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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 that 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 first atomic decay would have poisoned it. 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.

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 that 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 first atomic decay would have poisoned it. 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.

人们甚至可以设置相当荒谬的情况。在盖革计数器中，有一小块放射性物质，非常小，也许在一个小时的过程中，其中一个原子会衰变，但是，以相同的概率，也许没有; 如果发生这种情况，计数管放电，并通过一个继电器释放一个锤子，锤子砸碎一个小氰化氢的烧瓶。如果一个人把整个系统留给自己一个小时，就会说，如果同时没有原子衰变，猫还活着。第一次原子衰变会使它中毒。整个系统的 psi 功能可以通过将活猫和死猫(请原谅这个表达)混合或涂抹成等分来表达这一点。

人们甚至可以提出非常荒谬的案例。将猫与下面的设备（必须固定以防止猫直接干扰）一起放在钢制的房间里：在盖革计数器中，有一小块放射性物质，非常小，也许在一个小时的过程中，其中一个原子会衰变，但是，也有相同的概率，也许不会发生衰变; 如果发生这种情况，计数管放电，并通过一个继电器释放一个锤子，锤子会打碎一小瓶氢氰酸。如果一个人把整个系统留给自己一个小时，就会说，如果没有原子衰变，这只猫就还活着。如果第一次原子衰变会使它中毒。整个系统的 psi 功能可以通过将活猫和死猫(对等表达)两个状态的叠加来表达这一点。

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naïvely accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.}}

It is typical of these cases that an indeterminacy originally restricted to the atomic domain becomes transformed into macroscopic indeterminacy, which can then be resolved by direct observation. That prevents us from so naïvely accepting as valid a "blurred model" for representing reality. In itself, it would not embody anything unclear or contradictory. There is a difference between a shaky or out-of-focus photograph and a snapshot of clouds and fog banks.}}

Schrödinger's famous thought experiment poses the question, "when does a quantum system stop existing as a superposition of states and become one or the other?"  (More technically, when does the actual quantum state stop being a non-trivial linear combination of states, each of which resembles different classical states, and instead begin to have a unique classical description?) If the cat survives, it remembers only being alive. But explanations of the EPR experiments that are consistent with standard microscopic quantum mechanics require that macroscopic objects, such as cats and notebooks, do not always have unique classical descriptions. The thought experiment illustrates this apparent paradox. Our intuition says that no observer can be in a mixture of states—yet the cat, it seems from the thought experiment, can be such a mixture. Is the cat required to be an observer, or does its existence in a single well-defined classical state require another external observer? Each alternative seemed absurd to Einstein, who was impressed by the ability of the thought experiment to highlight these issues. In a letter to Schrödinger dated 1950, he wrote:

Schrödinger's famous thought experiment poses the question, "when does a quantum system stop existing as a superposition of states and become one or the other?"  (More technically, when does the actual quantum state stop being a non-trivial linear combination of states, each of which resembles different classical states, and instead begin to have a unique classical description?) If the cat survives, it remembers only being alive. But explanations of the EPR experiments that are consistent with standard microscopic quantum mechanics require that macroscopic objects, such as cats and notebooks, do not always have unique classical descriptions. The thought experiment illustrates this apparent paradox. Our intuition says that no observer can be in a mixture of states—yet the cat, it seems from the thought experiment, can be such a mixture. Is the cat required to be an observer, or does its existence in a single well-defined classical state require another external observer? Each alternative seemed absurd to Einstein, who was impressed by the ability of the thought experiment to highlight these issues. In a letter to Schrödinger dated 1950, he wrote:

薛定谔著名的思想实验提出了这样一个问题: “量子系统何时会停止作为叠加态而成为其中之一? ”(从技术上讲，什么时候实际的量子态不再是非平凡的线性组合状态，而是开始有一个独特的经典描述?)如果猫活下来了，它只记得活着。但是，对 EPR 实验的解释与标准的微观量子力学一致，要求宏观对象，如猫和笔记本电脑，并不总是有唯一的经典描述。这个思想实验说明了这个明显的悖论。我们的直觉告诉我们，任何观察者都不可能处于不同的状态ーー然而，从思想实验来看，猫可能是这样一种混合状态。猫是被要求成为一个观察者，还是它存在于一个明确定义的经典状态需要另一个外部观察者？对爱因斯坦来说，每一种选择都是荒谬的，他对思想实验突出这些问题的能力印象深刻。在1950年写给薛定谔的一封信中，他写道:

薛定谔著名的思维实验提出了这样一个问题: “量子系统何时会停止作为叠加态而成为其中之一? ”(从技术上讲，什么时候实际的量子态不再是非平凡的线性组合状态，而是开始有一个独特的经典描述?)如果猫活下来了，它只记得活着。但是，与标准微观量子力学相一致的EPR实验的解释要求宏观物体，例如猫和笔记本，并不总是具有独特的经典描述。这个思维实验说明了这个明显的悖论。我们的直觉告诉我们，任何观察者都不可能处于混合的状态——然而，从思维实验来看，猫可能是这样的状态。这只猫是否需要成为观察者，或者它在一个定义明确的经典状态下的存在是否需要其他外部观察者？对爱因斯坦来说，每一种选择都是荒谬的，他对思想实验突出这些问题的能力印象深刻。在1950年写给薛定谔的一封信中，他写道:

