Talk:Schrödinger's cat

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[edit] NO PARADOX HERE

The geiger counter did the measurement, hence it was the observer. There's no paradox. --Deng,siyi 01:23, 18 November 2006 (UTC)


Ahh, but the giger counter doesnt observe the cat actually being dead....

81.152.17.193 11:09, 18 November 2006 (UTC) Andrew Hilmy

Think it this way: in addition to detecting the radioactive decay, the giger counter only release the poison when it "observes" a dead cat. according to the original thought experiment's reasoning, there's still a 25% chance the poison will be released, since each observation collapes the superposition states.

If somebody really did this experiment, and did it 100 times (poor cats...), she would find 100 living cats, I guarantee.

--128.200.143.139 22:02, 20 November 2006 (UTC) Deng, Siyi

[edit] What The ...

Wiki editors, as a layman curious about the subject, I don't think this article succeeds in conveying the paradox to Joe Sixpack. Too long and rambling, with obscure references like this thread. If you physics grad students would like to take a break from arguing its finer points with each other, perhaps one of you could take a stab at editing the entry to communicate the concept to us poor shlubs. Furrowed brow, mustard on shirt, need mollfiying. 71.125.154.85 06:26, 29 January 2007 (UTC)

This whole subject is a non-starter for me :-| If you placed a cat in a sealed box with some radioactive material nearby you will get arrested ;-)

Schrodinger's Simple Way of Getting Arrested for Animal Cruelty ;-)

-Hardy har. Funny. Your comment is a non-starter as you wouldn't be able to place a cat in a sealed box anyway. Not even for a minute let alone an hour. C.G.

This shrodinger cat story is all nonesense. The collapse happens not at the moment of opening the box, but at the moment the quantom particle has an interaction with a macroscopic system (the cat). It's the cat who does the measurement, not us. If you don't believe so, testing it is quite easy. Do the experiemnt and wait 7 days before opening the box. If you find the dead cat, you'll find a rotten cat body (after 7 days).

          • R.P.

"Contrary to popular belief, Schrödinger did not intend this thought experiment to indicate that he believed that the dead-alive cat would actually exist;"

This seems like it is misleading. In Schrödinger writtings he talks about how the cat should exist in a superposition of being both dead and alive, and only later did he conclude that the rules that apply to the microscopic world do not apply to the macroscopic world. He also said that the macroscopic world does have consistency but it can not be known through logic but only through experience. This page doesnt even mention how Schrödinger said how he wished he never met that cat. -- Stevenwagner 00:04, 12 January 2006 (UTC)


There is one thing that has always puzzled me about Shrodinger's cat. If,in fact, the Shrodinger cat set-up was actually implemented and the box was opened and the wave function supposedly collapses and the cat is found to be dead this is not the end of the story. A forensic scientist could, with some accuracy, ascertain how long ago the cat died and that, in its turn, would tell us when the radioactive atom decayed. So surely the cat can never ever be in a nebulous neither dead nor alive state. So the whole experiment seems to be a crock. Surely the trouble is that for a cat there is not just a simple dichotomy of being dead or alive but a much more complex situation of being dead for a certain length of time or still alive. Indeed the cat might even die without the radiaoctive atome decaying and that also could be determined by a forensic test.

. . Ted Swart . .

You are pointing out that the two states "alive" and "dead" is too simplistic, and there would need to be different states corresponding to death at any moment in the box. Only one of these states would be "collapsed" at the time that the box was opened. But there is another question about what exactly constitutes a "measurement" in the Copenhagen interpretation. Surely it's not something that only physicists can do. Could the cat in the box not be performing it's own "measurements" while it was still alive, and thus reduce the number of quantum states? Horatio 09:55, 7 Aug 2004 (UTC)
The cat is obviously making it's own measurements during the experiment, but has no way of communicating it's findings to the outside world. Therefore, for the cat (and anyone else inside the box) the cat is either alive or dead. To anyone outside the box the probability that the cat is dead is still 50%.
Also for the forensic scientist problem above there are a (possibly infinate) number of states available to the cat. Each corrisponding to the time it died. After the box is opened, (at t=0), if the cat is dead, then all states when t>0 collapse and have a probility of 0. All the possibilites when t<0 are still valid and one is only "chosen" when the time of death is measured by the scientist. As I undertand it, one of the points of quantum theory is that all possibilities are valid until the measurement is taken. JP Godfrey 17:09, 12 January 2006 (UTC)
The concept of an observation in quantum mechanics is very different from the common definition - for one thing, there need be no living creature taking the observation, and communication of the observation doesn't matter except in things like superdense coding. Preskill in the first three or four chapters of his lecture notes here gives a good, if advanced, view of such things. The Schrödinger's cat experiment doesn't work practically because observations are happening all the time at a macroscopic level, and thus any pure state at this level would rapidly decohere (faster than the cat would die by many orders of magnitude). --Philosophus 07:21, 13 January 2006 (UTC)
What if the decay occurs at the instant the scientist opens the box?
Time exists over the set of real numbers, and so those two events could not occur simultaneously. Rather, the cat was either died just before the box open or just after, even if the difference in time is infintecimally small, it still is >0.


Reasonable people may well disagree that time is continuous (in the sense of being accurately quantified by real numbers, as opposed to, say rational numbers). See Loop quantum gravity, maybe? I'm not exactly an expert in the field. —HorsePunchKid→龜 03:14, 9 November 2005 (UTC)
What if you open the box, and the cat is comatose... only 50% of its biology is functional, wouldn't that be a state of both life and death?
It depends on your definitions of life and death, but regardless, those definitions are at a higher level than is relevant to the thought experiment. The distinction is between a cat that is bouncing around the box trying to claw its way out and an ex-cat that is doing little more than getting cold and stiff; no subtlety of definition is required. —HorsePunchKid→龜 03:14, 9 November 2005 (UTC)


I am probably wrong but I get the impression that Schrödinger is saying that the effects of destroying the field whould happing 4 dimensionally.i.e when it is know when the cat has died, then it is always being dead atfer that particular time to the observe. But it has only actually become like that when he has found out144.139.143.84 17:46, 11 November 2005 (UTC)

An explanation of Hawking's commentary "When I hear of Schrödinger's cat, I reach for my gun" would be nice to have. I presume the gist is that he finds the whole thought experiment rather silly. I've removed the implication that Hawking is famous for the statement (he's famous for many other much more significant things), and the "oft-made" bit (though the original paragraph remains in the Stephen Hawking article). Is there evidence that he's made this statement often? The best I could find was that he said it once in a conversation with Timothy Ferris. -- Wapcaplet 18:53, 27 Apr 2004 (UTC)

From the Stanford notes, it sounds like he's saying the Cat is overrated in today's world; that everyone talks of it in hushed tones to show they somehow understand Q physics, when that wasn't the purpose of the experiment. He said people overlay mysticism on it now. Didn't sound like he thought low of the original experiment, or what Schrödinger was trying to do. 82.93.133.130 09:42, 22 November 2006 (UTC)

[edit] First Idea

Was Einstein, and not Schroedinger, who had the idea, first. Einstein pointed out to Schroedinger that his equation could describe the evolution of (mesoscopic) stuff like gun powder. But this evolution, after a while, becomes really weird, a sort of superposition of explosion + not explosion. According to Einstein his 'gedanken experiment' showed Quantum Mechanics to be not complete.

[edit] Terminology

Superposition of states and mixed states refer to different things; the article seems to confuse them. An electron can be in a pure state; For example, in the position representation, the electron is regarded as being in superposition of classical states. A mixed state is the (limit of) a convex combination of pure states.CSTAR 23:57, 14 Nov 2004 (UTC)

[edit] Origin?

Where did the quote on the main article --the one that explains the experiment-- come from?

[edit] Nice job with the pictures

An esteemed physicist
An esteemed physicist

The cat pictures go nicely with the article. ^_^ Daleliop1 05:08, 10 Mar 2005 (UTC)

Yes! He is an esteemed physicist, of course, and he has actually read (with great interest!) The New Physics (well, more accurately, he napped on it – subtle difference though!). :) El_C 05:15, 10 Mar 2005 (UTC)

I took the picture out. While it is amusing, I don't see how it related to the article. commonbrick 18:54, 22 Apr 2005 (UTC)

Heart-breaking revert. He's a cat! Physics book! :( I see no harm in it. And I find your omission to be the greatest tragedy in the history of physics. El_C 02:34, 23 Apr 2005 (UTC)
I was just about to remove it, but then I thought, no, it's too funny, I can't bear to do it.. Everyking 10:47, 24 Apr 2005 (UTC)
I think it is amusing too but what does it add to the article? Yes, it adds humor, but this is supposed to be an encyclopedia. Should we have a picture of a cat next to a boat on the catamaran page? Perhaps a cat on the Kathmandu page? Maybe a cat on a log for catalog? A cat on a pillar for caterpillar. Category_5_cable, Cat o' nine tails, Cat (Unix)... I'm gonna take it out of the main article and put it here instead. commonbrick 19:43, 24 Apr 2005 (UTC)
—Except— that Schrödinger used a domestic cat in the example! More modrately stated, wrt to this is supposed to be an encyclopedia: I thought it could use a picture of a cat (it was imageless then) due to that reason. Obviously, there was bias in me picking that specific picture :), though not the credentials. Hrm, anyway, I hope you'll change your mind, but otherwise, sorry to have wasted your time. El_C 03:04, 25 Apr 2005 (UTC)
I think the pictures should go. They add nothing to this article, and I love cats. Sorry. protohiro 05:30, 27 Apr 2005 (UTC)

