I A bit confused about Schrödinger's cat

[Paul Colby]

No, there are certain cases where QM predicts outcomes that are certain

This is where I feel the confusion regarding the role of the state vector begins. Having a probability of 1 is a statement a single measurement can't verify any more than it can verify a 0.376 chance. The probabilistic nature of the formalism isn't effected by these limiting cases which are actually not particularly special from an experimental point of view.

 

[bhobba]

Having a probability of 1 is a statement a single measurement can't verify any more than it can verify a 0.376 chance.

The point is its what the theory predicts - verifying its validity is another matter.

My issue is reading more into the formalism than it implies. It is silent on the ontological status of the state.

Thanks
Bill

 

[Tollendal]

Dear Flyx and AlexCaledin,

As I observed in my April 7th commentary, a conscient observer's influence doesn't matter: the coupling with anything does the trick. And multiple universes is a desnecessary idea. Ours is enough!

 

[Ken G]

The point is its what the theory predicts - verifying its validity is another matter.

My issue is reading more into the formalism than it implies. It is silent on the ontological status of the state.

Indeed this was just as true in classical physics as in quantum mechanics, so it is curious in a way that interpretations are such a dicey topic in the latter but not the former. I think it is merely that we all learned our interpretations of classical physics when we were very young, and have kind of forgotten the choices that we had to make. But when you discuss the topic of realism vs. antirealism, which did already come up a bit in the above, that's when you discover that interpretations of classical physics are just as ontologically wide open as interpretations of quantum physics. In short, there is a cat paradox in classical physics too, because of deterministic chaos. There the issue is not whether the cat could be both alive and dead at the same time, it is if you put the cat in the box with the intention of releasing it after 5 minutes, did you decide the fate of the cat when you put it in that box, or did god roll dice over the 5 minute period? Nothing in classical physics answers that, the ontologies there are just as raw as any in quantum mechanics. We have simply stopped asking those questions, so the takeaway message is that ontology is always separate from the formalisms of any physics theory.

 

[Paul Colby]

The point is its what the theory predicts - verifying its validity is another matter.

This may express your point. Mine was more along the line, "The probabilistic nature of the formalism isn't effected by these limiting cases which are actually not particularly special from an experimental point of view."

 

[Gerinski]

Sorry to come into the discussion as I'm not an expert physicist, but I don't find the quantum "weirdness" so weird, at least not when we strip it down to the bones.

The universe demands consistency, that's what I see as the unbreakable rule. Take the infamous double slit experiment, even its modern versions such as the "delayed choice" or the "quantum eraser". If our experimental setup generates and records in any physical way which-path information, we do not need to look at that record, we may send it right away to outer space without looking at it. But the information exists somewhere in the universe, with the potential to influence the future.
If that record will ever, for whatever reason (no consciousness needed!) influence the future, perhaps millions of years from now and millions of light years from earth, the future will be different when the record says that the electron passed through slit A than when it says that it passed through slit B. The future will be contingent on the experiment we performed today in a lab on earth. This means that the present can not consist of a superposition of A and B (an interference pattern), that would mean that present and future are inconsistent. The present experiment outcome, even if we never looked at it, must have been either A or B, but not an interference pattern.

I insist, no consciousness is required at all, any physical interaction with our piece of information in the far future will do, but just to illustrate it better, let's imagine that a civilization in the far future millions of light years away from us does one day find our record and look at it. The future where they look at the record and it says that the electron in our experiment passed through slit A is definitely not the same future where they look and find a record which says that it passed through slit B. So as a demand of consistency, the outcome of our experiment in the present must have been either A or B, but it can not be an interference pattern (a superposition of both A and B).

On the other hand if our experiment does not generate and record which-path information, the future can never be contingent on our experiment. We may as well send the result also to outer space without looking at it. But in this case the future can never depend on the result of our experiment, on whether the electron passed through slit A or B, because the information A or B simply does not exist, our experiment did not generate that information. The future can never depend on a piece of information which does not exist. Any hypothetical civilization finding our record millions of years from now and millions of light years away from earth, will look at the record and find an interference pattern which does not tell them anything regarding whether our electron passed through slit A or B, so that future will be just one and the same one, not 2 possible different futures contingent on the result of our experiment. Since in that case, that future can never be contingent on our experiment, the outcome of our experiment in the present, even when we never looked at it, must have been a superposition of both A and B, i.e. an interference pattern, and that's what the hypothetical future observers will find.

 

[Nugatory]

But the information exists somewhere in the universe, with the potential to influence the future.

You are describing an explanation known as "superdeterminism". If you google for "t'hooft superdeterminism" you will find some of Gerard t' Hooft's writing on the subject (as well as a fair amount of criticism).

You are right that this line of thinking completely eliminates quantum weirdness, and it may be the only way remaining to preserve both locality and counterfactual definiteness. However, superdeterminism brings in its own rather indigestible weirdnesses. For example... Superdeterminism eliminates the quantum weirdness from Bell-type experiments, but at the cost of believing that random atomic decays that happen 4+ years ago (long enough for light to get here from there, so no relativity problems) on Alpha Centauri can influence the random number generator in a lab on Earth so strongly that the generated sequence is not in fact random.

 

[Nugatory]

This thread has met the fate of so many interpretation threads: As the question is not resolvable by experiment or logic, there is no natural way of bringing the discussion to an end... Instead it eventually reaches the point where everything that has been said in the thread has been said before and there's nothing new.

We're there, and the thread is closed.