{{Quote|You are the only contemporary physicist, besides [[Max von Laue|Laue]], who sees that one cannot get around the assumption of reality, if only one is honest. Most of them simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established. Their interpretation is, however, refuted most elegantly by your system of radioactive atom + amplifier + charge of gun powder + cat in a box, in which the psi-function of the system contains both the cat alive and blown to bits. Nobody really doubts that the presence or absence of the cat is something independent of the act of observation.<ref>{{cite journal|title=Induction and Scientific Realism: Einstein versus van Fraassen Part Three: Einstein, Aim-Oriented Empiricism and the Discovery of Special and General Relativity|first=Nicholas|last=Maxwell|date=1 January 1993|volume=44|issue=2|pages=275–305|doi=10.1093/bjps/44.2.275|jstor=687649|journal=The British Journal for the Philosophy of Science}}</ref>}}

{{Quote|You are the only contemporary physicist, besides [[Max von Laue|Laue]], who sees that one cannot get around the assumption of reality, if only one is honest. Most of them simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established. Their interpretation is, however, refuted most elegantly by your system of radioactive atom + amplifier + charge of gun powder + cat in a box, in which the psi-function of the system contains both the cat alive and blown to bits. Nobody really doubts that the presence or absence of the cat is something independent of the act of observation.<ref>{{cite journal|title=Induction and Scientific Realism: Einstein versus van Fraassen Part Three: Einstein, Aim-Oriented Empiricism and the Discovery of Special and General Relativity|first=Nicholas|last=Maxwell|date=1 January 1993|volume=44|issue=2|pages=275–305|doi=10.1093/bjps/44.2.275|jstor=687649|journal=The British Journal for the Philosophy of Science}}</ref>}}<br>

Note that the charge of gunpowder is not mentioned in Schrödinger's setup, which uses a Geiger counter as an amplifier and hydrocyanic poison instead of gunpowder. The gunpowder had been mentioned in Einstein's original suggestion to Schrödinger 15 years before, and Einstein carried it forward to the present discussion.

Note that the charge of gunpowder is not mentioned in Schrödinger's setup, which uses a Geiger counter as an amplifier and hydrocyanic poison instead of gunpowder. The gunpowder had been mentioned in Einstein's original suggestion to Schrödinger 15 years before, and Einstein carried it forward to the present discussion.

Note that the charge of gunpowder is not mentioned in Schrödinger's setup, which uses a Geiger counter as an amplifier and hydrocyanic poison instead of gunpowder. The gunpowder had been mentioned in Einstein's original suggestion to Schrödinger 15 years before, and Einstein carried it forward to the present discussion.

Note that the charge of gunpowder is not mentioned in Schrödinger's setup, which uses a Geiger counter as an amplifier and hydrocyanic poison instead of gunpowder. The gunpowder had been mentioned in Einstein's original suggestion to Schrödinger 15 years before, and Einstein carried it forward to the present discussion.

==Interpretations of the experiment==

==Interpretations of the experiment==<br>

Since Schrödinger's time, other interpretations of quantum mechanics have been proposed that give different answers to the questions posed by Schrödinger's cat of how long superpositions last and when (or ''whether'') they collapse.

Since Schrödinger's time, other interpretations of quantum mechanics have been proposed that give different answers to the questions posed by Schrödinger's cat of how long superpositions last and when (or ''whether'') they collapse.

Since Schrödinger's time, other interpretations of quantum mechanics have been proposed that give different answers to the questions posed by Schrödinger's cat of how long superpositions last and when (or whether) they collapse.

Since Schrödinger's time, other interpretations of quantum mechanics have been proposed that give different answers to the questions posed by Schrödinger's cat of how long superpositions last and when (or whether) they collapse.

自从薛定谔的时代以来，其他的量子力学诠释学派已经被提出，对于薛定谔猫提出的叠加态持续多久以及它们何时(或是否)崩溃的问题，他们给出了不同的答案。

自从薛定谔的时代以来，人们提出了其他的量子力学诠释学派，它们对于薛定谔猫提出的叠加态持续多久以及它们何时(或是否)坍缩的问题给出了不同的答案。

===Copenhagen interpretation===

===Copenhagen interpretation===<br>

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A commonly held interpretation of quantum mechanics is the Copenhagen interpretation.  In the Copenhagen interpretation, a system stops being a superposition of states and becomes either one or the other when an observation takes place. This thought experiment makes apparent the fact that the nature of measurement, or observation, is not well-defined in this interpretation. The experiment can be interpreted to mean that while the box is closed, the system simultaneously exists in a superposition of the states "decayed nucleus/dead cat" and "undecayed nucleus/living cat", and that only when the box is opened and an observation performed does the wave function collapse into one of the two states.

A commonly held interpretation of quantum mechanics is the Copenhagen interpretation.  In the Copenhagen interpretation, a system stops being a superposition of states and becomes either one or the other when an observation takes place. This thought experiment makes apparent the fact that the nature of measurement, or observation, is not well-defined in this interpretation. The experiment can be interpreted to mean that while the box is closed, the system simultaneously exists in a superposition of the states "decayed nucleus/dead cat" and "undecayed nucleus/living cat", and that only when the box is opened and an observation performed does the wave function collapse into one of the two states.