By pictures do you mean the book cover/back in the article? Or were you referring to the picture of El_C's cat? commonbrick 16:53, 27 Apr 2005 (UTC)


I don't field that either add to this article, but especially the cat and the snarky captions.protohiro 17:39, 27 Apr 2005 (UTC)

I guess I didn't notice someone added El C's cat back. I just took it out again. If someone wants it in please explain your reasons. As for the book covers, I thought about taking them out too but decided to leave them in since they have some relation to the article. I wouldn't object to taking them out since they don't add anything to the article. commonbrick 18:47, 27 Apr 2005 (UTC)
I agree with removing those too. They look like two plain black rectangles. At least the cat was cute and funny.--Nabla 19:08, 2005 Apr 27 (UTC)
I removed the pictures of the book covers because I think they add nothing to the article. If you want them back, please tell us why. protohiro 17:56, 28 Apr 2005 (UTC)
I also agree. When I first put them in, I had intended to somehow crop them down so that just the cats where showing in the thumbnails...also to scan my copy so that the back cover doesn't have copyright warnings on it. But I never got around to it, and I agree they don't really contribute anything but the visual interest of two black rectangles.--Joel 21:39, 28 Apr 2005 (UTC)
Great... but now the article look "naked". I hope someone finds a nice "cat-in-a-box" to put there. --Nabla 23:20, 2005 Apr 28 (UTC)


Why not put the house cat picture in the 'Related Humour' Section? I mean, for all the arguments for being 'encyclopedic' or what not, this part of the article doesn't give much substantial information to the topic itself, but is rather a nice place to throw in something like this.

[edit] Image deleted

The article needs a cat pic, but Image:Meow2.jpg has been mysteriously deleted. Please help find a pic for the page, thanks. Sam Spade 16:11, 30 Apr 2005 (UTC)

Excuse me, why does it need a pic rather than a schematic illustration?--CSTAR 16:42, 30 Apr 2005 (UTC)
All articles need pics, and where is this schematic illustration, pray tell? Sam Spade 16:47, 30 Apr 2005 (UTC)
It is not that hard to find a cat at WP, but even the the perfect article does not need a picture. I agree that that this one deserves it but just a plain cat is not good enough as it adds nothing to it. A schematic illustration would be great. We can try to find one, maybe at Google Images. We can also request it, as I just did, and wait for a while.--Nabla 17:44, 2005 Apr 30 (UTC)
I agree every article does not need a picture but a schematic would be nice for this page. Google turns up several images using Schrödinger's name with the umlaut and without the umlaut that might be useful. commonbrick 03:37, 1 May 2005 (UTC)

Sam, as I mentioned on your talk page please discuss here why you want the image included. All articles do no need pictures. Meow2 has no relevancy to the article. commonbrick

User:Comrade009 just added what IMO is a very nice image:Schrodingerscat.jpg. I'm presuming that gadget on the right is a radiation detector (if it isn't we should help Comrade009 in getting one) so I think I'll remove the image request I posted earlier.--Nabla 23:47, 2005 May 1 (UTC)
The image could be improved in the following way: The live and dead cat states can be superposed, and the set of all possible superpositions has a geometrical structure-- that of a Bloch sphere, where the north pole is the dead cat and the south pole is the live cat. It's possible I might incorporate your image into the XFIG source for the Bloch sphere image (which I have). --CSTAR 01:09, 2 May 2005 (UTC)

Great cat! I love it! :) But let's get rid of or rearrange the rest and try to have that cat picture within the conventional framework of the live/dead (two) box-centered diagram (I've seen several in textbooks). And perhaps something more subtle to symbolize the cat being dead rather than actually showing it dead (such as the skull and bones symbol) transparenet. Again, though, I just love the cat picture, s/he has such a nice smile. Great stuff! :) El_C 10:52, 2 May 2005 (UTC)

Yeah, sorry for not posting before removing or changing the image. I normally edit articles with no talk pages, so I guess it was a little inappropriate to just go when I realized you were actually discussing it. All these are good suggestions, and when I have the time, I'll redo the schematic. Quick question though. I made the entire image myself. However, the way I made the image was by compositing various other images. Is this fair use? The only ones I took directly were the cat and geiger counter, but I modified them quite a bit. What do you guys think? --User:Comrade009

Bring back Image:Meow2.jpg, it's cute! I realise that it's not particularly scientific, but there is a picture of a lightbulb at Lightbulb joke. There's no reason why we can't have both pictures in the article. JP Godfrey 16:23, 12 January 2006 (UTC)

One picture I can understand. It's okay for science to be "cute," but really, what's with the multiple images? That's just a bit much, although even one is unnecessary. - Kevingarcia 20:05, 30 November 2006 (UTC)

I posted the multiple pictures, so I'm biased. But it's customary to have multiple pictured depicting the same thing, as in the windmill and wind power articles, for instance. And I don't mine the cute factor. If anything, I'd like to see even more pictures. Sillybilly 00:44, 1 December 2006 (UTC)

The difference being, those are pictures of real windmills. There is no real Schrodinger's Cat. If it wasn't an image created by a theoretical physicist, I don't think they should be included here. People know what cats look like, they know what boxes look like and they know what dead looks like. - Kevingarcia 05:37, 1 December 2006 (UTC)
Oh come on! How can you just not love looking at the Katze.jpg ? Look how cute and funny the cat is lying on his back, showing his teeth! And what an adorable attitude the live cat has. How about the green glowing bottle with the skull on it? I personally love pictures in wikipedia. Yes, everyone has imagination, but sometimes it's nice to look at other people's imaginations too, how they see things. Without it we'd never need any paintings like Starry Night, because hey, use your imagination, based on the text that Vincent van Gogh writes. Why does he ever need to pick up a brush, when it's so much easier to just use a pen to write your ideas down in words? Sillybilly 10:41, 1 December 2006 (UTC)

Wikipedia is not a repository of cute images. It is an encyclopedia. Having four cartoony images adds nothing to the article, in fact it detracts from it. One image is required to more clearly explain the thought experiment, but four, especially four of these cartoony graphics, is ridiculous. If an image adds nothing to an article, then it does not belong there. Maelin (Talk | Contribs) 02:34, 8 December 2006 (UTC)

[edit] Decoherence

It seems to me that more consideration of decoherence in this article needs to be made. The article briefly mentions quantum decoherence, but I believe decoherence is critical to a (modern) understanding of the paradox. The suggested interpretations are: copenhagen, many-worlds, and consistent histories. However, they are described using the same language that was used >40 years ago to describe the conceptual difficulties. In the last 20 years, decoherence has solved alot of these problems. There are still conceptual difficulties, but the way this article is written ignores what has been discovered more recently (see also measurement problem).

Specifically, decoherence shows that a quantum system in a superposition will tend to decohere if it becomes entangle with an environment. That is, by becoming entangled with a large number of external degrees of freedom (which can occur due to air molecules colliding with the system, or even by emitting/absorbing photons in the sense of thermal radiation), a system's constituents tend to fall out of phase with each other. Superpositions only persist because of the phase relationship between the states. As the phase relationship becomes scrambled by interaction with the environment, the superposition is destroyed and is replaced with what looks exactly like a mixed state. Only classical-like states remain stable despite decoherence (a process called Einselection). That is, quantum correlations are replaced with correlations that are indistinguishable from classical correlations. It turns out (based on calculations and even recent experiments) that decoherence occurs very quickly for macroscopic systems. A typical macroscopic system (like a cat) that is found in a superposition will decohere in a ridiculously short time. Only very small and isolated systems (like an electron, etc.) can maintain these superpositions for very long. In a recent experiment, a beam of buckyballs was fired through a grating. An interference pattern was formed at a distant detector, demonstrating the usual quantum interference phenomenon. As the buckyball beam was made hotter, the interference pattern disappeared, because the superposition was being destroyed via decoherence. Hot buckyballs emit lots of thermal photons, which get entangled with the environment, and disrupt the superposition.

What does this have to do with the Schrodinger cat thought experiment? Well I think modern physics has resolved many aspects of it satisfactorily... to the point that the copenhagen interpretation is not needed (at least not how it is written in the current version of the article). For instance, decoherence shows that the cat is certainly not in a superposition: it would decohere very quickly... whereas the nucleus almost certainly is (until it's superposition becomes entangle with the environment, like the detector or whatever). Decoherence establishes a rigorous explanation of when the 'wave function collapse' really occurs, and elegantly proves that the cat is never in a quantum superposition... it exists in a classical mixed state (i.e.: we don't know if it is alive or dead, but it exists in one of these states).

I could update the article myself, but this is a delicate topic (and I'm no expert really). If anyone would like to make some adjustments or comments, that'd be great. Otherwise I'll try to make some changes and see what people think. Comments? Kebes 18:33, 25 May 2005 (UTC)

I put in a sentence similar to what you were saying, but not based on such recent work. It has long been known that the probabilities are the direct result of changing from the quantum to the classical description. What entanglement needed, in addition to this, was better rules of thumb. For example, a practical quantum computer would not be an experiment. David R. Ingham 16:04, 26 October 2005 (UTC)

[edit] Variation: Problem with Relativity as Well

In a version of the experiment (mysteriously missing from the article), the paradox poses a paradox for the standard interpretation of relativity as well.. Consider:

A cat places a physicist (Dr. Socks) in box #1 and Dr. Socks colleague, (Prof. Furball) in box #2. Each box is equipt with a closed can of poisoned catnip, connected to an electric can opener, triggerable by the entry of a spin up particle. The boxes are closed. The cat operates a device which creates an electron/positron pair from energy. The energy-matter conversion device (an Anti-A-Bomb?) is aligned so that the newly created particles are directed toward the can opener sensors in each box.

