Talk:Schrödinger's cat/Archive 4

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Logic

I'm not not a physicist, but wouldn't this experiment disprove whatever the Copenhagen interpretation is? Was that the idea? --75.173.18.129 (talk) 01:41, 10 April 2010 (UTC)

Quotes similar to the Weinberg quote, only shorter and better?

The problem with the Steven Weinberg quote is that he kind of mixes in where he disagrees with Bohr, and we get something layered. And what we really need are good, crisp, straightforward quotes that lay out the Copenhagen, the many worlds, the ensemble, the relational, and the objective collapse interpretations as clearly as possible. Just lay it on the table, and then we can have the give-and-take of the various criticisms and responses. FriendlyRiverOtter (talk) 22:42, 9 June 2010 (UTC)

I think the first paragraph of the Weinberg quote is excellent, perfect; a definitive "crisp" statement of the drawback of the CI - that it doesn't treat the rest of the world quantum mechanically, as for example the MWI does. In fact it's rather famous and is quoted widely. In addition it ties in with the Einstein quote above it in the article, referring to his doubts about quantum mechanics. I think the 2nd paragraph (which was added later) is unnecessary and could be cut, but I feel strongly that the first paragraph should stay. --Chetvorno^TALK 00:03, 10 June 2010 (UTC)

Steven: " . . . Bohr's version of quantum mechanics was deeply flawed, but not for the reason Einstein thought. . . " That's layered. That's complexed. And it seems like we want a good description of the interpretation (the subject matter in this case) first, and then a good description of the drawbacks and/or criticisms. FriendlyRiverOtter (talk) 18:04, 15 June 2010 (UTC)

I think the way the Interpretation sections are organized is to have a paragraph explaining the Interpretation, then include a quote (or sentence) which criticizes or reveals the weakness in the interpretation in explaining Schro's Cat. The Weinberg quote kind of goes with the Penrose quote in that respect. I agree the W quote is layered and complex, and should be cut in length which would reduce the complexity. But it just seems to fit so well with the rest of the article . . . --Chetvorno^TALK 11:45, 19 June 2010 (UTC)

I was going to summarize the Weinberg quote in the section Copenhagen interpretation but had difficulty finding useful information for the topic of Schrödinger's cat. Part of the Weinberg quote touched on a subject that I found interesting but there wasn't enough to use, and also it didn't mention Schrödinger's cat. Then a question came to mind: What is the point of the long Weinberg quote? Then another question came to mind regarding Wikipedia policy. Please note that the article that it is from does not mention Schrödinger's cat, and note the following excerpt from the lead of the Wikipedia policy WP:NOR,

"To demonstrate that you are not adding original research, you must be able to cite reliable published sources that are directly related to the topic of the article, and that directly support the material as presented."

The Weinberg source does not mention Schrödinger's cat and thus this source is not "directly related to the topic of the article", and the quote is also a digression into the Copenhagen interpretation in general. I removed the quote from the article. --Bob K31416 (talk) 12:32, 13 September 2010 (UTC)

What?

Alright, I'm not saying that this article should be simplified beyond belief, but as it stands it reads like it should be in a textbook, not an encyclopedia. I always thought that Schodinger's Cat was supposed to help illustrate quantum mechanics. Instead we get a page riddled with words that only someone well versed in quantum mechanics would understand. I'm just saying, because to a non-expert, this sounds like Schrodinger is trying to say that unknown variables add up into one thing- because we don't know what happened to the cat, for all intents and purposes it is dead AND alive. I'm sure that was not Schrodinger's point 72.199.100.223 (talk) 07:36, 19 June 2010 (UTC)

I've been writing an introduction for the article giving a more elementary explanation. It's not ready for prime time yet, but you can read it at Chetvorno/work4. I'd appreciate any comments you'd care to leave. --Chetvorno^TALK 11:59, 19 June 2010 (UTC)

You can look at the "simple.wikipedia" article of it here > http://simple.wikipedia.org/wiki/Schr%C3%B6dinger%27s_cat —Preceding unsigned comment added by 58.178.248.24 (talk) 20:48, 24 July 2010 (UTC)

Serial cat killer

A serial cat killer was performing the Schroedinger Cat Experiment when the police broke down his door and arrested him. Upon opening the box, the police found that the cat was dead. The police Crime Scene Investigators (CSI) were called in and determined the time of death (TOD) of the cat by measuring its body temperature rectally. It was found that the cat died long before the box was opened, proving that the cat was not both dead and alive during a period prior to opening the box.

The point of the above story is to raise the issue of whether a conscious observer is required to collapse a quantum wave-function. In the recently added section of the article Conscious observer requirement an experiment showed that a conscious observer, such as a person opening the box and looking inside, is not required.[1] --Bob K31416 (talk) 18:01, 10 September 2010 (UTC)

Sorry, but I am unclear as to the purpose of the above story. If you are questioning what is said in the article, then you have the wrong idea of the purpose of the article and this talk page. Any questions or counterpoints you may want to raise personally is original research unless you can cite a reliable source. That means it cannot go into the article, and is not open for debate here.