对量子力学的一个普遍的解释是哥本哈根诠释。在哥本哈根诠释中，一个系统不再是态的叠加态，而是在观测发生时成为一个或另一个。这个思想实验表明了一个事实，那就是测量的本质，或者说观察，在这个解释中并没有得到很好的定义。实验可以解释为，当盒子关闭时，系统同时处于“衰变核 / 死猫”和“未衰变核 / 活猫”两种状态的叠加状态，只有当盒子被打开并进行观测时，波函数才坍缩为两种状态之一。

对量子力学的一个普遍的诠释是哥本哈根诠释。在哥本哈根诠释中，一个系统不再是状态的叠加，而是在观测发生时成为一个或另一个。这个思维实验清楚地表明，测量或观察的本质在这个诠释中并没有被明确定义。实验可以解释为，当盒子关闭时，系统同时处于“衰变核 / 死猫”和“未衰变核 / 活猫”两种状态的叠加状态，只有当盒子被打开并进行观测时，波函数才坍缩为两种状态之一。

However, one of the main scientists associated with the Copenhagen interpretation, Niels Bohr, never had in mind the observer-induced collapse of the wave function, as he did not regard the wave function as physically real, but a statistical tool; thus, Schrödinger's cat did not pose any riddle to him. The cat would be either dead or alive long before the box is opened by a conscious observer. Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement, although the validity of their design is disputed. (The view that the "observation" is taken when a particle from the nucleus hits the detector can be developed into objective collapse theories. The thought experiment requires an "unconscious observation" by the detector in order for waveform collapse to occur. In contrast, the many worlds approach denies that collapse ever occurs.)

However, one of the main scientists associated with the Copenhagen interpretation, Niels Bohr, never had in mind the observer-induced collapse of the wave function, as he did not regard the wave function as physically real, but a statistical tool; thus, Schrödinger's cat did not pose any riddle to him. The cat would be either dead or alive long before the box is opened by a conscious observer. Analysis of an actual experiment found that measurement alone (for example by a Geiger counter) is sufficient to collapse a quantum wave function before there is any conscious observation of the measurement, although the validity of their design is disputed. (The view that the "observation" is taken when a particle from the nucleus hits the detector can be developed into objective collapse theories. The thought experiment requires an "unconscious observation" by the detector in order for waveform collapse to occur. In contrast, the many worlds approach denies that collapse ever occurs.)

然而，与哥本哈根诠释相关的主要科学家之一 Niels Bohr 从未想过观察者引起的波函数崩溃，因为他并不认为波函数是物理真实的，而是一个统计工具; 因此，薛定谔的猫并没有向他提出任何谜题。早在盒子被有意识的观察者打开之前，猫就已经死了或者还活着。对一个实际实验的分析发现，单靠测量(例如使用盖革计数器)就足以在有意识地观察测量之前使量子波函数崩溃，尽管其设计的有效性受到质疑。(原子核中的粒子撞击探测器时进行“观测”的观点，可以发展为客观塌缩理论。思维实验需要探测器进行“无意识的观察” ，以便发生波形崩溃。相比之下，多世界的方法否认崩溃的发生。)

然而，与哥本哈根诠释相关的主要科学家之一尼尔斯·玻尔从未想过观察者引起的波函数的坍缩，因为他并不认为波函数在物理上是真实的，而是一个统计工具;。因此，薛定谔的猫对他不构成困扰。早在盒子被有意识的观察者打开之前，猫就已经死了或者还活着。对实际实验的分析发现，单靠测量(例如使用盖革计数器)就足以在有意识地观察测量之前使量子波函数坍缩，尽管其设计的有效性尚有争议。(原子核中的粒子撞击探测器时进行“观测”的观点，可以发展为客观塌缩理论。思维实验需要探测器进行“无意识的观察” ，以便发生波形坍缩。相比之下，多世界的方法否认崩坍缩的发生。)

===Many-worlds interpretation and consistent histories===

===Many-worlds interpretation and consistent histories===<br>

[[File:Schroedingers cat film.svg|thumb|right|350px|The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.]]

[[File:Schroedingers cat film.svg|thumb|right|350px|The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.]]

The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.

The quantum-mechanical "Schrödinger's cat" paradox according to the many-worlds interpretation. In this interpretation, every event is a branch point. The cat is both alive and dead—regardless of whether the box is opened—but the "alive" and "dead" cats are in different branches of the universe that are equally real but cannot interact with each other.

 

{{Main|Many-worlds interpretation}}

{{Main|Many-worlds interpretation}}

In 1957, Hugh Everett formulated the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process. In the many-worlds interpretation, both alive and dead states of the cat persist after the box is opened, but are decoherent from each other. In other words, when the box is opened, the observer and the possibly-dead cat split into an observer looking at a box with a dead cat, and an observer looking at a box with a live cat. But since the dead and alive states are decoherent, there is no effective communication or interaction between them.

