Here's an example of it in action:

http://www.videosift.com/video/Cat-in-a-Box-II

Understanding this thought experiment is key to grasping the edge of Quantum Physics, which is the hardest part of actually studying Quantum Physics.

States of energy, atoms being several places at once and so on are concepts that aren't very intuitive and take a while to actually grasp.

There are, however, practical applications to this thought experiment:
http://www.videosift.com/video/The-Big-Bang-Theory-Schr-dinger-s-Cat

I think the experiment would've been more compelling if they used a Komodo Dragon...or some other cool creature.

Love his hair!

What?! Not even physicists can see through steel? My whole world is in ruins!

Well im going to put all the people i dislike from the sift into a quantum box.

They shall for ever be in a state of confuseoin, from an outside perspective at least.

The process by which quantum super-position collapses to classical state - for example through interaction with a macroscopic object - is called decoherence.

An introduction to decoherence can be found here:

http://www.ipod.org.uk/reality/reality_decoherence.asp

I've always seen this experiment as flawed. People assume the act of observation that causes the cat to either be dead or alive must be done by a human. But this is not the case I think, the Geiger counter is the observer and once it observes the decay or not, the cat will either die or not, irrespective of when the box is opened.

but it is the observation.. like with the double slit experiment.. the result of it, that is already on the back-screen, depends on wether or not you check the values of the electron counters at the two slits before seeing the back-screen

I came here to mention the double slit experiment... but is that true shole.. even with the measuring device, the photons still show an interference pattern unless a human observes the measurement?

I was under the impression that as soon as you placed the measuring device, the waveform collapsed.

I love the fact that physics videos do well on the Sift.

finally - something with intellectual merit for the *catsanddogs channel

Adding video to channels (Catsanddogs) - requested by SlipperyPete.

i agree with cybrbeast, in that the "observer" is miscategorized. in order to be the observer, you must be able to accurately detect change. the minute the steel box is closed in this experiment, the reliability of the human-as-observer falls to pieces. two points that are of interest to me:

1. if the click of the Geiger counter could be heard, it could be argued that the atomic decay state and thus the state of the cat remain binary and knowable. obviously this defeats the point of the steel box in obscuring observation, but it also circumvents the erroneous assumption that "observation" is the hinge upon which the state of an object rests. measuring the state of an object does not determine the state itself; it simply allows the state to be quantified for human application.

2. we must rely on the observer's observation of the cat being alive or dead as accurate, which it may not be.

the use of cyanide as the killing agent in the experiment makes the assertion that a cat cannot be "both alive and dead" debatable. cyanide inhibits cytochrome c oxidase, which is used in the electron transport system to make adenosine triphosphate (used by the body for energy) in an oxygen-dependent way. simply said, cyanide makes breathing useless and paralyzes everything in the body that needs oxygen. those things that need oxygen the most to live will die first. and since all tissue and organs in the body require oxygen at a different rate, there is an arbitrary, unknown time at which exactly half of the cells in the cat's body would be dead, and half alive. this would not coincide with the cat's brain or cardiac activity, since those are both highly oxygen-dependent tissues. so it could be said that if the exact moment the cat fell over from cardiac failure the steel door happened to be opened, the observer could observe a truly dual state of the cat's existence and still misclassify it as being in the state of "dead".

again, the observed state is independent of the actual state.

on a more humorous note, would the now-dead cat have muffled it's own sound upon falling?

>> ^andybesy:
The process by which quantum super-position collapses to classical state - for example through interaction with a macroscopic object - is called decoherence.
An introduction to decoherence can be found here:
http://www.ipod.org.uk/reality/reality_decoherence.asp


Awesome link, that clears up so much. The whole "observation" concept is a stupid, misleading term because it implies that we (humans, or our tools) are some sort of privileged observers. No. Anything macroscopic is. And the jump from superposed states to a single state is not a discrete, magical thing but a continuous transition.

This article you linked is exactly how I imagined it would work logically, but I'd never seen it explained properly.

I don't claim to be an expert on the subject, but as I understand it, quantum mechanics is all about statistics and probablity. I have always thought of this experiment as an illustration of the idea that when you can't probe a quantum object to determine what state it's in, but there exists the probability that it is in one particular state or another, then the object can be thought of as being in both states simultaneously until such time as you can probe it, at which point you can know the state of the object in question and hence it is no longer in both states at the same time.

By my understanding you can therefore extend this further, by considering the probability of the decay having occurred and actually hit the detector at any given point in time. You could then say things such as: "At time A the cat is 5% dead 95% alive, while at time B it is 99% dead and only 1% alive" etc.

