Double Slit Experiment: Questions Raised & Explanations Needed

[bhobba]

So decoherence is no more evidence of collapse than any other outcome.

I have zero idea what you mean by that.

Technically decoherence explains how a superposition is converted into a mixed state. The mixed state gives the probability of each of its parts occurring. We can say that happened just after decoherence or at any point in the process until it reaches a conscious observer. We can even say it occurs at the conscious observer.

Thanks
Bill

 

[sophiecentaur]

Is there something you can give as an example of possible physics many millions years ago, compared to physics now?

The light arriving here from a very distant star could well have been produced by a 'Physical Process' that took place a million years ago. If Physics had been that different in those days, the spectrum of the light would hardly be expected to be the same as light we observe that's produced in a lab. Fact is that the spectral patterns of all the light we see from distant objects are exactly the same as from local sources. The only difference is the Red Shift and the observed red shift seems to tie in with predictions pretty well.
So we can be pretty happy that Physics has not changed since humans have been 'observing' it.

But people are a bit too hung up on the term "observer" as if it only implies a guy in a white coat with a microscope. The atom that gets changed -or not- by the effect of an incident electron or photon is just as much an 'observer'. I'd bet the originator of the term 'observer' would be turning in his / her grave if they realized that people had failed to spot what they were getting at whilst using the term. But anthropomorphism is alive and well at a place near where you live.

 

[sophiecentaur]

until it reaches a conscious observer

Why does an 'observer' need to be conscious for an effect to take place? I could ask just how 'conscious' an observer needs to be, in order to be rated as one. Is my Aunt, who knows no Physics, qualified to identify a wave function collapsing? Would someone need to have a PhD to qualify? Could my dog do it? I could train him to bark when he sees it happen and, that way, he could make me conscious of the event.

 

[Nugatory]

This would seem to position wave function collapse precariously close to the domain of philosophy.
Am I on the right track?

That's as good of a track as any, and better than most.

 

[.Scott]

I have zero idea what you mean by that.

Let me rephrase it more explicitly: decoherence, as an experimental outcome, is no more an indication of wave function collapse as any other experimental outcome.

Technically decoherence explains how a superposition is converted into a mixed state. The mixed state gives the probability of each of its parts occurring. We can say that happened just after decoherence or at any point in the process until it reaches a conscious observer. We can even say it occurs at the conscious observer.

In my last post, a point I was making is that we can even say that collapse happens well beyond the point of the conscious observer.

 

[bhobba]

Why does an 'observer' need to be conscious for an effect to take place?

Of course it doesn't.

It can occur anywhere in the Von Neumann chain.

Technically its when an improper mixed state becomes a proper one which can be anywhere. There is no way to tell because an improper mixed state and a proper one are observationally the same.

In modern times its placed just after decoherence - that's where I place it in my interpretation because it resolves many issues - but you don't have to place it there.

Thanks
Bill

 

[bhobba]

In my last post, a point I was making is that we can even say that collapse happens well beyond the point of the conscious observer.

Well there you face a real problem because once a conscious observer is involved by the definition of conscious they experience an outcome as the result of the act of observation.

Thanks
Bill

 

[bhobba]

I could ask just how 'conscious' an observer needs to be, in order to be rated as one. Is my Aunt, who knows no Physics, qualified to identify a wave function collapsing? Would someone need to have a PhD to qualify? Could my dog do it? I could train him to bark when he sees it happen and, that way, he could make me conscious of the event.

Of course.

The reason its mentioned in this context is historical dating back to Von Neumann's original analysis. The above is just one of the many issues it faces and why most, including me, reject it.

Thanks
Bill

 

[.Scott]

Well there you face a real problem because once a conscious observer is involved by the definition of conscious they experience an outcome as the result of the act of observation.

It's not a real problem at all. Part of some outcomes is the conscious experiencing of the outcome. If it's not a problem for a video signal, it shouldn't be a problem for brain activity. If you allow video signals to be superimposed, why not the conscious experience of a human observer?

 

[abrogard]

It was developed by Schroedinger as an intuitive leap using rather dubious mathematics:
http://arxiv.org/abs/1204.0653

Ever since Dirac came up with his transformation theory the wave-function was recognised as no longer fundamental:
http://www.lajpe.org/may08/09_Carlos_Madrid.pdf

What's going on in the delayed choice experiment is well known and has been discussed in many threads on the forum:
https://www.physicsforums.com/threa...and-the-delayed-choice-quantum-eraser.623648/
'Decoherence is irreversible only when caused by a LARGE number of degrees of freedom. A quantum eraser involves a small number of degrees of freedom, which is why it is reversible.'

Thanks
Bill

I can't get that Carlos Madrid .pdf. Would you happen to have another source for it, please?

 

[bhobba]

I can't get that Carlos Madrid .pdf. Would you happen to have another source for it, please?

See attached

Thanks
Bill

 

[bhobba]

It's not a real problem at all. Part of some outcomes is the conscious experiencing of the outcome. If it's not a problem for a video signal, it shouldn't be a problem for brain activity. If you allow video signals to be superimposed, why not the conscious experience of a human observer?

By conscious observer is meant, and rather obviously so, an observer like us. We never experience superpositions. But even aside from that decoherence converts superpositions into mixed states so there is never a superposition to experience anyway.

As explained previously the entire issue is when does an improper mixed state become a proper one.

Thanks
Bill

 

[abrogard]

See attached

Thanks
Bill

Got it. Thank you, Bill.

:)

 

[zonde]

We never experience superpositions.

This is faulty argument. Superposition isn't something you could experience.

P.S. I like the way stevendaryl put it: https://www.physicsforums.com/threads/decoherence-question.808491/page-2#post-5079618

 

[Nugatory]

Many off-topic digressions and pieces of random misinformation have been removed from this thread in an attempt to flog it into a fair summary of the current understanding and issues around the role of consciousness in QM, and into a sensible response to @nnope's original (and quite reasonable) question. At this point I think that we've covered most of the ground, especially in an I level thread, so I am leaving the thread closed.

I may have overreached and removed some posts that raise interesting points around this discussion. If so, I apologize and would encourage you to either start another thread or PM me or one of the other mentors asking them to reopen this thread so you can add your post back in. The posts have been hidden, not deleted, so if you want a copy of one of the deleted posts, you can ask for it via PM as well.