In 1957, Hugh Everett formulated the many-worlds interpretation of quantum mechanics, which does not single out observation as a special process. In the many-worlds interpretation, both alive and dead states of the cat persist after the box is opened, but are decoherent from each other. In other words, when the box is opened, the observer and the possibly-dead cat split into an observer looking at a box with a dead cat, and an observer looking at a box with a live cat. But since the dead and alive states are decoherent, there is no effective communication or interaction between them.

When opening the box, the observer becomes entangled with the cat, so "observer states" corresponding to the cat's being alive and dead are formed; each observer state is entangled or linked with the cat so that the "observation of the cat's state" and the "cat's state" correspond with each other.  Quantum decoherence ensures that the different outcomes have no interaction with each other. The same mechanism of quantum decoherence is also important for the interpretation in terms of consistent histories. Only the "dead cat" or the "alive cat" can be a part of a consistent history in this interpretation. Decoherence is generally considered to prevent simultaneous observation of multiple states.

When opening the box, the observer becomes entangled with the cat, so "observer states" corresponding to the cat's being alive and dead are formed; each observer state is entangled or linked with the cat so that the "observation of the cat's state" and the "cat's state" correspond with each other.  Quantum decoherence ensures that the different outcomes have no interaction with each other. The same mechanism of quantum decoherence is also important for the interpretation in terms of consistent histories. Only the "dead cat" or the "alive cat" can be a part of a consistent history in this interpretation. Decoherence is generally considered to prevent simultaneous observation of multiple states.

当打开盒子时，观察者会与猫纠缠在一起，因此形成了与猫活着和死去相对应的“观察者状态” ; 每个观察者状态都与猫纠缠或联系在一起，以便“观察猫的状态”与“猫的状态”相对应。量子退相干保证不同的结果之间没有相互作用。量子退相干的相同机制对于一致性历史的解释也很重要。只有“死猫”或“活猫”才能成为这一解释中一贯历史的一部分。消相干通常被认为是为了防止同时观测多个状态。

当打开盒子时，观察者会与猫纠缠在一起，因此形成了与猫活着和死去相对应的“观察者状态” ; 每个观察者状态都与猫纠缠或联系在一起，以便“观察猫的状态”与“猫的状态”相对应。量子退相确保不同的结果之间不会相互影响。量子退相干的相同机制对于历史一致论也很重要。只有“死猫”或“活猫”才能成为这一解释的一部分。通常认为退相干是为了防止同时观察多个状态。

A variant of the Schrödinger's cat experiment, known as the quantum suicide machine, has been proposed by cosmologist Max Tegmark. It examines the Schrödinger's cat experiment from the point of view of the cat, and argues that by using this approach, one may be able to distinguish between the Copenhagen interpretation and many-worlds.

A variant of the Schrödinger's cat experiment, known as the quantum suicide machine, has been proposed by cosmologist Max Tegmark. It examines the Schrödinger's cat experiment from the point of view of the cat, and argues that by using this approach, one may be able to distinguish between the Copenhagen interpretation and many-worlds.

===Ensemble interpretation===

===Ensemble interpretation===<br>

The [[Ensemble Interpretation|ensemble interpretation]] states that superpositions are nothing but subensembles of a larger statistical ensemble. The state vector would not apply to individual cat experiments, but only to the statistics of many similarly prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial matter, or a non-issue.

The [[Ensemble Interpretation|ensemble interpretation]] states that superpositions are nothing but subensembles of a larger statistical ensemble. The state vector would not apply to individual cat experiments, but only to the statistics of many similarly prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial matter, or a non-issue.

The ensemble interpretation states that superpositions are nothing but subensembles of a larger statistical ensemble. The state vector would not apply to individual cat experiments, but only to the statistics of many similarly prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial matter, or a non-issue.

The ensemble interpretation states that superpositions are nothing but subensembles of a larger statistical ensemble. The state vector would not apply to individual cat experiments, but only to the statistics of many similarly prepared cat experiments. Proponents of this interpretation state that this makes the Schrödinger's cat paradox a trivial matter, or a non-issue.

This interpretation serves to discard the idea that a single physical system in quantum mechanics has a mathematical description that corresponds to it in any way.

This interpretation serves to discard the idea that a single physical system in quantum mechanics has a mathematical description that corresponds to it in any way.

===Relational interpretation===

===Relational interpretation===<br>

The [[Relational quantum mechanics|relational interpretation]] makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction [[Time evolution|evolution]], and all may be considered "observers". But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system.<ref>{{Cite journal|last = Rovelli|first = Carlo|authorlink = Carlo Rovelli|title = Relational Quantum Mechanics|journal = International Journal of Theoretical Physics|volume = 35|pages = 1637–1678|year = 1996|arxiv = quant-ph/9609002 |doi = 10.1007/BF02302261|bibcode = 1996IJTP...35.1637R|issue = 8 }}</ref> The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of its being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.