Immediately after detonation of the anti-A bomb, each physicist is in a mixed dead/live state. The cat is then offered the opportunity to open door #1, door #2 or to accept the refrigerator and vacation in Niagara Falls. After gaining approval from the Feline Association for the Prevention of Cruelty to Academics, he opens door #1 and Dr. Socks' wave function promptly collapses.

But there is more: simultaneously (that is without any delay for information to be transmitted between the boxes at some speed not exceeding c) Professor Furball experiences a queasy feeling and finally knows that that he is ....

--Philopedia 23:57, 26 September 2005 (UTC)

[edit] Schrödinger's cat in fiction

This section is getting out of hand. The tail shouldn't wag the cat. I will move it to an article of its own if it's not edited back shortly DV8 2XL 13:39, 21 October 2005 (UTC)

Why not get rid of it entirly? It adds nothing to the article. It has become a listing every time an author or director or whoever mentions a cat named Schrödinger or just alludes to the paradox if Schrödinger's cat. Wikipedia is not a repository. The related humor in the main article could also go. commonbrick 22:33, 24 October 2005 (UTC)

I've nominated Schrödinger's cat in fiction for deletion. Vote here. commonbrick 05:03, 11 November 2005 (UTC)

That page seems to have survived the deletion voting process. However, the article's own list of fictional references seems to have survived as well, relabelled as humour. Much of the information is duplicated in the Schrödinger's cat in fiction article. I propose
  1. that the fictional references be merged with Schrödinger's cat in fiction and deleted,
  2. that the plain jokes be removed, and
  3. that the section be replaced with a "See Schrödinger's cat in fiction" reference to discourage future additions that really belong in that article.
Any thoughts on the above three actions? — Wisq (talk) 19:33, 25 July 2006 (UTC)

[edit] the key to revival

if a cat can be both dead and alive what if we place some dead bodies in a vacuum chamber? it'll be both dead and alive so if we keep on looking at it maybe it will say 'We live again, hahahaha' sorry if i was being silly but i just want to clear this up

[edit] <blink>

I'm using mozilla firefox... why isn't the <blink> tags under humor working? I know this is minor, but it doesn't seem to work right and it looks kind of sloppy, especially since it goes on to explain blink tags. I guess maybe it should have some explanation of how it should be blinking for those who do not have a browser that supports the blink tag.

[edit] "That said" paragraph at the end of "Copenhagen interpretation" section.

Though I think this greatly improved the article, I think "macroscopic wavefunction" is an oxymoron. David R. Ingham 19:05, 26 October 2005 (UTC)

Okay- so as cats do, the cat had kittens. So Schrodinger built a second box and put one kitty in each, then positioned them so the photon, reflected or not, would strike one trigger. Next he put the new box on a spaceship and blasted it to Betelgeuse, whereupon the astronaut opening and examining the contents of the box was instantly aware of the state of the other. The real question of this would be answerable with chaos theory.Awtwaawtwa 20:03, 7 November 2005 (UTC)

[edit] merge

This topic was forked out of this one, it should not come back. See above. DV8 2XL 23:45, 22 November 2005 (UTC)

[edit] The effect of the observer on the effect of the observer.

With respect to the reference to Steven Hawking, et al, expressing the view that the Copenhagen system places too much emphasis on the role of the observer, I have come to the following conclusion:


[edit] Whether or not phenomena exist independently of the observer is entirely dependent on the viewpoint of the observer!

Oh man, paradox. Crab

[edit] What Schrödinger thought

According to the Feynman Lectures Erwin Schrödinger was one of very few who accepted quantum mechanics. So he was not seeing any weakness in the theory he had formulated.

The problem is that, rather than accept qm as the only reality, as he did, others were treating classical physics as though it were an exact description of some systems or objects. This led to the, then workable, but absurd treatment of measurement as a special case. David R. Ingham 21:01, 20 January 2006 (UTC)

Albert Messiah (1966) emphasizes that describing some things quantum mechanically and others classically leads to inconsistencies. David R. Ingham 21:59, 20 January 2006 (UTC)

To further support the notion that Schrödinger had conceptually left classical physics behind and understood that the difficulties were only with the relation of quantum mechanics to its classical approximation, I was taught in graduate school that he had originally found the more general Klein-Gordon Equation but had found that little can be done with it alone and taken its non-relativistic limit to get the Schrödinger equation. This shows that he was working on the assumption that all of nature is quantized, even before he found a formulation of the theory. David R. Ingham 20:50, 21 January 2006 (UTC)

I suppose someone will disagree with my recent changes in the article, but it is surely much closer to Schrödinger's point of view now. He would have been greatly disappointed to see it as it was. David R. Ingham 23:42, 21 January 2006 (UTC)

In the Feynman Lectures on Physics Vol. III, p. 2-9, he says "When the new quantum mechanics was discovered, the classical people—who included everyone, except for Heisenberg , Schrödinger and Born—said 'Look, your theory is not any good because you cannot answer certain questions like: What is the exact position of a particle?, which hole does it go through?, and some others.' Heisenberg's answer was 'I do not have to answer such questions, because you cannot ask such questions experimentally.' "

So Schrödinger does not appear to have been doubting the validity of his own theory when he proposed the cat experiment. David R. Ingham 07:26, 21 May 2006 (UTC)

Looking at the Cat article itself supports this. It says that the only discontinuity is a mental one. QM never stops applying, it just becomes impossible to calculate. David R. Ingham 02:12, 16 October 2006 (UTC)

[edit] "thought in term of mathematics"

It is a serious failure of ordinary language that it has so much difficulty describing quantum mechanics. Since the world is quantum mechanical, this means that what we talk about is, at least on an atomic scale, different from physical reality.

This is not a failure of philosophy and logic, because they are the foundation of the mathematics in which quantum mechanics is formulated. (See Bertrand Russell for example.) Of course, everything must be a failure of some philosophy, but even though quantum computer logic will differ from ordinary logic, it is describable in those terms.

makes a common mistake about the exact subject that Schrödinger was illustrating with his cat, but it makes a very important point about the difference between ordinary language and mathematical physics. This is that homeostasis simplifies the world of life by its negative feedback. This occurs on many levels, cellular, individual, social, etc. This helps to explain why language developed in a very different way than would make it easy to talk about quantum physics. David R. Ingham 04:02, 22 January 2006 (UTC)

[edit] New Image

About a year ago I made a rushed effort to add a diagram to this article, with the intentions to revise it later: Well I forgot, until today. I was browsing a forum, and some guy had the username "Schroedingers Cat." His avatar was actually cropped from the image I had made! I think the new one is a lot better:

Be sure to comment on my talk page if you think I should change it, because I still have all the source images. --Comrade009 21:19, 5 February 2006 (UTC)

The new picture is pretty awesome. If it were on a t-shirt or something I'd totally buy it. Kudos to you sir, and kudos again --Katt 10:30, 25 March 2007 (UTC)

[edit] Controversial pagagraph

"One view is that Schrödinger intended this thought experiment to indicate that the dead-alive cat would actually exist. Another is that rather he considered the quantum mechanical theory to be incomplete and not representative of reality in this case: "Since a cat clearly must either be alive or dead (there is no state between alive and dead, e.g. half-dead) surely the same must be true of the nucleus. It must be either decayed or not decayed." Whatever Schrödinger thought, the question of when measurement occurs remains an active area of research."

Previous version:

"One view is that Schrödinger intended this thought experiment to indicate that he believed that the dead-alive cat would actually exist. Another is that rather he considered the quantum mechanical theory to be incomplete and not representative of reality in this case: "Since a cat clearly must either be alive or dead (there is no state between alive and dead, e.g. half-dead) surely the same must be true of the nucleus. It must be either decayed or not decayed." Actually Schrödinger thought in term of mathematics rather than ordinary language, so whatever he thought cannot easily be described in ordinary language."


"One view is that Schrödinger intended this thought experiment to indicate that the dead-alive cat would actually exist." I don't think anyone thinks he thought exactly that.

"Another is that rather he considered the quantum mechanical theory to be incomplete and not representative of reality in this case" unlikely, considering that he had recently formulated it himself.

"Since a cat clearly must either be alive or dead (there is no state between alive and dead, e.g. half-dead) surely the same must be true of the nucleus." What about Terri Schiabo?

Schiavo's body was alive- vegetable state or no, machines or no. She was alive, and then she was dead. There is still no state between the two that anyone knows of. And don't even mention zombies. 82.93.133.130 09:56, 22 November 2006 (UTC)

"It must be either decayed or not decayed." If quantum mechanics were not more subtle than that, it would not agree with experiment to dozens of decimal places, in thousands of experiments.

