Schrödinger's Cat has acquired many descriptions and interpretations since its introduction in 1935. This paper returns to Schrödinger's original text and separates what Schrödinger explicitly constructed from what is inferred from the construction. Schrödinger specified a steel chamber, “a tiny amount” of radioactive substance, a Geiger counter, relay, hammer, poison, a one-hour interval, equal possibilities that one atom decays or none does, and “the first atomic decay” as the decisive occurrence. He then described the wave function of the entire system as containing the living and dead cat “mixed or smeared in equal parts.” However, not knowing which of two mutually exclusive states is true, or being unable to rule out either, does not imply that both are physically true. The distinction involves not only Schrödinger's Cat but also Schrödinger's YOU—the observer outside the steel chamber who lacks information. Moreover, the causal chain from atomic decay to the cat's death contains additional physical and biological conditions. The original construction should therefore distinguish the physical cat, its quantum-mechanical description, and the information available to YOU.
Schrödinger's Cat has acquired many descriptions and interpretations since its introduction in 1935. This paper returns to Schrödinger's original text and separates what Schrödinger explicitly constructed from what is inferred from the construction. Schrödinger specified a steel chamber, “a tiny amount” of radioactive substance, a Geiger counter, relay, hammer, poison, a one-hour interval, equal possibilities that one atom decays or none does, and “the first atomic decay” as the decisive occurrence. He then described the wave function of the entire system as containing the living and dead cat “mixed or smeared in equal parts.” However, not knowing which of two mutually exclusive states is true, or being unable to rule out either, does not imply that both are physically true. The distinction involves not only Schrödinger's Cat but also Schrödinger's YOU—the observer outside the steel chamber who lacks information. Moreover, the causal chain from atomic decay to the cat's death contains additional physical and biological conditions. The original construction should therefore distinguish the physical cat, its quantum-mechanical description, and the information available to YOU.
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.
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
Schrödinger's original Cat explicitly refers to both “one of the atoms decays” and “the first atomic decay.” This paper examines the first decay occurrence of a finite radioactive sample. Let t₁ denote the time of the first atomic decay. Existing quantities such as half-life, decay constant, mean lifetime, and activity describe radioactive decay collectively, whereas t₁ identifies the first actual decay occurrence of a particular sample. Probability theory contains well-developed treatments of first occurrences, including waiting times, first-arrival times, first-passage times, hitting times, and related stochastic processes. Such treatments require information about the underlying process. This raises two distinct questions for radioactive decay: what information determines the probability distribution of t₁, and what information, if any, determines the actual t₁ of a particular finite sample of a given radioactive isotope before the first decay occurs?
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!
“Shut up and calculate” is commonly associated with a pragmatic attitude toward quantum mechanics: instead of debating interpretation, calculate observable predictions. This paper applies that instruction directly to the original Schrödinger's Cat. Schrödinger specified “a tiny amount” of radioactive substance, an equal probability that one of its atoms decays or none does within one hour, and “the first atomic decay” as the decisive occurrence. These statements contain two quantitative questions: What is the amount? What is the probability of the first decay? Using Schrödinger's Quantity and the First Decay time t₁, these become: calculate the number of atoms n satisfying the one-half probability condition, and calculate the probability associated with the first decay occurrence. No interpretation of the cat is required for either question.
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!