The [[Relational quantum mechanics|relational interpretation]] makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction [[Time evolution|evolution]], and all may be considered "observers". But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system.<ref>{{Cite journal|last = Rovelli|first = Carlo|authorlink = Carlo Rovelli|title = Relational Quantum Mechanics|journal = International Journal of Theoretical Physics|volume = 35|pages = 1637–1678|year = 1996|arxiv = quant-ph/9609002 |doi = 10.1007/BF02302261|bibcode = 1996IJTP...35.1637R|issue = 8 }}</ref> The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of its being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.

The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered "observers". But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system. The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of its being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.

The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered "observers". But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system. The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of its being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to "collapse"; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to "collapse" into the same definite result, a cat that is either alive or dead.

关系的解释并没有从根本上区分人类实验者、猫或仪器，或者有生命的和无生命的系统; 所有这些都是受同样的波函数进化规则支配的量子系统，所有这些都可以被认为是“观察者”。但是关系解释允许不同的观察者根据他们所掌握的关于系统的信息，对同一系列事件给出不同的解释。猫可以被认为是仪器的观察者; 同时，实验者可以被认为是盒子里系统的另一个观察者(猫和仪器)。在盒子被打开之前，猫，由于其生存或死亡的性质，有关于设备状态的信息(原子要么衰变了，要么没有衰变) ; 但是实验人员没有关于盒子内容状态的信息。这样，两个观察者同时对这种情况有不同的解释: 对猫来说，仪器的波函数似乎是“塌缩”的; 对实验者来说，盒子里的东西似乎是叠加的。直到盒子被打开，并且两个观察者对所发生的事情有了相同的信息，两个系统状态才似乎“崩溃”成为同一个确定的结果，一只猫不是活着就是死了。

关系诠释并没有从根本上区分人类实验者、猫或仪器，或者有生命的和无生命的系统; 所有这些都是受同样的波函数进化规则支配的量子系统，所有这些都可以被认为是“观察者”。但是关系诠释允许不同的观察者根据他们所掌握的关于系统的信息，对同一系列事件给出不同的解释。猫可以被认为是仪器的观察者; 同时，实验者可以被认为是盒子中系统的另一个观察者(猫和仪器)。在盒子被打开之前，猫是活着还是死了，有关于设备状态的信息(原子要么衰变了，要么没有衰变) ; 但是实验人员没有关于盒子内容状态的信息。这样，两个观察者同时对这种情况有不同的解释: 对猫来说，仪器的波函数似乎是“塌缩”的; 对实验者来说，盒子里的东西似乎是叠加的。直到盒子被打开，并且两个观察者对所发生的事情有了相同的信息，两个系统状态才似乎“坍缩”成为同一个确定的结果，一只猫不是活着就是死了。

===Transactional interpretation===

===Transactional interpretation===<br>

In the [[transactional interpretation]] the apparatus emits an advanced wave backward in time, which combined with the wave that the source emits forward in time, forms a standing wave.  The waves are seen as physically real, and the apparatus is considered an "observer".  In the transactional interpretation, the collapse of the wavefunction is "atemporal" and occurs along the whole transaction between the source and the apparatus.  The cat is never in superposition.  Rather the cat is only in one state at any particular time, regardless of when the human experimenter looks in the box.  The transactional interpretation resolves this quantum paradox.<ref>{{Cite book|last=Cramer|first=John G.|url=https://www.researchgate.net/publication/280926546|title=The transactional interpretation of quantum mechanics|publisher=Reviews of Modern Physics|date=July 1986|isbn=|volume=58|location=|pages=647–685}}</ref>

In the [[transactional interpretation]] the apparatus emits an advanced wave backward in time, which combined with the wave that the source emits forward in time, forms a standing wave.  The waves are seen as physically real, and the apparatus is considered an "observer".  In the transactional interpretation, the collapse of the wavefunction is "atemporal" and occurs along the whole transaction between the source and the apparatus.  The cat is never in superposition.  Rather the cat is only in one state at any particular time, regardless of when the human experimenter looks in the box.  The transactional interpretation resolves this quantum paradox.<ref>{{Cite book|last=Cramer|first=John G.|url=https://www.researchgate.net/publication/280926546|title=The transactional interpretation of quantum mechanics|publisher=Reviews of Modern Physics|date=July 1986|isbn=|volume=58|location=|pages=647–685}}</ref>

In the transactional interpretation the apparatus emits an advanced wave backward in time, which combined with the wave that the source emits forward in time, forms a standing wave.  The waves are seen as physically real, and the apparatus is considered an "observer".  In the transactional interpretation, the collapse of the wavefunction is "atemporal" and occurs along the whole transaction between the source and the apparatus.  The cat is never in superposition.  Rather the cat is only in one state at any particular time, regardless of when the human experimenter looks in the box.  The transactional interpretation resolves this quantum paradox.

In the transactional interpretation the apparatus emits an advanced wave backward in time, which combined with the wave that the source emits forward in time, forms a standing wave.  The waves are seen as physically real, and the apparatus is considered an "observer".  In the transactional interpretation, the collapse of the wavefunction is "atemporal" and occurs along the whole transaction between the source and the apparatus.  The cat is never in superposition.  Rather the cat is only in one state at any particular time, regardless of when the human experimenter looks in the box.  The transactional interpretation resolves this quantum paradox.

===Zeno effects===

===Zeno effects===<br>

The [[Quantum Zeno effect|Zeno effect]] is known to cause delays to any changes from the initial state.

