Really naive question about the observer effect in QM

[PyramidHead]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

What, in short, is the operational definition of an 'observer' for the purposes of QM?

 

[Malintent]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

What, in short, is the operational definition of an 'observer' for the purposes of QM?

Yes, that is my understanding. "Observation" is influential due to the instrumentation of the observation. But I could be as 'naive" as you

 

[barbos]

That is The Question.
there are no theories, there are different interpretation.
Prevailing one among people who are concerned with The Question is Many World Interpretation (MWI)
Standard interpretation is Copenhagen Interpretation (CI) which is very minimalistic and does not really try to answer The Question. I am a MWI guy.

 

[PyramidHead]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

What, in short, is the operational definition of an 'observer' for the purposes of QM?

Yes, that is my understanding. "Observation" is influential due to the instrumentation of the observation. But I could be as 'naive" as you

But there are presumably detectors that don't directly contact the particle, right? And in the quantum eraser experiment, the wave function is restored by permanently destroying the information collected by the detector, which indicates to me that something other than bumping into the photon and knocking it off course is involved.

 

[barbos]

Yes, that is my understanding. "Observation" is influential due to the instrumentation of the observation. But I could be as 'naive" as you

But there are presumably detectors that don't directly contact the particle, right?

No, there are no such detectors.

And in the quantum eraser experiment, the wave function is restored by permanently destroying the information collected by the detector, which indicates to me that something other than bumping into the photon and knocking it off course is involved.

Quantum "eraser" experiments are subjects of interpretation. They don't really do what they claim to do.

 

[PyramidHead]

But there are presumably detectors that don't directly contact the particle, right?

No, there are no such detectors.

True, that should have occurred to me. But the detectors all interact with the particle after it has passed through the slits.

 

[barbos]

No, there are no such detectors.

True, that should have occurred to me. But the detectors all interact with the particle after it has passed through the slits.

Does not matter

 

[PyramidHead]

True, that should have occurred to me. But the detectors all interact with the particle after it has passed through the slits.

Does not matter

It does for my original naive idea, that the detector bumps or jostles the particle in some way thereby changing its behavior. But I am aware of the causality implications suggested by some experiments where they have tried to isolate this (delayed choice).

Anyway, my main purpose in asking about this is to understand whether consciousness is even required. A lot of people seem to think the observer effect has something profound to say about consciousness. But if unconscious mechanical detectors can stand in for conscious beings, then they are all talking a bunch of bullshit.

 

[Malintent]

well, information is meaningless without a consciousness to consume it. If there is indeed reason to believe that erasing information "uncauses" things in the past without the need to interact with the particles in question, then I would think consciousness would have to be involved in the phenomena. However, I do not believe that is or can be the case. I will read up on 'quantum eraser" as best as I can, but I suspect this 'information' that is destroyed is more likely the 'thing' itself, rather than an external accounting of "the thing".

 

[barbos]

Nothing is being erased in these experiments, simply because nothing is measured yet to be erased.

 

[Bomb#20]

But there are presumably detectors that don't directly contact the particle, right?

Right. It's called "Interaction-free measurement".

More precisely, there are detectors that have some non-zero probability of detecting the particle without contacting it -- there's always some chance of failing to detect it and some chance of contacting it. How high a probability of detecting it without contacting it can be achieved is a subject of active research. In theory it can be arbitrarily close to 100%; in practice there are all manner of engineering obstacles to this.

 

[Bomb#20]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Answers to that question are worth 2 cents. Answers to that question that include empirical evidence are worth 8 million krona from the Nobel Foundation.

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

Not really. It's a quantum effect; and in Newtonian physics you can't observe a particle without obstructing its path somehow.

What, in short, is the operational definition of an 'observer' for the purposes of QM?

There isn't any. It's one of the great embarrassments of quantum theory. Two formulas for what's going to happen; they disagree with each other; and the theory won't tell you when to use one and when to use the other. In practice it's not much of a problem -- you normally get the same answer whether you assume the detector is part of the observer or not -- hence the infamous "Shut up and calculate" interpretation.