"Whatever Schrödinger thought, the question of when measurement occurs remains an active area of research." Now we are getting down to the real meaning. The meaning of the gedanken experiment is to show that it is not the experiment that introduces probabilities, it is having to revert to a classical physics or ordinary language description. That is why it is important to understand that he thought in mathematics. David R. Ingham 04:15, 13 February 2006 (UTC)

Our ordinary notions of the world, like here or there and dead or alive are based on experience and expressed in language of our size scale. They are not absolute, like bits, they have limited precision like REAL or DOUBLE PRECISION numbers on a computer. The conceptual errors of describing the world in ordinary language are of the order of Avogadro's Number and Plank's constant. If we try to project these ideas to the atomic scale, as in radioactive decay, we get nonsense, like trying to calculate unstable recursions on a limited precision computer. David R. Ingham 06:24, 13 February 2006 (UTC)

[edit] Vandalism of gedanken toy

I am quite sure I checked last night that I had reverted to the original lightly humorous link and not to the disgusting replacement. I don't understand what happened. Trying again to fix it. David R. Ingham 22:03, 26 February 2006 (UTC)

The original vandalism was done with the edits 13:48, 24 February 2006 Faseidrnan m (new cat) and 13:33, 24 February 2006 Faseidrnan m (rv to last version by ClockworkSoul)

David R. Ingham 22:26, 26 February 2006 (UTC)

I restored it again and checked that it goes to "http://marionetteblog.blogspot.com/2005/08/shrdingers-cat-toy.html".

One can question whether it was worth restoring, but I want to start by going back as mush as possible to before the vandalism. David R. Ingham 22:39, 26 February 2006 (UTC)

Most of these changes are reverts to vandalism by 12:50, 24 February 2006 ClockwrokSoul m (Cleanup), as the comment states.

More of the damage still remains to be fixed. David R. Ingham 22:52, 26 February 2006 (UTC)

[edit] Practical applications section

I don't see how a thought experiment can have "Practical applications". These seem to belong to the quantum mechanics page, or to some other page related to it, perhaps entanglement. The thought experiment has contributed to many applications, but only through a better general understanding of physics. David R. Ingham 23:36, 26 February 2006 (UTC)

[edit] vandalism and 03:08, 27 February 2006 Mako098765 (rv obvious; remove uncited)

Some of that seems to be reverting vandalism and some legitimate disagreement. I thought I had fixed some of that. Do the vandals have methods that we do not yet understand? David R. Ingham 05:51, 27 February 2006 (UTC)

The link that I had fixed, and checked, is wrong in the history of my edit. It is about time to call in someone who is working on the software. David R. Ingham 06:21, 27 February 2006 (UTC)

gedanken toy cheks at this time. David R. Ingham 06:52, 27 February 2006 (UTC)

The vandal impersonated me by using "rn" to look like "m". Thanks to those who discovered this. David R. Ingham 08:18, 2 March 2006 (UTC)

[edit] http://en.wikipedia.org/w/index.php?title=Schrödinger%27s_cat&diff=41436104&oldid=41435612

This edit seems to have unintentionally reverted vandalism. David R. Ingham 08:15, 27 February 2006 (UTC)

[edit] Slashdotted

Just a heads-up: In the midst of comments on slashdot someone suggested coming to this article and vandalizing it.[1] —Wrathchild (talk) 18:26, 1 March 2006 (UTC)

That anon's edit summary makes sense now. - mako 19:08, 2 March 2006 (UTC)

Completed incomplete revert of vandalism. David R. Ingham 09:02, 4 March 2006 (UTC)

[edit] God's cat, or God's Schrödinger, if you prefer (LOL)

If the Judeo-Christian-Mulim god has total knowledge and computing power, "He" must know everything about the cat (as well as having decided when Schrödinger was to formulate the theory). His computer is not limited by such considerations as the size of atoms or the speed of light, because "He" can alter the laws of physics (if not of logic) at will. "He" knows the cat's entire wave function, and therefore all that there is about the cat. (If there were hidden variables they also would not be hidden from "Him".) So whether the cat is dead or alive, to the extent that that is an meaningful description of the cat, is contained in the wave function and known to "God". David R. Ingham 06:47, 12 March 2006 (UTC)

Acctually, if we must discuss logic and God in the same conversation, I might as well point out that by logical deduction, an omnisient-omnipotent God can not exist. If he knows everything, then he also know what he's going to do, and by knowing what he's going to do he has no free will and as such, can not be all powerful. >:) 134.37.255.5 12:01, 20 June 2006 (UTC)

You forgot you're using logic to make such statements, and as we said, even the rules of logic are flexible. The one religion you have to "know" is that "you don't know", you cannot assume any certainty in anything you know. It's a humble religion, where you're thankful for any little bit you know, or you think you know, feel like you know, feel like it's revealed to you, but it's in direct opposition with any other ultimate-truth-and-certainty faith-based religions. I only have faith in the limits of my capabilities, in the limits of my power. Everything else is debatable, even logical rules. Whether there are omnipotent beings without limits in their capability including modifying the Laws of Nature and the Laws of Logic, "I don't know." I really don't, and I have a hunch you don't either. Sillybilly 12:21, 18 November 2006 (UTC)

Boo-yah! no response to that! Embarassing for you! Qa Plar

If the God can change physics, then what's the point of finding the wave function? It's like playing Calvinball and then arguing over who won. 82.93.133.130 10:00, 22 November 2006 (UTC)

[edit] Schrödinger's cat & Life

Put a dead cat in the box & reverse time.

Penrose suggested that only two phenomena in physics display a direction of time... 2nd Law of Thermodynamics & Wavefunction collapse.

2nd Law of Thermodynamics requires a closed system...

Physics does not discuss Life? --Cave Draco 00:34, 23 June 2006 (UTC)

The closed system thing is a red herring; it's easy to apply the 2nd Law to open systems by recasting it as a continuity equation. Same with the 1st Law. But Penrose is right, collapse and the 2nd Law are irreversible. --Michael C. Price talk 00:49, 23 June 2006 (UTC)

It's more of a philosophical question... Are life & death are irreversible in time?

What phenomena in physice are simiiarly irreversible?

Does quantum decoherence allow immortality or is it just 2nd Law by another name? I have never seen a ghost, lol, MWI would appear to allow them... Schrödinger's cat's ghost!

Are all photons virtual? Can a Universe exist without observers?

Is Schrödinger's cat a restatement of the Anthropic principle? --Cave Draco 17:18, 28 June 2006 (UTC)

[edit] Cat

sounds a bit cruel to be honest poor poor cat...

Yes let's try Schrödinger's Kid next time.

[edit] Decoherence

"Nowadays, the mainstream interpretation is that the triggering of the device is the actual observation that collapses the wave function."

We know this to be false because of what is known as "decoherence". As a coin has a 50-50 chance as landing heads or tails, it DOES either land heads or tails. Similar reasoning applies for all other complex, nonisolated objects. If quantum mechanical calculations reveals that a cat sitting in a closed box has a 50-50 chance of being dead or alive, decoherence suggests that the cat will NOT be in some absurd mixed state of being both dead and alive. Decoherence suggest that long before the box is opened, the environment has already completed billions of observations that turned all quantum probabilities into there less mysterious classical counterparts. Decoherence forces much of the "weirdness" of QM's to "leak" from large objects since, bit by bit, the quantum weirdness is carried away by the innumerable impinging particles from the environment.Gagueci 17:46, 11 July 2006 (UTC)

Yes, I guess that sentence should be revised. It doesn't actually make sense if read literally, since the triggering of the device is not an observation -- but I know what they mean. --Michael C. Price talk 17:52, 11 July 2006 (UTC)
Now reads
Nowadays, the mainstream view is that the thermodynamically irreversible triggering of the device acts as if it were an observation, in that the triggering apparatus generates decoherence that appears to "collapse" the wave function.
--Michael C. Price talk 18:07, 11 July 2006 (UTC)

I also think "nowadays" should be changed. Seems rather casual.67.68.52.149 18:37, 11 July 2006 (UTC)

The experiment is really not about macro objects (for which decoherence is relevant), but rather about the relationship between making an observation and the change of the description from the superposition to a definite state. The technical issue is that, if quantum theory is a complete theory, it must also describe the measurement process, so there is no place for a "collapse" to occur. The modern theory of measurement addresses this issue, and I adjusted an early (previously misleading) paragraph to provide yet another link to a relevant article. DAGwyn 22:37, 18 August 2006 (UTC)

If there is a small computer device in a small sterile box with no air, nothing else at all, and it has a 50% chance of displaying a 1 and a 50% chance of display a 2 and for argument’s sake has no way at all of measuring itself, will it be displaying 1-2? --IronMaidenRocks 06:33, 21 February 2007 (UTC)

[edit] Entangled cat

Reading Penrose, though I don't always agree with him, my understanding of this cat is changing somewhat. The best description of Schrödinger's experiment is that the cat is already in a uniquely dead state before the box is opened. However that is not the only possible classical description of the true quantum state. Saying that he becomes fully dead when the box is opened is a valid, though not as useful, description.

Suppose we substitute an Einstein-Podolsky-Rosen type experiment for the radioactive decay. The event that kills or spares the cat is then entangled with one that can kill a canary in another box, in such a way that the a classical description contradicts the right answer. Then it does seem that the only correct descriptions have the cat and canary, as entangled linear combinations of dead and alive states. So the conclusion must be that classical descriptions of large objects are not always sufficient. The cat's being big and complicated does not always lead to his having a correct classical description.