The [[Quantum Zeno effect|Zeno effect]] is known to cause delays to any changes from the initial state.

On the other hand, the anti-Zeno effect accelerates the changes. For example, if you peek a look into the cat box frequently you may either cause delays to the fateful choice or, conversely, accelerate it.  Both the Zeno effect and the anti-Zeno effect are real and known to happen to real atoms. The quantum system being measured must be strongly coupled to the surrounding environment (in this case to the apparatus, the experiment room ... etc.) in order to obtain more accurate information. But while there is no information passed to the outside world, it is considered to be a quasi-measurement, but as soon as the information about the cat's well-being is passed on to the outside world (by peeking into the box) quasi-measurement turns into measurement.  Quasi-measurements, like measurements, cause the Zeno effects.  Zeno effects teach us that even without peeking into the box, the death of the cat would have been delayed or accelerated anyway due to its environment.

On the other hand, the anti-Zeno effect accelerates the changes. For example, if you peek a look into the cat box frequently you may either cause delays to the fateful choice or, conversely, accelerate it.  Both the Zeno effect and the anti-Zeno effect are real and known to happen to real atoms. The quantum system being measured must be strongly coupled to the surrounding environment (in this case to the apparatus, the experiment room ... etc.) in order to obtain more accurate information. But while there is no information passed to the outside world, it is considered to be a quasi-measurement, but as soon as the information about the cat's well-being is passed on to the outside world (by peeking into the box) quasi-measurement turns into measurement.  Quasi-measurements, like measurements, cause the Zeno effects.  Zeno effects teach us that even without peeking into the box, the death of the cat would have been delayed or accelerated anyway due to its environment.

另一方面，反芝诺效应加速了这种变化。例如，如果您经常查看猫箱，您可能会导致延迟决定性的选择，或者相反，加速它。芝诺效应和反芝诺效应都是真实存在的，并且已知会发生在真实的原子上。被测量的量子系统必须与周围的环境强烈耦合(在这种情况下，与仪器、实验室... ..。等等)为了获得更准确的信息。但是，尽管没有信息传递给外部世界，但它被认为是一种准测量，但是一旦有关猫的健康状况的信息传递给外部世界(通过窥视盒子) ，准测量就变成了测量。类似于测量的准测量会引起芝诺效应。芝诺效应告诉我们，即使不窥视盒子，由于它所处的环境，猫的死亡也会被延迟或加速。

另一方面，反芝诺效应加速了这种变化。例如，如果你频繁地窥视放置猫的盒子，则可能会导致延迟或加速你的决定性的选择。芝诺效应和反芝诺效应都是真实存在的，并且已知会发生在真实的原子上。为了获得更准确的信息，被测量的量子系统必须与周围的环境牢固的耦合(在这种情况下，与仪器、实验室... ..等等耦合)但是，当没有信息传递给外界时，这被认为是一种准测量，但是一旦有关猫的健康状况的信息传递给外部外界(通过窥视盒子) ，准测量就变成了测量。类似于测量的准测量会引起芝诺效应。芝诺效应告诉我们，即使不窥视盒子，猫的死亡也会因为它所处的环境而延迟或加速。

===Objective collapse theories===

===Objective collapse theories===<br>

According to [[objective collapse theories]], superpositions are destroyed spontaneously (irrespective of external observation), when some objective physical threshold (of time, mass, temperature, [[irreversibility]], etc.) is reached. Thus, the cat would be expected to have settled into a definite state long before the box is opened. This could loosely be phrased as "the cat observes itself", or "the environment observes the cat".

According to [[objective collapse theories]], superpositions are destroyed spontaneously (irrespective of external observation), when some objective physical threshold (of time, mass, temperature, [[irreversibility]], etc.) is reached. Thus, the cat would be expected to have settled into a definite state long before the box is opened. This could loosely be phrased as "the cat observes itself", or "the environment observes the cat".

According to objective collapse theories, superpositions are destroyed spontaneously (irrespective of external observation), when some objective physical threshold (of time, mass, temperature, irreversibility, etc.) is reached. Thus, the cat would be expected to have settled into a definite state long before the box is opened. This could loosely be phrased as "the cat observes itself", or "the environment observes the cat".

According to objective collapse theories, superpositions are destroyed spontaneously (irrespective of external observation), when some objective physical threshold (of time, mass, temperature, irreversibility, etc.) is reached. Thus, the cat would be expected to have settled into a definite state long before the box is opened. This could loosely be phrased as "the cat observes itself", or "the environment observes the cat".

根据客观塌缩理论，当某种客观物理阈值(时间、质量、温度、不可逆性等)存在时，叠加自发地被破坏(与外部观测无关)到达。因此，猫应该在盒子打开之前很久就已经进入了一个确定的状态。这可以不严谨地表述为“猫自己观察自己” ，或者“环境观察猫”。

根据客观塌缩理论，当达到某种客观物理阈值(时间、质量、温度、不可逆性等)时，叠加会自发地被破坏(与外部观察无关)。因此，猫应该在盒子打开之前很久就已经进入了一个确定的状态。这可以不严谨地表述为“猫自己观察自己” ，或者“环境观察猫”。

Objective collapse theories require a modification of standard quantum mechanics to allow superpositions to be destroyed by the process of time evolution.