However, if you do have a good cite, then adding that to the article would be better than inventing your own hypothetical stories to demonstrate. Thanks. --Escape Orbit ^(Talk) 16:21, 13 September 2010 (UTC)

What would you like to do? --Bob K31416 (talk) 21:31, 13 September 2010 (UTC)

I think Escape Orbit is saying that this discussion is irrelevant to the article and that no further action needs to be taken, unless you have a reliable source commenting specifically on the thought experiment. -Jordgette (talk) 21:42, 13 September 2010 (UTC)

Would it matter to anyone that I found and contributed the sourced material in the section Conscious observer requirement after I first put the idea in the above story on the talk page for discussion? I think one has to be careful about what one suppresses on a talk page because it might be something that leads to useful information for the article, which was what occurred in this case with the contribution of the section Conscious observer requirement. Sorry for the misunderstanding. I'll try to be more sensitive to the feelings of some of the editors here in the future. Regards, --Bob K31416 (talk) 02:55, 14 September 2010 (UTC)

No harm done. I was just unclear on what you were trying to do. It is not unusual for some editors to float their own personal theories and ideas on article talk pages like these. I'm no expert, but I can see what I think is a flaw in your example. But as I explained, my thoughts on the subject are irrelevant and this talk page is not a forum for debating things not related to improving the article. So it's always a good idea to produce a cite, or state up front that's what's you're looking for, to demonstrate that you are not just voicing your own ideas.

If you have a good cite, are avoiding fringe theories, and can introduce it into the article in a neural fashion, then feel free, be bold. If anyone has issue with it they can always revert and invite further discussion. --Escape Orbit ^(Talk) 13:48, 14 September 2010 (UTC)

Thanks. Re "I'm no expert, but I can see what I think is a flaw in your example. But as I explained, my thoughts on the subject are irrelevant and this talk page is not a forum for debating things not related to improving the article." - Your thoughts might be useful for the article because they might stimulate a search for sources related to your thoughts, or to looking at the source already in the article for an improvement to the article.

I think the problem that results from editors discussing their own ideas on the Talk page is when they go on and on with little hope of the discussion resulting in a useful sourced contribution to the article. So far, that certainly isn't the case with your thoughts and I would like to know what you feel is a flaw, not to argue but because I'm interested. Regards, --Bob K31416 (talk) 14:30, 14 September 2010 (UTC)

I thought your addition of "conscious observer requirement" was a good one, and useful. Regarding this talk thread, I don't think anyone's feelings were hurt -- I think we just aren't clear what the purpose of your story is. Usually people float an idea for an addition on the talk page before making the addition, not after. If that's all you meant to do, illustrate why you made that addition, then it's all good with me. -Jordgette (talk) 05:35, 14 September 2010 (UTC)

Re "Usually people float an idea for an addition on the talk page before making the addition, not after." -Actually, I did float the idea[2] before putting related material in the article.[3].

BTW when I put it in the article I inadvertently removed a section. I've made the correction.[4] In at least this regard, it's fortunate that we had this discussion, since the inadvertent removal may have gone unnoticed.

Thanks for your comments and kind remarks. --Bob K31416 (talk) 14:12, 14 September 2010 (UTC)

Can anybody simplify this?

Please simplify the article. I understand what it says, but it could be so much more simple.Glorthac (talk) 05:47, 25 September 2010 (UTC)

Since you understand what it says, perhaps you could make some suggestions for ways to explain it more simply. Thanks. --Bob K31416 (talk) 12:45, 25 September 2010 (UTC)

Merge Schrodinger's cat in popular culture into this article?

opposed, this article describes a proper and accepted theory of quantum mechanics and should not be dirtied by pop culture jargon. In the event that someone needs proper information on this article they would be bombarded with trivial and useless information about loose analogies to the scientific data —Preceding unsigned comment added by 70.53.106.90 (talk) 12:26, 21 May 2011 (UTC)

I oppose this merge. I would not like to see a big list of pop culture references in the main article. I think that the Schrodinger's Cat in popular culture article should be deleted and not merged. TurtleMelody (talk) 04:00, 23 April 2011 (UTC)

Agreed. Most of those factoids seem trivial to the extreme, and merging would overwhelm this article. Pick, say, the five most prominent if you must. – anna 10:05, 27 April 2011 (UTC)

Added merger tag and edited name of this section so everybody will know what we're talking about. I also oppose the merge, for the reasons given above. I think just a hatnote at the top of the article directing people to the other article is enough. --Chetvorno^TALK 16:49, 27 April 2011 (UTC)

Oppose merge and the deletion. -- cheers, Michael C. Price ^talk 16:53, 27 April 2011 (UTC)

Not seeing a consensus to merge. Suggest we remove the merge template. -- cheers, Michael C. Price ^talk 20:28, 30 June 2011 (UTC)

in between existance / time

See now what if the box was opened at the exact time of the cat is not dead or alive but about to die by the gas or dying and why was this not looked at unless the it has and then i apologize but does anyone have any idea about that. —Preceding unsigned comment added by 66.222.213.13 (talk) 23:50, 17 May 2011 (UTC)

Critique of of the Copenhagen interpretation?