In saying that, I don't think I'm breaking the experiment, because no matter how much time passes you can never be sure whether it is dead or alive (short of life expectancy constraints) so it is still in both states. What the numbers actually tell you is, if you ran the experiment many times opening it at various points, what the ratio dead vs live cats would be after each given time interval.

The connection between the particle state and the cat state via the Geiger counter cyanide, etc. is just to provide a more tangible framework for the idea. The validity of the connection is irrelevant to the experiment.

For me, the point of the thought experiment is to illustrate that you cannot separate the observer and the observed....is there such a thing as unobserved existence?

It's fun to think of stuff like that....like, in what degree of phase is a wave?

This video both sucked, and was awesome... until I watched it.

This is actually a fairly poor explanation, IMO, as they barely touch on what is so very ridiculous about quantum mechanics that makes the simultaneously dead and alive cat rather plausible.

Yes, it's not a question of whether the cat is alive or dead, or what is the probibility of it being in one state or the other. It's the fact that until the cat is observed, it is both alive and dead simultaneously. The key is that the cat is both alive and dead at the same time. Of course that is a ridiculous statement in the macro universe, which is what the thought experiment was illustrating.

>> ^cybrbeast:
I've always seen this experiment as flawed. People assume the act of observation that causes the cat to either be dead or alive must be done by a human. But this is not the case I think, the Geiger counter is the observer and once it observes the decay or not, the cat will either die or not, irrespective of when the box is opened.


But the geiger counter is not an "observer" as the term is accepted. It is simply an inanimate object like the collection of atoms that forms the isotope.

The geiger counter acts in a certain way when a certain set of conditions presents itself. When a radioactive particle/burst of energy travels through the gas inside the counter, the gas conducts electricity, the electricity stimulates an output such as clicks. Doesn't have to be clicks either, it could be a guage. Regardless, it is not something that observes. You may as well say that the isotyope itself is an observer because the reaction of the parts in the geiger counter is an extension of what occurs in the isotope.

Schrodingers cat is a great way of simplifying the idea of quantum mechanics, but you still need a basis of what the thought experiment is trying to convey. The cat is just a way of linking quantum mechanics to the real world, it's not particularly important. You can just put the isotope in a box, do away with the cat, hammer and geiger counter and say "we cannot know whether it has decayed or not."

That's the point - we do not know what's happening in the box, because we can't measure it. And until we can measure it, in a quantum mechanical sense, all (or both) states are true.

Walter: Why do I want a Ph.D. in this?
Catherine: Particle beam weapons, research grants...
Walter: A millionaire when I'm forty! Now I remember!

dannym, so are you then saying that an observer has to be a human observer? That implies that our consciousness effects the physical world in some way.

Phil Spector looks good here

>> ^dannym3141:
>> ^cybrbeast:
I've always seen this experiment as flawed. People assume the act of observation that causes the cat to either be dead or alive must be done by a human. But this is not the case I think, the Geiger counter is the observer and once it observes the decay or not, the cat will either die or not, irrespective of when the box is opened.

But the geiger counter is not an "observer" as the term is accepted. It is simply an inanimate object like the collection of atoms that forms the isotope.


What's the difference? As I read the article linked above, there is none. That's why "observer" is such a dumb term. It implies intelligence or sentience or even humanity, when interaction with any macro scale matter is just as good.

And I agree the video sucks. They never get at the fundamental issue of why the cat doesn't actually exist in superposition.

1:17 - 1:27... Play me out Keyboard Physicist.

It's the unseen cat Snoopy chases into a box while Schrödinger plays his piano.

I think the cat is hiding on one of their heads.

According to this theory, my unsifted videos are in a quantum state.

I like how this video is basically the equivalent of the Aristocrats for quantum physics...

*promote

Promoting this video back to the front page; last published Monday, July 13th, 2009 12:51am PDT - promote requested by MycroftHomlz.

If the cat survives does it get a cheeseburger?

This is a bit like getting over excited when you realize that a dice has the potential to return 6 possible states and that the dice is in a super state of chaotic flux - until it is rolled!!! only then does it return which actual state it is.


Me thinks the Physicists need to stay out of the Statisticians cafeteria.

No, that's wrong. Quantum super-position isn't just an acknowledgement of possible outcomes, statistics or probability. At the quantum level super-position is a very real physical effect, as observed in the interference patterns of the famous double-slit experiment.