Objective collapse theories require a modification of standard quantum mechanics to allow superpositions to be destroyed by the process of time evolution.

==Applications and tests==

==Applications and tests==<br>

Schrödinger's cat quantum superposition of states and effect of the environment through decoherence

Schrödinger's cat quantum superposition of states and effect of the environment through decoherence

The experiment as described is a purely theoretical one, and the machine proposed is not known to have been constructed. However, successful experiments involving similar principles, e.g. superpositions of relatively large (by the standards of quantum physics) objects have been performed. These experiments do not show that a cat-sized object can be superposed, but the known upper limit on "cat states" has been pushed upwards by them. In many cases the state is short-lived, even when cooled to near absolute zero.

The experiment as described is a purely theoretical one, and the machine proposed is not known to have been constructed. However, successful experiments involving similar principles, e.g. superpositions of relatively large (by the standards of quantum physics) objects have been performed. These experiments do not show that a cat-sized object can be superposed, but the known upper limit on "cat states" has been pushed upwards by them. In many cases the state is short-lived, even when cooled to near absolute zero.

所描述的实验是纯理论性的实验，目前尚不清楚所提出的机器是否已经构建好。然而，成功的实验涉及到类似的原理，例如:。相对较大的物体(以量子物理学的标准)的叠加已经完成。这些实验并没有表明一个猫大小的物体可以叠加，但是已知的“猫态”的上限已经被它们推上去了。在许多情况下，即使冷却到接近绝对零度，这种状态也是短暂的。

所描述的实验是纯理论性的实验，所提出的机器尚未被构造出来，但是已经进行了涉及类似原理的成功试验，例如:。相对较大的物体(按量子物理学的标准)的叠加已经完成。这些实验并没有表明可以将猫大小的物体叠加，但是已知的“猫态”的上限已经被它们向上推了。在许多情况下，即使冷却到接近绝对零度，这种状态也是短暂的。

* A "cat state" has been achieved with photons.<ref>{{cite web|url=http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|title=Schrödinger's Cat Now Made Of Light|date=27 August 2014|website=www.science20.com|url-status=live|archiveurl=https://web.archive.org/web/20120318091956/http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|archivedate=18 March 2012}}</ref>

* A "cat state" has been achieved with photons.<ref>{{cite web|url=http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|title=Schrödinger's Cat Now Made Of Light|date=27 August 2014|website=www.science20.com|url-status=live|archiveurl=https://web.archive.org/web/20120318091956/http://www.science20.com/news_articles/schr%C3%B6dingers_cat_now_made_light|archivedate=18 March 2012}}</ref><br>

* A beryllium ion has been trapped in a superposed state.<ref>[http://www.quantumsciencephilippines.com/seminar/seminar-topics/SchrodingerCatAtom.pdf C. Monroe, et al.  ''A "Schrödinger Cat" Superposition State of an Atom''] {{webarchive|url=https://web.archive.org/web/20120107013418/http://www.quantumsciencephilippines.com/seminar/seminar-topics/SchrodingerCatAtom.pdf |date=2012-01-07 }}</ref>

* A beryllium ion has been trapped in a superposed state.<ref>[http://www.quantumsciencephilippines.com/seminar/seminar-topics/SchrodingerCatAtom.pdf C. Monroe, et al.  ''A "Schrödinger Cat" Superposition State of an Atom''] {{webarchive|url=https://web.archive.org/web/20120107013418/http://www.quantumsciencephilippines.com/seminar/seminar-topics/SchrodingerCatAtom.pdf |date=2012-01-07 }}</ref><br>

* An experiment involving a [[superconducting quantum interference device]] ("SQUID") has been linked to the theme of the thought experiment: "The superposition state does not correspond to a billion electrons flowing one way and a billion others flowing the other way. Superconducting electrons move en masse. All the superconducting electrons in the SQUID flow both ways around the loop at once when they are in the Schrödinger's cat state."<ref>[https://physicsworld.com/a/schrodingers-cat-comes-into-view/ Physics World: ''Schrödinger's cat comes into view'']</ref>

* An experiment involving a [[superconducting quantum interference device]] ("SQUID") has been linked to the theme of the thought experiment: "The superposition state does not correspond to a billion electrons flowing one way and a billion others flowing the other way. Superconducting electrons move en masse. All the superconducting electrons in the SQUID flow both ways around the loop at once when they are in the Schrödinger's cat state."<ref>[https://physicsworld.com/a/schrodingers-cat-comes-into-view/ Physics World: ''Schrödinger's cat comes into view'']</ref><br>

* A [[piezoelectric]] "tuning fork" has been constructed, which can be placed into a superposition of vibrating and non vibrating states. The resonator comprises about 10 trillion atoms.<ref>[http://www.scientificamerican.com/article.cfm?id=quantum-microphone Scientific American :'' Macro-Weirdness: "Quantum Microphone" Puts Naked-Eye Object in 2 Places at Once: A new device tests the limits of Schrödinger's cat''] {{webarchive|url=https://web.archive.org/web/20120319021316/http://www.scientificamerican.com/article.cfm?id=quantum-microphone |date=2012-03-19 }}</ref>