Seeing as Copenhagen interpretation#Consequences states that Schrödinger resists "so naively accepting as valid a 'blurred model' for representing reality." I think Schrödinger's cat is well described as a critical view of the Copenhagen interpretation, or a caution against accepting the apparent consequences of the interpretation without thinking.

Thus I think we should keep the article as it was. Free Bear (talk) 15:18, 7 June 2011 (UTC)

I agree that "Schrödinger's cat is well described as a critical view of the Copenhagen interpretation", but I don't think that it shows a fundamental flaw in the interpretation. I think what I have have written is more precise and historically accurate, so it shouldn't be removed. I think something about Schrödinger's cat acting as a caution against "accepting the apparent consequences of the interpretation without thinking" should be added without deleting what is already there. A2326xyz — Preceding unsigned comment added by A2326xyz (talk • contribs) 16:18, 7 June 2011 (UTC)

I think what we have here is simply a matter of fine-tuning the wording. I have a particular problem with your definition of what a "fundamental flaw" is, which is unclear. When does a critique become an expose of fundamental flaws? I also really don't like the "contrary to popular belief". This almost always precedes a claim of "I'm right, everyone else is wrong". Unless you can cite what "popular belief" is, and equally cite a source demonstrating it is wrong, this is a bad introduction to the subject. --Escape Orbit ^(Talk) 16:50, 7 June 2011 (UTC)

You are already in breech of Wikipedia rules regarding your reverting on this. Please revert your changes and discuss what you're trying to do here. It is up to you to explain your changes and help maintain consensus. This doesn't work if you simply keep adding what you've had removed and challenge others to refute it. Thanks. --Escape Orbit ^(Talk) 16:57, 7 June 2011 (UTC)

And now it's worse. Again, I'm asking you to revert your changes and discuss what you'd like changed. You cannot say "it is sometimes incorrectly thought" when you make no effort to demonstrate it is "sometimes thought", never mind produce a cite to verify that it is "incorrect". All you're doing is putting one side of an argument, without any evidence that the argument even exists. Either way, Wikipedia doesn't care. Unless you can cite disagreement on this, all that should be in the article, and particularly the lead, is what is accurate, cited and sourced. What you are attempting to do is not verifiable and needlessly confuses the lead. --Escape Orbit ^(Talk) 12:46, 8 June 2011 (UTC)

I agree with Escape Orbit. And the introduction needs to be accessible to nontechnical readers and is not the place to make technical points about the Copenhagen Interpretation. The original intro was fine. --Chetvorno^TALK 20:54, 9 June 2011 (UTC)

Agreed. Yet A2326xyz has once again placed his/her changes back into the article with no attempt at discussion. I have reverted and warned them on their talk page of edit warring.--Escape Orbit ^(Talk) 10:13, 10 June 2011 (UTC)

The problems with the original introduction are that it is inaccurate and gives a false impression about what Schrödinger's cat is. Quantum physics is a technical subject and should never be simplified to the the extent that non technical readers are provided with false or misleading information.A2326xyz (talk) 10:29, 10 June 2011 (UTC)

Then please suggest here what you think should be done. You are still inserting into the lead "commonly misunderstood to be a paradox of quantum physics" when you present no evidence that any such common misunderstanding exists. It is also far, far better to start an article with a definition of what it is, not what it isn't, particularly when there is nothing to suggest that anyone believes it to be what it isn't. Note that I'm not saying you are wrong, just that what you are doing is unnecessary, confusing and difficult (if not impossible) to verify. --Escape Orbit ^(Talk) 11:14, 10 June 2011 (UTC)

It is also not uncommon to avoid cluttering the lead with cites if it is a summary (which is what it should be) of what is fully sourced and cited in the rest of the article. What you are adding about a common misunderstanding is not mentioned anywhere else in the article, far less cited. --Escape Orbit ^(Talk) 11:18, 10 June 2011 (UTC)

Agreeing. My last edit summary [5] was too simplistic: the lede should summarise properly referenced information lower down.--Old Moonraker (talk) 11:26, 10 June 2011 (UTC)

As a compromise I suggest that the intro be changed to what is written below.

