Please please please, mainstream answers only. Even if you think mainstream QM is wrong and disagree with the Copenhagen interpretation, I want to understand what it says.
It may be that you can answer my headline question without addressing all the bits in my long ramble which follows, in which case please do...
I'm an engineer not a scientist. So I understand things in a scientific way to a large extent but I never studied QM at University.
I have read and watched a lot of stuff about QM aimed at the layman and given that none of it makes any sense, I think I have a passing grasp of some of the principals. The one key part I can't understand is "what constitutes measurement / detection / observation?"
The reason I can't pin this down it that the believable sources of information like professors of physics tend to describe it very briefly and move on, without really addressing the questions it raises for me. Then I look on YouTube or whatever and search around for more information but the only people who address the issue directly (for the layman) seem to have personal view points which they are expounding and no credibility.
It seems that people, including me, are very confused about if it is human consciousness which needs to see the observations, or just that information has been recorded.
So for instance:
In the Young's double slit experiment it is found that detecting which slit a particle went through collapses the wavefunction and we no longer get an interference pattern.
I want to understand, what is the crucial part of the detection process. Detection or knowing the result.
So if I set up the detector and it increments a counter every time a particle goes through one slit and I record the hit of every particle on the screen, this is a standard version of the experiment which collapses the wavefunction.
**So what happens if we leave the detector there but disconnect the counter?**
Assume that we can only tell detections by looking at the counter and that the detector itself essentially returns to the same state after detection, so we can't get information out of it afterwards.
Does this still collapse the waveform? The particle has been forced to interact with the detector, so does that make the detector part of the wavefunction too? There is plenty about this on the net but unfortunately there is no consensus view, even though there will be a consensus view in standard QM.
**What happens if: we record all the events but don't look at them for a long while, then we erase the slit detection information, then we look at the screen hit detection?**
It is different to if we didn't erase the slit detection information?
This is similar to the quantum eraser experiments which indicate that erasing the information is equivalent to not dong the detection. But what interest me here is the quantum eraser experiments are complex and only deal with small times. Why have they been done like this? Is it because erasing the information is actually more than it sounds? Does 'erase' actually mean putting the universe into a state which identical for either slit having been used? If we printed the counter results onto paper as they happened it is already too late to erase them because the information has already had an effect on the macro universe and even if we burn the paper without looking at it, that effect is still in our universe?
Asking these questions it all seems silly because they are all pretty much like asking, what if we build a working detector but don't look at it. And it seems fairly likely that not looking at the detector cant affect the results. But then again, this is QM.