This is the same phenomenon as needing to give up geometric optics and use wave optics occasionally, while designing a telescope. The telescope is much larger than the wavelength of light, so one is tempted to suppose that its function can be described by geometric optics. (Geometric optics with individual particles, as we usually describe X rays, is the other "classical" description of light. In fact that was Newton's own theory of light.) However, a telescope is specially concocted to be sensitive to small differences in angle. So it can see its own diffraction. David R. Ingham 20:26, 23 August 2006 (UTC)

I'm not clear as to the details of your EPR-cat-canary experiment. Does it contradict the statement in this article:
Today, the mainstream view is that the thermodynamically irreversible triggering of the device acts as if it were an observation, in that the triggering apparatus generates decoherence that appears to "collapse" the wave function.
--Michael C. Price talk 22:21, 23 August 2006 (UTC)

I am not actually suggesting any change in the article at this time, though I might make changes related to my entry and responses to it at some later time, here or elsewhere.

My entry doesn't contradict that statement in the article. It is still a good way to look at the original gedanken experiment, and probably most other hard cases. But the EPR cases are concocted to not be describable classically, like a telescope, which is concocted not to be describable with geometric optics. Classical physics is an approximation. Like other approximations there are different ways of applying it to the same case. Sometimes all of them work. Sometimes none of them work. Sometimes some work and some don't. It depends on details of the case. Rules about the validity of approximations tend to be limited in scope. The clearest and most general way to look at EPR is that it is possible, in carefully arranged circumstances, for intuitively classical things like whether a cat is alive or dead to inherit the need to be described as superpositions from microscopic systems. (I am expanding Weinbergs view and seem to be disagreeing with what I have read so far of Penrose, were I read about EPR.)

Note that saying that the cat and bird become alive or dead when the boxes are opened doesn't really work either. It is better to say that the wave functions "collapse" when the notebooks are compared. David R. Ingham 03:20, 24 August 2006 (UTC)

I'm not clear what you are proposing, or to what purpose. Bear in mind WP:OR. --Michael C. Price talk 05:24, 28 August 2006 (UTC)

I have worked on it a little. The relevance of what I was saying, and especially now that I see that EPR had already published at that time, is that the article makes it look too simple. It is not just a matter of changing the prescription for when to apply the rules of observation. David R. Ingham 23:37, 7 September 2006 (UTC)

From the translation linked at the bottom of the page:

But laws of nature differing from the usual ones cannot apply during a measurement, for objectively viewed it is a natural process like any other, and it cannot interrupt the orderly course of natural events.

I take this to support some of my changes. David R. Ingham 19:40, 8 September 2006 (UTC)

Later on in [[2]] he says that the measured particle becomes entangled with the apparatus, as the whole system evolves according to the many body version of his equation, and that the only [fundamental] discontinuity is a mental one as the experimenter takes note of the result of the experiment. He explains quantum entanglement quite clearly and thoroughly, but seems not to have an answer to the EPR paradox. There is some real philosophy of science there, addressing issues that I have not seen covered in Wikipedia. David R. Ingham 21:57, 8 September 2006 (UTC)

[edit] Category

Shouldn't this be in category Category:Fictional cats? It's clearly a cat, and clearly fictional. JIP | Talk 15:43, 27 August 2006 (UTC)

Yes, that seems to me a good idea. It is well liked because it has more fictional value than numbers in a notebook have. (Though I do not think the possibility of a linear superposition of dead and alive is fictitious.) David R. Ingham 02:56, 28 August 2006 (UTC)

It's a thought experiment. --Michael C. Price talk 05:25, 28 August 2006 (UTC)

There is a good scientific reason for using a cat. It better shows the absurdity of saying that the laws of physics are fundamentally altered by an observation. In that view, the physics becomes dependent on whether or not one considers a cat to be a sentient being. David R. Ingham 20:02, 28 August 2006 (UTC)

Also because the cat is a macro-sized object expected to follow classical laws?? And its 2 states are to illustrate the quantum version of things, no? While people know a cat is either dead or alive, the idea of two states existing at the same time is an intriguing idea, and helps lead the novice to the idea of multiple states -- for quantum-sized objects. (I realise he was not trying to explain QP to the general public, but it can work that way) 82.93.133.130 10:08, 22 November 2006 (UTC)

[edit] "Related Humour" needs a cleanup

Just glacing through it, and it would appear that people are using it to promote their non-notable webcomic/other thing. Could be an idea to check if the links are actually anything useful, rather than blatant self-promotion. However, I've been wrong before, so I'm reluctant to delete anything in haste (apart from a YTMND link, which was pretty obvious). --Angry Lawyer 11:59, 7 September 2006 (UTC)

On first glance, the only thing I see wrong is that my Cat toy link [[3]] is missing. David R. Ingham 18:28, 7 September 2006 (UTC)

I'm reluctant to delete anything in haste (apart from a YTMND link, which was pretty obvious). --Angry Lawyer 11:59, 7 September 2006 (UTC)

Actually i found that YTMND quite educational, and as more entertaining and illustrated the concept better than the article did. Don't dismiss the link simply because it ends with ytmnd.com.

Qa Plar

The removed part in question was "YTMND user titanium-gecko used this theory to explain the "alternate universe fad" where alternate fads such as PTKFGS and YESYES existed through Hugh Everett's theory made to criticize Schrödinger's theory."

Not exactly stuff for an encyclopedia. --Angry Lawyer 07:05, 8 September 2006 (UTC)

Moved everything to the Schrödinger's cat in fiction article, where a lot of it was already duplicated, and added a {{main}} tag to where it was in this article. Virogtheconq 01:49, 27 September 2006 (UTC)

[edit] Organization

The Weinberg quote shouldn't really be under Copenhagen. Penrose calls this view "many worlds" in his section 29.2 of The Road to Reality, but it does not much resemble the Many worlds below it or the Many-worlds interpretation Wikipedia article. Nor does Penrose's description. David R. Ingham 23:26, 7 September 2006 (UTC)


[edit] Living Forever

OR

Why Highlander is based on the Life of Schrödinger's cat

Most of us would initially agree that from year to year, day to day, we remain the same person. i.e. though we don't contain exactly the same atoms at two separate points in our life we can agree that we are the same person because our consciousness remains. Thus, we don't consider ourselves dead merely because our bodies have removed some of our dead skin cells, stomach cells and brain cells. These were replaced by new ones constructed from new atoms ingested thrice daily more or less. So we're agreeing that it is the continued existence of our consciousness or "self" that defines us as alive. The shed dead cells no longer hold that consciousness and so have no bearing on whether we are alive or dead.

Ok. We take that as a priory. So then to the cat, it never dies. Because in some number of parallel universes there exists a living cat. So as far as the cat can remember: it never dies, the cats that existed in universes where it did die are dead and therefore not part of its continued consciousness. From the cat's frame of reference, it never experiences death (or it never remembers experiencing death). Its consciousness will always exist in a universe where the atom has not decayed and it is not dead. So eventually the cat dies from starvation. Or does it? In universes where a can of Whiskas does not apparate in front of the cat it dies, but to the cat this does not happen as the cat's consciousness only continues to exist in universes where this does happen. To the cat, it never dies from starvation. In fact, to the cat, it never 'dies' at all. in some universe its consciousness will always exist in some form (if the possiblities of Quantum flux are infinite).

Then let's extrapolate this to people; specifically, to me. I flew in a plane the other week. Let's say an aluminium atom in the fuselage of the plane might have decomposed at a certain time that would result in the plane losing cabin pressure and it crashing to the ground. According to Schrödinger, because an atom goes through every possibility in some parallel universe, I died last week. In some parallel universe this post never appears because i never land safely at my destination. In some other universe i died from a Brain aneurism just after finishing that last sentence. To extrapolate into insanity now, every moment, every opportunity for me to die, will in some universes be unsuccessful. And so from my point of view, i will never die. Instead of dying slowly of old age, in some universe i will live to see them invent a cure for ageing and i live forever. The universes where this doesn't happen are arbitrary to that existing consciousness. In some parallel universe my consciousness will always exist in some form. And how can one tell the difference between his universe and another where he died in that plane crash last week? I can't. So, in other alternate universes i will be able to look back and remember this moment decades or centuries from now. According to Schrödinger and his cat, the consciousness that wrote this, me, will never die. it will continue for an infinite amount of time in some form. I will live forever.

And so will you. -- Qa Plar 01:50, 8 September 2006 (GMT)

See the Quantum suicide thought experiment --Angry Lawyer 07:07, 8 September 2006 (UTC)

I don't find that very amusing. David R. Ingham 22:08, 8 September 2006 (UTC)

...I wasn't trying to be amusing. It's what he's just described - you can't die because you'll exist in an alternate universe. I didn't tell him to try it. --Angry Lawyer 08:50, 13 September 2006 (UTC)

Reductio ad absurdum... The MWI is wide open, the Copenhagen Interpretation is simpler; Occam's Razor rules! Cave Draco 01:02, 5 October 2006 (UTC)

Naturally the MWI folks, such as moi, regard the MWI as simpler. --Michael C. Price talk 00:52, 16 October 2006 (UTC)

[edit] Schrödinger's Cat Paradox Resolved

Does anyone think this is a reasonable statement?

