How non-conscious can an Observer be and cause wave function collapse?

[pholmes]

TL;DR Summary

Can a mere broken sensor, or not-wired-up sensor, or results never looked at "Consciously" by anyone, still cause "consciously indisputable" wave function collapse?

Please help me find websites describing easy to understand experiments discovering how little of a Conscious Observer is needed to cause wave function collapse?

Is just a sensor, that "could have been" attached to a reporting device, that "could have been" looked-at by a Conscious Human, enough?

What if that sensor's wires leading to the first stage of amplification were clipped by wire cutters?

If that still causes wave function collapse, then "a conscious observer" is not needed, it would seem.

I have heard it said: "But you could never know, so it is not possible to know if detached or broken sensor is enough."
That might be true in the Schrodinger's Cat experiment, but in the Double Slit experiment with sensors in the slits, there is a 2nd independent form of "observation" that I think everybody agrees doesn't cause the de-coherence, even if well observed by humans.

In the double slit experiment, you could successively have less and less "Observing" of which slit the electron went through, while still doing full human observing of the target screen where you either get an interference pattern from the 2 slits, or you don't.

This is such a simple obvious experiment, that I am sure it has been done.
Do you know what the result is?
What are some good internet sites for this?
All I have found is super-complicated modern experiments that I don't understand. This should be simple.

 

[PeterDonis]

The short answer to your title question is that consciousness is not required at all for a measurement to take place. ("Measurement" is a better term here than "wave function collapse" since what exactly the latter means is interpretation dependent, and discussion of QM interpretations belongs in the interpretation subforum, not here.) What is required, as we now understand, is decoherence.

In the double slit experiment, you could successively have less and less "Observing" of which slit the electron went through, while still doing full human observing of the target screen where you either get an interference pattern from the 2 slits, or you don't.

This is such a simple obvious experiment, that I am sure it has been done.

Yes, it has, with polarizers at each slit whose direction can be adjusted. We have had previous PF threads on this. @DrChinese can probably give a reference to a paper describing such an experiment.

 

[PeroK]

TL;DR Summary: Can a mere broken sensor, or not-wired-up sensor, or results never looked at "Consciously" by anyone, still cause "consciously indisputable" wave function collapse?

Please help me find websites describing easy to understand experiments discovering how little of a Conscious Observer is needed to cause wave function collapse?

Just to emphasise that wave function collapse is not a physical process, but part of some interpretations of QM.

Is just a sensor, that "could have been" attached to a reporting device, that "could have been" looked-at by a Conscious Human, enough?

The idea that conscious human beings are required to support QM is an old misconception, that seems to be kept alive inexplicably.

What if that sensor's wires leading to the first stage of amplification were clipped by wire cutters?

If that still causes wave function collapse, then "a conscious observer" is not needed, it would seem.

It's not in any case.

I have heard it said: "But you could never know, so it is not possible to know if detached or broken sensor is enough."
That might be true in the Schrodinger's Cat experiment, but in the Double Slit experiment with sensors in the slits, there is a 2nd independent form of "observation" that I think everybody agrees doesn't cause the de-coherence, even if well observed by humans.

In the double slit experiment, you could successively have less and less "Observing" of which slit the electron went through, while still doing full human observing of the target screen where you either get an interference pattern from the 2 slits, or you don't.

You get a mixture of the patterns if you observe some electrons and not others.

 

[PeroK]

... while still doing full human observing of the target screen ...

In any scientific experiment, if you want to confirm the results correctly match the theory, you must look at the results. QM is clear that the result of the experiment is on the screen, regardless of whether any human looks at it or not.

Similarly Schrodinger's cat is either alive or dead inside the box. It's not in a superposition. This was Schrodinger's point. In this case, however, it isn't so easy to understand or show mathematically that that is what QM predicts! The modern explanation of how QM predicts the un-superposed cat involves a concept known as decoherence.

 

[PeterDonis]

The modern explanation of how QM predicts the un-superposed cat involves a concept known as decoherence.

To be clear, decoherence does not show how QM predicts the un-superposed cat in a single state, either alive or dead. QM does not predict single outcomes; the best it can do is predict probabilities for the different possible outcomes.