Schrödinger's cat is a thought experiment, usually described figuratively as a paradox of quantum physics. Devised by Austrian physicist Erwin Schrödinger in 1935, it illustrates what he and others saw as the problems caused by thinking of the wave function as a real entity. Originally intended as a critique of the Copenhagen interpretation, it is now important to other interpretations as well. The thought experiment presents a cat that might be alive or dead, depending on an earlier random event. In the course of developing this experiment, he coined the term Verschränkung (entanglement). A2326xyz (talk) 12:19, 10 June 2011 (UTC)

The point about the lede is that it is supposed to introduce the information below: all the points in the lede need to be dealt with, and referenced, in the body of the article. For example (and this wasn't from one of your edits) "Verschränkung" doesn't appear anywhere else in the piece, and in following the wikilink it appears that the term didn't originate with Schrödinger, as is implied, but Einstein, Podolsky and Rosen. We're not there yet. --Old Moonraker (talk) 13:33, 10 June 2011 (UTC)

Not there yet, but a big improvement. If we could clear up the issue of "Verschränkung" I've no problems with this. I'd say unless it can be clearly resolved as being coined in Schrödinger's though experiment regarding the cat, it should be removed from the lead. The article isn't reliant on it at all. --Escape Orbit ^(Talk) 14:54, 10 June 2011 (UTC)

I think A2326xyz's text above will give nontechnical readers the impression that the wavefunction is not "real", whatever that means. The wavefunction is as "real" as anything else in quantum mechanica. I think the original intro was better. --Chetvorno^TALK 03:16, 1 July 2011 (UTC)

But the reality of the wavefunction is one of the central interpretational issues in QM, so giving the "impression" that it is not real might not be a bad thing.

On "entanglement" I failed to find the term in the EPR paper, yet it appears numerous times in Schrodinger's paper. So at first blush I would go with the claim that Schrodinger was the first to coin the term.

-- cheers, Michael C. Price ^talk 05:31, 1 July 2011 (UTC)

Isn't the health of the cat a detector?

Which would collapse the function? --62.1.19.35 (talk) 00:50, 4 September 2011 (UTC)

Yes it is, which is why the experiment as stated is broken. The cat is an observer and therefore the quantum entanglement collapses into a specific outcome as soon as it notices it is dying. But we can't add that unless someone has pointed it out in a reliable, verifiable, source. It seems most physicists don't put much stock in the sentience of animals. Which seems weird to me as it kind of implies physicists think humans are somehow spiritually superior, in spite of science showing we are, most likely, not. Colincbn (talk) 07:19, 20 September 2011 (UTC)

Actually in reading the whole article I see it does mention and link to Objective collapse theory, which pretty much covers that. So, good. Colincbn (talk) 07:31, 20 September 2011 (UTC)

In quantum mechanics, I believe the term observation doesn't necessarily entail a conscious observer; it means something like "any interaction with the external world". A movie camera, or even an atomic particle, can be an "observer". The idea that observation by a consciousness, cat or human, is needed to collapse the wavefunction (Consciousness causes collapse) is a fringe view, although it is held by a few scientists. --Chetvorno^TALK 21:02, 20 September 2011 (UTC)

Which means the Geiger counter would collapse the wave function as well. So at the end of the day the only thing the experiment as written gives you is a 50% chance of having a dead cat. Colincbn (talk) 06:29, 21 September 2011 (UTC)

Is this paradox illustrated by the grid illusion

I feel like there is a link between this paradox and the grid illusion whereby you think there are black dots, until you view the location of the perceived black dot, only to discover that its actually not a black dot, but as you look away, it looks like a black dot again, hence the act of observing the black dot makes it vanish... A bit like the Double-slit experiment, where the act of observation creates a predictable but unexpected result!

No it is not. There are several explanations in the grid illusion article. None of them is related to quantum physics. That is original research. Famousdog (talk) 13:04, 7 October 2011 (UTC)

There is no link at all between Schrödinger's cat and this illusion. What you are describing is that the grid illusion could be seen as a metaphor for the paradox. Which is true, it could be, but there is no factual link. What's more, the metaphor is just your opinion and original research. --Escape Orbit ^(Talk) 13:35, 7 October 2011 (UTC)

There is a link, but the link cannot be determined over 3 schrodinger degrees. Hence no link exists to the grid illusion until you see it. פשוט pashute ♫ (talk) 03:16, 31 October 2012 (UTC)

Incomplete sentence under "Many-worlds intepretation..."

"Although the mainstream view (without necessarily endorsing many-worlds) is that decoherence is the mechanism that forbids such simultaneous perception.[9][10]"

Could someone expert in this topic revise this into a meaningful sentence? Gwideman (talk) 20:02, 18 August 2012 (UTC)

Im neither an expert on the topic nor an expert on grammar, but I interpret the above as: "Decoherence is the mechanism that forbids such simultaneous perception" is the mainstream view. I doubt if this helps much. --RacerX¹¹ Talk to me^{Stalk me} 21:07, 18 August 2012 (UTC)

It wasn't a problem for Neils Bohr, or a problem for Werner Heisenberg - who else are we crediting as authors of 'the Copenhagen Interpretation'?

That Neils Bohr would have the detector 'collapse the wavefunction' is already covered in this article. Werner Heisenberg says that 'the wavefunction' (he calls it the 'probability function') is merely an expression of our knowledge of the system. Thus 'collapse' upon observation is merely the reduction of our knowledge from 'what might have happened' to 'what did happen'. Who exactly else is to be considered an author of the Copenhagen interpretation such that 'Schrodinger's Cat' can be considered an effective refutation of it? Von Neumann? I don't believe he ever worked in Copenhagen. — Preceding unsigned comment added by 95.145.220.141 (talk) 16:14, 6 November 2012 (UTC)

Correct interpretation?

