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)

What if the decay occurs at the instant the scientist opens the box?

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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 (http://www.stanford.edu/dept/HPS/WritingScience/Ferris.htm#fn27). -- Wapcaplet 18:53, 27 Apr 2004 (UTC)

Contents

1 First Idea 2 Terminology 3 Origin? 4 Nice job with the pictures 5 Image deleted 6 Decoherence

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.

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)

Origin?

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

Nice job with the pictures

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)

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 (http://images.google.com/images?as_q=Schr%C3%B6dinger+cat&svnum=10&hl=en&rls=GGLD%2CGGLD%3A2004-21%2CGGLD%3Aen&btnG=Google+Search&as_epq=&as_oq=&as_eq=&imgsz=&as_filetype=&imgc=&as_sitesearch=&safe=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  (http://images.google.com/images?q=Schr%C3%B6dinger's%20cat&hl=en&lr=&safe=off&client=firefox-a&rls=org.mozilla:en-US:official&sa=N&tab=gi) and without the umlaut (http://images.google.com/images?hl=en&lr=&safe=off&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&q=Schrodinger%27s+cat&btnG=Search) 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

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)