Register to reply

Cat in a box paradox

by ArielGenesis
Tags: paradox
Share this thread:
ArielGenesis
#1
Sep13-07, 04:51 AM
P: 235
I just learn the cat in a box paradox, where we cannot know whether the cat is dead or alive until we open the box, so the cat is in a superposition between life and death. yup, got it!

I am about to learn quantum physics. And I think it would be really good if I got a grasp of it first. So this cat thing, is analogy for particle, and its life, is for particle's properties. So far so good.

What I don't understand is that if we don't know the particle state, then I would assume that the particle state is irrelevant as it won't affect anything, because when it affect something, we know its state, in other words, the box had been opened. Thus would it really matter what the particle state is before the box is opened?
Phys.Org News Partner Physics news on Phys.org
Engineers develop new sensor to detect tiny individual nanoparticles
Tiny particles have big potential in debate over nuclear proliferation
Ray tracing and beyond
Demystifier
#2
Sep13-07, 05:01 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Basically, there are two schools of thoughts.

1. Until you look, the cat is neither dead nor alive.

2. It is allways either dead or alive even if you do not look. But in this case, a sort of nonlocal communication between physical objects is possible.

At the moment, nobody knows with certainty which view is the correct one.
genneth
#3
Sep13-07, 05:29 AM
P: 980
Or:

3. When you look, the world splits in 2, one for the possibility that it's alive, and one for it's dead.
4. Whether it's dead or alive only exists in your head, and so it's a trivial truism that it's neither dead or alive until you look. Any interaction where you learn more about the cat is going to have an effect on the cat, because you're a clumsy physicist and all you can do is a deliver a well-aimed poke.
5. ...

There's probably countless others. In practise, it doesn't matter: you model the problem in the language of quantum mechanics, follow the procedure, and you will be able to calculate the probability that the cat is alive or dead, without ever wondering about what exactly happened in between. It says a lot that experimentalists never worry about the measurement problem but the theorists do all the time.

ZapperZ
#4
Sep13-07, 05:43 AM
Emeritus
Sci Advisor
PF Gold
ZapperZ's Avatar
P: 29,238
Cat in a box paradox

Quote Quote by Demystifier View Post
Basically, there are two schools of thoughts.

1. Until you look, the cat is neither dead nor alive.

2. It is allways either dead or alive even if you do not look. But in this case, a sort of nonlocal communication between physical objects is possible.

At the moment, nobody knows with certainty which view is the correct one.
You are missing a #3: The cat is BOTH dead and alive. That is what a superposition implies, the existence of BOTH orthogonal states at the same time.

If it is #1 or #2, then you would never have bonding-antibonding in chemistry, and no coherence energy gap in the Delft/Stony Brook experiments. I certainly haven't seen any one formulating any physics using #1 and #2 to derive what have been observed.

Zz.
f95toli
#5
Sep13-07, 06:16 AM
Sci Advisor
PF Gold
f95toli's Avatar
P: 2,253
Someone should perhaps point out that the "cat in a box" is a higly idealized gedanken experiment. A real cat would always be EITHER dead or alive inside the box, regardless if you open it or not.

The reason is that any object the size of a real cat is an open quantum system meaning it couples to the enviroment. Hence, it can never be in a superposition of dead/alive for very long (its "wavefunction" will decay extremely fast).

This is the reason why it is so difficult to e.g. build good quantum bits out of macroscopic objects; they interact with the enviroment (or, more specifically, enviromental degrees of freedom) and decay very quickly leading to short coherence times.
Demystifier
#6
Sep13-07, 06:30 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Quote Quote by genneth View Post
Or:

3. When you look, the world splits in 2, one for the possibility that it's alive, and one for it's dead.
4. Whether it's dead or alive only exists in your head, and so it's a trivial truism that it's neither dead or alive until you look. Any interaction where you learn more about the cat is going to have an effect on the cat, because you're a clumsy physicist and all you can do is a deliver a well-aimed poke.
3. is a variant of my 1.
4. is a variant of my 2.
Demystifier
#7
Sep13-07, 06:36 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Quote Quote by ZapperZ View Post
You are missing a #3: The cat is BOTH dead and alive. That is what a superposition implies, the existence of BOTH orthogonal states at the same time.
The cat cannot be both dead and alive. It can be in a superposition of dead and alive, but this is neither dead nor alive, but something else - the superposition. But this is just a matter of language. In fact, your #3 is actually rephrased 1.
ZapperZ
#8
Sep13-07, 06:44 AM
Emeritus
Sci Advisor
PF Gold
ZapperZ's Avatar
P: 29,238
Quote Quote by Demystifier View Post
The cat cannot be both dead and alive. It can be in a superposition of dead and alive, but this is neither dead nor alive, but something else - the superposition. But this is just a matter of language. In fact, your #3 is actually rephrased 1.
No, it isn't. Being dead AND alive is different than being dead OR alive. The latter means that the cat has a DEFINITE state. We just don't know what it is. This is classical statistics where you've tossed a coin, but you haven't seen it yet whether it is head OR tail. This is not a superpostion.

My interpretation isn't something I invented. The Leggett paper that I've highlighted before many times on here regarding the measurement problem clearly stated this position. When you have a state being described as a linear sum of orthogonal states, then the obvious interpretation here is that ALL of those states exists at the same time. If not, then the Schrodinger Cat paradox isn't anything unusual. The cat is either dead or alive, which isn't new nor strange. Why would Schrodinger go to all that trouble illustrating something that is not unusual?