Surely the interpretation has changed since Copenhagen? The "observation" occurs, not when the box opens, but when any interaction occurs inside the box? (Eg, the cat peeing or eating food!) So, the cat is alive or dead far before the box is opened. 51kwad (talk) 08:36, 13 November 2012 (UTC)

How could one ever tell? The notion of 'correct' here isn't a scientific one (we need to 'observe' in order to investigate - so actually doing science restricts us to knowing what happens upon observation). As the article mentions, Neils Bohr (the 'father' of the Copenhagen Interpretation) would probably have viewed the detector as an 'observer' of sorts (and almost certainly most parts of the cat too). As I mention in the preceding section of this talk page, Werner Heisenberg (the other major figure in 'the Copenhagen Interpretation's' development) viewed 'the wavefunction' (which describes the cat as both alive and dead) as merely a representation of our knowledge of the system we are considering [thus unique for every individual]. If you accept that account, then there's really nothing counter-intuitive about Schrodinger's cat. The matter of a 'correct' interpretation is a philosophical one however - the point of the Copenhagen interpretation[s] is to attempt to keep 'the science' free from metaphysical (unscientific) speculation. I hope that clarifies a bit. 139.133.11.5 (talk) 10:44, 13 November 2012 (UTC) JJB

It's not just a philosophical issue; there is a scientific issue - we don't know when the superposition in the box collapses to a single state. We can only see the "end" of the process, when we open the box. We know, after we close the box, that the radioactive atoms are in a superposition of "decayed" and "undecayed" states. But we don't know whether the superposition collapses at a small scale, when the atom decays ("objective collapse" interpretations) so the cat is unambiguously alive or dead, or whether the multiple states extend to the geiger counter and poison, so the cat is also in a "dead/alive" superposition ("many worlds" interpretations and others). --Chetvorno^TALK 17:06, 13 November 2012 (UTC)

Progress is being made on this. There are ways to observe a small superposition without collapsing the superposition; by observing the interference pattern created by the different states. Recent experiments, which could be considered small scale "Schrodinger's cat" experiments, have shown that collections of thousands of atoms can be in superpositions - "cat states" - that is, in two or more positions at once. So the trend is toward believing that the cat is actually in a superposition. --Chetvorno^TALK 17:06, 13 November 2012 (UTC)

Progress? Interference patterns were observed long before quantum theory, or the advent of the term 'superposition' as used to denote a physical phenomenon. I'm really not sure how one could demonstrate interference generated by a superposition of 'collections of thousands of atoms', and I think it's safe to say that there isn't any evidence that this does actually happen - but I'm very happy to be shown wrong here - I'm very keen to learn more. I don't see how it's scientific and not philosophical though - since science requires that we perform some form of measurement in order to 'discover' what is going on - the question of what is going on prior to measurement would thus seem necessarily to be a philosophical and not scientific question. — Preceding unsigned comment added by 90.208.192.122 (talk) 13:33, 21 November 2012 (UTC)

It isn't "prior" to measurement, the entire experiment is a "measurement". The value of the SC experiment, although it is kind of old fashioned, is that it focuses attention on what is meant in QM by "measurement" or "interaction with the external world". And it's clear that "measurement" is a process of "amplification"; of the wavefunction affecting larger and larger numbers of particles. In the experiment a quantum state of a radioactive atom (decayed/undecayed) affects a few more atoms (ionized/unionized gas in geiger tube) which spreads (tiny current pulse/no pulse in geiger counter tube) and spreads (large current pulse/no pulse in geiger counter electronics) and spreads till it affects the macroscopic world (dead cat/live cat). At the beginning, the radioactive atoms are in this peculiar condition of superposition, in both states at once. Where in this process does the superposition end and the world settle into one or another definite state? (or does it at all?) That's the question.

It's being investigated by creating small superpositions in collections of particles, and exploring exactly when and how the superposition transitions from "coherent" to "decoherent" (the point at which the multiple states can no longer be distinguished).

And it isn't difficult to find experiments on superpositions relating to Schrodinger's cat; it's an active area of research. All you have to do is google: 1, 2, 3, 4, 5, 6. One experiment that produced superpositions of billions (not thousands) of particles was done with supercurrents in SQUIDs 7, 8 although the particles were electrons, not atoms as I claimed above. Each electron flowed around the superconducting ring in BOTH directions at once. This year's Nobel prize in physics went for progress on "cat states": 9, 10 --Chetvorno^TALK 16:43, 21 November 2012 (UTC)

Apostrophe

Why the heck does this have an apostroph? Is it sort for "Schrödinger is cat"? — Preceding unsigned comment added by 176.198.62.38 (talk) 01:35, 16 February 2013 (UTC)

The apostrophe is applying possession. - Camyoung54 talk 20:56, 10 April 2013 (UTC)

