[Colin2B]

I think you are making this much more complex and esoteric than it needs to be.
Reread the last paragraph of Alan's last post. Experiments with sources which release single photons at a time show the characteristic build up of the interference pattern over time.
A big problem here comes from the use of the word observation which is really used in the context of interaction. A photon hitting a leaf interacts with the atoms in the leaf whether seen or not. We are only talking about single interactions at a time, the microphone you mention might pick up millions of interactions in the microsecond before it is destroyed, but observation refers only to the individual interactions.

In your final sentence you use the word waveform, do you mean wavefunction? This is only a description of the item's probability of position etc. When it collapses the probability is 1 for position, momentum etc. Imagine you have a deck of cards, before dealing the top card you can only say the probability of it being a particular card is 1/52, once the card is dealt the probability of it being a particular card is 1, it's wavefunction has collapsed.
The wavefunction of the observing mechanism will change with the interaction eg a photon hitting a photoelectric material will change the energy of an electron causing it to move, hence its wavefunction will change, it would only collapse if it too was detected.

[geordief]

I think you are making this much more complex and esoteric than it needs to be.
Reread the last paragraph of Alan's last post. Experiments with sources which release single photons at a time show the characteristic build up of the interference pattern over time.
A big problem here comes from the use of the word observation which is really used in the context of interaction. A photon hitting a leaf interacts with the atoms in the leaf whether seen or not. We are only talking about single interactions at a time, the microphone you mention might pick up millions of interactions in the microsecond before it is destroyed, but observation refers only to the individual interactions.

In your final sentence you use the word waveform, do you mean wavefunction? This is only a description of the item's probability of position etc. When it collapses the probability is 1 for position, momentum etc. Imagine you have a deck of cards, before dealing the top card you can only say the probability of it being a particular card is 1/52, once the card is dealt the probability of it being a particular card is 1, it's wavefunction has collapsed.
The wavefunction of the observing mechanism will change with the interaction eg a photon hitting a photoelectric material will change the energy of an electron causing it to move, hence its wavefunction will change, it would only collapse if it too was detected.

I see . So in my microphone scenario  we are ,in theory really just  talking about the interaction  between two particles in the explosion and any one particle in the microphone ?

Can I still ask if there is  a symmetry between these three objects so that (like perhaps in a three card trick) any one of the three can in principle play the role of "observer"

Yes my use if "waveform" instead of "wave function"  shows the  threadbare state of my knowledge in this area   but I feel  in my own mind I  am making some progress in my understanding (it feels like a lot to me  -a matter of scale of course       )

If  others can learn anything  from my misunderstandings and the clarifications/redirections  that would be the icing on the cake.

[Colin2B]

Can I still ask if there is  a symmetry between these three objects so that (like perhaps in a three card trick) any one of the three can in principle play the role of "observer"

Which 3 objects do you refer to?
If we take the case of a photon hitting a detector the photon ceases to exist, it is hard to imagine how this could be an observation from the point of view of the photon. Remember, we are talking about the collapse of the photon's wavefunction being detected.

Don't t worry about misunderstanding, we all started in the same place.

[geordief]

Which 3 objects do you refer to?
If we take the case of a photon hitting a detector the photon ceases to exist, it is hard to imagine how this could be an observation from the point of view of the photon. Remember, we are talking about the collapse of the photon's wavefunction being detected.

Don't t worry about misunderstanding, we all started in the same place.

Well it would be the photon , the particle on the screen impacted and the first particle in the detector that received information about the event(if that is the right term )

 I see that there is an asymmetry in term of time (the detector is later than the other two ) and so my "threesome" scenario seems to have failed on that count anyway:(

What about a twosome?(the photon and the particle on the screen) Are they  equal partners? Do they both see their wavefunction collapse at the same time  dependent on a third party involvement albeit postponed in time?

[Colin2B]

What about a twosome?(the photon and the particle on the screen) Are they  equal partners? Do they both see their wavefunction collapse at the same time

If the photon is detected by the movement of an electron in the detector then the photon ceases to exist and the electron acquires energy hence its wavefunction will change (not collapse), eg it could become a free electron.
Don't get too hung up over this idea of the wavefunction collapsing, it is only a description of probability not a causative. It's like saying a car has hit a brick wall so it's speed has collapsed, the car does not hit the wall because it's speed collapsed. There is nothing magical about this.