The problem with the seeming paradox is that the cats motion does interfere with the decay of the nucleus. This would be determinist in interpretation, that every particle is in a spatial and temporal correspondence with every other particle -that had been set into motion- in the Universe of that box. The paradox is to include the notion of free-will in such a circumstance. Finally, the mere incomprehensibilty of the simultaneous coexistence of free-will and determinism (in the box) -in other words, the simultaneous states of complete free-will and complete determinism- is unnecessary to resolve, because ultimately, anything short of complete knowlege in a system of finite communication speed will always be receiving late information. So, once the cat comprehends the decay of the the nucleus, a short, finite-time afterward, it is dead; and, that the cat could have done something to change the outcome, but couldn't know what.

It could've known it was impossible for it to know everything there was to know, in real time, to do something about his circumstance; and known, for all practical purposes, that the outcome was inevitable. It could, however, hold its breath for a longer period of time and eek out a few more blips on the cosmological time-scale.

In other words, the mere time-idependence of the state vector is the substance of the contradiction, because time exists, and correspondence principles exist, such as histories and entanglement, Schrodinger's Cat Paradox isn't such a paradox afterall it just reflects the state of knowlege at any given moment while apparently random fluctuations in events exist.--Charlesrkiss 05:08, 9 October 2006 (UTC)

It's only a thought experiment and Schrodinger does explicitly say that the cat must be sealed apart from the radioactive trigger. --Michael C. Price talk 17:12, 15 October 2006 (UTC)

The intent of my statement is this: just because we may thermally seal a box that contains particles -from the rest of the Universe, doesn't mean there aren't corresponding particles elsewhere in the Universe influencing events inside the box. Unfortunately, the cat and the box are small and the Universe is large, so there is not much the cat can do but die sooner than it normally would. --68.48.244.84 00:47, 16 October 2006 (UTC)

If the two sides of the box are "sealed" from one another, ie. separate Universes, then you still don't have a paradox, you have a pair of boxes.--Charlesrkiss 00:48, 16 October 2006 (UTC)

Then interpret "sealed" as meaning it is isolated by definition. --Michael C. Price talk 00:50, 16 October 2006 (UTC)

Ha Ha, I was first. Proved my point. --Charlesrkiss 00:54, 16 October 2006 (UTC)

[edit] Sourced translation

I have replaced Schrodinger's text of the experment with a longer sourced translation. It differs from the old version in a few details. For instance it is clear that Schrodinger was envisaging a radioactive source of many atoms, not just one. --Michael C. Price talk 17:12, 15 October 2006 (UTC)

[edit] Quick question.... is this observation limited to sight?

Ok, i know this is probably a stupid question but i will ask it anyway...

if the observation is limited to that of a visual wavelength, would that mean that you would be able to hear the cat both alive and dead at the same time?

so hear the cat as it dies but also hear it alive?


- Andrew Hilmy

No. Observation is any measurement or interaction, including sound pressure waves hitting ya ear. You're asking if in the double slit experiment there'd be a "special" kind of measurement that picks up 35% of the electron wave traveling through one slit, 65% through the other, without collapsing the wavefunction. As it is today, we only get to know what's going on after we collapsed the wavefunction by the flashes on the screen behind the double slit, and deduce "what must have happened", using cause-effect relationships. If causality and determinism does not stand 100%, then our deductions backwards in time, this and this is what must have happened for us to get this answer, such deductions may not function well, which is another way explain what's going on. If the world is only 99% deterministic on a small scale, and less so the smaller you go, just like a single die roll, it's random(or random enough for this example, never mind that by knowing the motion of each of its atoms applying kinetic theory of gases and classical physics it would still be deterministic), but when you deal with large numbers, with an aggregate of many small scale things, the averages become deterministic, such as if you're rolling the fair dice 10 gazillion times, you will be fairly deterministically 1/6th of the time rolling a 2. Sillybilly 12:32, 18 November 2006 (UTC)

[edit] Mention in Bugs

Schrodinger's cat has been mentioned in an episode of "Bugs", season 2 episode 7, titled Schrodinger's Bomb. (First Transmission Date May 25th 1996, BBC1). Can this be mentioned?

Not sure what Bugs is, but you could probably fill a Bible (with all em ricepaper pages) with references to the cat. Guess people just really like cats, and funky German names. 82.93.133.130 10:12, 22 November 2006 (UTC)

[edit] Quantum series of articles

Hello; it seems that nowadays, many articles are put in a series on a broader topic, with a summary box on the right. Isn't there a series about quantum physics? This article and many others could be part of it. 219.68.141.35 05:11, 2 December 2006 (UTC)

Knowing where to stop might be a problem, since all of fundamental physics since 1925 is quantum physics, i.e. non-classical. --Michael C. Price talk 09:09, 7 December 2006 (UTC)

[edit] Useless images

These images are just excessive. We don't need four images of cats inside boxes. We don't need haphazard collages of cats and radiation detectors that look like they were stitched together in Photoshop within 30 seconds. We don't need HTML code with a blinking "not". We need a clear, schematic diagram that doesn't look like it was stuck together from whatever turned up on Google Images for "cat," "geiger counter" and "cannister". The page at the moment look ridiculous. Maelin (Talk | Contribs) 03:23, 5 December 2006 (UTC)

I agree, the images are totally useless, and make the page look like a circus. Which is why I deleted them, only to be reverted by Michael C. Price. I invite Michael to to inform us what these ridiculous cartoons contribute to this article, or I will delete them once more. --151.203.239.219 01:52, 8 December 2006 (UTC)
I restored the images because the edit comment was incorrect when it said they didn't add anything. The final diagram is the most physically instructive since it shows two cats simultaneously coexisting along with a flask that was labelled as radioactive poison, unlike the undeleted remaining image, which (apart from the text) is not clear. The deletion was not discussed on the talk page, so I restored it likewise without discussion. And BTW the comment on my talk page saying that I only said "I don't agree" is not correct. My edit comment said "I don't agree that the extra pictures don't add anything", which I thought was as clear an explanation that was given for the deletion. --Michael C. Price talk 08:08, 8 December 2006 (UTC)
First, I'd like to point out that the deletion of the images was in fact discussed on the talk page. Maelin recommended deletion, and I only deleted images two days later. Anyone who objected could have replied to Maelin's suggestion. Second, I am able to accept your argument that the fourth of the pictures, with the superposition, is the most articulate. Nevertheless, in your revert, you suggest that having all four pictures adds something to the article, and not that I was merely injudicious in selecting which of the four pictures to keep. Do you still believe that? If so, what do all four pictures add over any one of them in particular? Or, would you be fine with keeping just the fourth picture? In my opinion, all four pictures look like shit, and we'd probably be best off without any of them until a serious one comes along. --151.203.239.219 08:40, 8 December 2006 (UTC)
First, okay, I missed the earlier discussion and my apologies for that. Second, I would recommend keeping the 2nd (superior graphic quality) and 4th pictures (superior conceptual clarity), along with the text from the 1st. If that's okay I'll add some more text for which ever pictures we agree to keep. Generally, I go along with addage that a picture paints a thousand words and that better pictures are needed -- but let's improve not delete wholesale. --Michael C. Price talk 08:54, 8 December 2006 (UTC)
I disagree entirely. The second picture looks rubbish and it has zero information content. It's not obvious at all what is going on, but it -is- obvious the picture was made with about 3 minutes on Google Images and about 30 seconds in Photoshop. People are going to visit the Schrödinger's cat article looking to understand Schrödinger's cat, not hoping for pictures of cats. And I disagree that the fourth is the best for conveying conceptual information, too. It looks like two cats in a box with some kind of nuclear powered poison squirting machine. The first image is the best for conveying information because it alone shows what the whole thing is about, namely, detecting the decay of a nucleus, and it still looks crap. The rest are entirely superfluous. Maelin (Talk | Contribs) 09:16, 8 December 2006 (UTC)
The "zero information content" claim is absurd and makes your posititon difficult to take seriously. Of course it's not obvious what's going on: that's why I suggest copying/adding text to it/them. --Michael C. Price talk 09:25, 8 December 2006 (UTC)
I think Maelin's point is that the second picture has zero information content over the first picture, and I agree with him on that. It's true that the second cat looks prettier or whatever, but that is not what this article is for. I think the first picture is the only one that has all the requirements: the measurement of a decaying nucleus (absent from fourth picture), poison (absent in the second picture), and a superposition of two cats, even if it is executed rather poorly (absent from the second picture). The fourth picture, even though it does portray the superposition the best, fails to make it clear that there is a measurement going on which is causing the superposition. The fourth picture also fails to live up to the sort of seriousness that I think can reasonably be expected of Wikipedia. The first picture is the best, and the only one I think we should keep, but with the understanding that it still sucks and that a new one is badly needed. --151.203.239.219 09:40, 8 December 2006 (UTC)
(edit conflict) The image does not convey any useful information. Schrödinger's cat is not a thought experiment that is concerned with the properties of cats and miscellaneous scientific equipment contained within boxes. It's a thought experiment that is concerned with the theory of quantum mechanics extrapolated to macrocosmic systems. The cat and poison are merely accessories. The picture does nothing to help explain the key idea of the article. Picturing a cat inside a box with some apparatus is neither the core thrust nor the conceptually difficult part of the Schrödinger's cat idea and it is not something that images in this article should be focusing on. Perhaps if no better images were available, this image would be acceptable. But the top image is far superior at conveying the main idea and it renders the Google Images cat with the portable multimeter and metal thermos entirely redundant. Maelin (Talk | Contribs) 09:48, 8 December 2006 (UTC)
To address 151.203.239.219's clarification I don't think the relative merits are as clear as suggested. Schrodinger's text talks about a radioactive sample being watched, not a single nucleus, so the radioactive flask in the 4th picture is a better representation of Schrodinger's original conception. That it is a nucleus in the 1st picture is only evident because of the text. And what does the tick and cross signify in the 1st image, that the cat doesn't die? Since the 4th picture is the only one to illustrate the superposition principle applied to a cat -- which is the essential core concept of the experiment -- I don't think we can afford to lose this image. The 2nd and 4th images are the only ones that clearly show the cat "penned up in a steel chamber" (and the idea of containment and isolation are also important, to address Maelin's point). So I don't see any basis for claiming that images 1, 2 & 4 have zero information content over each other. Perhaps we should start from where we all seem to agree: shall we lose the 3rd image? --Michael C. Price talk 10:04, 8 December 2006 (UTC)
If any images are needed (and I do not feel any are), then use one image. More than that is pointless redundancy. As has been said, images are not needed to explain this pretty straight forward thought experiment, but if they were to be used, they should relate to the meaning of the experiment and not the example used to explain it. Schrödinger's statement had nothing whatsoever to do with cats, gas or death. I can understand the reason for a pop culture section or side article, but these drawings are not pop culture - they are just images someone threw together using pictures likely under someone else's copyright without permission on a photo manipulation program. That doesn't help anybody. - Kevingarcia 10:30, 10 December 2006 (UTC)
Some people find images helpful, some don't. That aside, I don't know where you're coming from with the statement "Schrödinger's statement had nothing whatsoever to do with cats, gas or death." --Michael C. Price talk 18:04, 10 December 2006 (UTC)
Well, taking a quote directly from the current version of the page, he was talking about a different question all together: "when does the actual quantum state stop being a linear combination of states, each of which resemble different classical states, and instead begin to have a unique classical description?" The whole "cat" thing was an analogy that has little to do with a quantum mechanics problem other than the essential question of what state the subject is in. - Kevingarcia 18:15, 10 December 2006 (UTC)
No doubt a valid point, but this article is about Schrödinger's cat. --Michael C. Price talk 19:11, 10 December 2006 (UTC)
Imagine if the Sorites paradox article was full of pictures of sand heaps. Imagine if the Ship of Theseus article was full of images of ship building. Sure, an image is useful to help people understand what the thing is talking about, but the cat in the box is not the important bit. Schrödinger wasn't trying to make a point about cats; he was trying to make a point about quantum theory. The cat and the box are merely concrete examples to help people recognise to the main issue, just as the sand heap and the ship are in the articles linked above. People don't need to see several images of cats in boxes. That's not the conceptually difficult part of the thought experiment, and it's not the main point of it either. Maelin (Talk | Contribs) 22:52, 10 December 2006 (UTC)
Would those articles be diminished if they were illustrated? --Michael C. Price talk 23:31, 10 December 2006 (UTC)
If they had several poor-quality images depicting the same thing, a thing that isn't the important aspect of the topic, then yes, they would be diminished. It reduces the quality of the article. Maelin (Talk | Contribs) 01:17, 11 December 2006 (UTC)
I agree with KevinGarcia and Maelin. These are bad and actually potentially confusing images that do not at all clarify the conceptually difficult aspects of this thought experiment. I think the article is better off without any of these pictures than with any of them (and especially all three of them). I think we discussed above the required features that an illustration for this page ought to have. None of these pictures have them all. I think they should all be deleted until someone who is interested produces a picture that actually clarifies this thought experiment. --151.203.239.219 07:40, 11 December 2006 (UTC)
Exactly. Bad images detract from the validity of the theoritical argument. Any image is unneeded, but one might be acceptable... none from the current crop. - Kevingarcia 03:53, 12 December 2006 (UTC)
Let's leave the pictures in until we find a better set. Improve, don't delete. As I have explained, the remainining pictures are illustrating different aspects of the experiment. --Michael C. Price talk 08:26, 11 December 2006 (UTC)