Zz.
Demystifier
#9
Sep13-07, 07:37 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Quote Quote by ZapperZ View Post
No, it isn't. Being dead AND alive is different than being dead OR alive.
But we agree on that. I said that being dead and alive is actually a clumsy way of saying that the cat is in a superposition. I also said that it is different from being dead or alive.
ZapperZ
#10
Sep13-07, 07:44 AM
Emeritus
Sci Advisor
PF Gold
ZapperZ's Avatar
P: 29,238
Quote Quote by Demystifier View Post
But we agree on that. I said that being dead and alive is actually a clumsy way of saying that the cat is in a superposition. I also said that it is different from being dead or alive.
Quote Quote by Demystifier
1. Until you look, the cat is neither dead nor alive.

2. It is allways either dead or alive even if you do not look. But in this case, a sort of nonlocal communication between physical objects is possible.
You have a funny way of saying that then.

Zz.
mattex
#11
Sep13-07, 07:53 AM
P: 20
Man, you guys are crazy.
genneth
#12
Sep13-07, 07:58 AM
P: 980
Quote Quote by mattex View Post
Man, you guys are crazy.
It really is a lot of arguing over something which doesn't actually affect any experiment that we can currently do. Moreover, each possibility has a different flaw/distaste to it, so it's pretty much subjective. Obviously Dany is in favour of Bohmian mechanics (does anyone here *not* already know that?), but that is, again, a matter of taste. If we all just sat down and did some calculations of well-posed problems, we'd all agree on the outcomes. How much Platonic reality can we really ask for from mathematical models?
Demystifier
#13
Sep13-07, 08:05 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Quote Quote by ZapperZ View Post
You have a funny way of saying that then.
You completely misunderstood me. My 1. and 2. refer to two mutually exclusive schools of thoughts. My later responses to you refer only to the 1. school of thought. My whole point is that there are essentially only TWO different schools of thought, while all others (3., 4., #3, ...) are nothing but variants of these two.

Of course, as a Bohmian, I prefer 2. Still, I believe that I am able to speak consistently about 1. as well.
ZapperZ
#14
Sep13-07, 08:13 AM
Emeritus
Sci Advisor
PF Gold
ZapperZ's Avatar
P: 29,238
Quote Quote by Demystifier View Post
You completely misunderstood me. My 1. and 2. refer to two mutually exclusive schools of thoughts. My later responses to you refer only to the 1. school of thought. My whole point is that there are essentially only TWO different schools of thought, while all others (3., 4., #3, ...) are nothing but variants of these two.

Of course, as a Bohmian, I prefer 2. Still, I believe that I am able to speak consistently about 1. as well.
OK, let's see...

Quote Quote by Demystifier
The cat cannot be both dead and alive. It can be in a superposition of dead and alive, but this is neither dead nor alive, but something else - the superposition. But this is just a matter of language. In fact, your #3 is actually rephrased 1.
1. So you are claiming that

#3 The cat is BOTH dead AND alive

is identical to

#1 The cat is neither dead nor alive?

2. When you toss a coin but don't look at the outcome, do you say that it is (i) either head OR tail, or (ii) head AND tail?


Zz.
Demystifier
#15
Sep13-07, 08:25 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Quote Quote by ZapperZ View Post
a) So you are claiming that

#3 The cat is BOTH dead AND alive

is identical to

#1 The cat is neither dead nor alive?

b) When you toss a coin but don't look at the outcome, do you say that it is (i) either head OR tail, or (ii) head AND tail?
a) You don't read what I say. So, let me repeat. The cat cannot be both dead and alive, it is a logical contradiction. Still, it can be in a superposition of dead and alive. In this case, it is neither dead nor alive. Sometimes we say for such a state that the cat is "both dead and alive", but it is simply an incorrect (or imprecise) language.

b) I say it is in the superposition of head and tail (recall that I am still talking within the 1. paradigm, despite the fact that I actually prefer 2.)

By the way, this is my 666th post.
genneth
#16
Sep13-07, 08:32 AM
P: 980
Guys ... come on! We're arguing over words, not meaning! We invented mathematics to make words less slippery! Dany and ZapperZ: I think you already understand each other, and agree that you use the same words in different meanings; as far as who's "correct", I say it doesn't matter.
Demystifier
#17
Sep13-07, 08:35 AM
Sci Advisor
Demystifier's Avatar
P: 4,612
Genneth, I think you are right!
nrqed
#18
Sep13-07, 08:56 AM
Sci Advisor
HW Helper
P: 2,957
Quote Quote by genneth View Post
It really is a lot of arguing over something which doesn't actually affect any experiment that we can currently do.
I disagree. That's the whole point of Bell's theorem. The only way to interpret EPR type experiments (liek the ones done by Alain Aspect) which violate Bell's inequality is to conclude that the photons are in linear superposition of two spin states before being observe (unless one introduces nonlocality). That's the wonderful thing about Bell's inequality: it permitted to teexperimentally something that seemed to be a purely philosophical issue!


Moreover, each possibility has a different flaw/distaste to it, so it's pretty much subjective. Obviously Dany is in favour of Bohmian mechanics (does anyone here *not* already know that?), but that is, again, a matter of taste. If we all just sat down and did some calculations of well-posed problems, we'd all agree on the outcomes. How much Platonic reality can we really ask for from mathematical models?


Register to reply

Related Discussions
1-D Box. Paradox? Quantum Physics 6
The Twin Paradox Paradox. Special & General Relativity 3
Resolving the Barber Paradox and the Russell's Paradox General Discussion 18
What is the resolution of the The Bug-Rivet Paradox paradox in special relativity? Special & General Relativity 4