 

[barbos]

But there are presumably detectors that don't directly contact the particle, right?

Right. It's called "Interaction-free measurement".

More precisely, there are detectors that have some non-zero probability of detecting the particle without contacting it -- there's always some chance of failing to detect it and some chance of contacting it. How high a probability of detecting it without contacting it can be achieved is a subject of active research. In theory it can be arbitrarily close to 100%; in practice there are all manner of engineering obstacles to this.

That's not quantum mechanical measurement, that can be called "determination"
Bomb is a macroscopic system and you are not measuring its quantum state here, merely macroscopic shape.
Simpler variant of that experiment would be determining the shape of some perfectly reflecting figurine using interferometer.

 

[Treedbear]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

What, in short, is the operational definition of an 'observer' for the purposes of QM?

Coincidentally I was just watching a video on TV from the "Closer to Truth" series by Robert Lawrence Kuhn entitled "Observing Quanta, Observing Nature" about the 2016 meeting of the Foundational Questions Institute (FQXi) in Banff, Canada. It's members include scientists as well as philosophers including Paul Davies and David Chalmers, both of whom he interviewed for the episode. His talk with Davies was interesting to me. As Kuhn said, Davies "makes consciousness fundamental." To paraphrase Davies: Acts of observation not only effect what happens in the future, but in some sense, constrains what happens in the past. He attributes this idea to John Wheeler and his delayed-choice experiment. It looks like retro-causation, but we're constraining the nature of the past that was. When we do our observation we reduce the number of pathways that exist. The emergence of conscious beings today is fundamental to the actual workings of the universe.

I myself am still very skeptical of consciousness per se as having any effect on anything outside of the direct influence of the brain's neurons. To me it seems more likely that the conscious choice to do an experiment in one particular way is the deterministic result of the past chain of events. And while the fact that we make that choice doesn't identify any particular pathway, it could be thought of in the quantum world as limiting the number of paths, i.e.; making the image less fuzzy. Let's not forget the experimental results always need to be interpreted as the average of many events.

But I like the idea of an event in the present reflecting a probability of something having happened in the past. It's really similar to what normally goes for cause and effect. Since the laws of physics are considered to be equally valid for either direction of time why shouldn't we think of an observation as influencing the past? It might reflect a kind of inverse MWI(?).

So that's my long and really naive answer.

 

[PyramidHead]

What is the prevailing theory on the mechanism behind the observer effect in quantum mechanics? To put it another way, what is the critical component of 'observation', itself a vague and wide-reaching concept, that is necessary/sufficient to collapse the wave function in e.g. a double slit experiment?

I know it doesn't have to be a human observer, as a detector will do the same thing (or will it just appear to when a human later checks the results of the detector?).

Does it have anything to do with the fact that particles can't be observed without either absorbing them or obstructing their path somehow?

What, in short, is the operational definition of an 'observer' for the purposes of QM?

Coincidentally I was just watching a video on TV from the "Closer to Truth" series by Robert Lawrence Kuhn entitled "Observing Quanta, Observing Nature" about the 2016 meeting of the Foundational Questions Institute (FQXi) in Banff, Canada. It's members include scientists as well as philosophers including Paul Davies and David Chalmers, both of whom he interviewed for the episode. His talk with Davies was interesting to me. As Kuhn said, Davies "makes consciousness fundamental." To paraphrase Davies: Acts of observation not only effect what happens in the future, but in some sense, constrains what happens in the past. He attributes this idea to John Wheeler and his delayed-choice experiment. It looks like retro-causation, but we're constraining the nature of the past that was. When we do our observation we reduce the number of pathways that exist. The emergence of conscious beings today is fundamental to the actual workings of the universe.

I myself am still very skeptical of consciousness per se as having any effect on anything outside of the direct influence of the brain's neurons. To me it seems more likely that the conscious choice to do an experiment in one particular way is the deterministic result of the past chain of events. And while the fact that we make that choice doesn't identify any particular pathway, it could be thought of in the quantum world as limiting the number of paths, i.e.; making the image less fuzzy. Let's not forget the experimental results always need to be interpreted as the average of many events.