Here is a better image (from: Bryce Seligman DeWitt, Quantum Mechanics and Reality, Physics Today,23(9) pp 30-40 (1970) ): [4] which is available for non-commercial purposes. Is this acceptable? --Michael C. Price talk 08:41, 11 December 2006 (UTC)

Yes, that one is much better. Maelin (Talk | Contribs) 10:22, 11 December 2006 (UTC)
Good. I suggest replacing the 3rd image with this? I'm not sure of the mechanism for uploading images -- if someone else could do it, and sort out the permissions side that would be great. --Michael C. Price talk 13:55, 11 December 2006 (UTC)
I'd suggest replacing all of them with this. We only need, and should only have, one picture if one picture will convey all the information possible. This picture, when combined with a suitable caption, will show everything that is important about the experiment. Maelin (Talk | Contribs) 00:13, 12 December 2006 (UTC)
I agree. We need only one picture that does a good job, and this is the best picture so far. I can only suggest adding a little black and white radioactive sign on the container that activates the lever, but I'm fine without it too. --151.203.14.187 00:25, 12 December 2006 (UTC)
At the very least. But don't add anything to the image, the conciet of an image at all is more than enough. - Kevingarcia 03:53, 12 December 2006 (UTC)
Since it's not obvious if the Creative Commons licence on the web page (see at bottom) extends to the image itself, I've sent the author a brief e-mail asking if we could use the image, but his automailer tells me he is away until December 19. Assuming it's okay, I will stick a black-and-white nuclear symbol on the image and upload it under the same licence (as required). We can then use it to replace the silly-looking pictures currently there. Maelin (Talk | Contribs) 08:19, 12 December 2006 (UTC)
We seem to be okay with respect the to Creative Commons licence, but it can't do any harm to inform him what we plan. BTW I like the idea of sticking a nuclear symbol to the detector. --Michael C. Price talk 08:27, 12 December 2006 (UTC)

Why are there still useless images on this page? - Kevingarcia 10:37, 31 December 2006 (UTC)

Unfortunately we can't use the good image found above, as it comes from a textbook. Maelin (Talk | Contribs) 05:44, 2 January 2007 (UTC)
From a textbook? It comes from an article by the late Bryce Seligman DeWitt, Quantum Mechanics and Reality, Physics Today,23(9) pp 30-40 (1970) --Michael C. Price talk 09:21, 2 January 2007 (UTC)
None of which explains why the current images should remain. They should be removed and kept off. - Kevingarcia 06:42, 6 January 2007 (UTC)
They are there because not everyone agrees with your view that all images should be destroyed. --Michael C. Price talk 09:52, 6 January 2007 (UTC)
That is a complete straw man argument. Nobody wants all images destroyed, what we want are good, clear and encyclopedic images that add to the article. We don't want cartoony grinning cats and incoherent collages of whatever turned up on Google Imagesearch. Maelin (Talk | Contribs) 01:59, 29 January 2007 (UTC)
While you're around, what about my point that the proposed image doesn't come from a textbook and therefore may be admissable?--Michael C. Price talk 02:11, 29 January 2007 (UTC)
"Textbook" wasn't my point, my point was that it wasn't the work of the fellow who owned the page, and that we presumably need permission from whoever is the copyright holder. Of course, I'm no copyright lawyer. Maelin (Talk | Contribs) 02:59, 29 January 2007 (UTC)
I'm no lawyer either, but it looks to me like the creative commons license does give us permission to copy, modify and use the image. That the image originates from elsewhere should make it easier, shouldn't it? --Michael C. Price talk 09:27, 29 January 2007 (UTC)
I shouldn't think so. Since the author of the article doesn't own the image, his CC licence wouldn't extend to it. Unless we can be sure he got that image legitimately and his article is legally a derivative work, we can't take the image back out of it, as far as I know. Maelin (Talk | Contribs) 11:06, 29 January 2007 (UTC)

[edit] Who needs decoherence? Feynman's Neutron Scattering from a Crystal

Yes that would cut it as an explanation but isn't there a simpler explanation than appealing to macroscopic effects?

For those who have it, read Feynman Lectures Vol 3. 3-3: "Scattering From a Crystal". A collapse of the wavefunction occurs if 'in principle' you could measure something.

To cut a long story short: A neutron propagates though a crystal and simultaneously travels through every gap interfering with itself creating a diffraction pattern analagous to the Young Two-Slit, but also creating a diffuse background. This diffuse background corresponds to a collapsing of the wave function. The reason for this collapse lies in the spin of the neutron; the spin state of the neutron will sometimes decide the spin state of an atom in the crystal (conservation of momentum), the spin state of an atom is changed, so nature knows which atom scattered the neutron (it no longer went through every slit). i.e: the crystal itself performed the measurement. Nothing to do with macroscopic decoherence. It wasn't that a person made an observation, but that 'in principle' a person 'could' go back and check the crystal.

In the same way, why cannot the detector collapse the decay state and some lazy scientist come back and check it later? Is half the physics community simply not listening to the other or something? Hate to sound hippy, but doesn't crystals fix everything? -- Rpf 16:21, 6 December 2006 (UTC)

You're right, the cat paradox is only a "paradox" to those physicists who have already convinced themselves that wavefunctions don't collapse until a physicist intervenes. --Michael C. Price talk 09:07, 7 December 2006 (UTC)

[edit] My cat.

If my cat is ill and sick, will it die?