What decoherence does is to make it clear that the "alive" and "dead" states of the cat do not interfere with each other, so it is not correct to think of the cat as "in a superposition of alive and dead" in any way that could be shown by experiment, as doing that would require quantum interference between those two states. But decoherence by itself cannot predict a single outcome; it can only, as above, explain why we can assign probabilities to the different possible outcomes instead of probability amplitudes (which would only be needed if interference were possible).

 

[PeroK]

To be clear, decoherence does not show how QM predicts the un-superposed cat in a single state, either alive or dead. QM does not predict single outcomes; the best it can do is predict probabilities for the different possible outcomes.

That there are probabilities involved in the either/or goes without saying.

 

[Lord Jestocost]

TL;DR Summary: Can a mere broken sensor, or not-wired-up sensor, or results never looked at "Consciously" by anyone, still cause "consciously indisputable" wave function collapse?

Please help me find websites describing easy to understand experiments discovering how little of a Conscious Observer is needed to cause wave function collapse?

Freeman Dyson in “The Collapse Of The Wave-Function” in John Brockman’s book “This Idea Must Die: Scientific Theories That Are Blocking Progress (Edge Question Series)” (New York, NY, USA: HarperCollins (2015)):

“Fourscore and eight years ago, Erwin Schrödinger invented wave functions as a way to describe the behavior of atoms and other small objects. According to the rules of quantum mechanics, the motions of objects are unpredictable. The wave function tells us only the probabilities of the possible motions. When an object is observed, the observer sees where it is, and the uncertainty of the motion disappears. Knowledge removes uncertainty. There is no mystery here.

Unfortunately, people writing about quantum mechanics often use the phrase “collapse of the wave function” to describe what happens when an object is observed. This phrase gives a misleading idea that the wave function itself is a physical object. A physical object can collapse when it bumps into an obstacle. But a wave function cannot be a physical object. A wave function is a description of a probability, and a probability is a statement of ignorance. Ignorance is not a physical object, and neither is a wave function. When new knowledge displaces ignorance, the wave function does not collapse; it merely becomes irrelevant.” [Bold by LJ]

 

[A. Neumaier]

a probability is a statement of ignorance.

This sentence does not state a fact but an interpretation issue, and belongs to the subforum.

A probability is much more correctly viewed as an informative fact about an ensemble, valid approximately for a statistical sample. Indeed, physicists publish tables of probabilities for the various pathways unstable particles or nuclide can decay, and these numbers are as factual as the nuclide masses, say. For example, in Wikipedia, one can read:

Some radionuclides may have several different paths of decay. For example, 35.94(6)% of bismuth-212 decays, through alpha-emission, to thallium-208 while 64.06(6)% of bismuth-212 decays, through beta-emission, to polonium-212. Both thallium-208 and polonium-212 are radioactive daughter products of bismuth-212, and both decay directly to stable lead-208.

 

[DrChinese]

The short answer to your title question is that consciousness is not required at all for a measurement to take place. ("Measurement" is a better term here than "wave function collapse" since what exactly the latter means is interpretation dependent, and discussion of QM interpretations belongs in the interpretation subforum, not here.) What is required, as we now understand, is decoherence.Yes, it has, with polarizers at each slit whose direction can be adjusted. We have had previous PF threads on this. @DrChinese can probably give a reference to a paper describing such an experiment.

@pholmes:

A conscious observer is not required to cause the pattern to switch from interference to no interference. The experiment below demonstrates this nicely - although a bit of theory is required.

Polarizers are placed in front of each slit, and they can be aligned parallel or perpendicular. When parallel, no useful information is present in the polarization of photons passing though each slit; interference is enabled. When perpendicular, the polarization of photons passing through is essentially marking which slit the photons go through. Keep in mind that at no time is that marker actually looked at. The mere possibility of obtaining that information is enough to eliminate the interference. The only variable here is the orientation of the polarizers relative to each other. Obviously, the presence of a conscious observer has nothing to do with the outcomes and the presence or absence of interference.https://sciencedemonstrations.fas.h...-demonstrations/files/single_photon_paper.pdf

 

[pholmes]

Thanks for many helpful replies.