[nilak (OP)]

In the delayed choice quantum eraser the photon is basically detected without any interaction or any energy lossless. The which way path is determined observing its twin. The problem is that since the twin pair is entangled when you do a measurement on one photon it affects the other. Now here comes another trick. They let the first twin hit the screen, and let the other free to fly further without any measurement. After a while ( some ten ns) they decide to make a measurement. Guess what? The photon goes back im time and takes a the route they actually detected.
My opinion is that for some reason photons that interfere cannot be detected and when they reach the screen they are filtered as background radiation.
The fact that the observer disturbs the measurement is acceptable. The measurement on the twin particle disturbing the interference is very weird, plus  entanglement we know  is about the spin not the wavefunction. But then photons going back im time or predicting the future! ? That is almost absurd. But if it is actually what happens then the implications get very exciting.

[alancalverd]

the photon is basically detected without any interaction

Amazing. Please describe a detector that does not require any interaction or energy exchange with the object detected. (Remember to patent your device before publication).

Here's a simple event. Hydrogen fuses to produce helium and releases several gamma rays at once from the sun. An observer on earth detects some gamma radiation 8 minutes later. An observer on Mars sees some 15 minutes later. An observer orbiting Betelgeuse sees one 650 years later. How did the hydrogen atoms know when to fuse?

[nilak (OP)]

the photon is basically detected without any interaction

Amazing. Please describe a detector that does not require any interaction or energy exchange with the object detected. (Remember to patent your device before publication).

the photon is split in two after passing the slits by a barium borate crystal. Then chosing to detect or not one twin changes the wavefunction of the other. Simultaneity is not required.

Here's a simple event. Hydrogen fuses to produce helium and releases several gamma rays at once from the sun. An observer on earth detects some gamma radiation 8 minutes later. An observer on Mars sees some 15 minutes later. An observer orbiting Betelgeuse sees one 650 years later. How did the hydrogen atoms know when to fuse?

Sorry, I can't see the analogy of your example with the DCQE experiment.

[alancalverd]

One photon in, two photons out, means that energy has been exchanged. But suppose that we have in fact generated two photons each with half the initial energy. Detect one, and you have absorbed half the energy.

MY example demonstrates that simultaneity of event and observation is not requied.

[nilak (OP)]

... Another is the introduction of "consciousness" into discussions of science, particularly if it is used without definition...

We don't quite need a good definition. It is simply a human watching a result on a display of a detector versus s  not watching the display but detector and display still plugged working.

Ps.
The fist simplistic definition useful im QM context was stated by Neumann. It basically says, that a device can make a measurement and then display the result. To read the result, you can use another device but it will still display its own measurement and so on. Human are capable of doing the measurement, but also to be selfaware of their own measurements. However, there are more recent experiments which demontrate that the wavefunction collapses when the "which way" is determinable regardless of a human mind being aware of the measurement.

[nilak (OP)]

One photon in, two photons out, means that energy has been exchanged. But suppose that we have in fact generated two photons each with half the initial energy. Detect one, and you have absorbed half the energy.

MY example demonstrates that simultaneity of event and observation is not requied.

I understand something elese from this experiment.
Imagine you let a snowball roll down a hill. There are two initial ditches (A and B) that lead to two gates. Each gate is fitted with a blade that cuts the ball into two equal parts. Then they roll down through one of  another 4 short ditches (d1 and d2 for Gate A and also e1 and e2 for B) then the ditches become flat. Down lower at 100m there are two gates (GAand GB) that catch the ball if the ball went  through d1 or e1. The other half goes through d2 or e2 and after 200m reaches a man, at a position m2 for path A or another man n2 if it came through path B. The man that is at m2 or n2 is not allowed to whatch the ball until it reaches him. If the man at m2 or n2 decides to watch the ball then the other ball always gets caught into GA or GB.Otherwise they spread out all over the place.
For path A the ball will always get to man m2 and for path B always to man at n2.
For me the fact that the ball is split into two makes no difference anymore because it doesn't influence  the which path at all.