But I like the idea of an event in the present reflecting a probability of something having happened in the past. It's really similar to what normally goes for cause and effect. Since the laws of physics are considered to be equally valid for either direction of time why shouldn't we think of an observation as influencing the past? It might reflect a kind of inverse MWI(?).

So that's my long and really naive answer.

I saw a bit of the Chalmers talk you are referring to, I think. What bugs me about that idea is that consciousness is a very late emergence in the universe, so far as we know. If everything was in a blurry superposition before the first conscious being (probably an animal) observed it, and then it all just suddenly solidified into place, wouldn't that event have effects that we could observe today? Or is it just a fantasy theory with no empirical predictions?

 

[Treedbear]

...
I saw a bit of the Chalmers talk you are referring to, I think. What bugs me about that idea is that consciousness is a very late emergence in the universe, so far as we know. If everything was in a blurry superposition before the first conscious being (probably an animal) observed it, and then it all just suddenly solidified into place, wouldn't that event have effects that we could observe today? Or is it just a fantasy theory with no empirical predictions?

You would think it would leave some milestone in the evolution of the universe. But then again nothing actually would have "happened" until the first conscious event. But my opinion is we don't yet understand what we mean by consciousness and its role as it effects living things. It's not an objective understanding anyway. Perhaps consciousness emerged gradually and it must be understood as having a range of complexity. Actually complexity may be the key feature of how its effect on probabilities is magnified. Every choice the brain makes involves thousands of smaller choices, further limiting the number of pathways.

 

[PyramidHead]

That also relates back to the topic of the thread. How conscious does an observer have to be in order to collapse a wave function? We know that consciousness is a spectrum, but in the double slit experiment there's either an interference pattern or not (I again assume naively, is this actually the case?). Does observation depend on understanding what is observed? Can a dolphin collapse the wave function? Can wave function collapse be used as a diagnostic test to figure out if something is conscious?

 

[Treedbear]

That also relates back to the topic of the thread. How conscious does an observer have to be in order to collapse a wave function? We know that consciousness is a spectrum, but in the double slit experiment there's either an interference pattern or not (I again assume naively, is this actually the case?). Does observation depend on understanding what is observed? Can a dolphin collapse the wave function? Can wave function collapse be used as a diagnostic test to figure out if something is conscious?

Perhaps. If intelligence is related to complexity than higher intelligence might produce a higher probability of wavefront collapse. Ergo more distinct interference pattern. But might it depend on the observer with the highest degree of intelligence? A dolphin might get one result, but if a human being observes the dolphin's reaction the result might be more distinct.

 

[Bomb#20]

Right. It's called "Interaction-free measurement".

More precisely, there are detectors that have some non-zero probability of detecting the particle without contacting it -- there's always some chance of failing to detect it and some chance of contacting it. How high a probability of detecting it without contacting it can be achieved is a subject of active research. In theory it can be arbitrarily close to 100%; in practice there are all manner of engineering obstacles to this.

That's not quantum mechanical measurement, that can be called "determination"

They're preparing a particle in a superposed state and seeing what detector it shows up in. How do you figure that isn't a quantum mechanical measurement?

Bomb is a macroscopic system and you are not measuring its quantum state here, merely macroscopic shape.
Simpler variant of that experiment would be determining the shape of some perfectly reflecting figurine using interferometer.

Macroscopic systems are made of microscopic systems. Do you know of any theoretical reason for why you can measure a septillion-atom object without interacting with any of those atoms, but you can't measure a one-atom object without interacting with that atom?

 

[ryan]

What, in short, is the operational definition of an 'observer' for the purposes of QM?

A really short explanation is anything that causes quantum decoherence. Exactly what causes decoherence is probabilistic. Quantum computers must be as close to absolute 0 as possible because even a little heat radiation can increase the probability of decoherence or the "collapse of the the wave function".

See https://plato.stanford.edu/entries/qm-decoherence/ .