I know it's been 6 days, I can't always engage with threads every 2 days. I should probably mark myself as "High School level" instead of college level. Even though briefly a Physics Major in college before switching to EE, I never took the Modern Physics class they offered, and I am not in school now.

I'm hearing from what you have said:

* Don't think "Collapse of Wave Function", think "Measurement".

* Measurement doesn't need any "Conscious Measurement" to have its full effect (contradicting much lightweight discussion on the internet). I was listening to an old Richard Feynman lecture where he was very engaging saying "It does A when you're looking, but does B when you aint looking!" I assume he knew better, and was talking loosely.

* Measurement can have its full affect of interfering with that which is measured, even if the measurement device doesn't even lead to any no-human mechanical or electrical storage of the information. So my example of sensors on each of the 2 slits, that could be used increment 2 counters, recording a very high percentage of the electrons passing through the slits, would still kill the interference pattern if the wires between sensors and counters were clipped with wire cutters.

That book: "Scientific Theories That Are Blocking Progress" sounds super interesting. I'm curious what other bad theories are in it!

 

[PeterDonis]

* Don't think "Collapse of Wave Function", think "Measurement".

Or even better, think "Decoherence". That way you don't have to bring in any of the connotations of "measurement" that are lurking behind your other two points. If you substitute "Decoherence" for "Measurement" in those points, it is obvious that you don't need "consciousness" and you don't need any information storage in a retrievable way.

 

[pholmes]

Oh yes, my first bullet * was wrong, should be "Decoherence" instead of "collapse of wave function".

Measurement would be a cause, Decoherence would be an effect.

Now I am seeing there was a thread back in December 2022 "Can we all agree consciousness is not required to collapse wave function".... and many others. Before asking a question like this, I should search several different wordings of what I want to ask about. And even though I just want straight-up actual experimental results, I should see if the subject is discussed in "Quantum Interpretations and Foundations" too.

But now I see someone asked back in 2021: "

Wave Function Collapse using faulty recording devices."​

and got the opposite answer from what I am getting so far in this thread. ... that they would not cause it.

I bet the exact details of how the recording device is "faulty" makes a huge difference in whether it still causes Decoherence. If somebody smeared the "business end" of the device, right next to the slit, with the substance with which you make the sides of non-measured slits, then I would assume Decoherence would not happen. By contrast, if you clipped the wires between sensor and counter, clipping those wires at a point one inch away from the slit, then I would assume Decoherence still happens.

This begs the question, exactly what causes Decoherence. If I am shooting electrons through a double slit, and right next to one of the slits I have little blob of iron with some resistant, or carbon, or a 1/4 inch long copper wire, something that's not even trying to be a sensor, just nearby junk, which the electrons have to fly by really close, will that cause Decoherence because a tiny blip of electrical current got induced in that bit of metal?

 

[PeterDonis]

Measurement would be a cause, Decoherence would be an effect.

No, decoherence is not an effect of measurement. Decoherence is a necessary requirement for a measurement. In other words, all measurements involve decoherence. But not all instances of decoherence are measurements.

This begs the question, exactly what causes Decoherence.

The short answer is, interaction with the environment--which just means any system with a very large number of degrees of freedom that cannot be individually tracked.

For a longer answer you can search these forums for previous threads on decoherence. In them you will find multiple references to discussions of decoherence in the literature.

 

[PeterDonis]

If I am shooting electrons through a double slit, and right next to one of the slits I have little blob of iron with some resistant, or carbon, or a 1/4 inch long copper wire, something that's not even trying to be a sensor, just nearby junk, which the electrons have to fly by really close, will that cause Decoherence because a tiny blip of electrical current got induced in that bit of metal?

Your description is too imprecise to answer this question. It would depend on many factors, most of which probably cannot be controlled experimentally to sufficient accuracy to test such a thing.

 

[gavin25]

In QM and QFT the best interpretation is "Shut up, and Calculate". :-D

 

[pholmes]

We're not talking about calculation here. I'm talking about overall behavior in the experiment. Take a double-slit with electrons being sent through causing a nice visible interference pattern on the detection screen some distance behind the slits. First I'll list what I think people are saying, then the last one is what I have a question about:

(a) Measurement devices are placed on one or more of the slits that do a good job of counting 98% of the electrons that go through, reporting to a conscious observer how many went through slit-A ... interference pattern Gone.

