat and of a living cat) contain equal (in separate worlds), or neither holds valid unless the observer opens the box and allows one of them to crystallize into reality. In the quantum world, the cat is neither dead nor alive, but somehow lying in an indeterminate state until
Schrodinger's conceptual model of probable described a closed box containing a cat and a vial filled with a radioactive, poisonous substance. Only if one atom decayed and emitted an electron, the vial would break. The chances that this would happen and the cat would die or that it would not and the cat would continue to live are 50-50. What does this mean? In the everyday world of common reality there is no such thing as a half-dead or half-alive cat, irrespective of the presence of an observer. In quantum physics, however, either both probabilities (of a dead cat and of a living cat) contain equal (in separate worlds), or neither holds valid unless the observer opens the box and allows one of them to crystallize into reality. In the quantum world, the cat is neither dead nor alive, but somehow lying in an indeterminate state until
In 1935 Erwin Schrödinger proposed a thought experiment to show the absurd consequences of applying quantum mechanics to everyday objects. Schrödinger imagined placing a cat in a box, along with a vial of deadly poison that is connected to a radioactive atom. If the atom decays, it releases the poison and kills the cat. When the box is closed we do not know if the atom has decayed or not, which means that it can be in a "superposition" of two states (decayed and non-decayed) at the same time. Therefore, protested Schrödinger, the cat can be both dead and alive at the same time – which is clearly absurd. There was obviously, he thought, some boundary between the microscopic world of atoms and quantum mechanics, and the macroscopic world of cats and classical mechanics.
Schrödinger's Cat is commonly summarized as a cat that is “both alive and dead until observed.” This paper compares that familiar formulation with Schrödinger's original 1935 construction. The original passage contains a radioactive substance, the possibility that one atom decays or none does, the first atomic decay, a Geiger counter, relay, hammer, poison, and a cat inside a steel chamber. Schrödinger then states that the Psi-function of the entire system contains the living and dead cat “mixed or smeared in equal parts,” followed by a warning against naively accepting a “blurred model” as an image of reality. Several ideas commonly associated with the Cat therefore need to be distinguished: the physical state of the cat, the mathematical description of the system, the probabilities assigned to alternatives, and the information available to an outside observer. The popular Cat is a useful shorthand, but it is not identical to Schrödinger's original Cat.
The physicist Erwin Schrödinger described, back in 1935, one aspect of this strange phenomenon. He placed his cat in a sealed box with a piece of radioactive material which might or might not send out a sub-atomic particle. If it did, the Geiger counter was designed to trigger a release of poisonous gas in the box, and thereby kill his cat. The Geiger counter was set up to be triggered just enough to give a 50-50 chance of a particle being detected, and therefore the cat an even chance of being poisoned or not. (In those days, this sort of experiment was acceptable, particularly as it was only a thought experiment.) Radioactive behaviour is unpredictable (except in a general, statistical probability way). There is no way of working out whether or not the Geiger counter will be triggered off. If the sub-atomic event does not occur-the cat lives. Otherwise, it dies. Just as the photon (in Problem 93) will quite happily go through both slits until someone tries to measure or detect it, at which point what the physicists call ‘the collapse of the wave function’ takes place, the particle can both trigger the poison gas and not trigger the poison gas. Until someone looks, Schrödinger’s idea is that his cat, for a while, is both alive and dead!
The physicist Erwin Schrödinger described, back in 1935, one aspect of this strange phenomenon. He placed his cat in a sealed box with a piece of radioactive material which might or might not send out a sub-atomic particle. If it did, the Geiger counter was designed to trigger a release of poisonous gas in the box, and thereby kill his cat. The counter was set up to be triggered just enough to give a 50-50 chance of a particle being detected, and therefore the cat an even chance of being poisoned or not. (In those days, this sort of experiment was acceptable, particularly as it was only a thought experiment.) Radioactive behaviour is unpredictable (except in a general, statistical probability kind of way). There is no rule for working out whether or not the Geiger counter will be triggered. If the sub-atomic event does not occur, the cat lives. Otherwise, it dies. Just as a photon (in that famous experiment from ‘real-life’ physics) will quite happily go through both of two parallel slits in a screen – until someone tries to measure or detect it, at which point what the physicists call ‘the collapse of the wave function’ takes place – the particle can both trigger the poison gas and not trigger the poison gas. That is, until someone looks, Schrödinger’s idea is that his cat, for a while, is both alive and dead!
