# Physicists: Am I saying the right thing about Schroedinger's Cat? **URL:** \ **Category:** Factual Questions\ **Created:** [March 19, 2010, 10:50pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075 "2010-03-19T22:50:02Z")\ **Posts on this page:** 9\ **Page:** 5
**Author:** ![Peremensoe](https://avatars.discourse-cdn.com/v4/letter/p/ce7236/32.png) [@Peremensoe](https://boards.straightdope.com/u/Peremensoe)\ **Post date:** [July 10, 2010, 7:26pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/81 "2010-07-10T19:26:36Z")
> [@Simplicio](#): > > Personally I’d say any state thats part of the superposition is “true”, and any state that isn’t in it (or has a coefficent of zero) is “false”, just out of desire to make the concepts of true/false useful in the context of quantum states. I agree with this interpretation, and would therefore mark the quiz: 1. The cat is alive. **True** 2. The cat is dead. **True** 3. The cat is not alive. **False** 4. The cat is not dead. **False**. ---
**Author:** ![jackdavinci](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackdavinci/32/3259_2.png) [@jackdavinci](https://boards.straightdope.com/u/jackdavinci)\ **Post date:** [July 12, 2010, 6:03am UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/82 "2010-07-12T06:03:41Z")
I wish you wouldn’t use cats. The cat metaphor was after all, a criticism of quantum theory. And rightly so - the example is of course merely a thought experiment and physically impossible. Likewise, talk of “observers” is equally nonsense. Quantum mechanics have nothing whatsoever to do with conscious observers, that’s also merely a metaphor. So decoherence, or if you prefer wave function collapse, vs superposition - is superposition all possible states, or merely not all impossible states? A little of both really - it’s clearly NOT all impossible states, however, it’s also not 100% all possible states (except for those that have collapsed and become truly 100% probable), rather, it’s probabilistic - it’s as much any particular state that is not impossible, as it probable. If we simply must use the impossible cat example, assuming enough time has passed such that it’s 75% probable that the cat has been poisoned (ignoring of course all of the states between starting to die and being completely dead): 1. The cat is alive. 25% true 2. The cat is dead. 75% true 3. The cat is not alive. 75% true 4. The cat is not dead. 25% true If the cat were truly able to be in some kind of quantum superposition (which sadly it cannot), then truth or falsity of any binary state would be only partial. Neither totally true nor totally not true. Unless you arbitrarily determine that the statement “The cat is alive” is equivalent to “The cat is 100% alive”, in which case you are correct. But your correctness has nothing to do with illuminating quantum theory. Since saying that the cat is alive is NOT the same as saying that the “cat is not alive” is true. If we have to use the binary choices, then the table most accurately would be as such: 1. The cat is (100%) alive. FALSE 2. The cat is (100%) dead. FALSE 3. The cat is (100%) not alive. FALSE 4. The cat is (100%) not dead. FALSE This is the sort of thing “fuzzy logic” is useful for… ---
**Author:** ![Dr\_Chicago](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@Dr\_Chicago](https://boards.straightdope.com/u/Dr_Chicago)\ **Post date:** [July 12, 2010, 7:27am UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/83 "2010-07-12T07:27:42Z")
> [@septimus](#): > > This comment somehow reminded me I was playing The Game, which I’ve now just lost. :smack: :mad: > > … or maybe there’s still an unobserved septimus somewhen who hasn’t lost The Game yet?? 😕 Damnit!:smack: ---
**Author:** ![Corner\_Case](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/corner_case/32/234_2.png) [@Corner\_Case](https://boards.straightdope.com/u/Corner_Case)\ **Post date:** [July 13, 2010, 5:33pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/84 "2010-07-13T17:33:33Z")
IANAP: In the experiment, I see a vacuum fluctuation causing a collapse and a photon being emitted. It flys off in a direction you could predict given the information on the nucleus and fluctuation - but you’ll never measure those with the photons, electrons, etc that we can manipulate. As the photon flies at c, the outside would is unaware of the coming chain of reactions. Perhaps you call this superposition. To me its just that reactions and information travelling at the speed of light haven’t interacted with you (the observer) yet. As th photon flies past another atom it can interfere and thus the system of radioactive nucleus, photon, and other-atom have now experienced each other. These interactions spread at the speed of light. Everything outside this “light cone” wouldn’t know it happened yet. At the end of the experiment, the cat in the box is dead (in this case since decay occurred). The observer can know about it (whether they have measured it and know or haven’t measured it and don’t know) if the wavicle interactions (the light cone) has expanded to include the observer. Perhaps you could watch a gravitometer and see the cat fell over. Only if the observer were disconnected from the light cone of interactions would the cat be in an indeterminate state. But then the observer and cat would effectively be in different universes if the quantum interactions from one never reached the other. So to me it still seems like pool. It’s not that you don’t know what’s happening. It’s that you have to measure and there’s no balls you can use to measure that won’t affect the table. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [July 13, 2010, 7:12pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/85 "2010-07-13T19:12:29Z")