(b) Measurement device does good job of counting how many went through slit-A, but no conscious observer views the physically-large number on the counter, which then clears to zero automatically 5 hours later. ... interference pattern Gone.

(c) Same Measurement device as above is on slit-A, but no counter is wired to it. ... interference pattern Gone.

(d) Same Measurement device, no counter, and no electric power provided to the overall measurement device electronic circuit, and the way the measurement device is designed, and was designed in the above cases too, is there's a tiny sensitive part right on the slit, that responds to electrons going through with a tiny (by macro physics standards) electric current pulse, that leads to a powered amplification first stage 1/10 mm away, that causes a larger electric current pulse to move further away from the slit in other electronics. The first sensitive part right on the slit has no difference in voltage or current in it depending on whether the amplification stages have power or not ... interference pattern Gone. (I think)

So, I think I am hearing ... not only is there no need for "conscious observer" to cause decoherence, as discussed in so many other threads in this forum, but no need for an AI or computer observer, as discussed in a thread, no need for a known retained record of the information, that may or may not be looked at later.

Not only that, there's no need for "Measurement" that could result in "Information", to cause decoherence. (or am I going to far in that one?)
Or would you say "measurement is not needed, but information getting out IS needed"?

So, what is the actual thing or action or interaction that is the minimal "whatever" that causes the decoherence?

I read on the internet. If you doubt me I'll go search again, find it: That it's a "non-elastic interaction" with something or some material on the side of the slit, which would be the minimal decoherence cause.

Certainly you can have some electrons change their path as they pass through the slits, and still get an interference pattern on the screen. It seems that way to me because a fair amount of the interference pattern is not located in a straight line from the electron source through either of the slits. But if an electron gets slowed down by wiggling an atom that part of the side of the slit, in a non-bounce-back-the-energy manner, losing a bit of energy to slit structure atoms, that would seem like enough to spoil the interference pattern.

Is that what's going on in the minimal interference case?

 

[PeterDonis]

(a) Measurement devices are placed on one or more of the slits that do a good job of counting 98% of the electrons that go through, reporting to a conscious observer how many went through slit-A ... interference pattern Gone.

Yes. (I'm assuming that by "measurement device" you mean "something that causes decoherence".)

(b) Measurement device does good job of counting how many went through slit-A, but no conscious observer views the physically-large number on the counter, which then clears to zero automatically 5 hours later. ... interference pattern Gone.

Yes.

(c) Same Measurement device as above is on slit-A, but no counter is wired to it. ... interference pattern Gone.

Yes.

(d) Same Measurement device, no counter, and no electric power provided to the overall measurement device electronic circuit, and the way the measurement device is designed, and was designed in the above cases too, is there's a tiny sensitive part right on the slit, that responds to electrons going through with a tiny (by macro physics standards) electric current pulse, that leads to a powered amplification first stage 1/10 mm away, that causes a larger electric current pulse to move further away from the slit in other electronics. The first sensitive part right on the slit has no difference in voltage or current in it depending on whether the amplification stages have power or not ... interference pattern Gone. (I think)

Yes. Here you've just given more elaborate detail on how the measurement device causes decoherence (through the amplification process).

So, I think I am hearing ... not only is there no need for "conscious observer" to cause decoherence, as discussed in so many other threads in this forum, but no need for an AI or computer observer, as discussed in a thread, no need for a known retained record of the information, that may or may not be looked at later.

Yes. All that is required is decoherence, and decoherence can occur without any of those other things occurring. (Note that the "information" about what happened is not destroyed, even if no readable record is made; the information is just dispersed into the environment.)

Not only that, there's no need for "Measurement" that could result in "Information", to cause decoherence. (or am I going to far in that one?)

It depends on what you mean by "information". See my comments on the last case above.

Or would you say "measurement is not needed, but information getting out IS needed"?

Again, see my comments on the last case above.

what is the actual thing or action or interaction that is the minimal "whatever" that causes the decoherence?

It depends on the particular situation. You don't even need a "measuring device" to cause decoherence. Macroscopic objects are constantly decohering themselves and being decohered by interactions with the environment--light falling on them, air brushing against them, etc., etc. None of these decoherence processes result in any "measurement result", except in the sense that they explain why macroscopic objects behave classically and don't show quantum interference effects.

