Is the observed Schrödinger's cat still in a superposition?

Question

Person A sets up the Schrödinger's cat experiment with a twist: The box also includes a camera, that streams to the monitor of Person B. When the experiment completes, person B knows if the cat is alive or not, however, person B does not inform person A.

Is it true, for person A, that "the cat is both alive and dead"?

Although I am fine with understanding the "simple" operation of addition that superposition is, I'm having great difficulty using "and" between different outcomes. I still feel that it is alive OR dead, despite the fact that I'll have to use $|\text{alive}\rangle+|\text{dead}\rangle$ in all calculations.

Answer 1

The cat is a macroscopic object obeying the classical mechanics etc equations. It cannot be described by a quantum wave function, so any observation will show whether the cat is alive or dead with no ambiguity. That a third observer knows nothing as far as the state of the cat has nothing to do with quantum mechanics.

It is like the fact that :if one does not know what number came up in the national lottery does not mean that there is no number for the people who have looked at it. The lottery number happened once at the draw, it was unknown before the draw but fixed after.

The draw for the cat's demise happens to be quantum mechanical, given by a probability of decay of a nucleus which is given by quantum mechanics. One does not know if a given nucleus is whole or has decayed until the decay is detected by a detector (in the lab). Unfortunately the cat is the detector in this thought experiment (I hope nobody has tried doing it, I like cats).

Answer 2

The cat is never both alive and dead. Schrödinger proposed his thought experiment in order to highlight the absurdity of extending quantum mechanical concepts to macroscopic objects. Sadly the distorted promotion of the idea in popular science has had the opposite effect, encouraging people to concoct even more ludicrous elaborations of the idea.

In the set-up proposed by Schrödinger a quantum mechanical phenomenon, namely the decay of an atom, is detected by the apparatus, which subsequently sets off a chain of events that kills the cat regardless of whether any observer opens the box to view the result.

The paradox of Wigner's friend arises only if one adopts the nonsensical view that an 'observer' is necessary to cause the collapse of a wave function, which immediately becomes unsustainable where there are nested experiments each involving separate observers. The resolution of the paradox is simple- the assumption upon which it is based is false.