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Line 1: − + + + + + + + + + − − We know that superposition actually occurs at the subatomic level, because there are observable effects of interference, in which a single particle is demonstrated to be in multiple locations simultaneously. What that fact implies about the nature of reality on the observable level (cats, for example, as opposed to electrons) is one of the stickiest areas of quantum physics. Schrödinger himself is rumored to have said, later in life, that he wished he had never met that cat. − Here is a famous letter asking about the phenomenon to [[Cecil Adams]], writer for the [[Straight Dope]].+ + + + + + + + + − Dear Cecil:+ − Cecil, you're my final hope − Of finding out the true Straight Dope − For I have been reading of Schroedinger's cat − But none of my cats are at all like that. − This unusual animal (so it is said) − Is simultaneously live and dead! − What I don't understand is just why he − Can't be one or other, unquestionably. − My future now hangs in between eigenstates. − In one I'm enlightened, the other I ain't. − If you understand, Cecil, then show me the way − And rescue my psyche from quantum decay. − But if this queer thing has perplexed even you, − Then I will and won't see you in Schroedinger's zoo. − − Dear Randy:+ − Schroedinger, Erwin! Professor of physics!+ − Wrote daring equations! Confounded his critics! − (Not bad, eh? Don't worry. This part of the verse − Starts off pretty good, but it gets a lot worse.) − Win saw that the theory that Newton'd invented − By Einstein's discov'ries had been badly dented. − What now? wailed his colleagues. Said Erwin, "Don't panic, − No grease monkey I, but a quantum mechanic. − Consider electrons. Now, these teeny articles − Are sometimes like waves, and then sometimes like particles. − If that's not confusing, the nuclear dance − Of electrons and suchlike is governed by chance! − No sweat, though--my theory permits us to judge − Where some of 'em is and the rest of 'em was." − Not everyone bought this. It threatened to wreck − The comforting linkage of cause and effect. − E'en Einstein had doubts, and so Schroedinger tried − To tell him what quantum mechanics implied. − Said Win to Al, "Brother, suppose we've a cat, − And inside a tube we have put that cat at-- − Along with a solitaire deck and some Fritos, − A bottle of Night Train, a couple mosquitoes − (Or something else rhyming) and, oh, if you got 'em, − One vial prussic acid, one decaying ottom − Or atom--whatever--but when it emits, − A trigger device blasts the vial into bits − Which snuffs our poor kitty. The odds of this crime − Are 50 to 50 per hour each time. − The cylinder's sealed. The hour's passed away. Is − Our pussy still purring--or pushing up daisies? − Now, you'd say the cat either lives or it don't − But quantum mechanics is stubborn and won't. − Statistically speaking, the cat (goes the joke), − Is half a cat breathing and half a cat croaked. − To some this may seem a ridiculous split, − But quantum mechanics must answer, "Tough @#&! − We may not know much, but one thing's fo' sho': − There's things in the cosmos that we cannot know. − Shine light on electrons--you'll cause them to swerve. − The act of observing disturbs the observed-- − Which ruins your test. But then if there's no testing − To see if a particle's moving or resting − Why try to conjecture? Pure useless endeavor! − We know probability--certainty, never.' − The effect of this notion? I very much fear − 'Twill make doubtful all things that were formerly clear. − Till soon the cat doctors will say in reports, − "We've just flipped a coin and we've learned he's a corpse."' − So saith Herr Erwin. Quoth Albert, "You're nuts. − God doesn't play dice with the universe, putz. − I'll prove it!" he said, and the Lord knows he tried-- − In vain--until fin'ly he more or less died. − Win spoke at the funeral: "Listen, dear friends, − Sweet Al was my buddy. I must make amends. − Though he doubted my theory, I'll say of this saint: − Ten-to-one he's in heaven--but five bucks says he ain't." − --CECIL ADAMS+ − [[Image:dingerscat.jpg|left|250px|thumb]]
Complete re-write; better logical organization; reference; a lot
[[Image:Schrodcat01.JPG|right|thumb|300px]]
[[Image:Schrodcat01.JPG|right|thumb|300px]]
'''Schrödinger's cat''' is a thought experiment that illustrates various paradoxes associated with the [[principle of superposition]] in [[quantum mechanics]], it was 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.
'''Schrödinger's cat''' is a thought experiment that illustrates a paradox associated with the [[principle of superposition]] in [[quantum mechanics]], it was 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.
==The Thought Experiment==
In a paper entitled ''The Present Situation in Quantum Mechanics'', Schroedinger wrote the following:
<blockquote>
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.<ref>http://www.tu-harburg.de/rzt/rzt/it/QM/cat.html#sect5</ref>
</blockquote>
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 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, the cat is both dead and alive according to quantum law, in 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.)
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 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, the cat is both dead and alive according to quantum law, in 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.)
==Explanation/Interpretations==
In lay terms, Schrödinger's experiment results in a paradox: According to the quantum mechanical model, because the cat's "live-ness" is not being measured directly, there is no way to know whether or not it is alive or not. As a matter of fact, quantum mechanics dictates that ''it is existing in both states simultaneously.'' Such behavior is not encountered in daily life, but is accepted as possible behavior for subatomic particles.
There are two primary interpretations of the theory: the Copenhagen interpretation and the many-worlds interpretation.
===Copenhagen Interpretation===
The Copenhagen interpretation is the interpretation dealing fundamentally with [[decoherence]]. Because quantum mechanics is a statistical method of describing the physical world, there are multiple states that a system can exist in at the same time; this is the principle of [[superposition]]. A quantum system is said to always be in a state of superposition until the system is measured, at which point the system ''decoheres'' and assumes a unique value. Such behavior has been the basis of revolutionary research into computing technologies (see [[quantum computer]]). This interpretation also questions at what time the "measuring" of the system takes place; for instance, a fundamental aspect of the system is measured when a nucleus decays and the event is recorded by the Geiger counter.
===Many-worlds Interpretation===
--Randy F., Chicago
The many-worlds interpretation deals with the concept that measuring the system is not a significant act. Instead, both states exist simultaneously, but are decoherent with each other, meaning that there is no communication between them. When the system is observed or measured (the box opened), the observer becomes [[quantum entanglement|entangled]] with the system, and essentially, two new observer states are formed - an observer who discovers a dead cat, and an observer who discovers a living cat. At this point, the [[universe]] "splits" into two branches or separate universes that are unable to communicate with each other.
==References==
<references/>
==See also==
==See also==
* [[Maxwell's demon]]
* [[Maxwell's demon]]
[[category:physics]]
[[category:physics]]