"Contradiction with QM" section

I don't see what relevance the statements in this newly added section have to the article. No objects are being detected at "two different places at once" in the experiment. In experiments on "cat states", the "cat states" (superpositions) are detected indirectly, by their interference pattern. Also the content needs to be sourced. --Chetvorno^TALK 08:17, 3 August 2013 (UTC)

The relevance is that all claims that QM implies real cat states are meterphysical, and not part of the mathematical formulation of QM itself. A “cat state, is the claim that an object really does physically exist in more than one of the states given by the general state vector at the same time. Position is just one representative example for illustrative purposes. The specific experiments being discussed are immaterial. It could be spin, momentum or whatever. E.g for |psy> = |1> +|2>, a cat state claim is a claim that in real physicality that the state |1> and |2> actually exist simultaneously. QM theory specifically denies that such a measurement can ever be made, therefore such claims should not be implied. A superposition of states should not be interpreted as if such superposition implies a cat can be both dead and alive at the same time. QM rejects that such a concept could ever be proved by an actual measurement, and does not require such a metaphysical interpretation. I can make my self invisible, but only if your back is turned to me sort of thing. There is nothing to source, any credible reference on the postulates of QM states that the result of any measurement must be a single eigenvalue. Its what state vector collapse means! Kevin Aylward 09:06, 3 August 2013 (UTC) — Preceding unsigned comment added by Kevin aylward (talk • contribs)

I don't see that the article says that an object will "physically exist in more than one of the states". The article makes it pretty clear that if an observation is made, the result will be either |live cat> or |dead cat>. The term "cat state", which is not used in the article's explanation of the experiment, refers to the superposition itself, not the result of a measurement (hence the term "state"). The existence of superpositions ("cat states") has been established "unambiguously" and is not in doubt. --Chetvorno^TALK 10:50, 3 August 2013 (UTC)

The article cites experiments, for example, http://www.scientificamerican.com/article.cfm?id=quantum-microphone. This article specifically states, “For example, a single electron can move along multiple different paths or an atom can be placed in two different places, simultaneously.” This sort of text is pretty much the norm whenever QM is discussed. It seems appropriate to dispel this common misunderstanding of QM and make a specific note that standard QM says no such thing. The existence of an object truly physically existing as a superposition has never been established, nor is that possible, according to QM. Producing measurements that rely on the notion of a summed state does not negate this view. QM is essentially, a mathematically calculation tool. The state vector “sum” of states is not a physical sum. The plus sign is a standard logical OR operator as due to the requirement that the state vector is a probability function. It is clear that it needs to be clarified that a cat state does not mean that an object can physically have two simultaneous eigenvalues as it is clear many do. Kevin Aylward 12:06, 3 August 2013 (UTC) — Preceding unsigned comment added by Kevin aylward (talk • contribs)

Many do what? It's pretty obvious that the cat state doesn't have two eigenvalues, it has no eigenvalues at all since it's not an eigenstate of the "cat alive" operator. The paragraph you inserted is, as it stands now, grammatically wrong, physically dubious, and worst of all, completely unsourced. I'm sorry, but at the moment I don't see a good reason for not removing it. — HHHIPPO 14:19, 3 August 2013 (UTC)

Many claim that superposition means two simultaneous states. I agree, the cat state does not have two eigenvalues. The point though, is that that the popular accounts regarding cat states ARE claiming that “two things at once” is the meaning of such superpositions. I already pointed out that that is exactly what one article referenced in this article actually stated. Regarding dubiousness. Is it true or not true that QM demands a measurement must result in a single eigenvalue? Is it true or not true that articles are going around saying that objects physically exist in two states at once? So what’s exactly your problem? What exactly wrong with the grammar also?Kevin Aylward 16:04, 3 August 2013 (UTC) — Preceding unsigned comment added by Kevin aylward (talk • contribs)

Regardless of the argument, without a source the paragraph is original research and should be removed. -Jordgette [talk] 22:57, 3 August 2013 (UTC)

The example you gave above 1 was an article in Scientific American for general readers, the same target audience this article has. It's statement that "an atom can be placed in two different places" was referring to the superposition - it said so in the next sentence - there was nothing about objects being "observed" in two different places. Some such language is needed to describe the eigenstates of the state vector to nonscientists. Regardless of whether we like it or not, as you pointed out this language is the "norm" in RSs, which is what WP must follow. --Chetvorno^TALK 00:16, 4 August 2013 (UTC)

The article states "...an atom can be placed in two different places, simultaneously..." This is unprovable waffle. The norm does not mean that that it should not be pointed out that the norm is wrong. Its relatively easy to explain to non scientists exactly what multiple eigenstates mean. Hint. Ensemble interpretation description of a state vector for classical dice throwing. Hands up those that believe that measuring two eigenvalues simultaneously is NOT a contradiction to QM. So...whats the problem...oh whatever...Kevin Aylward 07:10, 4 August 2013 (UTC) — Preceding unsigned comment added by Kevin aylward (talk • contribs)