I read on the internet. If you doubt me I'll go search again, find it: That it's a "non-elastic interaction" with something or some material on the side of the slit, which would be the minimal decoherence cause.

The issue with "I read on the internet" isn't a matter of "doubt". It's a matter of having a valid basis for discussion. For that we need to see the source you got this from.

Certainly you can have some electrons change their path as they pass through the slits

If the electrons are not measured, they don't even have a well-defined "path". The reason there is an interference pattern is not that "some electrons don't take the straight line path". It is that each individual electron's wave function goes through both slits and interferes with itself on the other side. Electrons are not little billiard balls that follow some particular path only we don't know what it is. They don't have a well-defined path at all unless we measure one.

Is that what's going on in the minimal interference case?

Not really, no. "Slowing down the electron" is not a good way to think about how decoherence removes the interference pattern.

 

[DrChinese]

But if an electron gets slowed down by wiggling an atom that part of the side of the slit, in a non-bounce-back-the-energy manner, losing a bit of energy to slit structure atoms, that would seem like enough to spoil the interference pattern.

Is that what's going on in the minimal interference case?

Focusing on just the slit edge issue: The edge has virtually nothing whatsoever to do with "spoiling". You actually already know this, as interference occurs in the first place - which it wouldn't if the edge were an issue.

The slit shape primarily determines the shape of each of the bars that appear on the screen. For example: were the slits of a diamond shape, the bars would be diamond shaped.

I had a good reference showing this visually, but can’t locate it…

 

[kith]

So, what is the actual thing or action or interaction that is the minimal "whatever" that causes the decoherence?

In interference experiments with quantum particles, the interference pattern is built up by the detection of many particles (see Wikipedia for a picture). In principle, a single scattering event of a beam particle with a background gas particle is enough to change the detection probability for a single particle. But if you only have a few particles which interact and many particles which don't, the impact on the overall pattern is negligible.

The way decoherence looks like in a real experiment is this: as you increase the pressure of the background gas, the visibility of the interference pattern is reduced. If you could start with a perfect vacuum (i.e. pressure zero), you would have no decoherence and perfect visibility. If you gradually increased the background gas pressure to the "decoherence pressure $p_0$" as defined in the paper, the visibility would gradually drop to $\frac{1}{e}$ of the initial value, and so on. There is no single moment when decoherence kicks in and in a real experiment, it is always present to some degree because pressure zero is not attainable.

 

[kith]

I think some of the confusion about this topic can be traced to the imprecise use of the term "measurement". The ancients may have lacked the precise terminology to describe what's going on but this has changed.

Phrases like "Has a measurement occured?" or "The environment measures the system" sound esoteric because they don't mesh well with the usual meaning of the term "measurement". Measurements don't occur, they are performed. Measurements involve physical processes but they aren't purely physical themselves because they also involve the intent of an observer to gather a result. Put like this, it is not mysterious at all that measurements seem to involve consciousness (although the spider which uses her web to catch a fly could also be called an observer).

When we want to talk about the actual physical process which happens when a certain measurement is performed, we should avoid the term "measurement" and use the precise language of the quantum dynamics of open systems whenever possible. This includes the term "decoherence" which itself has measurable consequences (see my previous post for an example). This allows us to replace phrases like in the paragraph above with more precise statements which make it easier to separate the actual physics from the question of interpretation.

 

[SCHROEDERFPM]

If a person opened the box, observed the cat, and then had their memory completely erased or died shortly afterwards would the cat still have been "observed"?

Also is the cat a good reference?
The cat is an observer and knows wether it is dead or alive.
If it knows it's not dead it's definitely not, and if it's dead it can't observe.
Does this not make the cat DEFINITELY one or the other?

 

[Lord Jestocost]

The cat is an observer and knows wether it is dead or alive.

But you cannot say anything about the actual condition of the cat as long as you have no kind of "indication" of the cat's actual condition.

 

[Hornbein]

I find that after 9.68 shots of Jim Beam I am no longer able to determine whether the cat is alive or dead.

 

[PeterDonis]

This thread has run its course and is now closed.