> [@Corner\_Case](#): > > IANAP: In the experiment, I see a vacuum fluctuation causing a collapse and a photon being emitted. It flys off in a direction you could predict given the information on the nucleus and fluctuation - but you’ll never measure those with the photons, electrons, etc that we can manipulate. > > As the photon flies at c, the outside would is unaware of the coming chain of reactions. Perhaps you call this superposition. To me its just that reactions and information travelling at the speed of light haven’t interacted with you (the observer) yet. > > As th photon flies past another atom it can interfere and thus the system of radioactive nucleus, photon, and other-atom have now experienced each other. These interactions spread at the speed of light. Everything outside this “light cone” wouldn’t know it happened yet. > > At the end of the experiment, the cat in the box is dead (in this case since decay occurred). The observer can know about it (whether they have measured it and know or haven’t measured it and don’t know) if the wavicle interactions (the light cone) has expanded to include the observer. Perhaps you could watch a gravitometer and see the cat fell over. Only if the observer were disconnected from the light cone of interactions would the cat be in an indeterminate state. But then the observer and cat would effectively be in different universes if the quantum interactions from one never reached the other. > > So to me it still seems like pool. It’s not that you don’t know what’s happening. It’s that you have to measure and there’s no balls you can use to measure that won’t affect the table. This is what I’ve never understood about the Schroedinger’s Cat thought experiment. It starts by linking a macroscopic event (the cat, dead or alive?) to a quantum phenomenon (radioactive decay) that’s supposed to be in a state of superposition. And yet I don’t see how an atom can be in a superposition of being decayed and not decayed; it’s always seemed to me that radioactive decay forces the information that’s it’s occured onto the rest of the universe, without anything that could be considered a “measurement”. ---
**Author:** ![alindallas](https://avatars.discourse-cdn.com/v4/letter/a/f17d59/32.png) [@alindallas](https://boards.straightdope.com/u/alindallas)\ **Post date:** [July 14, 2010, 11:18am UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/86 "2010-07-14T11:18:39Z")
> [@Lumpy](#): > > This is what I’ve never understood about the Schroedinger’s Cat thought experiment. It starts by linking a macroscopic event (the cat, dead or alive?) to a quantum phenomenon (radioactive decay) that’s supposed to be in a state of superposition. And yet I don’t see how an atom can be in a superposition of being decayed and not decayed; it’s always seemed to me that radioactive decay forces the information that’s it’s occured onto the rest of the universe, without anything that could be considered a “measurement”. “Superposition” is a description, in our own ignorance of actual fact, which describes our best guess in terms of probability (chance, statistics). Unless, of course, it is not. 😃 ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [July 15, 2010, 10:57am UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/87 "2010-07-15T10:57:17Z")
> [@alindallas](#): > > “Superposition” is a description, in our own ignorance of actual fact, which describes our best guess in terms of probability (chance, statistics). > Unless, of course, it is not. 😃 Well that’s what I thought, but smarter people always seem to say that “it doesn’t just mean we don’t know which it is, it’s that it _actually is both_”. I still fail to grasp the difference. Going back to this [macroscopic quantum resonator doohicky](http://scienceblogs.com/bioephemera/2010/03/wait_what_did_you_see_or_not.php?utm_source=sbhomepage&utm_medium=link&utm_content=channellink). One of the comments on that site explains it thus: > [@](#): > > You take a quantum bit of information. That’s a quantum object that has an unknown property – like its spin – that you could measure and know, but until you measure it, they don’t know it. > > They then hook that bit up – still without measuring it – to this resonating plate that’s 60 microns long. Then they measure whether the plate is resonating or not, and they find the probability distribution of the plate resonating corresponds to the probability distribution of the quantum bit they hooked up to it. To which my reaction is, well, so what? Of course it corresponds. Why is this any different from this, non-quantum based, example: Let’s say instead of a qubit, we have a metal ball. The metal ball is chosen from a large number of such balls, some of which are liquid-nitrogen cold, the rest of which are very hot. The experimenter doesn’t know the proportion of hot to cold, as the balls were prepared by someone else in secret. Instead of the resonator, we have a hollow metal case big enough to hold a ball. Now we “couple” our ball to our case, by placing it inside, without measuring the temperature of the ball in any way. We leave it for a few minutes, then we measure the temperature of the outside of the case. It is either hot or cold. We repreat the experiment, and note the probability distribution of hot vs cold cases. Then we measure the probability distribution of hot vs cold balls (by asking the person who prepared them). No doubt we will find that “the probability distribution of the case being hot (cf plate resonating) corresponds to the probability distribution of the ball (cf quantum bit) we hooked up to it”. Can anybody please explain to me why the quantum example is “weird” but the ball example isn’t? 😕 ---
**Author:** ![Indistinguishable](https://avatars.discourse-cdn.com/v4/letter/i/90ced4/32.png) [@Indistinguishable](https://boards.straightdope.com/u/Indistinguishable)\ **Post date:** [July 15, 2010, 6:03pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/88 "2010-07-15T18:03:07Z")
> [@Colophon](#): > > Can anybody please explain to me why the quantum example is “weird” but the ball example isn’t? 😕 See the laymen’s discussion of Bell’s theorem in posts #8 - 14 in this [thread](http://boards.straightdope.com/sdmb/showthread.php?p=12664124#post12664124). ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [July 15, 2010, 9:03pm UTC](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075/89 "2010-07-15T21:03:51Z")
> [@Lumpy](#): > > This is what I’ve never understood about the Schroedinger’s Cat thought experiment. It starts by linking a macroscopic event (the cat, dead or alive?) to a quantum phenomenon (radioactive decay) that’s supposed to be in a state of superposition. And yet I don’t see how an atom can be in a superposition of being decayed and not decayed; it’s always seemed to me that radioactive decay forces the information that’s it’s occured onto the rest of the universe, without anything that could be considered a “measurement”. Sorry to reply to my own post, but I just thought of adding: it seems to me that radioactive decay _is_ a decoherence of the quantum states of the original nucleus. The only difference is that apparently no external influence (that we know of anyway) imposes a measurement on the system. So imho, the answer to the Schroedinger’s Cat quandry is that by the time a radioactive decay occurs you don’t have a state of superposition anymore. [Previous page](https://boards.straightdope.com/t/physicists-am-i-saying-the-right-thing-about-schroedingers-cat/533075.md?page=4)