Your addition has a worse waffle. It implies that superpositions (cat states), the subject of this article, violate QM. "...if an experiment unambiguously, directly shows a true Shrödinger (sic) cat state... then QM would be falsified." Hands up those who believe with Kevin that there are no such things as superpositions in QM. --Chetvorno^TALK 08:58, 4 August 2013 (UTC)

"This poses the question of when exactly quantum superposition ends and reality collapses into one possibility or the other"

Why would "reality" collapse into one possibility or another? This just seems preposterous. I do not understand this part of the article at all. Perhaps it should be redone. 98.81.2.13 (talk) 09:21, 29 October 2013 (UTC)

It's hard to visualize, but the uncertainty principle of quantum mechanics says each radioactive atom is in a combination or "superposition" of two "states" simultaneously: one in which it has decayed and emitted a radioactive particle, and one in which it hasn't. Therefore, if the superposition doesn't collapse into one possibility or the other, the radioactivity detector will also be in two states: one in which it has detected the radiation particle and one in which it hasn't. So the flask of poison will also be in two states: broken and unbroken. And the cat will be in two states: dead and alive. Since we never see macroscopic objects like cats in two "states" simultaneously, somewhere in this chain of events the "superposition" must have "collapsed" and the world settled into the result we see: either the radioactive atom "did" decay, and the cat is dead, or the radioactive atom "didn't" decay and the cat is alive. The problem is scientists don't know where in the chain of events from atom to cat the collapse occurs. The Nobel prize in physics this year was given for progress on "cat states". --Chetvorno^TALK 16:19, 29 October 2013 (UTC)

If the cat is alive, it will know which state it is in. There is no superposed dead state in that case. The confusion is between (a) the QM uncertainty which produces a mixed state at the microscopic level, and (b) the superimposed uncertainty of those outside who are juggling ordinary probabilities of the cat being dead or alive. Imagine a repeating gun inside the box to see the latter. No QM, just a probability that the cat walks in front of the gun. Anyway, interactions are what, if anything, causes collapse, be they with humans or apparatus or cats or walls of boxes or air molecules. The wave collapse, if it happens, happens well before the box is opened. There is no live-dead cat in there, any more than there would be if the cat were replaced by a human. 51kwad (talk) 14:54, 7 November 2013 (UTC)

Relational quantum mechanics has a very nice treatment of such issues, for example Wigner's friend. -Jordgette [talk] 18:53, 7 November 2013 (UTC)

51kwad, the idea that collapse happens immediately, on the atomic scale, is one interpretation, called Objective collapse theory, but not the only one compatible with observations. The cat (or any observer inside the box) cannot resolve the question, because in those theories in which superpositions do not collapse reality "splits" and there are multiple cats, some alive, some dead. Due to "decoherence" the different realities do not interact, so each cat knows only its own history. We end up in only one branch of a branching reality. --Chetvorno^TALK 05:10, 30 May 2014 (UTC)

Chetvorno, you point out that 51kwad just uses one interpretation. However, is it not that your explanation is also just one interpretation namely the many-worlds one? Tomeasy _{T C} 16:55, 31 July 2014 (UTC)

I believe I said in my previous post above that 51kwad's version is one possible interperetation. I also mentioned the "many worlds" interpretation, but I didn't say that was the "true" interpretation. There are also many others. 51kwad was arguing for one interpretation, that the superposition collapses immediately. I said we don't know. "...scientists don't know where in the chain of events from atom to cat the collapse occurs" --Chetvorno^TALK 21:07, 31 July 2014 (UTC)

Exactly when does the world fork according to many-worlds?

This paragraph, intended to clarify the many-worlds interpretation, confuses me:

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.

I thought that the worlds split much earlier, at the instant when the particle decayed. Thereafter there would be two cats (one staying alive and one about to be killed in a few seconds), and also two persons that would some time later observe either the alive or dead cat.

Is this interpretation wrong? Mumiemonstret (talk) 10:24, 5 December 2013 (UTC)

The wavefunction inside the box splits when the particle decays (actually, because it is the time of decay that differs between states, and the particle can decay at any time, the split begins when the box is closed, and as time passes the amplitude - probability - of the "particle decayed|cat dead" eigenstates increases). When the box is opened, the internal wavefunction interacts with the wavefunction of the external world, and the external world splits. I believe the split propagates causally, at the speed of light, to more remote regions. --Chetvorno^TALK 11:01, 5 December 2013 (UTC)

But the wave function is constantly interacting with other things inside the box. Particles, cats, the walls of the box, maybe even a human observer. Why single out the opening of the box as the interaction that causes the collapse? The wave function inside the box will be extremely coherent, as either a dead cat or a live cat, before the box is opened. We just don't know from outside which one it is, any more than we would know the throw of a dice inside the box. There is no need for a split to propagate causally at the speed of light, any more than conventional probability would require that in the dice case. There are two probabilities going on here: (1) the quantum one, which immediately macroscopically resolves itself, and (2) the conditional probability one outside the box, whether the cat will leap out alive or will be dead. Opening the box resolves the latter probability but in no way affects the former. 51kwad (talk) 10:28, 5 June 2014 (UTC)

