B Schrödingers cat, is it just mumbo-jumbo?

[PeroK]

Just to point out that SC has nothing to do with whether someone can see the cat. It was once thought that observing - or seeing - the cat would somehow collapse its wave function. And yes, you can construct situations in which it is not entirely clear whether the cat has been observed. But SC is about the "quite ridiculous" situation where the cat is both alive and dead before it gets observed.

There's nothing ridiculous about QM. SC may or may not be an unresolved problem. And, even if in general it is difficult to fully explain the transition from microsopic processes described by QM to the macroscopic world described by classical mechanics, that in itself is not a reason to question QM. It's only if that transition were to look impossible that something woudl have to give.

In the same way neither QM not GR is ridiculous, despite there being no obvious way to explain GR in terms of microscopic processes.

 

[kered rettop]

I did not say QM is ridiculous. I said that the cat being alive and dead was "quite ridiculous". The quotes indicate that the words are Schroedinger's, not mine. With the benefit of hindsight, I do not agree with him.

 

[vanhees71]

I think this paper by Schrödinger is very worthwhile reading. For some reason it's not famous like the EPR paper, which occured around the same time and discusses the same "issues" with QM. Maybe it's because Schrödinger is utmost clear, while EPR is nebulous, and there is the even worse answer by Bohr to it.

Of course, Schrödinger was right in saying that the cat "in superposition of states "alive" and "dead" is ridiculous. He couldn't know about decoherence and the full development of quantum many-body theory.

 

[kered rettop]

TL;DR Summary: How about a second observer in the Schödering cat experiment?

If there is a person standing on the opposite side of the closed box with the poor cat containing a poisoning devise, and he can see the cat dying through a transparent window in the box. You stand on the other side of the box and you dont se the cat. What does this mean? Can you now say that the cat is both dead and alive? The person on the other side, that can see the cat will not experience this, he will just watch a cat die for no good reason?

The state of the cat does not depend on whether someone knows about it. In fact observation doesn't really come into Schroedinger's Cat. The "quite ridiculous" aspect of the experiment was that the wave function of the cat would contain both the living and the dead cat before the box was opened or anyone looked.

 

[PeroK]

The state of the cat does not depend on whether someone knows about it. In fact observation doesn't really come into Schroedinger's Cat. The "quite ridiculous" aspect of the experiment was that the wave function of the cat would contain both the living and the dead cat before the box was opened or anyone looked.

If, owing to decoherence, the wavefunction superposition is experimentally indistinguishable from a simple classical either/or probability, then it's not ridiculous.

It's a non classical explanation. But that is inevitable given the quantum probabilistic nature of radioactive decay.

A classical explanation for decay would involve some sort of ageing process for a radioactive atom. Ironically, of course, probability would still be needed in terms of the initial state of the atom or the speed of ageing. QM puts probabilities at the heart of physics, where they belong(!), rather than trying to explain an essentially probabilistic universe by having layers of deterministic hidden variables ad infinitum.

 

[kered rettop]

If, owing to decoherence, the wavefunction superposition is experimentally indistinguishable from a simple classical either/or probability, then it's not ridiculous.

Well, you'll have to take it up with Schroedinger because he gave the cat scenario as an example of a "quite ridiculous case". If you want to say that his scenario is flawed because we now know about decoherence, I would agree with you. That said, this particular flaw is quite easily fixed by making the box big enough so that everything which gets entangled with the cat remains inside the box. Obviously a faster trigger would make it more practical, otherwise the box would have to reach to Saturn.

 

[PeterDonis]

this particular flaw is quite easily fixed by making the box big enough so that everything which gets entangled with the cat remains inside the box

No, that doesn't change anything. The cat is already a macroscopic object and decoheres itself, so the box in the original thought experiment is already big enough to allow decoherence.

 

[kered rettop]

No, that doesn't change anything. The cat is already a macroscopic object and decoheres itself, so the box in the original thought experiment is already big enough to allow decoherence.

The question is not whether the box allows decoherence. The question is whether the box can contain everything affected by decoherence. (That includes everything in the environment that interacts with the cat.) If it can't then the box contains a mixture (as suggested by PeroK) instead of a pure state. This would defeat the point of Schroedinger's scenario, making it seriously flawed. By making the box vast, the entire interacting system - cat stuff and environment stuff - remains inside the box and Schroedinger's scenario is patched up.

 

[PeterDonis]

The question is not whether the box allows decoherence. The question is whether the box can contain everything affected by decoherence.

Sure it can. It contains the cat and the environment the cat interacts with. That's everything. By hypothesis the box is an isolated system until it is opened, so there is no interaction between inside and outside.

 

[kered rettop]

Sure it can. It contains the cat and the environment the cat interacts with. That's everything. By hypothesis the box is an isolated system until it is opened, so there is no interaction between inside and outside.

Yes I agree with that. I was just trying to make sure that we can keep the required isolation. I prefer a physically possible box but one that isolates by hypothesis would do.