# The heck with the Cat, what about the Human?

1. Feb 23, 2013

### jmoorhea

Just wondering about Schroedingers Cat experiment.

While in box, Cat is both alive and dead until you open box and measure it according to the Copenhagen interpretation. Thats fine.

But if you replace the cat with a human, then the human also is dead and alive until you open the box and measure what state it is in.

I'm just confused though. If you ask the human after the experiment, did you notice anything strange while you were in the box, then they will say no and describe how they were alive all along.
Yet from the perspective of the person outside of the box, the Copenhagen interpretation states that human in box is both alive and dead?????

So is there not a difference between the two perspectives?

2. Feb 23, 2013

### Whovian

Hmm.

No expert, but I think you might just be misinterpreting the meaning of "both alive and dead." Though maybe I'm misinterpreting the definition of a superposition.

Sorry this wasn't too helpful, I'll want to wait for someone more prominent in this to answer.

Last edited by a moderator: Feb 23, 2013
3. Feb 23, 2013

### JK423

Fast answer: Nobody knows what it means! :tongue:

Last edited by a moderator: Feb 23, 2013
4. Feb 23, 2013

### my_wan

This is a well known problem with the collapse postulate in general. Consider system A in a superposition of states. If system B observers A then B says that the wave function of A collapsed. However, if a system C has not observed the combined system AB then as far as C is concerned AB remains in a supposition of states until observed by C. If C collapses AB then D can still say ABC is a supposition of states, and so on.

Last edited by a moderator: Feb 23, 2013
5. Feb 23, 2013

### Whovian

For some reason, I thought that was specific to a single interpretation of QM, but maybe not.

Anyway, OP, the crux of this statement is that the person in the box sees nothing interesting. The person outside sees a superposition until it's opened. Sounds weird, but welcome to QM.

Last edited by a moderator: Feb 23, 2013
6. Feb 23, 2013

### my_wan

There are interpretations in which treats environmental interactions collapse the wavefunction, important for things like quantum computers. In this case the cat was never isolated from the environment to begin with. It also does address the fact that the problem is reintroduced once you assume observers A, B, and C are all outside each other light cone when the event occurs. Then the problem is reintroduced, even with these extra assumption, as first B then C enters the line cone of the event.

Last edited by a moderator: Feb 23, 2013
7. Feb 23, 2013

### jmoorhea

Hmmmm. I've probably a bit more to think about I suppose.

I just thought that this sort of situation kind of rubbished the Copenhagen Interpretation and brought the "Many Universes" interpretation of Everett more to the fore.

Its one thing to talk about an electron being in two states or a cat being alive and dead at the same time but another to talk about a human being alive and dead, especially when the human is 100% sure after the experiment that he was never in a superposition at any stage.

The "many worlds" interpretation just seems to make a bit more sense of the whole experiment to my mind.

Although maybe I have to take Wheelers Big U into consideration when considering the experiment????? As in, only after the measurement, is there any reality at all. So when I open the box and see the human alive, then he was always alive? But that still seems to conflict with the Copenhagen interpretation to my mind.

Copenhagen is unambigious about it. Superposition exists until measurement.

Last edited by a moderator: Feb 23, 2013
8. Feb 23, 2013

### Staff: Mentor

Schrodinger did indeed advance the cat in a box as a challenge to the Copenhagen interpretation, but it's a stretch to say that it makes MWI more attractive. There are other interpretations that avoid the superimposed cat as well.

I put this question to Mojo, the sole proprietor of a flourishing rodent control business in our neighborhood. She hissed and spat and suggested that we should experiment with a superposition of her claws and my ankles before assuming that a cat was any less able to appreciate superposition than a human.

And seriously, kidding aside, a cat is sufficiently complex macroscopic system to make Schrodinger's point. No conceivable experiment can, even in principle, preclude the possibility that the cat in the box was in a superposition before it interacted with something other than the radioactive sample. But that doesn't mean that you have to believe that the cat is both dead and alive, any more than you have to believe (to use Einstein's challenge) that the moon is not there when you're not looking.

Well, Copenhagen itself is not all that precisely defined, as Bohr's thinking evolved over time... But if you look for the intersection of everyone's definition of "Copenhagen", I think you'll find that the only thing that everyone agrees on is that certainty exists after measurement.

Last edited by a moderator: Feb 23, 2013
9. Feb 23, 2013

### Staff: Mentor

Thread closed for Moderation...

Re-opened.

Last edited: Feb 24, 2013