All the probabilities discussed in this article are the actual, quantum probabilities (1) it doesn't refer to conditional probabilities (2) due to lack of human knowledge about what's going on in the box. The article should probably clarify that, as a few other people have brought up that important point as you did.--Chetvorno^TALK 12:14, 5 June 2014 (UTC)

Mumiemonstret's original question was about the Many-Worlds interpretation; we were assuming that. In the Many-Worlds interpretation, there is no wavefunction collapse, the reality in the box "splits" , and each of the possible outcomes, "cat alive" and "cat dead", are equally "real", and evolve simultaneously in the box. Then, when the box is opened, the outside world becomes entangled in the split, and itself splits. However, I should have mentioned that within each of these "branches" of reality it appears as though wavefunction collapse has occurred. If you were in the box with the cat, you would only see one outcome, either the cat dying or staying alive, because of a phenomenon called decoherence. When the superposition is still on an atomic scale, the separate branches (eigenstates) become unobservable from each other. So by the time the geiger counter registers (or doesn't register) the atomic particle, you can't see the other reality. There are multiple realities (eigenstates) occupying the same space, multiple copies of you and the cat, but mutually undetectible. So while one of "you" watches the poison be released and the cat die, your "doppelganger" watches the cat sit around and lick himself and not die. And then the multiple copies of you go on and live your lives in separate universes, unaware of each other. In the Many-Worlds interpretation, due to quantum interactions, we are all splitting millions of times per second, and there are uncounted billions of versions of the universe.--Chetvorno^TALK 12:14, 5 June 2014 (UTC)

Of course, that's just one interpretation. There are other interpretations, such as Objective collapse theory, in which things happen as you said, the wavefunction collapses immediately, and the cat is unambiguously dead or alive. The problem is, scientists have found it impossible (so far) to determine by experiment which of these "interpretations" is the correct one, because the result for all of them (an apparent wavefunction collapse and either a dead cat or a live cat) looks the same to any one observer. That's why they are called "interpretations". --Chetvorno^TALK 12:49, 5 June 2014 (UTC)

Except that some interpretations are just absurd. The cat knows if it is dead or alive, instant by instant. There is no quantum probability as far as the cat is concerned. All we have is a conditional probability for outside observers, which matches the cat's perception when we open the box. As far as outside observers are concerned, there is only a conditional probability, seeded by an initial quantum probability caused by the radioactive decay. 51kwad (talk) 05:06, 21 August 2014 (UTC)

Bias?

"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" -- isn't this presenting opinion as fact? We'd all like to have a definite solution to this problem, but at the moment scientists are still arguing about it. The cited paper argues that by splitting the observation between two observers, an observation is avoided completely and yet the collapse still occurs. This is one of many dubious attempts to prove that consciousness has nothing to do with collapse, not an important breakthrough. No-one's ever said you have to actually look directly at the cat to make an observation. I think we should remove this bit and instead mention that there is still disagreement about whether consciousness is involved or not. Schrödinger's Cat is not considered a done and dusted paradox by all physicists as far as I know, nor anywhere near.

The conclusions of this paper seem to me to be just as silly as the opinions of those who claim the delayed quantum eraser "proves" consciousness IS involved. This article shouldn't get involved in pushing a particular opinion on the matter.

Johnwpurcell (talk) 18:26, 29 December 2014 (UTC)

I think the sentence accurately reflects current consensus. The "consciousness causes collapse" conjecture is a fringe and undeveloped view (since nobody even knows what consciousness is), too much so to state that there is disagreement about the question (see WP:UNDUE). A more accurate way to put it is that there is disagreement about where to place the Heisenberg cut, if it exists at all, and there is a spectrum on that issue. The consciousness-is-fundamental crowd are at the extreme end of the spectrum. -Jordgette [talk] 22:00, 29 December 2014 (UTC)

I agree. Mainstream science does not give special powers to human consciousness. There is still disagreement over the "interpretation" of collapse, but it does not include "Consciousness causes collapse". Outside of a few WP:OR speculations by prominent scientists, the only place that view persists is in New Age pseudoscientific tracts. --Chetvorno^TALK 22:49, 29 December 2014 (UTC)

Even if WP were to agree with the opinions expressed in this paper, the sentence is indeed overstated. The paper says, "Our results are consistent with the idea that a measurement from the Geiger counter is sufficient to collapse the quantum state". Some believe that the Geiger counter causes collapse, some believe that consciousness causes collapse, some believe in other causes for collapse, and some believe in no collapse. So far, no experiment unequivocally resolves this issue. Roger (talk) 22:56, 29 December 2014 (UTC)

The sentence is only saying the findings are consistent with the hypothesis. It's not stating that the hypothesis was confirmed. -Jordgette [talk] 00:09, 31 December 2014 (UTC)