[edit] the cat as an observer, and apples

Does the cat not count as an observer? If not, would that mean that as soon as a cat is not being observed by a truly conscious being, it would not actually exist in one particular state? And, could this experiment not be conducted using something which does not live, like an apple, and some sort of 'speed-up-rotting-process-of-apples' poison? Then everytime the experiment is conducted the outcome should be random, as in one time the apple is completely rotten, and the other time it is not. AppleHaven 13:54, 22 January 2007 (UTC)

That's not really the point. The whole point of the exercise is to demonstrate that we shouldn't arbitrarily separate microscopic scales from macroscopic ones. Nobody finds the idea of an atom existing in superposition of decayed and not decayed to be particularly troublesome, but we do find the idea of a cat existing in superposition of alive and dead to be somewhat hard to swallow. The thought experiment is supposed to show that we can't have our seemingly-acceptable "small scale" superpositions without necessarily accepting out repulsive "large scale" superpositions. Maelin (Talk | Contribs) 02:40, 23 January 2007 (UTC)

[edit] Is there a common misconception?

I've heard that the Schrodinger's cat theory is said to be "If you put a cat in a box, there is a 50-50 percent chance of it being DOA (Dead or Alive)." However, the article states otherwise. Clarify? —The preceding unsigned comment was added by The velociraptor (talk • contribs) 23:49, 26 January 2007 (UTC).

The purported coclusion is that there is a 100% chance of it being dead AND alive. As explained in the article.1Z 01:50, 27 January 2007 (UTC)

[edit] Has anyone actually tried this experiment in real life?

Animal cruelty aside, any scientists actually done this? Yes, even though I know the state of the cat is in lingo in theory, did anyone try this? —The preceding unsigned comment was added by The velociraptor (talk • contribs) 01:42, 29 January 2007 (UTC).

Highly doubtful. It's a thought experiment intended to demonstrate a necessary conclusion of a particular model. No rational scientist would attempt to actually do it, because there is nothing that could be learned. Maelin (Talk | Contribs) 01:55, 29 January 2007 (UTC)


As a matter of fact such an experimetn HAS been performed, not wit ha cat, of course, not even a fully macroscopic objext but a "mesoscopic one" (larger than microscopic, smaller than macroscopic) See http://arxiv.org/pdf/quant-ph/0307185 The result is, a mesoscopic system, just as a single atom, CAN be in a superposition, and experimental consequences of this superposition were indeed measured. Alfredr 22:17, 28 March 2007 (UTC)

[edit] Name of Schroedinger's Cat

Does anyone know what the name of Schroedinger's Cat actually was?

I've read a lot of papers on the theory and done a lot of searching, but I've never been able to find the answer to this question. —The preceding unsigned comment was added by 71.229.241.19 (talk) 11:01, 16 February 2007 (UTC).

I assume you mean the cat in the eponymous thought experiment. As far as I know it never had a name, since it was merely hypothetical. Otherwise, you could mean the cat that Erwin Schrodinger actually owned, which he presumably kept well-fed in his house. If he even owned a cat, I strongly doubt its name would appear in any scientific papers. Maybe a biography. Maelin (Talk | Contribs) 12:59, 16 February 2007 (UTC)

[edit] Cat in the Black Hole

"The experiment is a purely theoretical one, and the machine proposed is not known to have been constructed." Duh! I think the point that is often missed with this though experiment is that the "catbox" would have to be essentially a black hole. In order to completely isolate the internal environment from the outside to prevent de-coherence, space time would have to be massively warped in a sphere around the cat preventing information from leaving or penetrating the perimeter of the "catbox". Such a tremendous spherical space/time warping would probably have to be generated internally and result in the internal environment advancing to infinite time just at the instant communication of with the "outside" universe ceases. Of course, such a device would have to generate and magnify gravity (particle/waves) from an internal energy source; however, no one has yet to convert electrons or photons to gravitons much less a device for generating artificial gravity and focusing it. But, who knows: if the universities import more visa workers working on important research topics such as "how many quantum strings can dance on the head of a pin", the wages of physicists might be driven so low that they will have to invent it or go to work at McDonalds! Does McDonald's make their burger flippers sign non-disclosure agreements? Maybe God does shoot craps, modern physics is God's practical joke on sentient creation and the universe is laughing at you behind your back! —The preceding unsigned comment was added by 71.36.187.39 (talk • contribs).

But that's the point of thought experiments, you posit what may be possible and ignore technical details of implementation. --Michael C. Price talk 13:49, 16 March 2007 (UTC)
Further it might be worth pointing out in the article that it is not necessary to completely isolate the experiment from the environment: decoherence is not an all or nothing thing. All that is required is that the energy exchanged with the environment be << kT. --Michael C. Price talk 14:03, 16 March 2007 (UTC)

Michael Price is right. "Complete" isolation is not needed, all you need is "sufficient" isolation. In fact, the Schrödinger Cat experiment is not just a thought experiment and has actually been performed, disproving the Copenhagen Interpretation at least up to the level of mesoscopic systems. Not with a cat, of course, but with a mesoscopic measuring apparatus. Sufficient isolation could be maintained, not indefinitely, bur for several seconds which is a HUGE duration for atomic systems. One reference is the one I inserted in my edit of the main text, namely http://www.qis-jst.on.arena.ne.jp/kochi/poster/abst/11.pdf (and references quoted in that paper). Alfredr 20:40, 19 March 2007 (UTC)

How little energy are we talking about? Wouldn't a cat that was breathing generate a noticably different amount of heat to one that was not, and wouldn't the cat's movement -- at very least the movement of air in and out of its lungs and of blood circulating in its heart, arteries and vains -- cause changes to the position of the box's centre of mass? Outside of a black hole, it doesn't seem to be a very isolated system. 80.176.149.243 21:53, 2 April 2007 (UTC)

[edit] Copenhagen interpretation

I am going to edit down this section. There is far too much OR, under-sourced, confusing material.

To start with:

Though very recent developments show exactly the contrary, namely that measurements by a mesoscopic apparatus does NOT immediately alter the quantum state of the phenomenon, and the alteration happens only progressively, when the "fine-control" on the mesoscopic system is lost. See for instance http://www.qis-jst.on.arena.ne.jp/kochi/poster/abst/11.pdf. This proves the Copenhagen interpretation does not work at least up to the mesoscopic (thousands of atoms, or so) size.

The reference is only to an abstract. a proper reference would be needed to demonstrate the point. In any case, this is too specific and not notable enough for an overview article. (The copenhagen interpretation page might be more appropriate).

1Z 17:31, 23 March 2007 (UTC)

Under Copenhagen, the amount of uncertainty for a complex quantum system is predicted by quantum decoherence. Particles which exchange photons (and possibly other atomic or subatomic particles) become entangled with each other from the point of view of an observer, meaning that these particles can only be described accurately with reference to each other, which decreases the total uncertainty of those particles from the point of view of our observer. By the time one has reached "macroscopic" levels - such as a cat, which is made up of a number of atomic particles almost too large to express with words - so many particles have become entangled with each other so as to decrease the uncertainty to almost zero. (Quantum effects in huge collections of particles are only seen in very rare, and often man-made, situations, such as a Bose-Einstein condensate). Thus, at least from the point of view of the observer, any improbability regarding the cat as a system of quantum particles has disappeared due to the massive amount of entanglement between all of the particles that make it up, meaning that the cat does not truly exist as both alive and dead at the same time, at least from the point of view of any observer viewing the cat.

If "uncertainty" is meant in the sense of the Heisenberg uncertainty principle this passage is false: nothing can reduce the Heisenberg uncertainty below its minimum. It it "uncertainty" is mean as indeterminism -- that is, the passage is advocating the decoherence approach, and it is in the wrong place.

1Z 17:46, 23 March 2007 (UTC)

I can't believe it! You removed my edit because the reference I gave is, according to you, just an abstract. And you leave the sentence just before, TOTALLY unsupported (no reference at all!) and which is contradicted by the reference I gave, abstract or not! I was initially polite enough NOT to delete the previous sentence, but to add my edit after it! Now I have no choice but delete it. What "Recent developments.." was it referring to? The experiment I referred to, namely http://www.qis-jst.on.arena.ne.jp/kochi/poster/abst/11.pdf does exactly what I claim it does; disprove the Copenhagen Interpretation up to hte mesoscopic level. I did not say it formally disproves it up to macroscopic level, but up to mesoscopic level it does.Alfredr 13:02, 27 March 2007 (UTC)

The abstract only describes proposed experiments. If you have a better reference, please supply it. 1Z 14:30, 27 March 2007 (UTC)

Some more proposed experiments:

[5] [6] 1Z 15:10, 27 March 2007 (UTC)


OK, so what about this: http://arxiv.org/pdf/quant-ph/0307185 ? This will create a pdf file (10 pages) describing the experiement that was actually performed, with its results. It may be a bit heavy reading but believe you me, it shows that precisely coupling of an atom to a mesoscopic "Schrödinger cat" is reversible (at least for a finite duration, a few seconds, which is a HUGE duration in terms of the relevant time-scales). This shows that a mesoscopic measuring apparatus does not collapse the wave-function, or at least not immediately. Will you reinstate my edit in the main article, with this reference replacing the one I originally entered? Alfredr 22:26, 27 March 2007 (UTC)

Since you did not, I reinserted my comment that you removed, now substantiated by a much more detaizles article, describing a nexperiment that was actually performed, not just a "proposed" one. OK, now? Alfredr 22:11, 28 March 2007 (UTC)

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