The Schrödinger's Cat paradox was proposed in 1935 by Edwin Schrodinger, one of the founders of quantum mechanics, as an attempt to visualize the macroscopic realization of a quantum superposition state. A cat is placed in a sealed box together with a vial of poison. A two-state particle (e.g. an electron) is sent into a detector in the box resulting either in a broken or an intact vial and a dead or live cat, respectively. The main problem consists in whether the superposition state of a microscopic particle can be transferred upon the macroscopic cat, that is, whether the cat can exist in a superposition state, being simultaneously dead and alive. Since the standard Copenhagen interpretation is unable to assign any reality to the quantum superposition state, the paradox finds no resolution within the regime of this interpretation. Von Neumann's insistence on the uniform treatment of both microscopic (quantum) and macroscopic (classical) objects according to the laws of quantum mechanics provides a more consistent framework for the resolution of the paradox. In particular, the discovery of the phenomenon of decoherence, whereby the disappearance of the quantum interferences at the macro level is accounted for, suggests the onset of an extremely efficient interference relaxation process (10-23 s) upon the interaction of the two state particle with the detector. As a result, Schrodinger's cat can exist macroscopically either as dead or alive and never as a combination of both. Decoherence not only aids the resolution of the Schrodinger's Cat paradox but also sheds light upon the mechanisms by which the macro-world emerges from the microscopic quantum realm.
Letters from:
[ Andras Malnasi Csizmadia and Achilles J. Sanchez ][1]
[ Randy Morse ][1]
[ Barbara A. B. Seiders ][1]
[ Paul C. S. Hoaken ][1]
[ Andrew Ahlgren ][1]
When the Schrodinger cat paradox was first proposed in 1935, it was difficult to envision an experimental system in which to model Schrodinger's experiment. But C. Monroe et al. describe such a system in their research article “A ‘Schrodinger cat’ superposition state of an atom” ([24 May, p. 1131][2]). In an accompanying Research News article ([24 May, p. 1101][3]), Gary Taubes writes
> … Erwin Schrodinger described a cat shut up in what he called a “diabolical device”: a closed box also containing a small amount of a radioactive substance. Over the course of an hour, the radioactive substance has a 50-50 chance of decaying. If it does, the decay is detected by a counter, which shatters a flask of deadly acid, killing the cat. If it doesn't, the cat lives.
But for the experiment to be a true paradox, the box must contain only one radioactive atom, as specified by Schrodinger. If there are numerous atoms in the box, it is a statistical certainty that at least one atom (but we cannot know which one) will decay in the course of the experiment, and the unfortunate cat will undoubtedly be killed. If, on the other hand, there is only one or very few atoms in the box, we will not know whether the cat is dead or alive.
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As a naive molecular biologist, I am perplexed by one facet of the problem of Schrodinger's cat as it is usually presented. Why can't the cat be considered an observer and therefore remove the uncertainty about its own life or death status?
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My 12-year-old daughter Phoebe is a student of quantum paradoxes, but she was concerned about an error in the illustration accompanying the Research News article with regard to feline anatomy. Presumably, even Schrodinger's cat would have foreleg “elbows,” not “knees.”
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The title of the Research News article “Schizophrenic atom doubles as Schrodinger's cat—or kitten” perpetuates a misconception about schizophrenia—which is nothing like split personality—and trivializes a potentially disabling mental disorder.
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“Kitten,” as used by Taubes, seems needlessly macroscopic as a metaphor for a single trapped atom. How about “Schrodinger's furball”?
[1]: /lookup/doi/10.1126/science.273.5277.857e
[2]: /lookup/volpage/273/1131
[3]: /lookup/volpage/273/1101