* A [[piezoelectric]] "tuning fork" has been constructed, which can be placed into a superposition of vibrating and non vibrating states. The resonator comprises about 10 trillion atoms.<ref>[http://www.scientificamerican.com/article.cfm?id=quantum-microphone Scientific American :'' Macro-Weirdness: "Quantum Microphone" Puts Naked-Eye Object in 2 Places at Once: A new device tests the limits of Schrödinger's cat''] {{webarchive|url=https://web.archive.org/web/20120319021316/http://www.scientificamerican.com/article.cfm?id=quantum-microphone |date=2012-03-19 }}</ref><br>

*  An experiment involving a flu virus has been proposed.<ref>{{cite web|url=http://www.technologyreview.com/blog/arxiv/24101/|title=How to Create Quantum Superpositions of Living Things|first=Emerging Technology from the|last=arXiv|publisher=}}</ref>

*  An experiment involving a flu virus has been proposed.<ref>{{cite web|url=http://www.technologyreview.com/blog/arxiv/24101/|title=How to Create Quantum Superpositions of Living Things|first=Emerging Technology from the|last=arXiv|publisher=}}</ref><br>

* An experiment involving a bacterium and an electromechanical oscillator has been proposed.<ref>{{cite web|url=http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|title=Could 'Schrödinger's bacterium' be placed in a quantum superposition?|website=physicsworld.com|url-status=live|archiveurl=https://web.archive.org/web/20160730174613/http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|archivedate=2016-07-30}}</ref>

* An experiment involving a bacterium and an electromechanical oscillator has been proposed.<ref>{{cite web|url=http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|title=Could 'Schrödinger's bacterium' be placed in a quantum superposition?|website=physicsworld.com|url-status=live|archiveurl=https://web.archive.org/web/20160730174613/http://physicsworld.com/cws/article/news/2015/sep/21/could-schrodingers-bacterium-be-placed-in-a-quantum-superposition|archivedate=2016-07-30}}</ref><br>

In quantum computing the phrase "cat state" sometimes refers to the GHZ state, wherein several qubits are in an equal superposition of all being 0 and all being 1; e.g.,

In quantum computing the phrase "cat state" sometimes refers to the GHZ state, wherein several qubits are in an equal superposition of all being 0 and all being 1; e.g.,

在量子计算中，短语“猫态”有时指的是 GHZ 态，其中几个量子位都处于等量叠加态，全部为0，全部为1; 例如,

在量子计算中，短语“猫状态”有时是指 GHZ 态，其中几个量子位都处于等量叠加态，全部为0，全部为1; 例如,

According to at least one proposal, it may be possible to determine the state of the cat before observing it.

According to at least one proposal, it may be possible to determine the state of the cat before observing it.

==Extensions==

==Extensions==<br>

[[Wigner's friend]] is a variant on the experiment with two human observers: the first makes an observation on whether a flash of light is seen and then communicates his observation to a second observer. The issue here is, does the wave function "collapse" when the first observer looks at the experiment, or only when the second observer is informed of the first observer's observations?

[[Wigner's friend]] is a variant on the experiment with two human observers: the first makes an observation on whether a flash of light is seen and then communicates his observation to a second observer. The issue here is, does the wave function "collapse" when the first observer looks at the experiment, or only when the second observer is informed of the first observer's observations?

Wigner's friend is a variant on the experiment with two human observers: the first makes an observation on whether a flash of light is seen and then communicates his observation to a second observer. The issue here is, does the wave function "collapse" when the first observer looks at the experiment, or only when the second observer is informed of the first observer's observations?

Wigner's friend is a variant on the experiment with two human observers: the first makes an observation on whether a flash of light is seen and then communicates his observation to a second observer. The issue here is, does the wave function "collapse" when the first observer looks at the experiment, or only when the second observer is informed of the first observer's observations?

维格纳的朋友是两个人类观察者实验的一个变体: 第一个观察者观察一道闪光是否被看到，然后将他的观察结果传达给第二个观察者。这里的问题是，当第一个观察者观察实验时，波函数是“坍缩”的，还是只有当第二个观察者被告知第一个观察者的观察时，波函数才会“坍缩” ？

维格纳的朋友是该实验的一个变体，有两个人类观察者: 第一个观察者观察一道闪光是否被看到，然后将他的观察结果传达给第二个观察者。这里的问题是，当第一个观察者观察实验时，波函数是“坍缩”的，还是只有当第二个观察者被告知第一个观察者的观察时，波函数才会“坍缩” ？

In another extension, prominent physicists have gone so far as to suggest that astronomers observing dark energy in the universe in 1998 may have "reduced its life expectancy" through a pseudo-Schrödinger's cat scenario, although this is a controversial viewpoint.<ref>{{cite web

In another extension, prominent physicists have gone so far as to suggest that astronomers observing dark energy in the universe in 1998 may have "reduced its life expectancy" through a pseudo-Schrödinger's cat scenario, although this is a controversial viewpoint.<ref>{{cite web

  |last        = Chown

  |last        = Chown