Is the collapse of the particle wave function?

[Feeble Wonk]

. You could extend this chain of detectors detecting detectors for as long as you wanted and surely, each subsequent detector would simply pick up the superposition. This chain is interactions is called the Von Neumann chain and the million dollar question in all this is, "Where does it end?".

I have asked this question on PF in the past. From those discussions, I was under the impression that decoherence was believed to prevent the "Von Neumann Chain" or the similar "Wigner's Friend" dilemmas from being an issue.
Was I mistaken in that understanding?

 

[James White]

I have asked this question on PF in the past. From those discussions, I was under the impression that decoherence was believed to prevent the "Von Neumann Chain" or the similar "Wigner's Friend" dilemmas from being an issue.
Was I mistaken in that understanding?

You are correct to be under that impression as this is the current explanation insofar as it can be called an "explanation". It's more a of cheeky way out, like so many things are in quantum physics unfortunately. This is entirely my opinion but I've been studying QM for some time and it seems to me that the majority of physicists nowadays are so thoroughly confused by it that they are burying the problem in necessarily complex mathematics and many of the analytic solutions are "hacks" at best.

If you want a purely "scientific" answer (that is, the kind of answer that would not be ridiculed among mainstream physicists) then the answer is essentially, "We don't really know", QM is still very poorly understood (although there are things we understand quite well such as QED). But if you're anything like me, you want more than just a "We don't know" and if that's the case then I cannot urge you enough to dare to venture slightly beyond the confines of accepted theory. Read "The self-aware universe" by Dr. Amit Goswami PhD, he is a well respected quantum physicist, you might even have heard of him. He struggled with questions just like this for decades before stumbling onto the answer, it's still largely a work in progress but I'd be very surprised if it didn't change your entire interpretation of QM.

Remember, major breakthroughs in science as always ignored and ridiculed before being accepted. The trick is to not take what anyone tells you as gospel.

 

[HiggsBoson1]

It could definitely be caused by the first. I don't know about the second.

 

[Feeble Wonk]

I've been enjoying the exchange between Atyy and Vanhees71, and I don't want to distract from that debate... or worse, get the thread terminated for an overly philosophical tenure. Yet, I'd like to follow up on this.

Read "The self-aware universe" by Dr. Amit Goswami PhD, he is a well respected quantum physicist, you might even have heard of him.

I actually read Goswami's book several years ago, and was very intrigued by his perspective regarding QT's implications. However, I believe it was published in 1995, and my understanding is that the process of decoherence has become significantly more established since that time. Is there still a significant school of thought within the physics community that posits the requirement for a "conscious" observation of measurement to reduce (>_< trying to avoid the "collapse" term) the quantum state?

 

[atyy]

However, I believe it was published in 1995, and my understanding is that the process of decoherence has become significantly more established since that time. Is there still a significant school of thought within the physics community that posits the requirement for a "conscious" observation of measurement to reduce (>_< trying to avoid the "collapse" term) the quantum state?

If you look at bhobba's post #18, that is I believe the correct and consensus position. Decoherence alone is not enough to remove the need for a measuring apparatus or an observer to recognize a definite outcome, upon which the wave function collapses or an improper mixture is converted to a proper mixture. A "conscious" observer is not really any more defined than an "observer" or a "measuring apparatus", but if hidden variables or many-worlds are not postulated, there has to be something more that is able to register definite measurement outcomes.

In addition to the link in bhobba's post #18, other references agreeing with this point are
https://www.amazon.com/dp/0198509146/?tag=pfamazon01-20 p82
https://www.amazon.com/dp/3540610499/?tag=pfamazon01-20 p301

So yes, the pioneers of quantum mechanics did their job well. There were some errors, such as von Neumann's wrong proof of the impossibility of hidden variables, and the projection postulate is not the most general rule of state reduction, since it runs into trouble with continuous variables. However, although some textbooks like Bohm's wrongly stated the impossibility of hidden variables (Bohm corrected himself in later papers), others like Messiah's explicitly stated that hidden variables cannot be ruled out, but the Copenhagen interpretation will be used for simplicity since no experiments up to that time distinguished the interpretations. The state reduction rule has been generalized to continuous variables, eg. by Davies and Lewis, and Ozawa. So overall, the orthodox Copenhagen-style interpretation deserves its status, matching all experimental data to date, and yet recognizing its problems via the classical/quantum cut.

 

[bhobba]

I have asked this question on PF in the past. From those discussions, I was under the impression that decoherence was believed to prevent the "Von Neumann Chain" or the similar "Wigner's Friend" dilemmas from being an issue.
Was I mistaken in that understanding?

Decoherence shows the most natural place to put the von-Neumsann cut is right after decoiherence. When you do that all these issues disappear.

Thanks
Bill

 

[bhobba]

You could extend this chain of detectors detecting detectors for as long as you wanted and surely, each subsequent detector would simply pick up the superposition.

That isn't exactly what the issue is - its not really an issue with a chain of detectors because the cut can be placed before the detector - or even between detectors - however there is no need to go into the details here - start a new thread on the Von-Neumann regress if you are interested

Von-Neumanns analysis is out of date.

It has been superseded with our new knowledge of decoherence. What worried Von-Neumann was you can put the classical quantum cut pretty much anywhere before the conciousness of a human observer and since no place is different he chose to put it at the conciousness of the human observer. However such a view leads to all sorts of difficulties even in Von-Neumann's time but especially now in the computer age. For example in the double slit you can write the output to computer memory, copy that memory endlessly and then 100 years later view the output. Is that when the observation occurred? Did all the copies suddenly get observed then? If you promulgated such a view in a computer science class they would likely leave thinking you a bit loopy and try to contact some men in white.

It didn't catch on that much but did with a one very influential mathematical physicist - Wigner. Von-Neumann died young but Wigner lived to see the more modern work on decoherence. When he found out about some of the early work of Zurek he realized that Von-Neumanns analysis was no longer valid - there is a place that's different and that is just after decoherence. If you place it there all these type of issues disappear- some do remain - the most notable being the so called problem of outcomes which colloquially is why do we get any outcomes at all - or technically how does an improper mixed state become a proper one. Wigner did a complete 180% about face and advocate objective collapse models.

Thanks
Bill